8.5 - REPRODUCTIVE HORMONES Male Reproductive System

1. 8.5 - REPRODUCTIVE HORMONES • Male Reproductive System • at puberty, the hypothalamus secretes gonadotropin-releasing hormone (GrRH), which stimulates the anterior pituitary to release follicle-stimulating hormone (FSH) which directs the production of sperm cells in the seminiferous tubules, and luteinizing hormone (LH) which stimulates the interstitial cells of the testes to produce testosterone, which itself increases sperm production • testosterone stimulates spermatogenesis (spermatogonia divide and differentiate into mature sperm cells) (see “Spermatogenesis and oogenesis” animation) and influence development of secondary sexual characteristics (enlargement of testes and penis, sex drive, body and facial hair, enlargement of larynx, increased muscle mass, secretion of body oils) • Negative Feedback (see Fig. 2, P. 394) • high levels of testosterone deactivates the hypothalamus  less production of GrRH  less production of LH  less production of testosterone • FSH stimulates Sertoli (support) cells to secrete protein hormone inhibin, which inhibits the release of FSH from the anterior pituitary

2. Female Reproductive System • at puberty, the hypothalamus secretes gonadotropin-releasing hormone (GrRH), which stimulates the anterior pituitary to release FSH • (see Fig. 7, P. 398) • The Menstrual Cycle • (see Fig. 5, P. 396 & Fig. 6, P. 397) • Follicular Phase (day 6-13) • (see “The follicular phase of the menstrual cycle” animation) • FSH is carried in the blood to one of the paired ovaries and stimulates the development of several of 400 000 egg follicles, each of which contain the primary oocyte and granulosa cells • developing follicles secrete estrogen, which initiates development of the endometrium and stimulates the anterior pituitary to release LH (positive feedback)

3. Oogenesis and Ovulation • (see“Spermatogenesis and oogenesis” animation) • primary oocytes undergo meiosis I, in which 23 chromosomes (along with most of the cytoplasm and nutrients) form a secondary oocyte, while the remaining cell (polar body) dies •  granulosa cells develop and provide nutrients  fluid-filled cavity (antrium) forms •  as levels of LH rise, dominant follicle moves to outer wall of ovary  wall distends and bursts 2o oocyte is released (remaining follicles deteriorate and are reabsorbed into the ovary) •  increased levels of estrogen inhibit anterior pituitary from producing FSH (negative feedback)

4. Luteal Phase (day 14-28) • (see “The luteal and flow phase of the menstrual cycle” animation) • follicular cells remaining from ovulation differentiate into the corpus luteum, which secretes estrogen and progesterone for the further development of the endometrium (positive feedback), while preventing further ovulation and uterine contractions (negative feedback) • increased levels of estrogen and progesterone inhihit the release of FSH and LH from the anterior pituitary (negative feedback)  corpus luteum degenerates into scar tissue (corpus albicans) after 10 days if fertilization does not occur • 2o oocyte enters oviduct (Fallopian tube), drawn by rythmic action of fimbrae surrounding opening meiosis II is completed before entry of sperm during fertilization, resulting in an unequal division of resources and a mature oocyte (ovum) (and death of the polar body)

5. Flow Phase (day 1-5) • used to mark the beginning of the menstrual cycle because it is visible • decreasing levels of estrogen and progesterone as corpus luteum degenerates causes weak uterine contractions, pulling the endometrium away from the wall •  endometrium is shed through the vagina • Summary of Female Reproductive Hormones • – P. 399 • Lab Exercise 8.5.1 – Hormone Levels During the Menstrual Cycle • Section 8.5 Questions – P. 399, #1-11