ANS 316

Estrogens!

•Uterus -Stimulates uterine growth by hyperplasia and hypertrophy -Stimulates myometrial contractility -Induces the factors needed for regression of the CL in ruminants (more later) •Cervix -Stimulates mucus secretion -Participates in cervical softening at parturition •Secondary sex characteristics in the female •Brain - induces behavior associated with estrus (heat); sexual receptivity to the male •Mammary gland - supports duct development •Skeletal system - increase calcium deposition and bone ossification; accelerates epiphyseal closure of the long bones •Anabolic in ruminants - stimulates growth Three principal estrogens: estrone (E1), estradiol (E2) and estriol (E3) -Estrogen nomenclature based on the number of -OH groups in each hormone -Estradiol (E2) has the greatest biological activity +At least 10 Xs more potent than either E1 or E3

Myths about the female tract abound!

•Vagina dentata: folk tale that the woman's vagina has teeth - it appears in several cultures. -Europe - Chaco and Guiana tribes of South America -Hinduism -Ainu and Shinto: a sharp-toothed demon hid inside the vagina of a young woman and emasculated two young men on their wedding nights. Consequently, the woman sought help from a blacksmith who fashioned an iron phallus to break the demon's teeth. The legendary iron phallus is considered to be enshrined at the Kanayama Shinto Shrine in Kawasaki, Japan, and there the popular Festival of the Steel Phallus (かなまら祭り) is held each spring. Also, prostitutes once considered that praying at that shrine protected them against sexually transmitted diseases. -Māori •Female Hysteria caused by a wandering uterus/womb, hence the term Hysterectomy: Female hysteria was once a common medical diagnosis for women, which was described as exhibiting a wide array of symptoms, including anxiety, shortness of breath, fainting, nervousness, sexual desire, insomnia, fluid retention, heaviness in the abdomen, irritability, loss of appetite for food or sex, (paradoxically) sexually forward behavior, and a "tendency to cause trouble for others". It is no longer recognized by medical authorities as a medical disorder. Its diagnosis and treatment were routine for hundreds of years in Western Europe. In Western medicine hysteria was considered both common and chronic among women. The American Psychiatric Association dropped the term hysteria in 1952. Even though it was categorized as a disease, hysteria's symptoms were synonymous with normal functioning female sexuality. In extreme cases, the woman may have been forced to enter an insane asylum or to have undergone surgical hysterectomy •Victorian era myth: women could not participate in "sport" since their uterus would fall out.: The myth of the uterus exiting the body during sport activities was thought to have originated as an attempt to explain some uterine prolapses. -Persisted even into 2010: Gian-Franco Kasper, president of the International Ski Federation, commented on ESPN's Outside the Lines that the female uterus might burst during landing from a ski jump, reiterating a statement he made in a 2005 NPR interview that ski jumping is "not appropriate for ladies from a medical point of view."

Leydig cells (Interstitial cells of Leydig)

•Very important testicular cell!! •Produce androgens! -Testosterone •Located in the peritubular spaces (interstitium) adjacent to capillaries for secreting androgens into the male's circulation!

The Pituitary Gland, Pars Nervosa

+-Involved in endocrine function, but only a site for storage and release of hormones -NO SYNTHESIS -No releasing hormones for pars nervosa hormones (produced in hypothalamic nuclei) -Composed of +Axons and axonal termini of neuroendocrine cells whose cell bodies are located in the hypothalamic paraventricular and supraoptic nuclei (PVN and SON) and +Pituicytes = population of neuroglial cells associated with the axons; no known endocrine function -Axons of the neuroendocrine cells in the PVN and SON extend thru the pituitary stalk and terminate in the pars nervosa = large neuroendocrine cells = magnocellular neurons!! -Hormone secretion occurs at the axonal termini in the pars nervosa (hormones are stored in secretory vesicles in the termini) but actual synthesis of the hormone occurs in the cell bodies located in the hypothalamus! -Because of the differential sites of synthesis vs release, it would not be incorrect to refer to the hormones released from the pars nervosa as pituitary or hypothalamic hormones! -Oxytocin and vasopressin (anti-diuretic hormone; ADH) -Milk letdown may be considered a neuroendocrine reflex. The stimulation of the teat induced a neural signal to the hypothalamus to release oxytocin from the neurohypophysis, which stimulates the myoepithelial cells to constrict the alveoli, resulting in milk secretion.

Follicle-stimulating hormone (FSH)

+•Control: -GnRH -Gonadal Steroids -Gonadal peptides Biological Effects -Female +Stimulates growth and maturation of the ovarian follicle; primary factor in ovarian growth +With LH, supports antral follicle estrogen production -Male +Maintains testicular growth +Maintains early stages of spermatogenesis (A0-spermatogonia to 2°-spermatocytes) +Supports Sertoli cell function, e.g., androgen binding protein (ABP) synthesis Target cells -Granulosa cells in female and Sertoli cells in male -aka Follitropin -Glycoprotein -MW ranges: +32-38 kD -a,b-subunit structure; shared with TSH, CG and LH -a-subunits are similar; b-subunits are distinct and confer the specific biological activity -Both subunits are glycosylated -Control of FSH Secretion: +Hypothalamic releasing hormone --GnRH - route for reaching the pars distalis? ---Effect of pituitary stalk transection? +Gonadal steroids --Progestins, androgens and estrogens ---Negative feedback, except for high concentrations of estrogen in the female --Neuroendocrine reflex arc in induced ovulators (will discuss this arc later) --Inhibin = gonadal polypeptide hormone that selectively inhibits FSH, involved in determining how many follicles ovulate (levels vary by species!) --Activins = gonadal polypeptide hormones that selectively stimulates FSH secretion --Follistatin = gonadal protein in follicular fluid that selectively modulates FSH section

Review the structure of the cell membrane!

- lipid bilayer with proteins spanning the membrane -Because the polypeptide-type hormones cannot pass thru the cell membrane, their mechanism of action depends on the generation of an intracellular "second messenger" -Generation of the second messenger occurs after the hormone interacts with it's membrane-bound receptor Two basic mechanisms of hormone action -Protein kinase A system and Protein kinase C systems +Aka. Protein/Peptide mechanism of action +Focus on PKA system for simplicity -Steroid hormone mechanism +Genomic and non-genomic/rapid actions

The Pineal Gland 7

-"Short days" - in a 24-h period, more melatonin during this photoperiod -Stimulatory to a short-day breeder because high melatonin causes increased GnRH activity - increased LH output! -Increased GnRH activity because of High levels Kisspeptin - GnRH release is stimulated during "short" days

Tonic control of LH/FSH Secretion

-All feedback for tonic secretion is negative - in that these hormones inhibit GnRH release and release of FSH and LH from the anterior pituitary. Net effect - low levels of steroid production maintains function of the tissues. If these levels fall (menopause, gonadectomy) hypersecretion of GnRH, LH and FSH occurs for a short time. -The surge center will be discussed in detail in the follicular phase and ovulation! -Effect of gonadectomy +Monitor [LH] in a ram, castrate, implant with testosterone +Demonstrates negative feedback effect of the gonadal steroid hormones on LH production; gonadal steroids suppress [LH]!

Net effect of hormone action on a target cell

-Alters the target cell's biological function Examples of changes to biological functions: -LH causing the granulosa cells to luteinize -Hypothalamic Gonadotropin Releasing Hormone (GnRH) causing the gonadotropes to release LH & FSH -Estrogen causing the cervical goblet cells to produce mucus -Change in myometrial contractility +Estrogen → ↑ ion channel permeability → ↑ myometrial contractility +Progesterone → ↓ ion channel permeability → ↓ myometrial contractility

Gonadal Polypeptide Hormones: AMH

-Anti-Mullerian Hormone (AMH)/ Muellerian-inhibiting factor -Member of the TGFβ superfamily: 140 kD -In utero, causes regression of the paramesonephric or Mullerian duct in the ♂ fetus; Sertoli cell product After birth in the ♀, AMH is produced by the granulosa cells of growing follicles up to the early antral stage -Growth of follicles from the primordial to secondary phase does not require gonadotropins FSH and LH - Gn independent. -Growth of follicles from secondary on requires gonadotropins -AMH modulates the response of the follicle to Gonadotropins! Species-specific functions: -All species: Inhibits primordial follicle recruitment into the primary follicle pool -Rodents: Inhibits FSH-dependent growth of pre-antral follicles -Primates: Promotes FSH-dependent growth of preantral follicles (secondary and tertiary) -All Species: Inhibits FSH-dependent growth of small antral follicles (small Graaffian)

Ovarian senescence

-Associated with advanced age -Low follicle numbers in the female's ovary -Aberrant or termination of cycles; reduced conception rates and litter sizes -Loss of follicular responsiveness to the reproductive hormones -Menopause in primates and elephants

The Pineal Gland 4

-BUT, what about sheep and goats who are reproductively active during the fall/winter months = "short day breeders" -Does melatonin stimulate gonadal activity in these species? +Yes! - It is exactly opposite in short day breeders compared to long day! -Treatment of ewes during late summer with melatonin (boxes) decreases time to mating (Top chart) and time to get all ewes lamed (bottom chart)! -Melatonin functions as a regulator for species that are seasonal breeders or who have reproductive cycles dependent on season of the year and photoperiod! -We call the changes in daylight throughout the year "Photoperiod". Photoperiod is a major factor controlling ovarian activity in several species -"Long day" breeders - ovarian activity in spring/summer +Queen (Jan-Oct) and mare (March-Oct) -"Short day" breeders - ovarian activity in fall/winter +Ewe and goat (late July-Feb/March) +Some breed differences, e.g., breeds developed in regions with less change in daylight length by season of the year (nearer the Equator) have less-defined and longer breeding seasons

Os penis (baculum)

-Bony or cartilaginous structure imbedded in the CCP -Found in dogs, cats, rodents, marine mammals and some primates (not humans!)

Spermatic Cord

-Collective structure; runs from the dorsal pole of the testes to the body wall -Two cords, one for each testis -Components (several) +Tunica vaginalis = continuous with the scrotum so also part of the spermatic cord - encasing majority of spermatic cord components, testis, epididymis & vas deferens +Cremaster muscles --External cremaster - outside the tunica vaginalis

the capillary network collecting products of the pars nervosa

-Control of posterior lobe (pars nervosa!) hormone secretion -No RH or RIH involved as in pars distalis hormone release -Mechanism for inducing oxytocin release +Mechanical sensory stimulus initiates a reflex arc that is transmitted thru the spinal cord to the PVN and SON +Neuroendocrine cells in PVN and SON respond to the sensory inputs by depolarizing and liberating OT, stored in secretory vesicles in the axonal termini, into the circulation -Target organs +Oxytocin --Mammary gland, muscularis of oviduct, uterus, vas deferens, ampulla and epididymis and the corpus luteum --Myokinetic effects on all organs +Vasopressin --Distal tubule and collecting ducts of kidney = water reabsorption

Scrotum issues

-Cryptorchid = testes are retained in the abdomen and have not descended into the scrotum = male is infertile •Bilateral = both testes retained in the abdomen = infertile •Unilateral = one testis retained in the abdomen = fertile -Meiotic events in spermatogenesis are temperature-sensitive and are interrupted if the temperature approaches core body temperature (more at end of section) •Exceptions are marine mammals and elephants -Secondary sex characteristics and libido (sex drive) are unaffected in cryptorchid males because androgen (testosterone) production is not altered by the increase in testicular temperature

Techniques applied to the spermatic cord

-Dashed line shows horizontal "cut" through spermatic cord to show cross-section. -Techniques applied to the spermatic cord +Castration = severing the entire spermatic cord = eliminates sperm and androgen production --Aka "neutering" +Vasectomy = excision of a section of the vas deferens and ligation of both ends --Hormone production is unaffected but sperm are prevented from passing thru the vas deferens to the pelvic urethra

Penis Muscle

-Each vascular body has a skeletal muscle associated with it +Each crus penis is surrounded by an ischiocavernosus muscle (left and right) +The penile bulb is surrounded by the bulbospongiosus muscle (also paired) -Fibroelastic sp possess a retractor penis muscle (RPM) +Paired smooth muscle extending from the coccygeal vertebrae to the ventrolateral sides of the penis +Chronically contracted; maintains the sigmoid flexure +Some vascular sp have a RPM, e.g., stallion and dog, yet neither have a sigmoid flexure

Primordial follicle

-Earliest, simplest in structure and typically most numerous -Surrounding the oocyte is a single squamous layer of follicle (granulosa) cells = membrana (stratum) granulosa perched on a basement lamina (basal lamina; basement membrane) -Oocyte is small at this stage and possesses a nucleus called the germinal vesicle -Primordial follicles are generally located in clusters close to the outer edge of the ovarian cortex -Primordial follicles are formed during fetal life and will persist into ovarian senescence Fate of a primordial follicle -Remain as a primordial follicle throughout the female's lifespan -Undergo atresia and degenerate -Develop into a primary follicle

Terminology!

-Endocrinology: branch of science that studies endocrine glands and hormones -Hormone: physiologic, organic chemical substance produced by certain specialized cells, which passes directly or diffuses into the circulation for the purpose of either stimulating or inhibiting the functional activity of a target organ, tissue or cell aka Chemical messenger -Endocrine glands: secretion(s) enter the circulation -Exocrine glands: secretion(s) enter a duct -Target Cells •Receptors -Half-life •2 factors influencing biological activity of hormones: Presence of Receptors & Half-life of hormone Other types of chemical messengers -Neurotransmitters: substances produced by neurons and released at synapses or myoneural junctions for propagation of the electrical impulse and not generally transferred to the circulation -Neurohormone: substance produced by a neuroendocrine cell ("excitable cell") that enters the blood and acts on a target organ, tissue or cell -Pheromones: substances (often volatile) released into the environment and perceived by the olfactory system of other individuals within the species -Classifications are not mutually exclusive, e.g., norepinephrine, which is both a neurotransmitter and a neurohormone! Two factors influence the biological activity of a hormone 1.Presence of cellular receptors for a specific hormone -Target cells: cells that possess receptors for a specific hormone +The endometrial cells are target cells for ovarian estrogen because they have estrogen receptors! -Cellular location of the receptor varies depending on the type of hormone +Protein/glycoprotein hormones = plasma membrane +Steroid hormones = cytoplasm, nucleoplasm, plasma membrane +Prostaglandins = plasma membrane -A cell is not responsive to a hormone unless it has a receptor for it!! 2.Half-life of the hormone: period of time during which a hormone is reduced to half of its concentration in the circulation -Two hormones with similar biological activities can have different degrees of biological potency due to half-life differences +Example, two hormones with similar biological activities but one has more glycosylation (carbohydrate; CHO) associated with it +The greater amount of CHO retards degradation in the circulation so the half-life is longer and the overall biological potency is greater

Uterus and Prostaglandins

-Endometrial cells produce these 20 C fatty acid derivatives of arachidonic acid Endometrial cells produce prostaglandins! -Several classes of PGs, e.g., A, B, D, I, etc Many tissues produce PGs! -Two significant PGs in reproduction: PGF2a & PGE2 +"F" series: hydroxyl on C9 +"E" series: ketone on C9 +"2" indicates number of C=C bonds: C5-6 and C13-14 +The a refers to the position of the -OH group on C9 in PGF2a Ovulation -PGs are involved in ovulation at the local or cellular level - we will discuss later in follicular phase lectures. -Stimulate oviductal and myometrial contractions +Sperm transport during mating --Seminal plasma is rich in PGs (vesicular gland!!) +Fetal delivery at parturition (placental source of PG) -In the male, PGF2a stimulates smooth muscle contractions in the epididymis and vas deferens during emission. -PGF2a is luteolytic in all domestic species -Endometrial product in ruminant and several other species +Ovarian in primates ('cause we're weird..) -Causes regression of the CL in either the nonpregnant female near the end of her estrous cycle or in the pregnant female near the end of her pregnancy -In the nonpregnant ruminant female, PGF2a release occurs about 5 days before the end of an estrous cycle -This is sufficient time to eliminate the CL and end progesterone production, which will then permit final follicle maturation and maximal estrogen production to stimulate an ovulation for the next cycle

Tunica vaginalis

-Extension of the body wall or peritoneum -Source/origin •During fetal life, the testes are abdominal and in a retroperitoneal position •When testicular descent into the scrotum occurs, the testes are pulled into a double-walled pocket of peritoneum (vaginal process) by the transitory ligament, the gubernaculum •The gubernaculum eventually regresses in the adult but the vaginal process persists as the tunica vaginalis -Layers •Outer layer = tunica vaginalis parietal = adjacent to the scrotal fascia •Inner layer = tunica vaginalis viscera = adjacent to the tunica albuginea •Cavity of the tunica vaginalis = space between the two layers

GnRH

-Female - Two "centers" in the hypothalamus for GnRH release +Tonic +Preovulatory or Surge -Male - Only one center for GnRH release +Tonic -As many as six hypothalamic nuclei can be dedicated to producing GnRH - blips represent firing of neurons within the hypothalamic nuclei -Gonadal steroids have similar effects for GnRH as for FSH and LH +Progestins and androgens have classic negative feedback effects +Estrogens have differential effects --Tonic center responds to estrogen in a negative feedback manner --Preovulatory (surge) center responds to estrogen in a positive feedback manner but only when the plasma [estrogen] reaches a threshold level associated with a dominant, preovulatory follicle present on the ovary. -Neuroendocrine reflex arc! Now we can fill in the general HPG axis - GnRH (RH), LH/FSH (SH), Steroids (PH)!

The Pineal Gland 3

-First evidence that the pineal gland was involved in reproduction was established in hamsters! -Hamsters are considered "long day breeders" or a species that has reproductive cycles in the spring-summer months -If you evaluate the total amount of melatonin secreted in a long day (summer) vs a short day (winter), in a 24-hour period the animal is exposed to more melatonin in a short day because short days have longer dark periods -So...the hamster is reproductively inactive during periods of the year when plasma [melatonin] is higher!! -Is melatonin antigonadotropic (does it suppress gonadal function)? Experiments with hamsters -Adult male hamsters maintained in a long-day light period are injected every afternoon with saline (Control) or melatonin (melatonin mimics increased length of dark period). -Male hamsters receiving melatonin have decreased testes weight! +From these experiments, it appears melatonin is antigonadotropic......

Oviduct

-First segment of the tubular portion of the female reproductive tract -Delicate tube extending from the uterus to the ovary -not physically connected to the ovary -Mesosalpinx = portion of the broad ligament that suspends the oviduct in the female's body cavity "salpinx" refers to oviduct +Hydrosalpinx = fluid in the oviduct +Salpingitis = inflammation in the oviduct -Oviduct is oriented in a C-shape about the ovary -Fimbria = delicate membranous structure extending from the infundibulum and covering the ovary +Possesses smooth muscle cells +Epithelial cells are ciliated (kinocilia) -Ostium = oviductal opening -Ovarian bursa = "bag" composed of the mesosalpinx and fimbria that surrounds the ovary and functions to capture the oocyte -At ovulation, movement of the fimbria in an undulating wave-like motion, coupled with the current generated by the beating kinocilia, shuttle the oocyte into the ostium. Properties/functions -Recovery of the ovulated oocyte -Ovum and sperm transport -Site of fertilization -Site of early embryo development -Tubal pregnancy = embryo fails to enter the uterus and implants in the oviduct; form of ectopic pregnancy (pregnancy in an abnormal site); most common in humans; rare in other species

Ovarian Cortex

-Follicles and follicle-derived structures, e.g., corpus luteum -Mesenchymal cells - undifferentiated population of stromal-type cells interspersed among these structures; give rise to two types of endocrine cells: •Thecal cells - associate with the follicle in later stages of follicular development •Interstitial cells - remain in ovarian cortex as scattered aggregates of cells -Species variation with respect to presence or absence and degree of differentiation

Glans penes

-Glans penis = terminal end of the penis -Species modifications +Corpus spongiosum glandis = well-developed vascular body in the glans penis of some males; fills with blood during erection; prominent in the stallion +Urethral process (filiform appendage) = hair-like structure extending from the ram glans +"Corkscrew" shape = boar and camelids (camelid females do not possess cervical interdigitating prominences?) +Spiny processes = tom (felids); keratinized "barb-like" structures; females in these sp are induced/reflex ovulators and depend on cervico-vaginal stimulation for ovulation, hence these structures may augment the stimulation process -Bulbus glandis +Structure found in dogs +Bulb-like enlargement on the shaft of the penis, behind the glans +Becomes blood-engorged during erection +Responsible for the classic "locking" of the dog's penis in the female's vagina during mating -Prepuce = sheath of skin in which the non-erect penis retracts; 2 parts +Penile prepuce = portion of the prepuce immediately surrounding the penis +Pre-penile prepuce = portion of the prepuce immediately cranial of the penis +Prepuce = Pre-penile prepuce + Penile prepuce -Preputial pouch/diverticulum in the boar's pre-penile prepuce +Collects urine, epithelia, semen --> gives the boar his strong odor!

Onset of Puberty 2

-Gonadotropin profile is a reliable measurement of puberty due to large differences in patterns between pre-pubertal and pubertal individuals: -Prepubertal female: 2 markers of immaturity +GnRH pulse frequency is reduced compared to the pubertal female +Tonic center in the hypothalamus has a greater sensitivity to the negative feedback effects of E2 Result? Slower pulses and lower concentrations of LH (read as [LH]). -Prepubertal male - Similar markers of immaturity as in prepubertal female +GnRH pulse frequency is reduced +Hypothalamus has a greater sensitivity to the negative feedback effects of testosterone and E2 -Prepubertal male - Similar markers of immaturity as in prepubertal female +GnRH pulse frequency is reduced +Hypothalamus has a greater sensitivity to the negative feedback effects of testosterone and E2 +Result is same in prepubertal male as the female! Slower pulses ad lower concentrations of LH. -Puberty onset in the Female occurs when the hypothalamic tonic center increases the frequency of tonic GnRH secretion causing increased tonic [LH] ( and FSH...) -Coincident with the tonic GnRH/LH frequency increases, the tonic center becomes less sensitive to E2 negative feedback -Increased tonic gonadotropins stimulates follicular E2 production to reach threshold leads to increase in surge center activity® now the female has enough E2 to generate a pre-ovulatory (PO) GnRH surge ® leads to a PO LH surge ® leads to first ovulation and estrous cycles commence +In the Male, increased frequency of tonic GnRH ® increased tonic [FSH/LH] ® stimulates androgen production (also, decreases negative feedback effects on hypothalamus) leads to induction & maintenance of spermatogenesis!

Sexual Differentiation of the Brain 2

-If E2 is the factor for defeminization, why is the female hypothalamus not defeminized, considering the female fetus would be exposed to estrogens from the placenta and maternal ovaries????? -E2-binding glycoprotein, a-fetoprotein, is produced by the yolk sac and, later, the fetal liver +Produced by BOTH male and female fetuses!! +Plasma [a-fetoprotein] = high in fetus; low in adults!! -a-fetoprotein (AFP) only binds E2, and prevents it from crossing the Blood-Brain Barrier, therefore preventing interaction with the cells of the hypothalamus! -Because Estradiol does not enter the cytoplasm of the cells of the hypothalamus, it cannot interact with the estradiol receptor and initiate the genomic mechanism of action for the steroid hormone. Because of this, the surge center develops in the hypothalamus of the female.

Onset of Puberty 3

-In both male and female primate species, early puberty is marked by nocturnal (sleep-associated) increases of LH amplitude and LH (GnRH) pulse frequency, with reduction during the following day. +Termed: "First night-time rise in LH" +The graph shows the hormone patterns over one sleep period of a boy who attained puberty 1.8 years after this measurement. Notice how LH increases both in average concentration and in frequency of pulses (marked by small black arrows) after ~21:00 hours (~9pm). Also notice how after 8 am these levels fall. +Blamed for correlation between teenagers and sleep!

Biological Activities of Androgens

-Maintains latter stages of spermatogenesis (2°-cyte thru spermiogenesis) -Supports development and maintains integrity of the epididymis, vas deferens, accessory sex glands and external genitalia -Supports secondary sex characteristics in the male and libido (brain) -Anabolic in skeletal muscle (protein deposition) -Substrate for estrogen synthesis

seminiferous tubules (testes)

-Majority of testicular mass = s. tubules -Vital statistics for the bull +Each s. tubule = 50-100 cm in length +Estimated overall length if lined up "end-to-end" = 3 miles!! +Highly active sperm-producing epithelium +Sperm production = 13-19 million sperm/gram testis/day +Mass of both bull testes = 800 grams +For both testes, average sperm production = 10-15 billion sperm/day +Single ejaculate contains 5-10 billion sperm +Recommended ejaculation frequency = 4-7 Xs/week -The sperm and endocrine-producing cells of the testes are located within and around the seminiferous tubules

•Reflex Arc #2 to induce warming

-Movement from thermoneutral to cold temp +Net effect - induce warming = motor responses -Tunica dartos contracts +raises testes closer to body cavity +scrotal skin wrinkles ® ¯ scrotal surface area ® conserves heat -Contribution of the external cremaster muscle in testicular thermoregulation - (recall contraction cannot be maintained for prolonged periods of time) -Abrupt shift in temperature --> muscle contracts or relaxes for testicular positioning -Cycling of contraction/relaxation for heat transfer in pampiniform plexus - high for warm temperature; ¯ low for cool temperature +Contracting/working muscles generate heat? -Most significant function is in the "fight or flight" response

Kisspeptin controls GnRH release

-Neuropeptides encoded by the KISS-1 gene +KISS-1 gene was originally identified as a human metastasis suppressor gene because it's product, metastin, suppressed melanoma and breast cancer metastasis --Later discovered metastin stimulated GnRH secretion --Renamed as kisspeptin (Kp) by the team of researchers who discovered its GnRH link --- the lab was in Hershey, PA, the home of the chocolate "Hershey Kisses" +Four polypeptides: Kp-54, -14, -13 and -10; number designates number of amino acids -Produced by the arcuate, preoptic and other nuclei within the hypothalamus. -Synapse with GnRH-secreting neurons in the hypothalamus -Stimulates GnRH release!!!! +Inject a prepubertal rat with kisspeptin stimulates the LH surge and ovulation!!! -Kisspeptin-secreting neurons are sensitive to the reproductive steroid hormones; possess steroid hormone receptors

Tertiary or small Antral Follicle

-No change in oocyte size -Major changes in follicle cell layers +Granulosa cells have proliferated so membrana granulosa is thicker +Mesenchymal cells have differentiated into theca cells and aggregated around the basement lamina of the membrana granulosa, contributing to a secondary outer layer of cells = theca folliculi -Antrum develops; antrum = cavity in the m. granulosa filled with follicular fluid (liquor folliculi) -Follicular fluid is a plasma transudate that accumulates in the m. granulosa -No blood vessels in the m. granulosa; only in theca folliculi and elsewhere in the ovary -Fate of a tertiary follicle: atresia or develop into a Graafian follicle

Control of Pineal Gland Function Long Term

-Note how the impact of high melatonin is different on the long-day breeder than the short-day breeder! WHY????? -In mare - the high levels of melatonin decrease GnRH levels and suppress ovarian activity - same phenomena in males! -You can actually stimulate a mare and stallion to come out of season early by keeping them under lights in winter months!

Prolactin (Prl)

-Older name = luteotrophic hormone (LTH) -Early research in rodents observed that Prl was luteotrophic because it supported the CL and maintained progesterone production -Prl has a limited luteotrophic role in non-rodent species, but because of its effects in rodents (and a few other species), it is considered gonadotropic -LTH was dropped and prolactin was adopted because this hormone has a major role in lactation! -Protein; 24 kD; similar in structure to growth hormone (somatotropin; STH; GH) -Luteotrophic in rodents +Upregulates LH receptors in rodent CL -Part of luteotrophic complex in sheep and dogs (cats?) -New evidence suggests PRL moderates gonadal estradiol by moderating GnRH and FSH via Kisspeptin neurons in the tonic center of rodents - no data from higher species yet... In figure TIDA are tuberoinfundibular dopamine (TIDA) neurons in arcuate nucleus -Major role in supporting lactation -Stimulates maternal behavior +Nest building, mothering ability -Discrete role in male not known - studies where the PRL gene was silenced or "knocked out" result in infertility in female mice but not male mice. However, high levels of prolactin in males are associated with infertility, we just don't know if it is direct or indirect through other hormones. Altered metabolism was seen in both sexes lacking prolactin -Target organs: luteal cells, mammary gland epithelium and brain/hypothalamus

Secondary Follicles

-Oocyte has reached its peak size -Zona pellucida appears = acellular glycoprotein matrix produced by and surrounding the oocyte +Zona pellucida functions in sperm recognition at fertilization and cellular organization during early embryo development -Membrana granulosa has 2 or more layers of cells Fate of a secondary follicle -Similar to primary follicle: remain, atresia or develop into a tertiary follicle

Primary Follicles

-Oocyte is growing, so it is larger than the primordial follicle oocyte -Squamous layer of membrana granulosa becomes cuboidal -Not located in clusters like primordial follicles Fate of a primary follicle -Similar to primordial follicle: remain, atresia or develop into a secondary follicle

Gonadotropin-releasing hormone (GnRH)

-Pharmaceutically active agents: Gonadoliberin; luliberin Produced in the Tonic (♀︎♂︎), and Surge (♀︎) Center of the Hypothalamus (You should know cell bodies in these areas) -Causes the release of both FSH and LH from the anterior pituitary -Decapeptide +pyroGlu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-NH2 1,182 D = 1.2 kD -In 1977, Andrew Schally shared the Nobel Prize for Medicine for his isolation of the structure of GnRH ++Collected 250,000 pig hypothalami to provide 10 mg of purified GnRH -Mechanism of hormone action +Membrane receptor and protein kinase C mechanism of action -Because of the simple sequence of this polypeptide, one can generate "designer" analogs for various purposes -Analog (in the hormone sense) = modified synthetic hormone +Simple aa substitutions can change biological activity +Stimulatory analogs = agonists --Biological activity of the agonist is often greater than the endogenous (natural) hormone! +Inhibitory analogs = antagonists --Biological activity of the antagonist is reduced compared to the endogenous hormone! +The D-Leu6 agonist is 10-50 Xs more potent than the natural hormone +The D-Phe2 antagonist inhibits the GnRH response

The Pituitary Gland, Anatomy

-Pituitary gland is one of the most important endocrine glands in all vertebrate species -Considered the "Master Gland" of the body because of its importance and its role in several physiologic functions: growth, metabolism, reproduction -Anatomy of the Pituitary Gland (mammals) +Located at the base of brain in a depression in the sphenoid bone called the sella turcica +Connected and located ventrally to the hypothalamus +Dorsum sella = thin bony plate covering the pituitary gland --Present in ruminants --Absent in humans, rodents and swine

Corpus luteum

-Polytocus species - numerous corpora lutea develop; each representing an ovulated follicle -Monotocus species - 1 or 2 CL develop; may take up 2/3 of the ovarian volume -If no embryo present, the CL persists for 2/3 of the duration of the estrous cycle (most species, 12-15 days) or ½ of the menstrual cycle (14 days) -For almost all species, an embryonic signal is required to prevent CL regression in order to maintain the pregnancy; exceptions are the dog and cat!! -Process of CL regression = luteolysis •Corpus luteum spurium = CL of the cycle •Corpus luteum verum = CL of pregnancy •Nature of the embryonic signal -Luteotropin = a substance that supports and maintains the CL and progesterone production -Antiluteolysin = a substance that prevents the luteolytic mechanism from destroying the CL, allowing it to be maintained and continue producing progesterone

Estrogen

-Production of the steroid hormone estrogen begins during the transition from secondary to tertiary follicle stage; concerted effort of the theca interna and membrana granulosa -Preovulatory Graafian/Antral follicle produces high [estrogen] +Drives the female into "heat" or estrus for the estrous cycling species; heat is the behavior associated with sexual receptivity to the male, so estrogen has direct effects on the brain!! -In spontaneous ovulating females (those not requiring copulation for ovulation), high [estrogen] from the preovulatory Graafian follicle induces ovulation -Fate of all Graafian/antral follicles: atresia or ovulation Follicle Timeline -Development from primordial to secondary follicles does not require the reproductive hormones (hormonally independent), whereas development from secondary to Graafian follicles requires reproductive hormone support (hormonally dependent) -Peptide hormones: follicle stimulating hormone (FSH) and luteinizing hormone (LH) -Primordial, primary and secondary follicles can be found throughout a female's life: fetal to ovarian senescence -Tertiary and Graafian follicles would be found peri- pubertal and into adult life but not in menopause

Uterus

-Prominent organ in the female reproductive tract -Mesometrium = portion of the broad ligament that supports the uterus in the body cavity Properties/functions -Site of embryo and fetal development, implantation and placenta formation +Placenta = organ composed of fetal membranes and endometrium = responsible for physiologic exchange between the dam and fetus and hormone production -Capable of undergoing tremendous changes in size to accommodate fetal growth during pregnancy yet retains the ability to regain its pre-pregnancy size -Myometrial contractions +Fetal expulsion at parturition (birth) +Sperm transport at mating = myometrial contractions move sperm from the site of semen deposition to the site of fertilization; sperm can't "swim" that far!! +Uterine involution = restoration of the uterus to its pre-pregnancy size -Source of luteolytic effect from prostaglandin hormone prostaglandin F2α (PGF2α) in domestic species -Immunosuppressive effect +Uterus produces a class of pregnancy-specific proteins (PSP) under the influence of progesterone that suppresses the maternal immune system +Important in preventing rejection of the fetus by the dam because it possesses the sire's "foreign" genetics -Site of semen deposition for several rodent species, mare, dog and, to some extent, the sow +Male's penis does not actually penetrate beyond the cervix but in these species (except the sow): the cervical folds are flaccid due to high estrogen and semen is jetted thru the cervix into the uterus +Pigs: Boar's penis engages the female's cervix and then semen, due to the large ejaculate volume, is deposited in both the cervix and the uterus

Onset of Puberty 6

-Pubertal onset GnRH/FSH/LH surge center may not result in an immediate ovulation, and typically estrus behavior is absent/ "weak" +Instead of an ovulation, a short-lived luteinized follicle develops that produces some progesterone +Progesterone priming with E2 required for estrus behavior --No CL in prepubertal female so no source of progesterone!! -Second GnRH/FSH/LH surge can produce an ovulation but may also be unaccompanied by full range of estrus behavior +Insufficient progesterone produced by the luteinized follicle to effect sufficient priming for estrus behavior!! -Third GnRH/FSH/LH surge results in ovulation accompanied by full estrus because of sufficient progesterone from previous CL for priming with E2!! -Photoperiod considerations for seasonal breeders - i.e. Sheep, Horses, hamsters! -Onset of puberty is affected by the time in the year the female attains pubertal age +If the female reaches pubertal age during the period of the year coinciding with the breeding season, puberty will occur +If the female reaches pubertal age during the period of the year coinciding with the non-breeding season, puberty will be delayed until the next breeding season

Onset of Puberty

-Puberty = onset of reproductive life -Benchmarks of puberty onset - female has several! +First ovulation - best marker for puberty onset in the female -Benchmarks of puberty onset - male also has several! +Ability to generate a pregnancy in a fertile female -Onset of Puberty is absolutely dependent on attaining a specific body size or mass, e.g., many dog breeds reach 75% of their adult size before pubertal onset; 17% body fat in humans •Undernutrition and weight loss will delay onset of puberty!!! -Benchmarks of puberty in females can be defined by several measures! •Estrous cycling species = onset of sexual activity at the first estrus (heat) = reproductive behavior •Primate we discussed Tanner Staging, also menarche = first menses •Ability to support a pregnancy •First ovulation - best marker for puberty onset in the female -Benchmarks of puberty onset - male also has several! +Less obvious +Reproductive behavior = mounting, erection +First ejaculation +Sperm first appear in the ejaculate +Ability to generate a pregnancy in a fertile female +Best marker is age at which sperm numbers in the ejaculate are great enough to achieve a pregnancy

The Hypothalamic-Pituitary-Gonadal Axis

-RH= releasing hormone, SH=Stimulating Hormone, PH= peripheral hormone. -Generic version of the hypothalamic-pituitary-gonadal axis +The hypothalamus receives input from many different areas of CNS & responds by secreting a releasing hormone (RH) into the hypothalamic-pituitary portal system rather than entering the general circulation +The RH stimulates specific cells of the pituitary to secrete a particular peptide hormone that stimulates the gonad (SH) that is released into the general circulation & travels to its target gonad/endocrine organ. +The gonad secretes another hormone (PH) that acts on target cells to bring about the appropriate biological response & at the same time exerts negative feedback effects on the hypothalamus &/or the pituitary to turn off the system

Prostaglandins (PG)

-Recall PGs are 20 C fatty acid derivatives of arachidonic acid. -Several classes of PGs, e.g., A, B, D, I, etc -Many tissues produce PGs -Two significant PGs in reproduction: PGF2a & PGE2 +"F" series: hydroxyl on C9 +"E" series: ketone on C9 -+"2" indicates number of C=C bonds: C5-6 and C13-14 -The a refers to the position of the -OH group on C9 in PGF2a -Mechanism of hormone action: +Membrane receptor and protein kinase C mechanism of action -Ovulation +PGs are involved in ovulation at the local or cellular level +Blocking ovarian or follicular PG syntheses can block or retard ovulation +PGs cause contraction of smooth muscle in ovarian follicle wall = myokinetic effect!! --Contractions tear the follicle wall +PGs stimulate follicle cells to release proteases for follicle wall degradation -Stimulate oviductal and myometrial contractions +Sperm transport during mating --Seminal plasma is rich in PGs (vesicular gland!!) +Fetal delivery at parturition (placental source of PG) -In the male, PGF2a stimulates smooth muscle contractions in the epididymis and vas deferens during emission -PGE2 may participate in pregnancy recognition in the mare and ewe -PGF2a is luteolytic in all domestic species -Endometrial product in ruminant and several other species +Ovarian in primates -Causes regression of the CL in either the nonpregnant female near the end of her estrous cycle or in the pregnant female near the end of her pregnancy -In the nonpregnant ruminant female, PGF2a release occurs about 5 days before the end of an estrous cycle -This is sufficient time to eliminate the CL and end progesterone production, which will then permit final follicle maturation and maximal estrogen production to stimulate an ovulation for the next cycle •Sources? -Vesicular glands, Granulosa cells, Endometrial cells and luteal cells (primates) •Biological Activities? -Ovulation -Oviductal and myometrial contractions -Sperm transport -Fetal delivery -Emission (F) -Pregnancy recognition (E) -Luteolytic in all species (F)

The Pineal Gland 2

-Recall the SCN is a hypothalamic nucleus located dorsally to the optic chiasma -Retinohypothalamic tracts run from the retina to the SCN; separate from the optic nerve -SCN is regarded as the circadian clock because it indirectly is light-sensitive and reports changes in daylight length within a 24-h period to the brain - the directly light sensitive portion are the rods and cones in the retina. -Light, perceived by the retina, stimulates the SCN which in turn stimulates the superior cervical ganglion (SCG) -The stimulated SCG inhibits melatonin release from the pineal gland thereby causing plasma [melatonin] to be low during periods of light. -Conversely, when light is low (night), this inhibition is lost and melatonin levels rise.

Control of Pineal Gland Function: Transition from long to short days

-Recent evidence for WHY mares (Long day breeders) and sheep (Short day breeders) differ in response to melatonin....... -RFRP = RF-amide Related Peptides +Family of neuropeptides that have an RF-amide at the C-terminus of the polypeptide +R = Arg and F = Phe; Arg-Phe-NH2 +RFRP-1 (12 aa); RFRP-3 (8 aa) -Role as a a seasonal mediator of Kisspeptin, GnRH & FSH/LH release +RFRP neuronal tracts project from the dorsal medial nucleus into the preoptic area and the median eminence and the hypothalamic-hypophyseal portal system. +Norepinephrine carries the signal from the SCG to the pineal gland - this removes the inhibition on the pineal gland. -Note how a long-day breeder (Mare) reacts to high Melatonin by decreasing the amount of RFRP-3 released, which decreases Kisspeptin & GnRH -However, a short-day breeder (Ewe) will react to high melatonin by also decreasing the amount of RFRP-3 released, however this increases Kisspeptin levels and activates GnRH production. FOR THIS MORE complicated pathway - just know that it is RFRP that mediates the "switch" between Long and Short day breeders and Kisspeptin/GnRH

Oviductal Transport

-Refers to transit of ova and sperm, as well as fertilized oocyte and embryos -Ampulla - fast - 2-3 hours for the ovulated oocyte to reach the AIJ -Isthmus - slow - 2-6 days (sp. dependent) for the ovum or embryo to reach the UTJ (mare possesses the ability to exclude unfertilized ova from entering the uterus!) +Swine - 2 days +Rodents, humans - 3 days +Ruminants - 4 days +Mare - 4-5 days +Dogs, cats - 6-7 days Ampulla vs isthmus -Ampulla has: +Larger lumen +More folds in the lumen +Greater number of ciliated cells +Thinner muscular wall +Overall, appears wider and less rigid

Gonadal Steroid Hormones Biosynthetic Pathway

-Review - the 2 cell, 2 gonadotropin model - recall similar pathways for Leydig cell (Theca) and Sertoli cell (Granulosa). Three major classes of gonadal steroid hormones -Progestins (21 C) +Progesterone +Pregnenolone -Androgens (19 C) +Dihydrotestosterone _Testosterone -Estrogens (18 C) +Estradiol (E2) +Estriol (E3) +Estrone (E1)

Two physiologic conditions elicit Prl release via neuroendocrine reflex arcs

-Rodents are spontaneous ovulators but require mating for induction of the luteotropic effect of Prl on the CL +Mice & rats have a 4-5 day estrous cycle +"True" CL do not form in unmated females in these sp = little, if any, progesterone is produced! +Sterile mating = CL form, produce progesterone and persist for 10-12 days = pseudopregnancy!! +Fertile mating = CL form, produce progesterone and persist for 20-21 days = pregnancy!! -Suckling in nursing females to maintain lactation and milk production (red pathway)

Other features of the uterine mucosa

-Ruminants possess button-like structures called caruncles that line the endometrium +Very prominent in ewe +Serve as sites of attachment with complementary structures located on the outer fetal membrane called cotyledons -Caruncles fuse with cotyledons to produce a composite structure called the placentome +Maternal caruncle + fetal cotyledon = placentome

Cervix Mucosa

-Secondary structure = cervical crypts; deep penetrations of the mucosa +Similar to tubular glands but differ in that the crypt epithelium is similar to the lumenal epithelium +In the endometrial tubular glands, regional differences exist within the gland epithelium, e.g., neck vs base of the tubular gland -Cervical lumenal epithelium is rich in mucus-secreting cells +Goblet cells +The stained mucus droplet in the cell takes on a goblet appearance -Like the uterus, reproductive hormones affect the cervix -Estrogen +Induces mucus formation and secretion by the goblet cells +Causes the cervix to dilate -Progesterone (antagonistic to estrogen effects) +Suppresses mucus formation and secretion by the goblet cells +Causes the cervix to constrict

Testes Tubular components

-Seminiferous tubules •Tubulus contortus "convoluted tube"; the seminiferous epithelium is in here!! (#2) •Tubulus rectus "straight tube"; duct only, no sperm-producing epithelium (#4) -Rete testis (#6) •Duct located in the central core of the testis •Transports sperm from the s. tubules (tubulus rectus) to ducts located at the dorsal pole of the testis = efferent ducts -Efferent ducts (#5) •Last set of testicular ducts •Sperm leave the efferent ducts and enter the epididymal duct

Equine ovary

-Several organizational differences compared to other species •Ovary is supported by a more extensive and "chalice-shaped" mesovarium •Somewhat of a reversal of cortex-medulla arrangement •Germinal epithelium is restricted to one site on the ovary •The one site with germinal epithelium = site of ovulation = ovulation or ovarian fossa; ovulations do not occur elsewhere

The Pineal Gland

-Small conical-shaped gland at the back of the brain called the pineal gland or pineal body -Gland is composed of pinealocytes that synthesize and secrete melatonin, a tryptophan derivative -Neural tracts exist between the retina and the pineal gland, and in mammals, this gland is indirectly photosensitive - which means it responds to changes in light perceived by the retina. -Functions as a translator of photoperiod -Plasma [melatonin] is high during periods of darkness, low during periods of light -Melatonin secretion by the pineal gland is regulated by neural activity in the suprachiasmatic nucleus (SCN)

Efferent ducts (ductus efferentes)

-Small series of ducts located at the dorsal pole of the testis -Epithelium = pseudostratified columnar epithelium -"Pseudostratified" because the epithelium appears to have more than one layer of cells ("stacked") but only one layer is present; the nuclei in the cells comprising the epithelium are at different heights which gives the impression of a stratified layer!! -Comprised of principal columnar cells with kinocilia and "flask-shaped" secretory basal cells -Muscularis is unique; thin circular smooth muscle only! -Lumen is collapsed and the surface is uneven

The Pineal Gland: Melatonin and puberty onset

-Some evidence suggests melatonin may be involved in regulating puberty onset even in species without a photoperiod! +Recall we stated that in species with a photoperiod if they reach pubertal size during their non-breeding season onset of adult reproductive activity would be delayed. -Dark period plasma [melatonin] is greatest in children 1-5 yrs of age -Steady decrease with age until puberty when [melatonin] is 25% of the 1-5 yr age group -No change in light period [melatonin] (low!!) -This suggests in a non-photoperiod species - humans - melatonin is still involved in the inhibition of GnRH to delay pubertal onset!

Cervix

-Specialized portion of the female reproductive tract -Characterized by a rigid, thick connective tissue wall -Ruminants, camelids and swine +Cervix is arranged in ring-like structures = annular rings --Ruminants and camelids = 3-4 distinct rings that decrease in size from a caudal to cranial perspective --Pigs = the rings are fused in a spiral fashion (resembling a spring) = interdigitating prominences --Boar's glans penis has a "corkscrew" shape to it --During mating, the boar's penis actually makes turns and the glans penis "threads" the female's cervix -Most species, cervix is arranged as longitudinal folds that run in a caudal to cranial direction +How prominent the folds are varies by species: prominent in the mare, somewhat smooth in the dog and cat -Cranial end of the cervix opens into the uterus +Opening = internal os -Caudal end of the cervix opens into the vagina +Opening = external os -Fornix vagina: pocket formed by the caudal portion of the cervix protruding into the vagina; present in mare, dog and ruminants Properties/functions -Reservoir for sperm before transport to the uterus and oviduct; localized in the crypts -Mucus serves as a vehicle or medium for sperm transport and may serve to select the passage of only the most viable sperm -As progesterone is suppressing mucus secretion, the cervical mucus thickens and seals the cervical lumen = "cervical plug" +The cervical plug, coupled with the constrictive effect of progesterone, keeps the cervical lumen tightly closed, preventing entry of microorganisms into the uterus that may jeopardize the success of the pregnancy -Like the uterus, the cervix is also capable of great expansion and changes in rigidity +Nonpregnant female = cervix is small and rigid except when under the influence of estrogen +Pregnant female at parturition = cervix is large and becomes greatly softened and dilated to allow passage of the fetus and placenta +Softening is due to hormonally-induced proteolytic degradation of the connective tissue by fibroblasts producing collagenase (enzyme that digests collagen!) -Site of semen deposition in swine

Gonadal Steroid Hormones

-Steroids are a family of lipid soluble hormones characterized by the steroid nucleus -Steroid nucleus =17-carbon ring known as cyclopentanoperhydrophenanthrene -Steroid hormones include the gonadal steroids and the hormones produced by the adrenal cortex, e.g., aldosterone, cortisol, etc. -Steroid hormones are classified based on the number of carbons comprising the base steroid nucleus (A-D rings) -Estrane = 18 C -Androstane = 19 C -Pregnane = 21 C Recall - Steroid hormone synthesis involves a biosynthetic pathway where cholesterol (27 C) is the starting steroid substrate.

Differentiation of the Reproductive Tracts ♂

-Testes form near rib cage, must move down into scrotum in males with temperature-sensitive sperm (recall discussion in Male Tract lectures) -Gubernaculum at base of testes fuses to the peritoneum outside of an opening in the abdominal wall called the inguinal ring -Testes are "pulled" down into scrotum through the inguinal ring by growth of viscera surrounding testes artery and ductus deferens, and growth and regression of gubernaculum +Controlled by Insulin-like growth factor 3 (INSL3) binding to receptor LGR8! 4 phases: 1.Transabdominal - fusion of gubernaculum and peritoneum occurs 2.Early Inguinal-Scrotal - visceral growth begins/distal gubernaculum grows rapidly: testes pulled into inguinal canal 3.Mid Inguinal-Scrotal - gubernaculum regresses/ viscera still growing: testes held near inguinal ring within scrotal pouch 4.Late Inguinal-Scrotal - testes are pulled deeper into scrotal pouch by further regression of gubernaculum, encapsulated by visceral vaginal tunic (tunica vaginalis)

Bulbourethral (Cowper's) gland

-The Bulbourethral/Cowper's gland is embedded (bull) or adjacent to (boar/stallion) the Bulbospongiosis muscle. It has a distinct histology associated with this type of glandular tissue. -the size of the bulbourethral glands can be used to differentiate the cryptorchid from the castrated state. After prepubertal castration, the bulbourethral glands shrink.

Major function of the follicle - ESTROGEN

-Theca Interna cells produce most of the precursors for estradiol production! Steroid production starts once the theca begin to form as the follicle begins to transition between the secondary and tertiary stages! -STAR: STeroidogenic Acute Regulatory enzyme: brings cholesterol into the mitochondria where steroidogenesis (act of making steroids) takes place! -The pituitary gonadotropin, LH acts on the theca cells to induce enzymes for conversion of cholesterol to testosterone, and another pituitary gonadotropin, FSH acts on the granulosa cells to induce the enzyme that converts testosterone to estradiol - 2 cell, 2 gonadotropin model!

Degree of folding and cilliation vary by region of oviduct

-Transversal sections of the deferent regions of the oviductal wall are shown. Structural layers are digitally-colored to show the difference in the thickness of the tunicae between the regions (blue: tunica serosa; red: tunica muscularis; purple: tunica mucosa). -Microphotographs of the oviductal luminal epithelium (i-iii), note the difference in cellular populations among regions +Regions: A, a, and i: cranial segment of the ampulla; B, b, and ii: caudal segment of the ampulla; C, c, iii: cranial segment of the isthmus; D, d, iv: caudal segment of the isthmus; -Black arrows: secretory cells; Red arrows: ciliated cells. Pictures are from the oviduct of a single animal that recently ovulated.

Connective tissue components of Testis

-Tunica albuginea (#2) +Outer fibromuscular coat encapsulating the entire tubular components +Contains smooth muscle cells +Contractile as well as support function -Tunica vasculosa +Vascular layer underlying the t. albuginea -Septa +Connective tissue radiations that run from the t. albuginea inwards to the central core of CT in the testis (#3) +Partition the tubular components into lobules (#7) +T.vasculosa tracks with the septa -Mediastinum (#10) +Central core of CT in the testis +Supports the rete testis

Corpus cavernosum penis (CCP)

-Tunica albuginea of the penis defines penis structure +Dense and thick in fibroelastic species vs thin in vascular species +Trabeculae = CT extensions of the t. albuginea of the penis that penetrate into the CCP -Erection canals = specialized structures in the fibroelastic penis +Facilitate blood movement during erection to distal regions of the CCP +Two sets: dorsal and ventrolateral erection canals -CCP is larger than the corpus spongiosum penis (CSP) -Accommodates greater blood engorgement and blood pressure development during erection than the CSP -Pressures can reach as high as 7000 mm Hg +If average aortic blood pressure is 100 mm Hg, then pressures in the CCP can be 70-fold greater!!! +How possible? --Blood volume has increased --Venous drainage is blocked --Muscular contractions compress the volume of blood in the CCP -Blood pressure also in the CSP during erection but some venous drainage is maintained so pressures are not as great +Makes "physiologic sense" - Recall the penile urethra (PU) is in the CSP!

Cell membrane is a phospholipid bilayer!!!

-Water soluble hormones cannot penetrate the cell membrane, hence their receptors must be bound to the extracellular surface of the membrane -Lipid soluble hormones can penetrate the cell membrane by simple diffusion, hence receptors are located in either the cytoplasm or nucleoplasm -Exceptions: +Prostaglandins which are fatty acids that use cell membrane-bound receptors +Several steroid hormones also have membrane receptors/actions!

Genetics as an important determinant of biological sex

-Year: 1959 - Testis Determining Factor (TDF) Identified -1990's: Analysis of Y chromosomes from Turner and Klinefelter Syndrome ID'd region for male gonad and tract development -SRY In 1959, chromosomal analysis of two human disorders, Turner syndrome and Klinefelter syndrome, demonstrated for the first time that genetic factors on the Y chromosomes of mammals are important determinants in male sex. This was called "Testis Determining Factor (TDF)", but the exact gene remained a mystery until 1990 when DNA sequencing was finally used to identify the gene, now called Sex Determining Region Y (SRY) gene. SRY has a fundamental role in sex determination and is the "ON" switch that initiates testis development. -In Turner's syndrome, the affected individual only has 1 sex chromosome, X, (45 X), and in Klinefelter Syndrome these individuals have 2 X chromosomes, and one Y chromosome (are 47 XXY). Both of these disorders are not inherited, they occur when chromosomes do not segregate equally after fertilization. The image is from the publication "A gene from the human sex-determining region encodes a protein with homology to a conserved DNA-binding motif" published in Nature in 1990. In all the species analyzed the PCR probe were missing or different in males verses females. Notice the image from the rabbit the female is missing the dark band (area of positive ID) at the 4.4 kb region, while the male has both the ~2.5 and 4.4 kb sequences.

luteinizing hormone (LH)

-aka Lutropin -Glycoprotein -MW ranges: +25-34 kD -a,b-subunit structure; shared with CG, TSH and FSH -Both subunits are glycosylated Female -With FSH, supports follicular estrogen production by antral follicles -Induces OVULATION and LUTEINIZATION -Removes meiotic block on oocytes during ovulation, allows resumption of meiosis for fertilization -Is LUTEOTROPIC = supports the corpus luteum (CL) and progesterone production Male (Interstitial Cell Stimulating Hormone, ICSH) -Supports androgen production by the Leydig cells -Indirectly maintains the latter stages of spermatogenesis (2°-spermatocyte thru spermiogenesis) via androgens Target cells -Theca interna, granulosa and luteal cells in female and Leydig cells in male Hypothalamic releasing hormone -GnRH - route for reaching the pars distalis? +Effect of pituitary stalk transection? Gonadal steroids -Progestins, androgens and estrogens -In general, negative feedback, except for high concentrations of estrogen in the female - surges at ovulation +Effect of gonadectomy? Neuroendocrine reflex arc for induced ovulators

Graafian or Antral follicle

-terminal follicle stage -Large; for monotocus species, may take up 2/3 of the ovarian volume -Classic blister-like appearance with straw-colored liquor folliculi -Large antrum that causes the follicle to protrude from the surface of the ovary -Theca folliculi has further differentiated into two distinct cell layers +Theca interna = vascular/endocrine tissue surrounding the basement lamina +Theca externa = connective tissue surrounding the theca interna -Pooling of follicular fluid in the antrum has isolated a "mound" of granulosa cells about the oocyte and the zona pellucida -Hillock = "mound" of granulosa cells that the oocyte is perched upon -Oocyte orientation in the follicle = directly opposite the free surface -Species may have a corona radiata = flattened layer of granulosa cells pressed between the zona pellucida and the cumulus oophorus -Cumulus oophorus = specialized cluster of granulosa cells surrounding the corona radiata or the zona pellucida; c. oophorus communicates with the oocyte thru cellular processes that actually penetrate the zona pellucida

Urethra Male

-•Two parts -Pelvic urethra=located dorsal to the pelvis -Penile urethra = tube continuous with the pelvic urethra extending thru the penis, bulb or "start" can typically be found embedded within the bulbospongiosis muscle in the bull Function -Urine and semen transport -Emission = semen transport between the cauda epididymis and the pelvic urethra -Ejaculation = semen transport thru the pelvic and penile urethra Pelvic urethra -Composed of the actual urethra or tube surrounded by a dense, thick skeletal muscle = urethralis muscle -Receives secretions from the accessory sex glands, semen from the vas deferens/ampulla (sp) and urine from the bladder -Colliculus seminalis = site where the vas deferens/ampulla joins the pelvic urethra -Urethral glands = exocrine glands located in the pelvic urethra that are histologically distinct from disseminate prostate, e.g., boar Penile urethra -Located in penis -Loss of skeletal muscle associated with the tube once the urethra enters the penis

Development of the Male and Female Reproductive Tracts

1.Development of the Tracts & Gonads 2.Differentiation of the Reproductive Tracts 2 Major Phases: Phase 1=DEVELOPMENT, Phase 2= DIFFERENTIATION

Trace the path of the sperm into the female tract!

1.Site of production - Seminiferous Epithelium within the Tubulus Contortus 2.Tubulus rectus 3.Rete Testes 4.Caput epididymis 5.Corpus epididymis: Can't see on image 6.Cauda epididymis 7.Vas/ductus deferens 8.Ampulla 9.Pelvic urethra 10.Penile urethra

components of the Hypothalamic-Pituitary-Portal System to collect Pars Distalis (anterior pituitary) hormones!

=Neuroendocrine cells (parvicellular neurons; smaller than magnocellular) in the hypothalamus produce hormones that regulate the release of pars distalis hormones +Releasing hormones (RH) +Release-inhibiting hormones (RIH) -How do the hypothalamic RH/RIH reach the p. distalis?? +Hypothalamic neuroendocrine cells void their secretions (RH or RIH) into the primary capillary plexus (refer to figure)!! +RH, RIH transported through portal vessels to secondary capillary plexus where they interact with target cells in the p. distalis and regulate hormone synthesis and release

Sertoli cell's interaction

A schematic illustration and transmitting electron microscope depiction of the Sertoli cell's interaction with germ cells at different stages during spermatogenesis and other key functions, including: (1) transport of micronutrients across the junctional complex; (2) management of waste and recycled leftover cytoplasm during germ cell development; (3) maintenance of the blood-testis barrier (BTB); (4) establishment of germ cell adhesions and communication; (5) inhibition of immune reactions and maintenance of immune privilege; (6) initiation and response to endocrine signaling pathways; (7) initiation and regulation of the cycle of the seminiferous epithelium; (8) maintenance of stem cell homeostasis. -Most autoimmunogenic germ cells are sequestered within the adluminal compartment of the seminiferous epithelium behind the BTB, where Sertoli cells surround them. -Sertoli cells secrete immunoregulatory factors (5) that modify the immune response and induce regulatory immune cells such as macrophages (M2) and T cells (Tregs). -(A) Actin filaments (green) are seen along the basal Sertoli/Sertoli tight junctions but also lining the heads of elongated spermatids -(B) Claudin-11 (red) stains only the basal junctional complex.

Major endocrine units of the female reproductive tract

A.Ovary - GONAD B.Uterus -The major endocrine units of the female are in the ovary (female GONAD) and the uterus. The other tissues of the female reproductive tract are hormone RESPONSIVE.

Supportive Tissues of the Male Tract

A.Spermatic Cord B.Accessory Sex Glands C.Urethra D.Penis

Supportive Structures in the female tract

A.Uterus B.Oviduct C.Cervix D.Vagina -If the ovary and the uterus are the main functional structures in the female tract, these other structures (oviduct, cervix, vagina) are just as important!

Which Structure in the ovary produces E2?

Antral Follicles

Urethra Distinction

As long as the urethra remains located within the pelvic region it is termed the "pelvic urethra", it rests within the "Symphysis Pelvis" or pelvic symphysis. After it passes over the brim of the pelvis and into the penile tissue it becomes the penile urethra.

Anti-Mullerian Hormone Clinical Applications

Because AMH is produced by growing follicles, plasma [AMH] provides an indication of the size of the primordial follicle pool (ovarian reserves). The above graph shows the AMH and antral follicle count (AFC) of women using oral contraception (OC) and those who did not (non-users). The lines virtually overlap, showing no differences between the 2 groups of women. We can predict how many follicles a women has on both her ovaries by using her AMH levels (green line). A women with an AMH level of ~20 pmol/l has ~18 antral follicles on her ovaries. Women -[AMH] used in IVF procedures to predict patient responsiveness to ovarian stimulation -Women with higher [AMH] tend to have more oocytes retrieved!!! Cattle -Antral follicle count (AFC) determined by ultrasound is a reliable and repeatable indicator of future fertility in heifers -Plasma [AMH] is correlated to AFC in mature heifers

Changes in Dairy Cow Milk production vs. fertility

Better reproductive techniques as well as breeding strategies leading to increase in fertility among dairy cows while still increasing milk yield to help feed a growing population!

Summary of the Hypothalamic-Pituitary-Gonadal Axis in the Female

Complete HPG axis/hormone cascade for the female! Releasing hormone= GnRH, Stimulatory Hormone = LH/FSH, Peripheral Hormones: Inhibin, Activin (dashed line), Estrogen, Progesterone. Note the separate actions of estrogens (low levels negative feedback, high levels positive feedback)

Summary of the Hypothalamic-Pituitary-Gonadal Axis in the Male

Complete HPG axis/hormone cascade for the male! Releasing hormone= GnRH, Stimulatory Hormone = LH/FSH, Peripheral Hormones: Inhibin, Activiin, Testosterone. Note how both Inhibin and testosterone have negative feedback in BOTH the pituitary and the hypothalamus. Notice how activin (dashed line --) is the only PH with positive feedback on FSH

Seminiferous epithelium testes

Components -Four to five rows of sperm cells in various stages of spermatogenesis +Least developed at base of epithelium (adjacent to basal lamina) -Sertoli cell (nurse or sustentacular cell) spans height of s. epithelium -No capillaries within the s. tubule!! A barrier exists - Blood-Testis Barrier -to prevent sperm antigens (proteins that could be recognized as foreign by the male's immune system) from entering the male's bloodstream -Why recognized as foreign? +Sperm are haploid and all other cells in the male's body are diploid (germ cells vs. somatic cells) -If sperm antigens were to leak out of the tubule and gain access to the bloodstream, the male's white blood cells would respond to the foreign proteins and mount a cell-mediated immune response where they would enter and destroy the seminiferous epithelium +Autoimmune infertility can result where the male destroys his own sperm-producing epithelium -The Blood-Testis Barrier (BTB) refers to the cellular and acellular components constituting the barrier that prevent haploid sperm from being recognized as foreign by the male's immune system Components of Barrier -Capillary endothelium (wall) = not very exclusive to antigens -Myoid layer = some tight apposition of adjacent membranes but gaps exist -Basal lamina = not exclusive -Tight junctions between adjacent Sertoli cells = most exclusive component of the BTB!! +Form a very selective permeability seal +In order for a substance to leave or enter the lumen of the seminiferous tubule, it must be permeable to the Sertoli cell plasma membrane!! -The position of the Sertoli cell tight junctions divides the s. epithelium into two compartments -Basal = sperm cells in mitosis (diploid) (2N-4N)! -Adluminal = sperm cells in meiosis & spermiogenesis (transition from 4N to 1N) (haploid 1N)!

Other Hypothalamic Releasing Hormones important for reproduction - Corticotropin Releasing Hormone (CRH)

Corticotropin Releasing Hormone (CRH) -Polypeptide; 41 aa; 4.5 kD -Produced by the median eminence -Causes release of ACTH by the pars distalis (cells are called corticotropes) which causes release of cortisol by the adrenal cortex -Important factor involved in initiating parturition cascade -Stress mediated

Differentiation of the External Genitalia

Development of the external genitalia is a 3 step process: 1.The first phase is the pre-androgen phase in both genetic sexes during which the lateral genital swellings emerge bilaterally adjacent to a primitive genital structure called the cloacal membrane or genital tubercle. 2.During the second phase DHT production by the XY fetus leads to sexually dimorphic differences in outgrowth and urethral formation readily apparent. 3.The third phase of external genitalia development, which is more genetically complex and relevant in the male than in the female due to the increased distal outgrowth, is the successful tubularization of the urethra throughout the length of the penis. -If the male urethra does not tubularize completely, the result is a common congenital defect termed hypospadias wherein the tubal opening of the urethra is located somewhere along the ventral aspect (underside) of the penile shaft rather than at its distal-most tip. In humans, the incidence of hypospadias is approximately 1 in every 250 live male births and is typically corrected with a complex surgical procedure. -The labioscrotal folds differentiate along with the penis/clitoris to become the scrotum/labia. This process is illustrated by the images above. a)Scanning electron microscopy of the ontogeny of the developing human fetal penis (A-F) from 7.5 to 13 weeks and developing human clitoris (A1-F1) from 8 to 13 weeks of gestation. White arrowheads indicate the junction of the penile and clitoral shaft with the glans (ages 7.5-11 weeks A-D & A1-D1). At 12 weeks of gestation in both males and females note advance of the prepuce over the glans (white arrowheads, fix) (E, E1, F & F1). Red arrowheads denote the epithelial tag. The blue arrowheads indicate the median penile raphe. Yellow arrowheads indicate the open urethral groove in males and vestibular groove in females. The green arrows in A & A1 denote the urethral plate in males and vestibular plate in females which is not canalized based on histologic analysis and light sheet fluorescence microscopy with E-cadherin. b)In males, the lateral edges of the urethral groove (urethral folds) subsequently fuse in the ventral midline, thus converting the urethral groove into a tubular urethra within the penile shaft. c)In females, the vestibular folds (homologues of the urethral folds) do not fuse in the midline and instead remain separate as the labia minora defining a structure called the vaginal introitus. d)From about 12 weeks onward the angle of the male genital tubercle (developing penis) to the body wall approaches 90°, while in contrast the orientation of developing clitoris remains closer to the body wall.

Phase 1) Development of the Reproductive Tracts

Development of the genital tubular system and the external genitalia occurs in the male once the gonad forms the testes and produces AMH and Testosterone. In 1947, a French Endocrinologist named Alfred Jost published the results of a remarkable set of experiments establishing the mechanism by which sexual differentiation of the reproductive tracts occurred. If he used microsurgery to remove the gonad in the indifferent stage of fetal development in rabbits (A), both XX and XY fetuses acquired the duct system of females. If he grafted fetal testis adjacent to the ovary of an XX embryo he could drive development of the male duct system in female fetuses. This became known as "Jost's paradigm": the testes drive development of the male tracts, and the female tract system is the default status. We now know that this is not the case! There is another transcription factor within the cells of the primitive male tract - COUP-TFII (chicken ovalbumin upstream promoter transcription factor II) regresses the Wolffian/mesonephric duct in the absence of the testis. Because we know maintenance of the Wolffian tract requires testosterone if you block COUP-TFII & remove the testis the fetus retains both duct systems. So, development of the duct systems of the tract under normal conditions follows this sequence: A. Two sets of ducts exist at the indifferent stage of fetal development: Wolffian/mesonephric and Mullerian/paramesonephric ducts B. The gonads of the XX and XY fetus form into ovaries and testes: -Sertoli cells in the XY feus produce anti-Müllerian hormone (AMH), which regresses the Müllerian/paramesonephric duct -Lack of Leydig cells/testosterone in the XX fetus results in activation of COUP-TFII and regression of the Wolffian/mesonephric duct C. The remaining duct systems in the XX and XY fetus differentiate under the influence of local steroid hormone milieu -Differentiation of the male tubular system (Wolffian ducts) and external genitalia is absolutely dependent on testosterone (Leydig cells)

Vas (ductus) deferens

Duct transporting sperm from the cauda epididymis to the ampulla/pelvic urethra -Lumen = iron cross-shaped +Mucosa = similar to the epididymis; pseudostratified columnar epithelium composed of principal columnar cells with stereocilia and basal cells +Muscularis = smooth muscle; most well-defined of all the reproductive tract organs --Thick outer longitudinal layer --Thick middle circular layer --Thin inner longitudinal layer +Outer Serosa- connective tissue surrounding the muscularis of the vas

Phase 1) Development

Each mature ovum contains a species-specific number of autosomal chromosomes and one X sex chromosome. A mature sperm contains the same number autosomal chromosomes and either one Y or one X sex chromosome. A fertilized egg, therefore, contains complete pairs of autosomal chromosomes and one pair of sex chromosomes, either XX (genetic female) or XY (genetic male). At least 100 autosomal genes are present on the X chromosome and mutations of these genes cause a variety of sex-linked disorders including color blindness, hemophilia and Duchenne muscular dystrophy. In contrast, the Y chromosome has very few autosomal genes. One of the X chromosomes in females is inactivated, producing the Barr body. The inactivated chromosome must be reactivated when cells replicate and divide. -The genes present in the Y chromosome drive male development, and in order for the complete female tract and gonad to develop these specific male genes must be absent. One gene is required for female tract development. •The Tracts and Gonads develop in tandem, in order for the tracts to develop properly, the gonad must develop as well. -In early gestation male and female fetuses are indistinguishable termed "biopotential" - both gonads develop from the Intermediate Mesoderm (#1). -Then, either SF1 (Male) or WNT1 (female) induces the intermediate mesoderm to change into the mesonephros (#2), ultimately forming a structure within termed the Bipotential Gonadal ridge (#3). +As far as we know, at this point the fetus can still possess either male or female (or both) structures!!! -At this point, if there is a functioning SRY gene, which encodes the SRY protein (transcription factor) the biopotential gonad will develop into a testis (Male, #4m). The genes SOX9 and SOX3 (previously called Desert hedgehog DHH complex - this is what Senger test refers to. I will accept both) cooperate with SRY to induce Testis development (#5m). +SRY functions as a "master switch" for genes involved in male sexual differentiation -SRY stimulates the development of Sertoli Cells and SOX9/3 cause differentiation of the Leydig Cells +Sertoli cells produce AMH to regress the Mullerian Duct (female structure), and Leydig cells produce T to help male fetus proceed to Phase 2 (differentiation) •In the absence of SRY, it was previously assumed there were no genes on X-chromosome that controlled female tract development → this was called the "theory of the default path" - this was because there were no naturally occurring mutations identified in humans or livestock species where defects in prepubertal or adult individuals were identified lacking any form of female structures! -Now know that gene "Dosage-Sensitive Sex Reversal on Chromosome X, gene 1; DAX-1" (#4f) must be turned on for proper female tract development! +Interactions hypothesized between DAX-1 and SRY, SRY thought to inhibit DAX-1 in XY male fetuses -In absence of SRY, DAX-1 inhibits testes development, allowing the biopotential gonad to develop into an Ovary (#5f). -Because only very low levels of testosterone are detected in XX female fetuses, the Wolffian duct regresses (male structure), and the estradiol produced by the Ovary helps the female fetus proceed to Phase 2.

Epididymis and steroid hormones

Estrogens influence spermatogenesis in the testis, transport and maturation of sperm within extra-testicular regions (such as efferent ductules and the epididymis). CYP19A1 (aromatase) is expressed in the Cauda Epi., and can convert T into E2. Seminal fluid of many species contains measurable amounts of estradiol. Testosterone enters the epididymis by 2 routes. It can enter through the efferent ducts after leaving the rete testis, where it is mostly bound to androgen-binding protein (ABP), or through the circulation. ABP is highest in the proximal (caput) and lowest in the distal (cauda) region. This means there is more free testosterone in the corpus and cauda regions than the caput. DHT is important to maintain the health of the cells of the epididymis - DHT deficiencies result in necrotic changes to the epididymis and the seminiferous epithelium.

Most (correct) Reproductive Knowledge generated only in last ~100 years

Even after the discovery of sperm in the 16th century, it was thought they contained entire, microscopic fully-formed adults.

Basic Characteristics of Hormone Event Cascades

Event Cascades begin with an environmental signal that is transmitted to the CNS & then propagated to the hypothalamus, anterior pituitary & the peripheral target gland for generating the appropriate biological response. Proceeding down the cascade shown from the central nervous system to the peripheral hormone, there is an increasing amount (mass) of the hormone released at each stage: the hypothalamic releasing hormones are secreted in nanogram amounts, the anterior pituitary hormones in microgram amounts into the circulation from which it reaches its specific receptor in a target cell, & the terminal hormone in microgram to milligram amounts. These biochemical features of the hormones at different points of the cascade indicate a high degree of amplification stemming from a unique event, the initiating signal from either the external or internal environment. A signal transduction process, specific to the hormone, its receptor, & the target cell, ensues which culminates in the release of the target cell hormone, usually in milligram or high microgram quantities. Each of the cascades initiated in the brain & hypothalamus is subject to negative (and in some rare cases positive) feedback control from the peripheral gland that is affected by the anterior pituitary hormone. These feedback effects can be exerted at the anterior pituitary, at the hypothalamus, or in the central nervous system outside the hypothalamus. In addition, short feedback loops, such as the inhibition of the secretion of a hypothalamic releasing hormone by the anterior hormone it controls, play a role in this regulatory network. The cascade systems are kept in check by negative feedback loops, long ones from the distal target gland to the hypothalamus, anterior pituitary, or central nervous system & shorter ones from, for example, the pituitary to the hypothalamus. The hypothalamic releasing hormones function to control the secretions of the anterior pituitary hormones, either positively or negatively. The hormones secreted by the distal endocrine glands exert, in general, negative feedback effects in the brain & in the anterior pituitary.

Cremaster Muscle

External cremaster muscle -Cone and C-shaped skeletal muscle -Runs from the dorsal aspect of the testes to the body wall -Located outside the tunica vaginalis parietal but beneath the scrotal fascia -Involved in the "fight" or "flight" response -Minor role in thermoregulation Internal cremaster muscle -Thin smooth muscle surrounding the spermatic artery, veins, nerve and lymphatics

Sexual Differentiation of the Brain

Female = tonic and surge (Ovulatory - PO) centers for GnRH release Male = Only tonic center for GnRH release Why does this happen? Male fetuses (early in pregnancy) have the precursors for both tonic and surge (Ovulatory - PO) centers for GnRH What happens?? Testosterone "defeminizes" the male fetus' hypothalamus!!! Testosterone defeminizes the hypothalamus but the biologically active steroid in this mechanism is estradiol!! 1.Testosterone diffuses across the blood-brain barrier in the developing male fetus. 2.Once testosterone enters the cytoplasm of neurons within the hypothalamus, it is acted on by CYP19A1/Aromatase and converts it to Estradiol (Recall steroid biosynthesis!) 3.Though the genomic mechanism of steroid hormone action, this "defeminizes" the brain. The surge center regresses and only the tonic center is maintained

Follicles

Functional Structures in Ovaries: Follicles -Cellular envelope that encloses the ovum = oocyte -Basic structure: layer(s) of cells surrounding the oocyte -Several types based on stage of development and degree of differentiation -Types: primordial, primary, secondary, tertiary and Graafian (quaternary) Requires histology = microscopic study of tissues sectioned in a thin slice = microanatomy

Mechanism of hormone action

How does a hormone alter its target cell's biological function? -Hormones interact with receptors in/on target cells, and thru their respective mechanisms of action, induce biochemical changes that cause the alteration in biological function +LH acting on the granulosa cells to induce luteinization! -Think of a game of baseball - hormones as the ball, and the receptor as the glove - baseball gloves were designed for catching baseballs, not basketballs!

Control of Prl Secretion

Hypothalamic releasing or release-inhibiting hormones: -"Prl releasing hormone" (PRH) +Thyrotropin RH (TRH) +Vasoactive intestinal peptide (VIP) -"Prl inhibiting hormone" (PIH) +Dopamine - in tuberoinfundibular dopamine (TIDA) neurons in the arcuate nucleus +Gamma-amino butyric acid (GABA) -Major control of secretion +PIH. Why? Recall effect of pituitary stalk transection!! -Lactotropes produce Prl via cAMP/PKA system = "turned on" by PRH -Controlled by PIH, mainly dopamine +Dopamine decreases cAMP which decreases transcription of Prl gene -Estrogen - can Prl by TRH receptors and ¯ dopamine receptors. -Neuroendocrine reflex arcs

Phase 1) Development Part 2

Immediately prior to SRY or DAX1 activation the Bipotential gonadal ridge aka. Genital ridge - (defn: mass of mesenchymal cells surrounded by an epithelium (coelomic epithelium)) forms outside the mesonephros. For a species with a 9-month gestation, at 4-6 weeks, primordial germ cells (PGC) migrate from the yolk sac endoderm and colonize this genital ridge ® once these germ cells arrive this structure is now known as a "primitive gonad" Cells from the coelomic epithelium (germinal epithelium) proliferate and form cords of tissue in the gonad at 6-8 weeks.....sex cords (aka primary sex cords (female) or testis cords (male)) .... Therefore, the Primitive gonad (A), is transformed into the Indifferent Gonad (B). -At this time the fetus still is "bipotential" - this is prior to SRY activation!

Phase 1) Development of the♀

In the absence of SRY, after DAX-1 activation PGCs do not track with the primary sex cords; the primary sex cords regress (blue bar) and the PGCs sort with a secondary proliferation of epithelial cells ("secondary sex cords") and the cortex develops - Now this is considered an OVARY (D). •Epithelial cells in the secondary sex cords give rise to granulosa cells and the PGCs to oogonia •Mesenchymal cells will differentiate into thecal cells •Development of the ovary typically occurs later than the testis (8-10 weeks)

Inhibin and Activin and Tonic FSH

In the female, granulosa cells produce Inhibin and Activin. Inhibin depresses FSH production in the follitropes of the pars distalis. In contrast, activin produced by the granulosa cells increases production of FSH from the follitropes, and promote expression of FSH receptors on the granulosa cells of growing follicles. Levels of activin are similar to estradiol levels in serum of females. Similar effects are seen in the male with these peptides being produced by the Sertoli cell.

Differentiation of the Reproductive Tracts

In the fetus, the first structure that functions to filter waste in the Pronephros (not pictured): this is an embryonic remnant of primitive kidney (the functioning kidney in amphibians, etc.). The Pronephros regresses early in embryonic development in both sexes, and is replaced by the Mesonephros, which drains into the mesonephric duct (#1). While the fetus has a pronephros, the bladder is referred to as the cloaca. Once the mesonephros forms the cloaca is now transformed into the urogenital sinus (UGS). As the gonads develop, the fate of these paired ducts depends on the presence or absence of anti-Mulllerian Hormone (AMH) and testosterone. Metanephros forms as the mesonephros either regresses (Female) or is transformed into reproductive tract structures (Males). This becomes the functioning adult kidney in mammals - once this forms the fetal bladder is no longer a cloaca or UGS, it is now the bladder.

Phase 1) Development of ♂

In the presence of SRY, PGCs associate with the primary sex cords and the medulla develops. •Primary sex cords enlarge (blue bar), increase in number, become tubular and interconnected and will eventually become the seminiferous tubules - this is now considered a TESTIS (C) •Epithelial cells within the tubules give rise to Sertoli cells and PGCs will develop into spermatogonia •Mesenchymal cells in the peritubular compartments will become Leydig cells •Cortex becomes germinal epithelium and tunica albuginea

Gonadal Polypeptide Hormones: Inhibin & Activin

Inhibin and activin: Structurally related polypeptides yet different actions •Inhibin - two polypeptides: A-, B-subunits •Activin - two inhibin B-subunits •Source: Granulosa and Sertoli cells Granulosa and Sertoli cell products •Biological effects -Inhibin -32-34 kD; selectively suppresses FSH release -Activin - 28 kD; selectively stimulates FSH release Follistatin •Binding protein for activin •Source: Granulosa cells and the pituitary •Biological effects -Prevents activin from stimulating FSH release

Anatomy of the Female Reproductive Tract

Major Structures: A.Ovary B.Oviduct C.Uterus D.Cervix Vagina

Uterus Types

Mammalian females can be classified as having one of three uterine types -Duplex -Bicornuate -Simplex Classification depends on presence or absence of uterine horns or uterine body

Onset of Puberty 4

Metabolic factors! -Current model: Metabolic factors act directly on kisspeptin-secreting neurons -How does the hypothalamus increase its release of GnRH and reduce its sensitivity to the negative feedback effects of the steroids so that puberty can be attained? Two explanations 1. Age-dependent changes = "maturation" of the hypothalamus where it releases more GnRH and loses its enhanced sensitivity to the gonadal steroids 2. Metabolic changes = as the animal grows, metabolic rate decreases +A state of energy surplus must be attained +Metabolic factors can stimulate GnRH release +There is more evidence for metabolic changes! Metabolic factors: -Leptin - hormone produced by adipocytes -Plasma [leptin] is related to body fat -Increased body fat --> Increased plasma [leptin] -Leptin can stimulate GnRH release +Directly thru kisspeptin-secreting neurons +Indirectly by acting on Neuropeptide Y (NPY)-secreting neurons and suppressing NPY release +NPY secretion by these neurons suppresses GnRH release Also: Plasma glucose Plasma fatty acids

Oviduct is a lumenal organ!

Microanatomy (histologic perspective) -Oviduct, like other portions of the female tract, is a tubular organ -Similar in anatomy and function to the gut, another tubular organ, with respect to movement of contents -Tubular organs are comprised of three tissue layers +Outer layer = serosa or adventitia +Middle layer = muscularis +Inner layer = mucosa -Serosa = layer of connective tissue surrounded by a single squamous epithelium -Adventitia = serosa without the epithelium -Muscularis = smooth muscle layer +Outer longitudinal smooth muscle +Inner circular smooth muscle --Enables "peristaltic"-like movements -Mucosa = limiting epithelium adjacent to the lumen (lumenal epithelium) supported by an underlying connective tissue layer containing blood vessels, etc. (lamina propria; Senger uses "submucosa") -Oviductal mucosa +Secondary structure = large, penetrating folds of mucosa enter the lumen; not a smooth tube!!

Steroid Hormone Model

Non-genomic

Timeline of Development of Repro Tract

Note species differences in descent of the testes! In colts, the testicles should pass through the inguinal canal within days to weeks after birth - any longer and the colt is likely a high flanker or cryptorchid. The testes are still very small, and because they are still entering the scrotum they may or may not be palpable in the groin region, so this is why many equine vets wait until 18 to 24 months before a diagnosis depending on breed

Differentiation of the Reproductive Tracts ♂︎

Now, Male! What transcription factor is present in the XY fetus compared to the XX? - SRY! +SRY - +Sertoli cells. Sertoli cells - produce AMH to regress the Paramesonephric/Müllerian Duct! Leydig Cells produce Testosterone= Blocks COUP-TFII and Wolffian/mesonephric tubules develops into the efferent ducts (Vasa efferentia), while the lower portion of the Wolffian/mesonephric duct develops into the epididymis and ductus deferens (vas deferens). Testosterone is converted to DHT and drives development of the penis, scrotum, and accessory sex glands.

Embryonic Development of Pituitary

Occurs early in first trimester - species dependent Humans: 9 month gestation -42 days Rathke's pouch appears - invagination of the roof od the fetal mouth! -60 days stalk of Rathke's pouch regresses 4 months - differentiation of "tropes" begins -Corticotropes are the first pituitary cells to achieve terminal differentiation, followed by melanotropes, thyrotropes, somatotropes, mammotropes, and finally gonadotropes -Vascular portal network complete by term Please review the steps in Figure 4-2! Follow the figure in the counter-clockwise direction as the pituitary forms.

Vagina

Outermost portion of the female reproductive tract -Anterior (cranial) vagina +Tube that is continuous with the cervix and the posterior (caudal) vagina -Posterior (caudal) vagina or vestibule +Recall the "dividing line" that separates the two chambers of the vagina +Urethral orifice is in the vestibule; cranial of the urethral orifice is anterior vagina -External genitalia +Clitoris and vulva Vestibule includes: -Urethral orifice = opening of the urethra in the floor of the vestibule -Suburethral diverticulum = blind sac located caudally to the urethral orifice; shares the same site; no known physiologic function; present in sow and cow -Vestibular glands (Glands of Bartholin) = paired exocrine glands located in the wall of the vestibule with ducts emptying into the lumen +Secrete a viscous, mucus-like fluid +Hormone responsive; active at estrus when estrogen is high -Gartner's tubules = vestige or fetal remnant of a paired duct (Wolffian or mesonephric ducts) that contributes to the male's reproductive tract +Do not change hormonally in the female External genitalia -Includes the clitoris and the vulva (collective term for labia majora and labia minora) -Clitoris +Structural analog of the penis in the male +Develops from the same indifferent fetal structure = genital tubercle +Contains some erectile tissue -Vulva +Part of the perineum = region surrounding the anus and the vulva +Only visible part of the female tract +Responsive to reproductive hormones --Estrogen = high at estrus or heat = vulva becomes enlarged, edematous and reddens --Progesterone = high during pregnancy or mid-cycle = vulva is reduced in size and pale -Contains bundles of smooth muscles = constrictor vulvae muscles = function to keep the vulva closed; prevent entry of microorganisms into cranial portions of the tract Properties/functions -Passageway for semen at mating and fetus and placenta at parturition -Site of semen deposition for most species +Exceptions are the dog, mare, sow, rodents

Ovary

Ovary = female gonad -Exocrine and endocrine organ +Endocrine = releases hormones into the circulation +Exocrine = releases gametes into a duct Shape varies: -Cow, ewe, human = monotocus sp (single or twin-bearing sp) = almond-shaped -Pig, dog = polytocus sp (litter-bearing sp) = grape-like shape •Mesovarium = portion of the broad ligament; suspends ovary in body cavity •Hilus = base of the ovary; where mesovarium attaches and where blood and lymphatic vessels and nerves enter/exit the ovary Follicles: Contain oocytes, support growth of oocyte and secrete estrogen to induce estrus behavior and prepare tract for ovulated oocyte. CL: Formed after ovulation, secretes progesterone to prepare tract for implanting embryo and sustains pregnancy

Four major parts (pars) of pituitary gland

Pars tuberalis -"Stalk" of the pituitary gland; not really a stalk -No known endocrine function Pars intermedia -Wedge-shaped pars that bifurcates the pituitary into two sections -Limited endocrine function -Site of melanocyte stimulating hormone (MSH) production -Melanotropes = pars intermedia cells that produce MSH Pars distalis -Major endocrine pars in the pituitary gland -Site of synthesis, storage and secretion of several hormones -Comprised of several populations of distinct endocrine cells -Histologically, two cell populations +Chromophobes = cells that do not take up much histologic stain and appear pale in color +Chromophils = cells that take up the histologic stain (two types) --Acidophils = acidic-staining cells (eosinophilic); stain pink/red --Basophils = basic-staining cells (hematoxylinophilic); stain blue -Chemistry of the hormones defines the histologic properties of the cells that produce them +Chromophils --Acidophils = produce GH and Prl; protein hormones --Basophils = produce FSH, LH and TSH; glycoprotein hormones +Chromophobes --Regarded as immature chromophils --Some produce ACTH Pars nervosa -Involved in endocrine function, but only as a site for storage and release of hormones

Thermoregulatory reflex to effect cooling, Reflex Arc #1

Reflex Arc #1: Sweating and Polypnea -The effect of increased temperature is particularly acute in the ram. There are two ways the male's body reacts to being placed into a warm (>39◦C) environment from a thermoneutral (<39◦C) location. Follow the pathway!!! End result is scrotal (and peripheral) sweating and rapid panting (polypnea). This is to rapidly cool down those testes to ensure they contain functional primary spermatocytes.

Thermoregulatory reflex to effect cooling, Reflex Arc #2

Reflex Arc #2 to to effect cooling - tunica dartos relaxes -Movement from thermoneutral to warm temp, Tunica dartos relaxes +lowers testes away from body cavity +weight of testes stretches scrotal skin and scrotal surface area --> promotes heat loss -At same time reflex arc #1 still active! +Sweating - scrotal skin/systemic +Panting (polypnea) -Net effect - induce cooling = motor responses

Oviductal mucosa

Secondary structure = large, penetrating folds of mucosa enter the lumen; not a smooth tube!! -Lumenal epithelium +Simple (only one layer of cells) columnar (rectangular shape) epithelium +Two populations of cells +Ciliated cells (kinocilia) +Non-ciliated secretory cells

Oxytocin Biological Effects

Sensory stimulus -Cervico-vaginal stimulation at mating or parturition Motor responses -Oviductal and myometrial contractions for moving sperm to site of fertilization at mating due to coital stimulation -Myometrial contractions for moving fetus thru birth canal at parturition due to fetus moving against cervix Pitocin = pharmaceutical preparation of OT used therapeutically to stimulate uterine contractions during parturition -OT has no direct effect on cervical dilation (another hormone has a specific effect on cervical dilation!!) Biological effects of oxytocin: -Uterine involution = restoration of uterus to its pre-pregnancy status +OT stimulates myometrial contractility and facilitates uterine involution +high suckling frequency --> high rate of uterine involution = shortens the interval between parturition and complete uterine involution -Luteolysis +Specialized process and independent from myokinetic effects +Luteal oxytocin and estrogen are involved in inducing endometrial synthesis of PGF2a to cause regression of the CL!! -Emission = movement of sperm from the cauda epididymis thru the vas deferens and ampulla to the pelvic urethra -Neuroendocrine reflex arc for emission in the male: +Sensory stimulus --Erotogenic (sexual) stimulus ---Glans penis ® pudendal nerve; brain +Motor response --Contraction of smooth muscle in muscularis of cauda epididymis, vas deferens and ampulla during emission

The 2 cell types which comprise the endocrine component of the testes are the

Sertoli Cells -Tight junctions are not static +Separate and reform to allow sperm cells to move between the Sertoli cells as they advance towards the lumen during spermatogenesis -Intercellular fluid composition varies between the adluminal and basal compartments and reflects the exclusive properties of the tight junctions. Sertoli cell functions -Protects the spermatogenic epithelium (sperm in meiosis) from being recognized as foreign by the male's immune system -Provides a specialized fluid microenvironment for the developing sperm cells -Removes the residual body (excess cytoplasm) from the mature spermatozoan and discharges sperm from its apical surface = spermiation Endocrine functions of Sertoli Cells: -Produces androgen-binding protein, some estrogens, by forming the tight BTB, these cells establish high testosterone concentrations in the lumen of the seminiferous tubule for application to the seminiferous epithelium or other aspects of the excurrent duct system, e.g., epididymis Leydig cells (Interstitial cells of Leydig) -Very important testicular cell!! -ENDOCRINE POWERHOUSE OF TESTES: Produce androgens! +Testosterone -Located in the peritubular spaces (interstitium) adjacent to capillaries for secreting androgens into the male's circulation!

Testes parts

Spermatic artery and veins -Straight vessels at dorsal aspect of cord -Intertwine to form pampiniform plexus Pampiniform plexus -Highly convoluted network of the spermatic artery and veins -85% of the artery and veins are intertwined in the p. plexus -Functions in testicular thermoregulation Spermatic nerve and lymphatic vessels

Oxytocin

Structure -Octapeptide/Nonapeptide +Amino acids 1 and 6 are Cys that are disulfide linked; 2 cysteines = 1 cystine -Hypothalamic or pituitary gland hormone? +Sites of production vs storage and release -Synthesized as a prohormone in the cell bodies of the SON and PVN and packaged into secretory vesicles (example is PVN, but similar for SON). +Prohormone includes a large polypeptide = Neurophysin I and the oxytocin peptide +The secretory vesicle is transported to the axonal termini in the pars nervosa by "axoplasmic flow" +Upon stimulation for release, oxytocin is cleaved from Neurophysin I and released into the circulation from the pars nervosa by exocytosis -Produced by the CL of several sp, e.g., ruminants, primates -Mechanism of hormone action: +Membrane receptor and protein kinase C mechanism of action -Myokinetic +Stimulates contraction of smooth muscle in oviduct, myometrium, mammary gland, cauda epididymis, vas deferens and ampulla -Biological effects are augmented by estrogen +Estrogen induces oxytocin receptor synthesis in target cells --Example = estrogen myometrial receptors for oxytocin --Net effect = amplitude or force of contraction by myometrium -Participates in regression of the CL

Notables in Male Reproductive Physiology

The drawing of the rat Sertoli cell was taken from a photograph of a plastic model created from 675 micrographs of 372 serial electron microscopic sections. Cellular processes and cup-like hollows show the intimate relationship with adjacent germ cells.

hypothalamus structure

The hypothalamus is located dorsally to the pituitary gland and is continuous with the pars nervosa. Hypothalamus consists of neurons, neuroendocrine cells and glial cells organized into clusters of cells called areas, bodies or nuclei. The dotted areas make up the surge center, while the hatched areas comprise the tonic center. Also, you should know what the PVN and SON are and their relative locations. Areas above the dotted line are considered the hypothalamus, while area below in Sphenoid bone is the pituitary.

Phase 1) Development of the ♂ Testes

These diagrams show how the sex cords develop as the gonad transitions from the Primitive gonad (A) to the Indifferent Gonad (B), and the testis (C). Note how the Mullerian duct is lost by the time the testis develops.

Phase 1) Development of the ♀ Ovaries

These diagrams show how the sex cords develop as the gonad transitions from the Primitive gonad (A) to the Indifferent Gonad (B, C), and the Ovary (D). Note how the sex cords are lost by the time the fetal ovary forms the primitive follicles (precursors to primordial follicles).

Hypothalamus is associated with many endocrine disorders

These types of diseases are difficult to diagnose because of the variability in characteristics due to different mutations of the same gene. Also, the Hypothalamus regulates most processes involved in body homeostasis, so many disorders are associated with a broad spectrum of similar symptoms. - We know the functions of the hypothalamus, hormones and genes by studying disorders of function! HOH: This syndrome is only recently characterized after the affected individuals underwent extensive diagnostic testing to rule out other similar disorders. The symptoms are associated with congenital hydrocephalus, centripetal obesity, hypogonadism, intellectual deficit and short stature. May be transmitted by X-linked recessive inheritance. Common Hypothalamic diseases are associated with disorders caused by damage to the hypothalamus from malnutrition, including anorexia and bulimia eating disorders, radiation, surgery, head trauma, lesion, tumor or other physical injury to the hypothalamus.

Reproductive Knowledge to Benefit Global population challenges

This population estimate from the UN assumes a decline in fertility for developing countries and an increase in fertility for countries with shrinking populations!

Penis

Three parts -Base ("root" - attached to the ischial arch) -Shaft -Glans penis = terminal end Two types of penes (plural) -Vascular = stallion, dog, tom, primates, rodents, etc. -Fibroelastic = ruminants, camelids and the boar -Basic anatomical difference = proportion of vascular (spongy) tissue to fibroelastic (CT) tissue Basic penis structure -Large, sponge-like vascular bodies, that can accommodate blood engorgement, supported by fibroelastic tissue -The fibroelastic tissue ranges in density and thickness by species Penis is composed of two vascular bodies surrounded and separated by a CT sheath (tunica albuginea of the penis) -Corpus cavernosum penis (larger; CCP; dorsal) -Corpus spongiosum penis (CSP; ventral) +The penile urethra runs thru the CSP!! -The two vascular bodes each have vascular origins located caudally near the ischial region of the pelvis +Crura = collective term for the left and right crus penes which are thumb-like structures that lead into the CCP +Penile bulb = bulb-shaped mass of vascular tissue which the CSP extends from in a cranial direction -Fibroelastic penis (Ram and Bull) +Fibroelastic CT is very dense and firm, hence, the penis is moderately rigid in the non-erect male +Contains proportionately more fibroelastic than vascular tissue +When blood engorgement of the vascular bodies occurs during erection, there is little change in penile size despite a significant change in rigidity -Vascular penis (Stallion) +CT or fibroelastic tissue is not dense and firm +Contains proportionately more vascular than fibroelastic tissue +Vascular bodies can accept large volumes of blood +Blood engorgement of the vascular bodies is the major force driving the increase in penile size and rigidity during erection

Microanatomy of Uterus

Tubular organ, 3 tissue layers!! -Serosa = Perimetrium -Muscularis = Myometrium; well-defined layers of thick inner circular and thin outer longitudinal smooth muscle -Mucosa+lamina propria/submucosa = Endometrium; +Lumenal epithelium is similar to the oviduct +Simple columnar epithelium with secretory cells +Secondary structure = tubular glands; continuous with the lumenal epithelium, penetrate the mucosa and contact the myometrium. Tubular glands are not static!!! -Respond to hormones dominating the female's circulation at the time -Estrogen and progesterone affect: +Degree of growth and differentiation +Composition of secretions, e.g., pregnancy-specific proteins under the influence of progesterone -Produce biochemical secretions supporting embryo development before a direct connection with the uterus is established in implantation

Microanatomy of Cervix

Tubular organ, 3 tissue layers!! -Serosa = prominent!! Composed of very dense connective tissue which gives the cervix its rigidity; rich in collagen (c) -Muscularis = reasonably thin and consists of irregularly arranged bands of inner circular and outer longitudinal smooth muscle (m) -Mucosa = populated by simple columnar epithelium with ciliated cells (kinocilia) and non-ciliated secretory cells supported by a lamina propria (blue arrow) Schematic of the bovine cervix. A) longitudinal section of the cervix: V = vaginal, M = mid, and U = uterine segment, 1 = external os/vagina, 2 = Internal os/uterine lumen, 3 = cervical canal. B) cross-section of the cervix: a) mucosal epithelium, b) superficial loose stromal band (outer serosa) c) inner serosa: deep dense collagenous layer, d) circular and e) longitudinal oriented muscle layer, f) outer thin layer of very loose connective tissue with blood vessels underneath.

Microanatomy of Vagina

Tubular organ, 3 tissue layers!! -Serosa or adventitia, depends on species -Muscularis = irregularly arranged bands of inner circular and outer longitudinal smooth muscle -Mucosa Different cellular composition depending on location relative to posterior -Anterior vagina +Livestock species = Presence of a lamina propria supporting a simple columnar epithelium with ciliated cells (kinocilia) and non-ciliated secretory cells; these secretory cells contribute to vaginal fluid +Lamina Propria = contains elastic fibers, blood vessels, lymphatics and nerve supply +Other species (primates, rodents, dogs, cats, etc.) = stratified squamous epithelium --Several layers of flattened cells --No secretory cells --Sweat, sebaceous glands, and Plasma transudate (fluid leakage from vessels) contribute to vaginal fluid -Vestibule +Stratified squamous epithelium = several layers of flattened cells --No secretory cells --Sweat, sebaceous glands, and Plasma transudate (fluid leakage from vessels) contribute to vaginal fluid

Divisions of the pituitary gland

Two classifications -Lobes: Anterior and Posterior -Hypophyses ("pituitary gland"; hypophysectomy?) +Criterion for this classification is based on embryologic tissue origin +The pituitary gland develops from the fusion of two layers of ectoderm --Gut (oral, stomodeal) ectoderm in the form of an evagination ("pocket") in the roof of the mouth called Rathke's pouch --Neural ectoderm outgrowth from the ventral wall of the hypothalamus (infundibulum)

Summary of Fetal Tract Development

Use this handy guide for a summary. NNOTE on terminology - the vestibule in the Posterior vagina in the female. We did not cover the Urogenital sinus in detail, please see Senger text Figure 4-12 for the 3 steps of fusion between the paramesonephric duct and urogenital sinus to form the vagina. All of the reproductive structures develop in a retroperitonal position - that is they from behind the developing peritoneum. When all of these structures descend into their final positions they are surrounded by a layer of tissue consistent with the peritoneum! In testes this is the visceral vaginal tunic. In the uterus this becomes the broad ligament!

The Pituitary Gland Vascular Anatomy

Vasculature of the pituitary -Anterior lobe part of the hypothalamic-hypophyseal +portal system with retrograde venous blood flow - Complex Capillary Network! +Significance of the hypothalamic-hypophyseal portal system = control of anterior lobe (pars distalis!) hormone secretion --Neuroendocrine cells (parvicellular neurons; smaller than magnocellular) in the hypothalamus produce hormones that regulate the release of pars distalis hormones ---Releasing hormones (RH) ---Release-inhibiting hormones (RIH) --How do the hypothalamic RH/RIH reach the p. distalis?? ---Hypothalamic neuroendocrine cells void their secretions (RH or RIH) into the primary capillary plexus (refer to figure)!! RH, RIH transported thru portal vessels to secondary capillary plexus where they interact with target cells in the p. distalis and regulate hormone synthesis and release +Significance of retrograde venous blood flow --Feedback mechanism --As pars distalis hormones are draining in the venous system, some hormone makes its way to the same hypothalamic neuroendocrine cells involved in regulating that hormone's release --This mechanism "informs" the hypothalamic neuroendocrine cells of the p. distalis' response to the RH or RIH -Posterior lobe simpler capillary network +Arterial supply +Venous drainage

The Pineal Gland 6

We also see similar results if we measure sperm production by the testes of the ram. Conversely we see similar impacts in male Stallions as they transition to the long day photoperiod of their breeding season!

The Pineal Gland 5

We see effects of photoperiod in both males and females for these species! If you measure the testes size in rams during the different photoperiods (non-breeding, transitional (late summer/early fall), and breeding season (mid-winter, short day breeder), along with serum gonadotropins (LH/FSH), and steroid (Testosterone) you can see the rise in hormones and testes size (related to fertility) as daylight changes.

Differentiation of the Reproductive Tracts: Development of the genital tubular system

We will now discuss the transformation of the paired ducts (mesonephros and paramesonephric/Mullerian Duct) of the fetus with an indifferent gonad into the tubular structures of the tracts in female and male fetuses.

Differentiation of the Reproductive Tracts ♀

What transcription factor is missing in the XX fetus compared to the XY? - SRY! No SRY - no Sertoli cells: Granulosa cells develop under influence of DAX1. No Sertoli cells - no AMH No AMH - Paramesonephric/Müllerian Duct develops into the oviduct, cervix, and anterior vagina under influence of E2. COUP-TFII active & no Testosterone from Leydig Cells. The Wolffian/mesonephric duct regresses. Paramesonephric/ Müllerian ducts will fuse in the female fetus! Recall the "degree of fusion" concept with reference to tract morphology Extent of fusion varies with species to give the range of tract morphologies between duplex (low) and simplex (high)

Testicular Thermoregulation

Why important? -Most mammalian males, testes are suspended in a scrotum outside the body cavity -If the testicular temperature is raised to core body temperature, spermatogenesis is interrupted and the male is infertile, e.g., cryptorchid males -Androgen synthesis is unaffected, hence libido, secondary sex characteristics, etc., are not altered -Temperature-sensitive stage = primary spermatocyte How are the testes maintained at a temperature 4-6° C lower than body temperature? -Temperature in spermatic artery before spermatic cord: 39-40° C -Temperature in testicular veins: 33-34° C -Testes are outside the body cavity - exposed to environmental temperatures usually cooler than body temperature -Counter-current heat exchange mechanism in the pampiniform plexus - warm arterial blood is cooled by cooler venous blood -Testicular artery - coils over surface of testes before arborizing and penetrating into testicular parenchyma -Mechanisms to regulate testicular temperature in response to environmental changes = "reflexes" with sensory and motor axes Testicular thermoregulation as a priority physiologic process? -Warm testes - sweating and panting (polypnea = respiratory rate) ® systemic response!!!! -Cool testes - shivering ® systemic response!!!! How is this effected? -Thermoreceptors (heat and cold-sensitive neurons) in the scrotal skin generate impulses to the hypothalamus = sensory axis of the reflex!

Change in steroid production between Follicle and CL

Yellow color due to high levels of cholesterol in the lutein (luteal) cells!

Hypothalamic releasing and inhibiting hormones

produced by hypothalamus; regulate release of hormones by anterior pituitary

Marsupial tract

the kangaroo (and opossiums) have 3(!) Vaginas, and 2 cervices.

Testis sperm trail

•"Follow the sperm"!! •Seminiferous tubules (tubulus contortus (#2) --> tubulus rectus (#4)) --> rete testis (#6) --> efferent ducts (#5) --> epididymal duct --> deferential duct (duct in the vas deferens) --> ampulla (species*) --> pelvic urethra --> penile urethra

Genomic vs. non-genomic responses

•"Slow" vs "fast" responses -"Slow" response because gene expression is changed and a protein synthetic event is required (genomic); this takes some time... -"Fast" response because gene expression event is not involved; protein synthetic event is not part of response (non-genomic)

Reproductive Biology of the Future

•12-15% of couples are unable to conceive 1 year of unprotected sex, and after 2 years, 10% remain infertile •50-60% decline in sperm production in Western countries 1981-2013 •Successful pregnancy rates from assisted reproductive techniques flat (less than 50% in most fertile women) over last decade - similar phenomena in cattle •25% of mammals, 12% of birds, 20% of reptiles, 30% of amphibians, 20% of fishes, 30% of invertebrates and 55% of plant species threatened with extinction •3% increase in fertility of domestic livestock species would lead to: -1 million more beef calves/year -3.2 million more pigs/year -3.7 million more gallons of milk/year

Corpus albicans (CA)

•= "white body" -CL regresses into this structure at either the end of a cycle or pregnancy -Endocrine cells in the CL break down -Gradual reduction in size during CL to CA transition -CT cells (fibroblasts) predominate -Structure takes on the appearance of scar tissue

Anatomy of Male Reproductive Tract

•A. Testis •B. Epididymis •C. Scrotum •D. Spermatic Cord •E. Accessory Sex Glands •F. Urethra •G. Penis •H. Testicular Thermoregulation

Endocrine Organs of the Male Reproductive Tract

•A. Testis •B. Epididymis* -While the epididymis is marked, several other peripheral tissues in the male contain steroidogenic enzymes. We will cover the epididymis due to it's very important role in hormonally regulated sperm maturation and transport •C. Important for normal exocrine function: Thermoregulation!

Thermoregulatory reflex to effect warming Same 2 Arcs!

•Arc #1: Dorsomedial portion of posterior hypothalamus = "primary motor center for shivering" •Impulses thru spinal cord to anterior motor neurons -->Increase skeletal muscle tone •Muscle contractions increase causing shivering --> increase muscle metabolism in contractions --> increase heat production

The Field of Reproduction

•Aristotle, 4th century BC, -De Generatione Animalium: Generation of Animals: First Scientific work on embryology -Suggested Fetus was formed by menstrual blood, stimulated by seminal fluid •Falliopius, (1523-62) -Discovered fallopian tubes and named vagina, placenta, and clitorius •Ragnier de Graaf (1641-73): -Described development of Graafian follicles

Modern Era of Reproductive Physiology 1855-Present

•Artificial Insemination •Reliable, cheap biochemical pregnancy detection •Contraception •Embryo culture/transfer •Cloning •Estrous Synchronization/ Endocrinology •Cryopreserved gametes •In vitro fertilization •Sex selection of livestock species semen and embryos •Assisted reproductive technology for endangered species preservation

Androgens (19 C)

•Biosynthetic pathway for Steroids in Leydig and Sertoli Cells! -LH Stimulates Leydig cells to produce Testosterone and Androstenedione -FSH stimulates Sertoli cells to produce Estradiol and androgen binding protein Most common androgen = testosterone -Sources +LH Stimulates Leydig cells to produce Testosterone and Androstenedione +FSH stimulates Sertoli cells to produce Estradiol (For simplicity, Sertoli cell pathway outlined in green.) Plasma transport -Sex hormone binding globulin (SHBG)/Androgen Binding Protein (ABP) = plasma carrier glycoprotein produced by the liver that binds androgens and estrogens -Serum albumin (most abundant plasma protein) also binds and transports steroid hormones -97-99% of the steroid is bound to transport proteins with 1-3% free to interact with the target tissue -Transport proteins also protect the bound steroid hormone from degradation (conjugation and excretion)

CL Terms

•Corpus luteum spurium = CL of the cycle •Corpus luteum verum = CL of pregnancy •Nature of the embryonic signal +Luteotropin = a substance that supports and maintains the CL and progesterone production +Antiluteolysin = a substance that prevents the luteolytic mechanism from destroying the CL, allowing it to be maintained and continue producing progesterone

Ovary Structure

•Cortex: -Outer layer = functional component of the ovary -Parenchyma Layer = where follicles and follicle-derived structures are located •Medulla: -Medulla = support component of the ovary -Stroma = where connective tissue (CT) components, e.g., blood and lymphatic vessels and nerves, are located •Limiting epithelia -Ovarian cortex is surrounded by a limiting epithelium = germinal epithelium = single cuboidal cell layer -Tunica albuginea = "white coat" = thin CT layer (has somewhat of a white band appearance) in the ovarian cortex that supports the germinal epithelium -Mesovarium is surrounded by a limiting epithelium = mesothelium = single squamous (flat) cell layer -Follicles are found throughout the ovarian cortex, Medulla contains blood supply - as follicles grow the migrate closer to medulla

TERMS!

•Endocrinology: branch of science that studies endocrine glands and hormones. •Hormones a.k.a Chemical messengers: physiologic, organic chemical substance produced by certain specialized cells, which passes directly or diffuses into the circulation for the purpose of either stimulating or inhibiting the functional activity of a target organ, tissue or cell •Endocrine Glands: secretion(s) enter the circulation •Exocrine Glands: secretion(s) enter a duct

Amount of Ova

•Females are regarded as not continually gametogenic, that is, the proliferation phase for gamete production does not continue throughout their entire lifespan, unlike the male, who is considered continually gametogenic •In females, the proliferation phase in oogenesis ceases in fetal life (early in fetal life), hence all the ova a female will ever produce are present at this time •The female has her peak number of ova as a fetus; once this peak number is attained it declines with age due to follicular degeneration = atresia

Accessory Sex Glands of male

•Four major exocrine glands •Vesicular, prostate and bulbourethral (Cowper's) glands and ampulla -The prostate and bulbourethral glands pour their secretions into the urethra, where at the time of ejaculation, they are mixed with the fluid suspension of sperm and ampullary secretions from the ductus deferens. -Vesicular glands produce the bulk of seminal plasma - the bulbourethral glands are hormonally responsive - they require testosterone to maintain their size and function. Prostate glands are associated with prostate cancer - one of the treatments for prostate cancer antagonize the actions of FSH and LH, lowering testosterone levels. Basic structure -Glandular epithelium supported/surrounded by a smooth muscle cell layer -Smooth muscle layer contracts and compresses gland, moving fluid out of the gland into ducts Semen = spermatozoa + seminal plasma -Seminal plasma is the fluid vehicle for sperm -Several sources of seminal plasma: seminiferous tubules, rete testes, epididymis but majority of fluid is contributed by the accessory sex glands

Ovulation changes the function of the Follicle

•High levels of E2 cause a spike in LH from the pituitary, inducing ovulation •Transforms the granulosa and theca cells of the follicle into granulosa lutein and theca lutein cells of the Corpus Luteum (CL) •Function: PROGESTERONE PRODUCTION! •No embryo/pregnancy? CL regresses -Ovulation depression = "crater" that remains from the ovulated antral follicle +Induced by peptide hormone luteinizing hormone (LH) +Palpable in some species, e.g., cow, mare +Persists for about a day -Corpus hemorrhagicum (CH) = "bleeding body" +Appears as a blood clot; semi-solid structure +Hemorrhagic mass of tissue is undergoing cellular reorganization and differentiation due to influence of LH! +Former estrogen-producing follicle cells are transforming into progesterone (different steroid)-producing cells; some sp, e.g., dog, start producing progesterone shortly ovulation +Persists for 2-3 days -Corpus luteum (CL) = "yellow body" +"Yellow body" term derived from appearance in cow and mare +Produces progesterone to maintain pregnancy in event of fertilization +Germinal epithelium and tunica albuginea have repaired +Cords of luteal tissue are surrounded by a thin CT sheath (derivative of the theca externa) = Capsule of the CL +Antral remnant (small) can persist = Cavity of the CL (arrow)

Regulation of the Pituitary Gland by the Hypothalamus

•How can you tell if a p. distalis hormone is regulated by a hypothalamic releasing hormone (RH) or a release-inhibiting hormone (RIH)? - old experiments where they transected the pituitary stalk and measured hormone output... •Gonadotropins are regulated by a hypothalamic neuropeptide RH -Gonadotropin RH - GnRH (from GnRH neurons in hypothalamus) •Prl is actually controlled by both hypothalamic neuropeptide RH and RIH -BUT MAJOR control is by a prolactin RIH - Prolactin-Inhibiting Factor (PIF)!!

Epididymis Concept

•In concept, when sperm leave the cauda epididymis, all should be motile and capable of fertilization and none should have cytoplasmic droplets •In reality, in the average ejaculate, only 70-90% are regarded as "normal" •High incidence of cytoplasmic droplets may be an indication of a pathology associated with epididymal transit •Epididymal transit time = time required for sperm to complete passage thru the epididymis = 8-13 days (species-specific)

Other Estrogens

•Phytoestrogens or plant estrogens -Coumestrol = phytoestrogen found in legumes, e.g., alfalfa, clovers -Such compounds can be a cause of poor fertility -Mimics estradiol, suppresses follicle development (more later)!! •Mycoestrogens or fungal estrogens -Zearalanone = naturally occurring compound -Zeranol = related synthetic compound used as the growth promoting agent in the product Ralgro •Diethylstilbestrol (DES), synthetic estrogen -Lots of history!! -Growth stimulant in cattle -Withdrawn because of carcinogenic potential -Approved for some veterinary applications -Urinary incontinence in spayed dogs ( urethral tone) -Between 1938-1971, thousands of pregnant women were prescribed DES to help prevent pregnancy complications -Daughters developed rare carcinomas, lead to FDA to discourage use in 1971 -Pulled FDA approval in 2000 -Associated with cancers, infertility and reproductive abnormalities in children and grandchildren •Have same functional group as estradiol and mimic or inhibit actions •ENDOCRINE DISTRUPTERS

Gonadal Hormones

•Polypeptide hormones -Inhibin, activin and follistatin -Anti-Mullerian Hormone -Relaxin •Steroid hormones -Androgens -Estrogens -Progestins •Prostaglandins

Prostaglandin and Steroid Hormone Applications

•Prostaglandins (PGF2a) -Estrous synchronization: Estrumate/Lutealyse -Abortant -Uterine infections •Steroids -Growth promotion -Birth Control/prevent miscarriage -Progestins +Estrous synchronization +Behavioral estrus suppression

Biochemistry of the classical reproductive hormones

•Proteins, glycoproteins and polypeptides -Follicle stimulating hormone (FSH) -Luteinizing hormone (LH) •Steroids -Testosterone, estrogen and progesterone •Fatty acids -Prostaglandins -Hormone chemistry determines mechanism of action as well as cellular location of its receptor -Two basic types of hormones +Water soluble = protein, glycoprotein and polypeptide hormones +Lipid soluble = steroid hormones (e.g. progesterone, estrogen, androgen) -Key difference between water and lipid soluble hormones → ability to penetrate the cell membrane

Scrotum

•Scrotum = outer protective covering of the testes •Three layers -Skin (outer) •Comprised of 3 layers: epidermis, dermis and hypodermis •Covered with hair/fiber and infiltrated with sweat and sebaceous glands -Tunica dartos = smooth muscle •Continuous with the scrotal skin •Gives rise to the scrotal septum (septum scroti) = segment of the t. dartos that partitions the scrotum into two chambers with a testis confined to each chamber •Raphe = indentation in the base of the scrotum between the two chambers caused by the scrotal septum •Can maintain long periods of tone or sustained contractions •Contraction causes the testes to be brought closer to the male's body cavity whereas relaxation causes the testes to drop away Scrotal fascia = multiple layers of loose CT -Functions •Mechanical protection •Thermoregulation - functions to regulate testicular temperature by regulating proximity of the testes to the male's body cavity; hair and sweat glands also participate in thermoregulation •For most mammals, testes must be maintained at a temperature 4-6°C cooler than core body temperature to preserve fertility •If testes maintained at core body temperature, male is infertile

Gonadal Polypeptide Hormones: Relaxin

•Source? -CL, placenta, uterus •Biological effects? -Inhibit myometrial contractions -Cervical and Vaginal Dilation at term -Stimulate mammary growth

Progestins (21 C)

•Source? -Theca interna, theca lutein cells, Leydig cells, placenta, adrenals •Biological Activities -Hypothalamus and pituitary gland - negative feedback on GnRH and gonadotropin release -Principle hormone of pregnancy -Sensitizes the brain for reproductive behavior +Brain - pre-sensitizes brain to estrogen for induction of behavior (sexual receptivity to the male) during estrus (heat) -Growth of mammary glandular epithelium +Mammary gland - stimulates growth of the glandular epithelium in the alveoli Plasma transport -Transcortin [corticosteroid binding globulin (CBG)] +Plasma carrier protein produced by the liver that binds 21 C steroid hormones, e.g., corticosteroids and progestins -Serum albumin Cytosolic receptor -Requires translocation to nucleus once P binds -Membrane Rs have also been identified

Estrogens (18 C)

•Sources -Granulosa cells in ovarian follicle; placenta; Sertoli cells in testes; adrenal cortex _Note the male and female cells involved in androgen and estrogen synthesis!! +Theca interna and Leydig cells under influence of LH produce testosterone!! +Granulosa and Sertoli cells under influence of FSH produce estradiol!! --"2 gonadotropin, 2 cell hypothesis" •Biological Actions? Hypothalamus -Two centers in female for GnRH release +Tonic center- negative feedback on GnRH release +Surge center- positive feedback on GnRH release --Threshold [estrogen] must be reached!! Pituitary gland -Negative feedback unless override by GnRH surge Uterus -Supports endometrium and myometrium; stimulates uterine growth by hyperplasia and hypertrophy -Stimulates myometrial contractility; augments effects of oxytocin and PGF2a Cervix -Stimulates mucus secretion -Increases relaxin receptors and participates in cervical softening at parturition Supports secondary sex characteristics in the female Brain - induces behavior associated with estrus (heat); sexual receptivity to the male +Progesterone is also involved Mammary gland - supports duct development Luteolytic in ruminants -Induces PGF2a synthesis! Luteotrophic in swine and rabbits -Embryonic estrogens Non-reproductive effects -Skeletal system - increase calcium deposition and bone ossification; accelerates epiphyseal closure of the long bones -Anabolic in ruminants - stimulates growth +Estrogen induces GH release

Androgens (19 C) 2

•Sources? -Leydig cells, theca interna cells, placenta, adrenal cortex •Biologic Activities? -Hypothalamus and pituitary gland - negative feedback on GnRH and gonadotropin release -Maintains latter stages of spermatogenesis (2°-cyte thru spermiogenesis) -Supports development and maintains integrity of the epididymis, vas deferens, accessory sex glands and external genitalia -Supports secondary sex characteristics in the male and libido (brain) -Anabolic in skeletal muscle (protein deposition) -Substrate for estrogen synthesis Plasma transport -Sex hormone binding globulin (SHBG) = plasma carrier glycoprotein produced by the liver that binds androgens and estrogens -Serum albumin (most abundant plasma protein) also binds and transports steroid hormones -97-99% of the steroid is bound to transport proteins with 1-3% free to interact with the target tissue -Transport proteins also protect the bound steroid hormone from degradation (conjugation and excretion) Nuclear receptor -For most tissues, the biologically active hormone is not testosterone (T), but dihydrotestosterone (DHT) +Exception is the Wolffian duct!! -5a reductase in cytosol of target cells reduces C=C at 4-5 Cs -DHT binds androgen receptor with greater affinity than T

Testis

•Testes (pl.) = male gonads -Endocrine and exocrine organ +Endocrine = releases hormones into the circulation +Exocrine = releases gametes (sperm) into a duct -Basic structure = bundle of microscopic tubules - Seminiferous Tubules supported by a connective tissue matrix -Actual site of spermatogenesis -Tubule possesses a seminiferous epithelium = sperm-producing epithelium +Parenchyma = seminiferous tubules + endocrine cells located just outside the tubule +Stroma = Connective tissue sheathing supporting the seminiferous tubules -Think of the testis as a grapefruit with the outer layers and lobules arranged in a similar fashion - without the seeds

Epididymis

•Three segments: -caput (head) -corpus (body) -cauda (tail) Convoluted tube in close apposition to the testis -Consists of the epididymal duct and the CT layer supporting the duct -Epididymal duct +Epithelium is similar to the efferent ducts = pseudostratified columnar epithelium with principal columnar cells and basal cells +BUT, principal columnar cells possess stereocilia instead of kinocilia +Muscularis possesses a prominent layer of circular smooth muscle +Lumen of epididymal duct is open and even -Functions +Transport of sperm from the efferent ducts in the testis to the vas deferens --Stereocilia and peristaltic-like contractions +Concentration of sperm by fluid absorption in the caput epididymis; [sperm] +Secretion of various biomolecules, e.g., membrane proteins involved in sperm-oocyte binding and fusion at fertilization +Storage of sperm in the cauda epididymis --Major storage component of the extragonadal reserve = sources of sperm outside of the testes --Extragonadal reserve includes cauda epididymis, vas deferens and the ampulla (sp?) +Maturation of sperm during transit

Other Hypothalamic Releasing Hormones important for reproduction - Prolactin Releasing Hormones (PRH) & Release Inhibiting Hormones (PIH)

•Thyrotropin RH (TRH) -Tripeptide: Glu-His-Pro -Causes release of TSH & Prl -Produced by dorsal medial and preoptic nuclei •Vasoactive intestinal peptide (VIP) -28 amino acids -Causes release of Prl -Produced by the paraventricular nucleus (PVN) -Unlike the supraoptic nucleus, PVN composed of both magnocellular (long) and parvicellular (short) neurons •Dopamine (DOPA) -Produced by the median eminence - Inhibits Prl release -Primary factor controlling Prl release!!!! •g-Aminobutyric Acid -GABA +GABA has a dual role - produced by the GABA-ergic neurons in the arcuate nucleus it antagonizes the actions of DOPA in the median eminence to increase prolactin levels, but can also inhibit prolactin secretion from the anterior pituitary. -Control of secretion = neuroendocrine reflex arcs, similar to GnRH

Androgens

•Unique among the steroids -Biologically active hormone is metabolite dihydrotestosterone (DHT) -DHT is "stronger androgen" -For most tissues, the biologically active hormone is not testosterone (T), but dihydrotestosterone (DHT) -In males, a large amount of T is converted to DHT in the epidydimus +Exception is the Wolffian duct during fetal life!! -5a reductase in cytosol of target cells reduces C=C at 4-5 Cs -DHT binds androgen receptor with greater affinity than T

Biological Activities of Progesterone

•Uterus +Principal hormone of pregnancy +Stimulates development and differentiation of the endometrial glands +Inhibits myometrial contractility •Brain - pre-sensitizes brain to estrogen for induction of behavior (sexual receptivity to the male) during estrus (heat) •Mammary gland - stimulates growth of the glandular epithelium in the alveoli