Endocrinology

  The ovarian cycle has follicular (FSH, estrogen), ovulation (LH flow), and luteal (progesterone) phases, regulated by the hypothalamic–pituitary–ovarian axis through a delicate balance of feedback mechanisms. 1. Ovarian Cycle – Phases The ovarian cycle lasts about 28 days (average) and has three main phases: A. Follicular Phase (Day 1–14, variable) Begins with menstruation . FSH stimulates growth of several ovarian follicles. One follicle becomes dominant (Graafian follicle) → secretes estrogen . Rising estrogen → proliferation of endometrium (preparing for implantation). B. Ovulation (Around Day 14) High estrogen levels (positive feedback) → LH surge . LH surge causes: Final maturation of oocyte. Rupture of Graafian follicle → release of ovum. C. Luteal Phase (Day 15–28, fixed ~14 days) Remaining follicle forms corpus luteum . Corpus luteum secretes progesterone (main) + estrogen . Progesterone prepares endometrium (se...

  1. Chemistry Progesterone is a C-21 steroid hormone , belonging to the progestogen group. Chemical formula: C₂₁H₃₀O₂ . Derived from cholesterol via the steroidogenesis pathway. It is a lipid-soluble hormone and acts via intracellular nuclear receptors (Progesterone Receptors: PR-A and PR-B) . 2. Secretion • Progesterone is synthesized in the ovaries mainly from cholesterol. • Normal secretions level  • Female pre ovulation/male/post-menopausal=1ng/ml • Female mid cycle=5-20ng/ml • Pregnancy   1st trimester=11 to 90ng/ml  2nd trimester=25 to 89ng/ml  3rd trimester=48 to 150/300ng/ml. In Females Secreted mainly by the corpus luteum after ovulation. Also produced by the placenta during pregnancy (from ~8–12 weeks onward). Minor secretion by adrenal cortex . In Males Secreted in small amounts by testes (Leydig cells) and adrenal cortex. 3. Functions Reproductive Functions Prepares the endometrium for imp...

Estrogen – Chemistry, Secretion, Functions, and Regulation 1. Chemistry Estrogen is a steroid hormone, derived from cholesterol. Belongs to the female sex hormone group. Three main natural estrogens in humans: Estradiol (E2) → most active, dominant in reproductive years. Estrone (E1) → present after menopause. Estriol (E3) → major estrogen in pregnancy. Lipid-soluble and acts through intracellular receptors (nuclear receptors). 2. Site of Secretion Females: Mainly from ovarian follicles (granulosa cells). Also secreted by corpus luteum and placenta (during pregnancy). Males: Very small amounts secreted by testes and adrenal cortex. In blood, estrogens are bound to sex hormone-binding globulin (SHBG) and albumin; only a small free fraction is active. 3. Normal Secretion Adult Women: Blood estradiol levels: 50–350 pg/mL (varies with menstrual cycle). Peaks just before ovulation. During Pregnancy: Very high levels (estriol predominates). After Menopause: Levels fall drastically. 4. Functi...

Testosterone – Chemistry, Secretion, Functions, and Regulation 1. Chemistry Testosterone is a steroid hormone. It belongs to the group of androgens (male sex hormones). Derived from cholesterol in the Leydig cells of testes. It is lipid-soluble and easily passes through cell membranes. 2. Site of Secretion Males: Mainly secreted by Leydig (interstitial) cells in testes. Females: Secreted in very small amounts by the ovaries and adrenal cortex. In blood, testosterone is mostly bound to sex hormone-binding globulin (SHBG) and albumin; only 2–3% is free and biologically active. 3. Normal Secretion In Males: Average adult production: 6–7 mg/day. Blood levels: about 300–1000 ng/dL. Secretion starts during fetal life (for male sex differentiation), decreases after birth, rises again at puberty, and gradually declines after 40–50 years (andropause). In Females: Much lower levels (20–70 ng/dL). Contributes to libido, bone health, and muscle strength. 4. Functions of Testosterone ✅ ...