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Flashcards in reproductive axis Deck (33):

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


3. 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.


compare the gonadal cells in both sexes

Leydig (male) and theca (female) cells: interstitial cells, have LH receptors, make androgens and lack aromatase. Sertoli (male) and granulosa (female) cells: have FSH receptors, make inhibin, contain aromatase


Function of Leydig cells

In response to LH, Leydig cells produce 95% of testosterone in males. It stimulates conversion of Cholesterol into pregnenolone by increasing amount of desmolase and enhancing its affinity for cholesterol.


Function of Sertoli cells

In direct contact with spermatozoa - support cells. Organized into tubular epithelium called the seminiferous tubule with gap junctions btw cells. Maturing spermatogonia are located btw the sertoli cells and gap junctions btw sertoli cells and spermatozoa allow for maturation of gametes. Testosterone acts on the Sertoli cells


FSH binding to Sertoli cells results in …

Increased production of androgen binding protein, enhanced conversion of testosterone from the Leydig cells into estradiol, and the production of inhibin. The Sertoli cells are the primary source of inhibin in males


Function of Theca cells

In ovarian stroma surrounding follicles. In response to LH, they produce progesterone and androgens. Androstenedione diffuses to nearby granulosa cells


Function of granulosa cells

In direct contact with oogonia, forming the primordial follicles. Androstenedione from theca cells is converted to estradiol by aromatase. Also produces progestins which are converted to androgens by the theca cells


8. Describe the 2-cell theory of sex steroid production and name the gonadal cell responsible for the production of sex steroids in men and women.

Sex steroid production requires 2 cells in both males and females


Be able to label FSH, LH, estrogen, progestin, inhibin on a chart of the female menstrual cycle

ok see chart


read the extra handouts if you have time

ya ok