BMS100 Chapter 19 Part 2

Brain-Endocrine Axis (Fig. 11.5a)
1. anterior pituitary gland
   • is under control of hypothalamus
   • secretes "tropic hormones" (gonadotropins and others)
     • tropic hormones = hormones that stimulate other glands (thyroid, adrenal, testes & ovaries)
       • gonadotropins = tropic hormones that stimulate gonads (ovaries & testes)
2. peripheral endocrine glands (thyroid, adrenal, testes & ovaries) secrete "target hormones"
   • target hormones affect various target cells
   • "negative feedback" - target hormones cause inhibition of hypothalamus & pituitary (high level of target hormone "shuts off" production of more)

Hormonal Control of Male Reproductive Functions (p. 499)
1. gonadotropins: FSH - stimulates sperm production; LH - stimulates testes to produce testosterone, etc.
2. testosterone and other "androgens"
   • primary effect: stimulate development of male reproductive organs (necessary for reproduction)
   • cause male secondary sex characteristics (not directly necessary for reproduction)
   • negative feedback - testosterone inhibits hypothalamus & pituitary

Hormonal Control of Female Reproductive Functions (p. 506)
1. gonadotropins = follicle-stimulating hormone (FSH) + luteinizing hormone (LH)
2. ovarian hormones
   1. estrogens cause development of reproductive system and affect fat metabolism, bone growth, etc.
   2. progesterone affects the uterus and other organs during the uterine cycle

Ovarian/Uterine Cycle (standard = 28 days; menstruation occurs on days 1-4 approx.)
1. Week One - increasing FSH initiates cycle by stimulating follicle maturation
2. Week Two - maturing follicles secrete estrogens, which thicken the uterine lining
   • "LH surge" - late in Week Two, sudden rise in LH triggers ovulation
3. Week Three
   1. following ovulation, remaining follicular cells change into corpus luteum, which has a life span of approx. 10 days
   2. corpus luteum secretes progesterone
   3. effects of progesterone
      • causes endometrium to become thicker and more vascular (preparation for implantation)
      • negative feedback - progesterone inhibits hypothalamus & pituitary (prevents start of new cycle)
4. Week Four
   • if woman is not pregnant:
     1. corpus luteum begins to degenerate, concentrations of estrogens and progesterone decline
     2. consequences of drop in progesterone (late in Week 4)
        • endometrium disintegrates - menstruation
        • negative feedback effect "wears off" - allows start of new cycle
   • if woman is pregnant, progesterone cannot be allowed to drop
     1. embryo produces human chorionic gonadotropin (hCG)
     2. hCG keeps corpus luteum "alive" so it can produce progesterone
     3. eventually, placenta produces most progesterone and other hormones of pregnancy

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Chapter 19 Study Questions - 1, 2, 4, 5, 7, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 20, 21, 22, 23, 24, 25, 30, 31, 32, 38, 40, 41

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Fall 2010