8.5 - REPRODUCTIVE HORMONES

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