Topic 2 Human Reproductive Anatomy: Hormonal Control of Human Reproduction

Question 1

• Consists of ovarian cycle (in the ovary) and the menstrual cycle (involves uterus)

Answer 1

1. Female Reproductive Cycle

Question 2

• Is divided into the proliferative, secretory, and menstruation (menstrual flow) phases. Menstruation begins with the disintegration of the endometrium (menstrual flow phase).

Answer 2

a. Menstrual Cycle

Question 3

• Monitor estrogen and progesterone in blood. Low levels of estrogen and progesterone stimulate hypothalamus → secretes GnRH → stimulates anterior pituitary to release FSH and LH →

Answer 3

Hypothalamus and anterior pituitary initiate

Question 4

• FSH stimulates follicle to secrete estrogen → lots of estrogen (positive feedback on hypothalamus) → produces GnRH → anterior pituitary produces sudden mid cycle surge of LH →

Answer 4

Follicle Develops

Question 5

• Triggers ovulation (follicle is now the corpus luteum, which develops and is maintained by LH, which, along with estrogen, begins to decrease after ovulation), secretes estrogen and progesterone, which stimulate →

Answer 5

LH Surge

Question 6

Thickens in preparation for implantation of fertilized egg. If no implantation occurs, then negative feedback on anterior pituitary from increased estrogen and progesterone terminates production of FSH and LH, due to low GnRH from hypothalamus →

Answer 6

Development of Endometrium

Question 7

• Becomes corpus albicans; no estrogen and progesterone results in the endometrium shed during the menstruation flow phase!

Answer 7

Corpus luteum disintegrates (no longer maintained by LH)

Question 8

• If implantation occurs, then the embryo, and later the placenta, secretes chorionic gonadotropin (hCG), which maintains the corpus luteum.
• The production of estrogen and progesterone remains high, so the endometrium is not shed. The placenta still continues to make hCG throughout pregnancy, just at lower levels after the first trimester. Without hCG, menstruation would begin, and the embryo would abort, as hCG “maintains” pregnancy. This is why pregnancy tests check the presence of hCG in urine to deduce if a female is pregnant or not. If a fertilized egg implants anywhere other than the endometrium of the uterus, it is considered an ectopic pregnancy, and usually spontaneously aborts.
• The follicle that releases the secondary oocyte is also called the Graafian follicle

Answer 8

Note

Question 9

a. Follicular Phase: development of egg and secretion of estrogen from follicle (ends at ovulation)
b. Ovulation: mid-cycle release of egg
c. Luteal Phase: secretion of estrogen and progesterone from corpus luteum after ovulation (shedding of the uterine lining lasting approximately 5 days)
- Note that the secretory phase of the menstrual cycle overlaps with the luteal phase of the ovarian cycle

Answer 9

b. Ovarian Cycle

Question 10

• Remember, estrogen serves to thicken the endometrium, while progesterone serves to develop and maintain the endometrial wall. Progesterone also inhibits lactation during pregnancy. The fall in progesterone after delivery allows for milk production.

Answer 10

Note

Question 11

a. GnRH → FSH + LH (also known as ICSH, interstitial cell stimulating hormone → testosterone and androgens from testes)
b. FSH and testosterone → influence Sertoli cells to promote development of sperm (nourish sperm during development, or spermatogenesis). Hormone and gamete production are constant unlike in females.
c. LH stimulates Leydig cells (in the interstitium between seminiferous tubules) to release testosterone + androgens that promote spermatogenesis in tubules. Sertoli cells secrete inhibin that acts on the anterior pituitary to inhibit FSH secretion.

Answer 11

2. Male Reproductive Cycle

Question 12

a. Female hormonal contraception: estradiol and/or progesterone are spiked artificially high → negative feedback suppresses LH/FSH surge → no ovulation can occur → no fertilization possible
b. Male Contraception: a pill would interfere with LH and FSH to decrease sperm production

Answer 12

3. Contraceptive Methods