Ch. 28 Review Questions
Describe the hormonal events associated with the ovarian cycle.
As follicular development proceeds, the concentration of circulating estrogen rises and the level of circulating inhibin rises. The ris- ing estrogen and inhibin levels inhibit hypothalamic secretion of GnRH and pituitary production and release of FSH. (GnRH pulse frequency is increased by estrogens and decreased by progesterone.) As tertiary ovarian follicles develop and estrogen levels rise, the pituitary output of LH gradually increases. Estrogens, FSH, and LH continue to support follicular development and maturation despite a gradual decline in FSH levels. In the second week of the ovarian cycle, estrogen levels sharply increase, and the dominant tertiary ovarian follicle enlarges in preparation for ovulation. By day 14, estrogen levels peak, triggering a massive outpouring of LH from the anterior lobe of the pituitary gland. The rupture of the follicu- lar wall results in ovulation. Next, LH stimulates the formation of the corpus luteum, which secretes moderate amounts of estrogens but large amounts of progesterone, the principal hormone of the postovulatory period. About 12 days after ovulation, declining progesterone and estrogen levels stimulate hypothalamic recep- tors and GnRH production increases, leading to increased FSH and LH production in the anterior lobe of the pituitary gland; the cycle begins again.
Summarize the events that occur in sexual arousal and orgasm. Do these processes differ in males and females?
During sexual arousal, erotic thoughts or physical stimulation of sensory nerves in the genital region increases the parasympathetic outflow over the pelvic nerve, leading to erection of the clitoris or penis. Orgasm is the intensely pleasurable sensation associated with perineal muscle contraction and ejaculation in males, and with uterine and vaginal contractions and perineal muscle contraction in females. These processes are comparable in males and females, but only males undergo emission and ejaculation.
In the follicular phase of the ovarian cycle, the ovary
matures a dominant tertiary ovarian follicle
Developing sperm are nourished by
nurse cells
The main hormone of the post ovulatory phase is
progesterone
Identify the three regions of the male urethra.
prostatic urethra, membranous urethra, and spongy urethra.
A sudden surge in LH secretion causes the
rupture of the follicular wall and ovulation
Describe each of the three phases of a typical 28-day uterine cycle.
(1) The menstrual phase is the interval marked by the degeneration and loss of the functional layer of the endometrium, lasts 1-7 days, and 35-50 mL (1.2-1.7 oz) of blood is lost. (2) The proliferative phase features growth and vasculariza- tion, resulting in the complete restoration of the functional layer; it lasts from the end of menstruation until the beginning of ovula- tion, around day 14. (3) During the secretory phase, the uterine glands enlarge, accelerating their rates of secretion, and the arteries elongate and spiral through the tissues of the functional layer; this phase begins at ovulation, occurs under the combined stimula- tory effects of progesterone and estrogens from the corpus luteum, and persists as long as the corpus luteum remains intact.
List and summarize the important steps in the ovarian cycle.
(1) the development of a dominant tertiary follicle, or mature graafian follicle, (2) ovulation, (3) the formation of the corpus luteum and its degeneration into the corpus albicans.
Identify the main structures of the male reproductive system in the diagram on the right.
(a) prostatic urethra (b) spongy urethra (c) ductus deferens (d) penis (e) epididymis (f) testis (g) external urethral orifice (h) scrotum (i) seminal gland (j) prostate (k) ejaculatory duct (l) bulbo-urethral gland.
List the functions of testosterone in males.
In males, testosterone stimulates spermatogenesis and promotes the functional maturation of spermatozoa; maintains the male accessory reproductive organs; determines male secondary sex characteristics; stimulates metabolic operations, especially those concerned with protein synthesis and muscle growth; and influences brain development by stimulating sexual behaviors and sexual drive
What types of cells in the testes are responsible for functions related to reproductive activity? What are the functions of each cell type?
Interstitial endocrine cells (Leydig cells) produce male sex hormones (androgens), the most important of which is testosterone; nurse cells maintain the blood testis barrier, support spermatogenesis and spermiogenesis, and secrete inhibin, and androgen-binding protein.
What are the main differences in gamete production between males and females?
Males produce gametes from puberty until death; females produce gametes only from menarche to menopause. Males produce many gametes at a time; females typically produce one or two per 28-day cycle. Males release mature gametes that have completed meiosis; females release secondary oocytes held in metaphase of meiosis II.
How does the aging process affect the reproductive systems of men and women?
Men aged 50-60 experience the male climacteric, a time when circulating testosterone levels begin to decline and circulating levels of FSH and LH rise. Although sperm production continues, a gradual reduction in sexual activity occurs in older men. Women ages 45-55 experience menopause—the time that ovulation and menstruation cease, accompanied by a sharp and sustained rise in the production of GnRH, FSH, and LH and a drop in the concentrations of circulating estrogen and progesterone. The decline in estrogen levels leads to reductions in the size of the uterus and breasts, accompanied by a thinning of the urethral and vaginal walls. In addition to neural and cardiovascular effects, reduced estrogen concentrations have been linked to the development of osteoporosis, presumably because bone deposition proceeds at a slower rate.
Trace the path of milk flow from its site of production to outside the female.
Path of milk flow: secretory lobules of glandular tissue (lobes) -- ducts -- lactiferous duct -- lactiferous sinus, which opens onto the surface of the nipple.
In a condition known as endometriosis, endometrial cells are believed to migrate from the body of the uterus into the uterine tubes or by way of the uterine tubes into the peritoneal cavity, where they become established. A major symptom of endometriosis is periodic pain. Why does such pain occur?
Regardless of their location, endometrial cells have receptors that respond to estrogen and progesterone. Under the influence of estrogen at the beginning of the menstrual cycle, any endometrial cells in the peritoneal cavity proliferate and begin to develop glands and blood vessels, which then further develop under the control of progesterone. The dramatic increase in size of this tissue presses on neighboring abdominal tissues and organs, causing periodic painful sensations.
Birth control pills contain estradiol and progesterone, or progesterone alone, administered at programmed doses during the ovarian cycle to prevent tertiary ovarian follicle maturation and ovulation. Explain how such pills are effective.
Slightly elevated levels of estrogen and progesterone inhibit both GnRH release at the hypothalamus and the release of FSH and LH from the anterior lobe of the pituitary gland. Without FSH, tertiary ovarian follicles do not begin to develop, and levels of estrogen remain low. An LH surge, triggered by the peaking of estradiol, is necessary for ovulation to occur. If the level of estradiol is not al- lowed to rise above the critical level, the LH surge will not occur, and thus ovulation will not occur, even if a tertiary ovarian follicle managed to develop to a stage at which it could ovulate. Any mature follicles would ultimately degenerate, and no new follicles would mature to take their place. Although the ovarian cycle is interrupted, the level of hormones is still adequate to regulate a normal menstrual cycle.
What is the role of the clitoris in the female reproductive system?
The clitoris—a part of the external genitalia of females that is derived from the same embryonic structures as the penis— contains erectile tissue that becomes engorged with blood during sexual arousal and provides pleasurable sensations.
Describe the erectile tissues of the penis. How does erection occur?
The corpora cavernosa extend along the length of the penis as far as the neck of the penis, and the erectile tissue within each corpus cavernosum surrounds a central artery. The slender corpus spongiosum surrounds the urethra and extends from the superficial fascia of the urogenital diaphragm to the tip of the penis, where it expands to form the glans penis. The sheath surrounding the corpus spongiosum contains more elastic fibers than the corpora cavernosa, and the erectile tissue contains a pair of arteries. When parasympathetic neurons innervating the penile arteries release nitric oxide, smooth muscles in the arterial walls relax, dilating the vessels and increasing blood flow; the resulting engorgement of the vascular channels with blood causes erection of the penis.
Describe the hormonal events associated with the uterine (menstrual) cycle.
The corpus luteum degenerates and progesterone and estrogen levels decrease, causing degeneration of the endometrium and the onset of menstruation. Next, rising levels of FSH, LH, and estrogen stimulate the repair and regeneration of the functional layer of the endometrium. During the postovulatory phase, the combination of estrogen and progesterone causes the enlargement of the uterine glands and an increase in their secretory activity.
Summarize the roles of the hormones in the ovarian and uterine cycles.
The hypothalamic secretion of GnRH triggers the pituitary secretion of FSH and LH. FSH initiates follicular development, and activated follicles and ovarian thecal endocrine cells produce estrogens. High estrogen levels stimulate LH secretion and increase anterior pituitary lobe sensitivity to GnRH, causing the release of LH. Progesterone is the main hormone of the luteal phase. Changes in estrogen and progesterone levels are responsible for maintaining the uterine cycle.
Describe the histology of the uterine wall.
The myometrium is the middle, muscular layer of the uterine wall; the endometrium is the inner, glandular layer; and the perimetrium is an incomplete outer serosal layer.
The ovaries are responsible for
The production of female gametes, the secretion of female sex hormones, and the secretion of inhibin
Female bodybuilders and women with eating disorders such as anorexia nervosa commonly experience amenorrhea. What does this fact suggest about the relationship between body fat and menstruation? What effect would amenorrhea have on achieving a successful pregnancy?
These observations suggest that a certain amount of body fat is necessary for menstrual cycles to occur. The nervous system appears to respond to circulating levels of the adipose tissue hormone leptin; when leptin levels fall below a certain set point, menstruation ceases. Because a woman lacking adequate fat reserves might not be able to have a successful pregnancy, the body prevents pregnancy by shutting down the ovarian cycle, and thus the menstrual cycle. Once sufficient energy reserves become available, the cycles begin again.
Diane has peritonitis (an inflammation of the peritoneum), which her physician says resulted from a urinary tract infection. Why might this condition occur more readily in females than in males?
Women more frequently experience peritonitis stemming from a urinary tract infection because infectious organisms exiting the urethral orifice can readily enter the nearby vagina. From there, they can then proceed to the uterus, into the uterine tubes, and finally into the peritoneal cavity. No such direct path of entry into the abdominopelvic cavity exists in men.
In females, meiosis II is not completed until
fertilization occurs
Which accessory structures contribute to the composition of semen?What are the functions of each structure?
the seminal glands (seminal vesicles), which provide the nutrients that sperm need for motility; prostaglandins that stimulate smooth muscle contractions along the male and female reproductive tracts thereby propelling sperm and fluids; fibrinogen that temporarily clots the ejaculate within the vagina; buffers that counteract the acidity of the prostatic secretions and urethral and vaginal con- tents; the prostate gland, which aids the activation of the sperm (with seminal gland secretions); and the bulbo-urethral glands, which buffer acids in the penile urethra and lubricate the glans penis. The fluids secreted by the accessory glands make up about95 percent of the volume of semen.