Deck 20: B--The Reproductive System

Question 1

Describe the hormonal regulation of spermatogenesis.

Answer 1

The hypothalamus secretes gonadotropin-releasing hormone (GnRH), which causes the anterior pituitary to release follicle-stimulating hormone (FSH). The FSH stimulates Sertoli cells in the testes to secrete androgen-binding protein (ABP), which binds testosterone and concentrates it in the seminiferous tubules where it stimulates spermatogenesis. As more sperm are produced, the Sertoli cells release more inhibin, which inhibits the release of FSH from the pituitary gland. With less FSH, the Sertoli cells secrete less ABP resulting in less spermatogenesis. As sperm production declines, Sertoli cells secrete less inhibin, which allows the pituitary to secrete more FSH, and the cycle repeats.

Question 2

Describe the endocrine events that help maintain pregnancy after the blastocyst implants.

Answer 2

Fertilization occurs around day 14 of the ovarian cycle when estrogen levels are the highest. After ovulation, the ovarian follicle becomes a corpus luteum and secretes progesterone, which stimulates thickening of the endometrium and is necessary for implantation of the developing embryo (blastocyst). About one week after fertilization, the blastocyst implants in the endometrium and the placenta develops. The placenta secretes estrogen, which helps maintain the endometrium, and human chorionic gonadotropin (hCG), which maintains the corpus luteum. The corpus luteum continues to secrete progesterone, which also prevents the endometrium from detaching from the uterine wall.

Question 3

Describe the regulation of the ovarian and uterine cycles. Include all stages of each cycle in your answer.

Answer 3

The ovarian cycle is under the influence of a variety of hormones. At the beginning of the cycle, FSH and LH from the pituitary gland stimulate oocyte development and follicle growth in the ovary; this is the follicular phase of the ovarian cycle. Estrogen secreted from the growing follicle also stimulates follicle growth and causes thickening of the endometrial lining; this is the proliferative phase of the uterine cycle. Elevated estrogen levels in the blood begin to inhibit FSH release from the pituitary, but LH levels continue to rise. About halfway through the cycle LH levels surge, causing the ovarian follicle to rupture and release a secondary oocyte. The ruptured follicle differentiates to form a corpus luteum that secretes progesterone; this begins the luteal phase of the ovarian cycle. Progesterone causes extensive thickening of the endometrial lining; this is the secretory phase of the uterine cycle. By about day 22, if fertilization does not occur the corpus luteum begins to degenerate and progesterone levels begin to decline. Around day 28 the endometrial lining detaches and menstruation begins; this is the menstrual phase of the uterine cycle. Low levels of estrogen and progesterone during this phase allow the pituitary to secrete more FSH and LH, and the cycles for the ovary and uterus repeat.

Question 4

Discuss the pros and cons of estrogen replacement therapy following menopause.

Question 5

Summarize the current modes of contraception and their effectiveness.