Chapter 17 physiology
Identify when mitotic divisions of germ cells occur in males and females
Male: puberty female: during fetal development
the location and function of the Leydig cells is where
The Leydig cells, or interstitial cells, which lie in small, connective-tissue spaces between the convoluted seminiferous tubules, are the cells that synthesize and release testosterone
What is the function of the bulbourethral glands
The bulbourethral glands contribute a small volume of lubricating mucoid secretions; drain into the urethra just after it leaves the prostate
describe the functions of Sertoli cells in spermatogenesis.
The ring of interconnected Sertoli cells forms the Sertoli cell barrier (blood-testes barrier), which prevents the movement of many chemicals from the blood into the lumen of the seminiferous tubule and helps retain luminal fluid. This ensures proper conditions for germ cell development and differentiation in the tubules.
describe how steroids interact with their intracellular receptors and how this affects cell protein synthesis.
They bind to intracellular receptors, and the hormone-receptor complex then binds to DNA in the nucleus to alter the rate of formation of particular mRNAs.
describe the effects of estrogen on sex accessory organs
uterus: increases myometrial contractions and responsiveness to oxytocin, secretion of mucus, prepares endometrium breast: stimulates growth and ducts; stimulates prolactin but inhibits prolactin's actions on breasts vagina: increases layering of epithelial cells
describe the effects of progesterone on sex accessory organs
uterus: thick mucus, decreases contractions breast: stimulates breast growth, especially glandular tissue; inhibits milk inducing prolactin vagina: decreases proliferation of epithelial cells
when female fat distribution lessens, a beard appears along with male body hair and distribution, voice lowers, skeletal muscle mass increases, clit enlarges and breasts shrink
virilization
Menopause
when plasma estrogen levels become very low, plasma gonadotropin concentrations are very high—a classical example of escape from negative feedback
understand how gonadal steroids are synthesized from cholesterol.
- starts with cholesterol. Testosterone belongs to group of steroid hormones that have similar masculinizing patterns (androgens) - cholesterol making androstenedione which yields testosterone
describe the effects of estrogen secondary sex characteristics
- stimulates external genitalia growth - stimulates narrow shoulders, broad hips, female fat distribution (hips/breasts) - stimulates bone growth and cessation of bone growth
effects of estrogen effects on other tissues.
- stimulates fluid secretion from lipid-producing skin glands (opposes acne-producing androgen) - vascular effects - feedback on hypothalamus and ant-pit - protects against atherosclerosis by effects on plasma cholesterol, blood vessels, blood clotting
Know the sequence of events that occurs in the female reproductive system after testes do not develop.
-the Müllerian system does not degenerate but rather develops into fallopian tubes and a uterus -the Wolffian ducts degenerate and a vagina and female external genitalia develop from the structures at the body surface
A decrease in testosterone release from the testes
hypogonadism
why precocious puberty may occur
usually caused by early increase in gonadal steroid production caused by premature activation of GnRH, LH, and FSH potentially by tumors or infections
What is the function of granulose cells
they secrete estrogen, small amount of progesterone just before ovulation, and peptide hormone inhibin
What is the function of the vas deferens
thick walled tube of smooth muscle receiving from epididymis; storage reservoir for sperm until ejaculation
hormonal control of the corpus luteum
- secretes large quantities of progesterone, estrogen, and inhibin - if pregnancy does not occur (gonadotrpoins do not continue to increase), CL degrades within 2 weeks - FSH, LH and GnRH increase and progesterone and estrogen decrease
Describe the pathway traversed by sperm from seminiferous tubules to the exterior of the body.
(1) Smooth muscles of the epididymis, vas deferens, ejaculatory ducts, prostate, and seminal vesicles contract as a result of sympathetic nerve stimulation, emptying the sperm and glandular secretions into the urethra (emission) (2) the semen, with an average volume of 3 mL and containing 300 million sperm, is then expelled from the urethra by a series of rapid contractions of the urethral smooth muscle as well as the skeletal muscle at the base of the penis
patterned sequence of discharge of the efferent neurons for ejaculation
(1) The smooth muscles of the epididymis, vas deferens, ejaculatory ducts, prostate, and seminal vesicles contract as a result of sympathetic nerve stimulation, emptying the sperm and glandular secretions into the urethra (emission); and (2) the semen, with an average volume of 3 mL and containing 300 million sperm, is then expelled from the urethra by a series of rapid contractions of the urethral smooth muscle as well as the skeletal muscle at the base of the penis.
Describe the role of the sympathetic nervous system and also nonadrenergic, noncholinergic neural input in erection and ejaculation.
- Erection involves inhibition of sympathetic nerves (to the small arteries of the penis), whereas ejaculation involves stimulation of sympathetic nerves (to the smooth muscles of the duct system). Sympathetic neurons that release norepinephrine, which causes the arterial smooth muscle to contract. - Much more important is the activation of nonadrenergic, noncholinergic autonomic neurons to the arteries (Figure 17.14). These neurons and associated endothelial cells release nitric oxide, which relaxes the arterial smooth muscle.
-describe the methods by which one's genetic sex (and general chromosome composition) can be determined.
- When two X chromosomes are present, only one is functional; the nonfunctional X chromosome condenses to form a nuclear mass called the sex chromatin, or Barr body, which is readily observable with a light microscope. Scrapings from the cheek mucosa or white blood cells are convenient sources of cells to be examined. The single X chromosome in male cells rarely condenses to form sex chromatin. - karyotyping: tissue culture visualization of all chromosomes
stages of oogenesis
- a bunch of mitotic divisions of oogonia - oogonia go to primary oocytes (46 chromosomes) - 1st meiotic division - meiotic arrest until puberty - division of primary oocytes to secondary oocyte (gets only half the chromosomes but all nutrient rich cytoplasm) and polar body (nonfunctional) - second meiotic division in fallopian tube AFTER ovulation only if fertilized - daughter cells each get 23 chromosomes with a single chromatid - one daughter cell called ovum and other called secondary polar body
What occurs during the secretory phase of the menstrual cycle
- after ovulation, under influence of progesterone and estrogen, endometrium beings to secrete glycogen into glandular epithelium followed by glycoproteins and mucopolysaccharides - occurs during luteal phase
What is the function of the seminal vesicles and prostate gland
- secretes most of fluid in which ejaculated sperm are suspended - secretions contain a large number of different chemical substances, including (1) nutrients, (2) buffers for protecting the sperm against the acidic vaginal secretions and residual acidic urine in the male urethra, (3) chemicals (particularly from the seminal vesicles) that increase sperm motility, and (4) prostaglandins.
describe the progression of follicles from primordial to late antral and dominant.
- begin as primordial follicles - size of oocyte increases, proliferation of granulose cells into multiple layers and separation of oocyte from inner granulose cells by zona pellucida - follicle grows with mitosis of granulosa cells and connective tissue surrounding differentiate and form theca - primary oocyte at full size and antrum begins to form by fluid secreted by granulosa - during menstrual cycle, preantral and early antral develop into larger antral follicles - after a week, a larger, dominant follicle develops and all others die
Compare granulosa cells to Sertoli cells
- both control microenvironment in which germ cell develops and matures - both stimulated by FSH and and major gonadal sex hormone
state the ways theca cells are analagous to Leydig cells
- both produce mainly androgens and is stimulated to do so by LH
describe the hormonal control of the events in the uterine cycle
- by estrogen and progesterone - proliferative phase: inc in estrogen stimulates growth of endometrium and myometrium - after formation of corpus luteum, progesterone converts endometrium to secretory tissue and get glycogen etc and make it more hospitable. also opposes myometrial contractions - estrogen causes cervix mucus to be abundant, clear, watery. Progesterone thickens it creating a "plug" - decrease of these causes menstruation
describe the mechanism of virilization in female fetuses with congenital adrenal hyperplasia.
- congenital adrenal hyperplasia is caused by the production of too much androgen in the fetus. -increase in fetal androgen production results in virilization of an XX fetus (masculinized external genitalia). If untreated in the fetus, the XX baby is usually born with ambiguous genitalia
describe the neural control of erection and ejaculation.
- dominant input is from sympathetic neurons that release norepinephrine, which causes the arterial smooth muscle to contract. During erection, this sympathetic input is inhibited. - Much more important is the activation of nonadrenergic, noncholinergic autonomic neurons to the arteries (Figure 17.14). These neurons and associated endothelial cells release nitric oxide, which relaxes the arterial smooth muscle. - Primary stimulus comes from mechanoreceptors in the genital region, particularly in the head of the penis. - The afferent fibers carrying the impulses synapse in the lower spinal cord on interneurons that control the efferent outflow. - mediated by afferent pathways from penile mechanoreceptors. When the level of stimulation is high enough, a patterned sequence of discharge of the efferent neurons ensues. This sequence can be divided into two phases (on other slide)
What occurs during the menstrual phase of the menstrual cycle
- entire duration of menstruation (3-5 days) - epithelial lining of uterus (endometrium) degenerates, causing flow - occurs during follicular phase
effects of progesterone effects on other tissues.
- feedback effects on hypothalamus and ant-pit gland - inhibits prolactin - decrease contractions of fallopian tubes and myometrium
Compare and contrast oogenesis and spermatogenesis, in terms of both time frames and end results.
- females already born with all the eggs they'll ever have - primary oocytes analogous to primary spermatocytes (similar divisions to 23 chromosomes) - one primary oocytes yields ONE ovum where primary spermatocyte produce FOUR viable spermatozoa
Estrogen on LH and FSH
- in low concentration inhibits FSH and LH in response to GnRH (-) during early/middle follicular phases - dramatic increases cause increase of LH and FSH and sometimes even GnRH (+ for LH surge)
describe the response of the female to sexual intercourse.
- increased blood flow/muscular contraction - clit increases in diameter/length with blood flow - vaginal epithelium lubricates with mucus - orgasm: increase in skeletal activity involving almost all parts of the body -heart rate/bp increase - contractions of vagina and uterus
describe the effects of progesterone secondary sex characteristics
- increases body temperature
describe the effects of the LH surge on ovulation and the formation of the corpus luteum.
- increasing plasma concentrations of estrogen acts on ant-pit to enhance sensitivity of LH-releasing cells to GnRH and may stimulate release of GnRH from hypothalamus (+) - rapid increasing estrogen levels leads to LH surge; midcycle induces ovulation - high plasma LH acts on granulosa cells to cause ovulation; releases progesterone and decreases release of estrogen - remaining granulosa cells of ruptured follicle become corpus luteum
-describe the functions—both endocrine and paracrine—of testosterone in the male.
- initiates/maintains spermatogenesis - decrease GnRH secretion via hypothalamus - Inhibits LH secretion via anterior pit - induces differentiation of male accessory reproductive organs/maintains their function - induces male secondary sex characteristics - opposes action of estrogen on breast - stimulates protein anabolism, bone growth, and cessation of bone growth - sex drive, aggressive behavior - stimulates erythropoietin secretion by kidneys
What occurs during the proliferative phase of the menstrual cycle
- menstrual flow ceases and endometrium beings to thicken/regenerate under influence of estrogen (10 days) - occurs between menstruating ending and ovulation beginning - occurs during follicular phase
describe the sources and effects of androgens in women
- result of production by adrenal glands and ovaries - stimulate growth of pubic hair, axillary hair, and possibly skeletal muscle and maintenance of sex drive - excess may cause virilization
describe the events that precede and accompany ovulation, including the formation of a corpus luteum
- walls of follicle and ovary rupture, secondary oocyte carried out of ovary and onto ovarian surface - mature follicle discharges its antral fluid and egg then collapses around antrum and undergoes rapid transformation - granulosa cells enlarge and corpus luteum is formed - if not fertilized, after ten times the CL dies via apoptosis and menstruation occurs
Describe the events in meiosis that lead to genetic variability in the daughter cells.
-Because of the random orientation of the homologous pairs at the equator, it is unlikely that all 23 maternal chromatids will end up in one cell and all 23 paternal chromatids in the other. Over 8 million (223) different combinations of maternal and paternal chromosomes can result during this first meiotic division. -two events during the first meiotic division contribute to the enormous genetic variability of the daughter cells: (1)crossing-over and (2) the random distribution of maternal and paternal chromatid pairs between the two daughter cells.
describe the three major types of estrogens found in humans and where they are synthesized.
-Estradiol is the predominant estrogen in the plasma. It is produced by the ovary and placenta and is often used synonymously with the generic term estrogen - Estrone is also produced by the ovary and placenta. - Estriol is found primarily in pregnant women in whom it is produced by the placenta.
describe the synthesis and release of gonadotrophin-releasing hormone (GnRH) and how it works in the anterior pituitary.
-GnRH is one of the hypophysiotropic hormones involved in the control of anterior pituitary gland function. It is secreted by neuroendocrine cells in the hypothalamus, and it reaches the anterior pituitary gland via the hypothalamo-pituitary portal blood vessels. In the anterior pituitary gland, GnRH stimulates the release of the pituitary gonadotropins—follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which in turn stimulate gonadal function.
describe the synthesis and release of follicle-stimulating hormone (FSH) and leutienizing hormone (LH) from the anterior pituitary.
-GnRH stimulates the release of the pituitary gonadotropins—follicle-stimulating hormone (FSH) and luteinizing hormone (LH) -The two hormones act upon the gonads, the result being (1) the maturation of sperm or ova and (2) stimulation of sex hormone secretion.
roles of LH in controlling male reproductive functions.
-LH exerts an essential indirect effect because the testosterone secretion stimulated by LH is required for spermatogenesis. - acts primarily on the Leydig cells to stimulate testosterone secretion.
How is secretion of LH controlled by secretions from he testes?
-Testosterone inhibits LH secretion in two ways (see Figure 17.15): (1) It acts on the hypothalamus to decrease the amplitude of GnRH bursts, which results in a decrease in the secretion of gonadotropins (2) acts directly on the anterior pituitary gland to decrease the LH response to any given amount of GnRH.
describe the general functions and understand the importance of the SRY gene.
-sex-determining region of the Y chromosome -In the absence of a Y chromosome and, consequently, the SRY gene, testes do not develop. Instead, ovaries begin to develop in the same area.
How is secretion of FSH controlled by secretions from the testes.
-The major inhibitory signal for FSH, exerted directly on the anterior pituitary gland, is the protein hormone inhibin secreted by the Sertoli cells
describe the sequence of events that occurs in the male reproductive system after the testes begin to differentiate.
-These testes secrete testosterone and a protein hormone called Müllerian-inhibiting substance (MIS) -MIS then causes the degeneration of the Müllerian duct system. -testosterone causes the Wolffian ducts to differentiate into the epididymis, vas deferens, ejaculatory duct, and seminal vesicles. -a penis forms and the tissue near it fuses to form the scrotum
secondary sex characteristics of the male are dependent on
-androgens: (you already know most obvious) - stimulate bone growth, through stimulation of GH secretion. - terminate bone growth by causing closure of the bones' epiphyseal plates. - "anabolic steroids" = exert a direct stimulatory effect on protein synthesis in muscle. - stimulate secretion of the erythropoietin by kidneys; major reason men have a higher hematocrit than women.
describe the sequence of events in gametogenesis.
1. The first stage in gametogenesis is proliferation of the primordial (undifferentiated) germ cells by mitosis. 2. The second stage of gametogenesis is meiosis, in which each resulting gamete receives only 23 chromosomes from a 46-chromosome germ cell, one chromosome from each homologous pair.
describe the uterine events that are associated with menstruation
1. constriction of uterine blood vessels = diminished supply of oxygen and nutrients to endometrial cells 2. disintegration starts in entire lining and uterine smooth muscles contract 3. Endometrial arterioles dilate, hemorrhaging weak capillary walls
identify the hormones that are produced by ovaries and the cells that produce them
1. estrogen during follicular phase by granulosa cells during ovulation, by corpus leuteum after ovulation 2. progesterone by granulosa and theca cells just before ovulation but major source of corpus luteum 3. inhibin by granulosa cells and CL
What are the phases of the ovarian cycle?
1. follicular 2. luteal
Phases of menstrual cycle
1. menstrual phase 2. proliferative phase 3. secretory phase
roles of GnRH in controlling male reproductive functions.
GnRH reaching the anterior pituitary gland via the hypothalmo-hypopheseal portal vessels during each pulse triggers release of both LH and FSH
Increasing plasma concentration of estrogen during late follicular phase stimulates
LH surge that is necessary for ovulation
identify the hormones of the anterior pituitary that influence ovarian hormone secretion.
LH, FSH
Describe the pattern of the changes of all anterior pituitary hormones during a menstrual cycle (page 627)
LH: stays relatively normal then has a major burst at ovulation FSH: Increases at first, then decrease around day ten causing atresia and then a slight surge - after ovulation both decrease and their secretions are inhibited - then they both begin to increase again for a new cycle - both increase in follicular phase and decrease in luteal
describe the stages of spermatogenesis.
Undifferentiated germ cells, spermatogonia, begin to divide mitotically at puberty. Daughter cells of first division divide again and again for specified # division cycles so a clone of spermatogonia is produced from each stem cell spermatogonium. Some differentiation occurs. The cells resulting from final mitotic division/differentiation in the series are primary spermatocytes, and are the cells that undergo the first meiotic division of spermatogenesis. Each primary spermatocyte increases in size and undergo first meiotic division (Fig 17.11) to form 2 secondary spermatocytes, each containing 23 two-chromatid chromosomes. Each secondary spermatocyte undergo the second meiotic division to form spermatids. So, each primary spermatocyte containing 46 two-chromatid chromosomes produces four spermatids containing 23 one-chromatid chromosomes. Final phase of spermatogenesis is differentiation of spermatids to spermatozoa (sperm). This involves extensive cell remodeling, including elongation, but no further cell divisions.
Inhibin on FSH and LH
acts on pituitary gland to inhibit secretion of FSH
roles of FSH in controlling male reproductive functions.
acts primarily on the Sertoli cells to stimulate the secretion of paracrine agents required for spermatogenesis. LH, by contrast, acts primarily on the Leydig cells to stimulate testosterone secretion.
describe the hormonal changes that induce puberty in a female
alteration in brain function that causes increase in GnRH which stimulates pituitary gland gonadotropins which stimulate estrogen
failure to have menstrual flow
amenorrhea
What is the fate of the overwhelming majority of primordial follicles?
atresia
understand the importance of pulsatility in hypothalamic release of GnRH.
because the cells of the anterior pituitary gland that secrete the gonadotropins lose sensitivity to GnRH if the concentration of this hormone remains constantly elevated.
What does menstrual flow consist of
blood mixed with endometrial debris
contribution of adrenal androgens to the onset of puberty
cause the very early development of pubic and axillary (armpit) hair, as well as the early stages of the pubertal growth spurt in concert with growth hormone and insulin-like growth factor I
describe the endocrine changes that promote further sexual maturation.
causes increased secretion of pituitary gonadotropins, which stimulate the seminiferous tubules and testosterone secretion. Testosterone, in addition to its critical role in spermatogenesis, induces the pubertal changes that occur in the accessory reproductive organs, secondary sex characteristics, and sex drive.
function of zona pellucida
contains glycoproteins that play a role in binding of a sperm cell to the surface of an egg after ovulation
What is responsible for the genetic difference between males and females?
difference in one chromosome
understand the difference between testosterone and dihydrotestosterone in terms of potency.
dihydrotestosterone is much more potent
describe the secondary sex characteristics in females and the hormonal changes that cause them.
estrogen induces these changes; enlarged breasts, body hair, thigh muscles behind femur, widening hips, small hands/feet, smaller waist, labia minora
throughout their life in the ovaries, the eggs exist in structures known as
follicles
phase where mature follicle and secondary oocyte develop
follicular phase
discuss the importance of adipose tissue to the timing of puberty
hormone leptin is known to stimulate secretion of GnRH which may play a role in puberty
Describe the disorder known as premenstrual syndrome.
includes swollen breasts, headache, backache, depression, anxiety, irritability and other physical emotional and behavioral changes attributed to estrogen and progesterone excess
Progesterone on FSH and LH
inhibit GnRH secretion, (-) on FSH and LH and prevention of LH surge during luteal phase and pregnancy
returning undifferentiated spermatogonia to the spermatogonium pool does what
keeps the number available for spermatogenesis high throughout a man's life
phase beginning after ovulation and lasting until death of corpus luteum
luteal phase
Identify the site of sperm formation (spermatogenesis)
many tiny, convoluted seminiferous tubules in the testes
Primary oocytes are in what from fetal life until puberty
meiotic arrest
primordial follicles consist of
one primary oocytes surrounded by a single layer of granulosa cells
What is the boundary between the follicular and luteal phases?
ovulation
very premature appearance of secondary sex characteristics
precocious puberty
causes of amenorrhea (primary and secondary)
primary: excessive exercise and anorexia nervosa; brain may sense a loss in body fat possibly by decreased leptin secondary: pregnancy and menopause
In what stage of follicle growth does size of oocyte increase, proliferation of granulose cells into multiple layers and separation of oocyte from inner granulose cells by zona pellucida
primordial follicle stage
describe the anatomy of the female reproductive system.
two ovaries and the female reproductive tract - 2 fallopian tubes (oviducts), uterus, cervix, vagina
period during which the reproductive organs mature and reproduction becomes possible.
puberty
Explain the reason for the location of the testes in the scrotum.
sperm formation requires a temperature approximately 2°C lower than normal internal body temperature
What involves returning undifferentiated spermatogonia to the spermatogonium pool
spermatogenesis
describe changes in the male reproductive system with aging.
steady decrease in testosterone secretion beginning at about 40 years of age, which reflects slow deterioration of testicular function and failure of the gonads to respond to the pituitary gland gonadotropins. - Along with the decreasing testosterone concentrations in the blood, libido decreases and sperm become less motile. Despite these events, many elderly men continue to be fertile. With aging, some men manifest increased emotional problems, such as depression, and this is sometimes referred to as the andropause (male climacteric).
What is the function of the epididymis
storage reservoir for sperm until ejaculation
describe the two functions performed by the testes in male reproductive physiology.
store and transport sperm to the exterior, the glands that empty into these ducts, and the penis
causes of hypogonadism primary: secondary:
testicular failure (primary hypogonadism) or a failure to supply the testes with appropriate gonadotrophic stimulus (secondary hypogonadism).
How is secretion of GnRH controlled by secretions from the testes.
testosterone has a negative feedback control over GnRH