Ovarian Hormones

Ovarian Hormones


OVARIAN HORMONES

Two important ovarian hormones

  • Estrogen
  • Progesterone

ESTROGEN:

  • Primarily secreted by granulosa cells of ovarian follicles, corpus luteum & placenta.
  • 18-Carbon steroids
  • Naturally occurring estrogens – 
  • Estradiol, Estrone & Estriol
  • Estradiol 
  • Major estrogen secreted by ovary in normal adult women.
  • Estrone
  • Major in postmenopausal women
  • Estriol
  • Major in pregnant women

Mechanism of action:

  • Estrogen binds to Estrogen receptors (ERs) – Nuclear type
Receptors:
  • Two ERs designated ER-α & ER-β
  • ER-α – Uterus, vagina, breast, hypothalamus & blood vessels.
  • ER-β – Prostate gland of males & ovaries of female.

Major physiological actions of estrogen:

1. In Sex organs:

  • Brings pubertal changes in female.
  • Growth of uterus, fallopian tube & vagina.
  • Vaginal epithelium gets thickened, stratified and cornified.
  • Endometrium proliferation in preovulatory phase.
  • Estrogen sensitizes uterus to oxytocin.

2. Secondary sexual character development: 

  • Growth of breast-proliferation of duct & stroma
  • Fat accumulation.
  • Appearance of pubic & axillary hair.
  • Feminine body contours & behaviour influenced.
  • Acne common in girls at puberty 
  • Due to androgens.

3. Metabolic effects:

  • Anabolic
  • Promotes fusion of epiphysis
  • Maintain bone mass by reducing bone resorption.
  • Promote positive calcium balance by inducing renal 1α-hydroxylase
  • Cause salt & water retention.
  • Decrease LDL while increasing HDL & triglycerides
  • Atherosclerosis is rare before menopause.
  • Blood coagulability increased –
  • Due to increased synthesis of factor II, VII, IX & X.
  • Increase bile lithogenicity –
  • By increasing cholesterol secretion & decreasing bile secretion.

PROGESTERONE:

  • 21 carbon steroid.
  • Secreted by corpus luteum, placenta, & follicle (small amounts).

Major physiological actions:

1. In Uterus

  • Secretory changes in estrogen-primed endometrium.
  • Decrease uterus sensitivity to oxytocin.
Applied physiology:
  • Lack of progesterone support (Progesterone withdrawal).
  • Causes mucosal shedding & bleeding during menstruation.

2. In Cervix

  • Converts watery cervical secretion induced by estrogen to viscid & scanty.
  • Hostile to sperm penetration.

3. In Vagina

  • Induces pregnancy like changes in vaginal mucosa
  • Leukocyte infiltration of cornified epithelium.

4. In Breast:

  • Causes proliferation of mammary glands acini.
  • Prepares breast for lactation along with estrogen.

5. On CNS:

  • Sedative effect

6. On Body temperature:

  • Causes a slight (0.5°c) rise in body temperature.

7. On Metabolism

  • Raises LDL 
  • Lowers HDL
  • Impaired glucose tolerance.

8. On Pituitary

  • Inhibits LH secretion by feedback inhibition – “Anovulatory action”

OTHER OVARIAN HORMONES:

1. Inhibin:

  • Secreted by granulosa cells & corpus luteum in ovary & Sertoli cells in males.
  • Inhibits FSH secretion in feedback manner.

2. Activin:

  • Secreted by granulosa cells in females & Sertoli cells in males.
  • Stimulates FSH secretion.

3. Relaxin:

  • Secreted by corpus luteum in ovary & from placenta.
  • Structurally similar to insulin & Insulin-like Growth Factor (IGF).
  • Relaxes symphysis & sacroiliac joints during pregnancy.
  • Helps in cervical ripening.
Exam Question
 

OVARIAN HORMONES

ESTROGEN:

  • Primarily secreted by granulosa cells of ovarian follicles, corpus luteum & placenta.
  • Estradiol – Major estrogen secreted by ovary.
Receptors:
  • Two ERs designated ER-α & ER-β.
  • ER-β receptor present in Ovaries.

Major physiological actions of estrogen:

1. Metabolic effects:

  • Maintain bone mass by reducing bone resorption.
  • Decrease LDL while increasing HDL & triglycerides

PROGESTERONE:

  • 21 carbon steroid.

Major physiological actions:

1. In Uterus

  • Progesterone withdrawal (Lack of progesterone support) causes mucosal shedding & bleeding during menstruation.

2. On Body temperature:

  • Causes a slight (0.5°c) rise in body temperature.

3. On Metabolism

  • Raises LDL 
  • Lowers HDL

4. On Pituitary

  •  Inhibits LH secretion by feedback inhibition – “Anovulatory action”

OTHER OVARIAN HORMONES:

1. Inhibin:

  • Secreted by granulosa cells & corpus luteum in ovary & Sertoli cells in males.
  • Inhibits FSH secretion in feedback manner.
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