reproductive axis Flashcards
Precursor of steroid hormones
choleserol- 27 carbon steroid molecule
Major classes of steroid hormones
glucocortocoids (ie. cortisol -C-21), mineralocorticoids (ie. aldosterone- C-21), and sex steroids
Major classes of sex steroids
progestins (C-21), androgens (C-19), and estrogens (C-18)
Principle sources of sex steroids
gonads, the adrenal cortex, and the placenta
List methods by which cholesterol is made
De novo from Co-enzyme A or from LDL in the circulation.
Where are sex steroids made
in the gonads, plus the adrenal cortex, skin and adipose tissue
- Describe key features in the biosynthesis of the sex steroids and describe the rate-limiting step.
Cholesterol is converted to steroid hormones by reduction of hydrocarbon side chains and hydroxylation of the 4 ring steroid nucleus. Rate limiting step is cleavage of the Cholesterol side chain to produce pregnenolone by 20,22 desmolase in the mitochondrial membrane. cholesterol > pregnenolone > progestins > androgens > estrogens
List the progestins
21-carbon sex steroids: pregnenolone, 17-alpha-hydroxy-pregnenolone, progesterone (major), and 17-alpha-hydroxy-progesterone (17-OH-P) (major).
Non-repro function of progestins
Progestins are also precursors for the production of aldosterone and cortisol by the adrenal gland.
Repro functions of progestins
Growth and development of the tissues and organs related to ovulation, menses, pregnancy, and lactation. Is a key feedback inhibitor at the hypothalamus and pituitary
List the androgens
19 carbon sex steroids: testosterone, dehydroepiandrosterone (DHEA), dehydroepiandrosterone-sulfate (DHEA-S), dihydrotestosterone (DHT), and androstenedione
Main sources of testosterone and DHEA
Test: 95% from testes, rest is from adrenal cortx. DHEA: mainly from adrenal cortex (marker of adrenal androgen activity)
Functions of androstenedione
In ovary: from the theca cells, precursor for ovarian estradiol by granulosa cells. Liver and adipose: precursor for extraglandualr estrogen formation
5-alpha reductase
converts testosterone to DHT in prostate and skin. DHT has much higher activity than testosterone and cannot be converted to estrogens
Testosterone functions
Androgenic: development of internal and external genitalia, devlopment/maintenance of secondary sex characteristics, spermatogenesis, libido, sebum production. Anabolic: growth of somatic tissues (bone,muscle, etc). Also feedback inhibitor at pituitary and hypothalamus
List the estrogens
18- carbon sex steroids: estrone (E1), estradiol (E2) and estriol (E3). They have one, two, and three hydroxyl groups, respectively
How are estrogens made
androgens are converted into estrogens via aromatase in gonads, adipose tissue, liver, CNS
Potency and location of estrone, estradiol and estriol
Estradiol is most potent (produced by granulosa cells of ovary, sertoli cells in testes). Estriol is least potent but serves as placental product. Estrone is derived from androstenedione in adipose tissue
Functions of estradiol
Growth and development of the tissues and organs related to ovulation, menses, pregnancy, and lactation. Also feedback inhibitor of hypothalamus and pituitary
How are sex steroids carried in bloodstream
bound to albumin, sex hormone binding globulin or corticosteroid binding globulin
Where is GnRH produced
in neurons of the arcuate nucleus and preoptic area of the hypothalamus
GnRH secretion
pulsatile- In adult males, approximately 8-14 pulses are released every 24 hours. In adult females, patterns of GnRH, FSH, and LH secretion vary throughout the menstrual cycle. Constant administration of GnRH actually suppresses the pituitary response
Strcture of LH and FSH
The alpha subunits of LH, FSH, hCG and TSH are identical. The beta subunits are distinct and confer specific functional and immunologic characteristics to the intact molecule
what is inhibin
Released by gonads. Exerts negative feedback on reproductive axis at the level of the pituitary.
