Reproductive Processes Detailed Notes

HPG Axis: Hypothalamus-Pituitary-Gonad Axis
- Regulates the production of gametes and sex hormones.
- Hypothalamus secretes gonadotropin-releasing hormone (GnRH), which prompts the anterior pituitary to release:
- Follicle-stimulating hormone (FSH)
- Luteinizing hormone (LH)
- Gonads (ovaries and testes) respond by secreting sex hormones: testosterone, estrogen, and progesterone.
- Inhibin: Inhibits FSH release to regulate hormone levels.

Puberty: Marks the onset of GnRH secretion, leading to the first viable sperm release or first menstrual cycle.
- Initiated by a surge in GnRH.
- Developments: Activation of the reproductive system.
Adolescence: Transition from puberty to adult stature.

HPG Axis in Males:
- GnRH from hypothalamus stimulates LH and FSH from the anterior pituitary.
- LH stimulates testosterone production in interstitial endocrine cells.
- FSH stimulates nurse cells to secrete androgen-binding protein (ABP) and inhibin.
- Consequences of High Testosterone Levels: Inhibits GnRH secretion, regulating hormone balance.
Puberty Changes in Males:
- Spermatogenesis: Development and maturation of sperm.
- Development of secondary sex characteristics: body hair, increased sebaceous gland activity, and growth.

Erection:
- Involves the stiffening of erectile tissues.
- Mechanism: Blood flow increases via a parasympathetic reflex (stimulated by nitric oxide).
- Expansion compresses drainage veins, maintaining erection.
Ejaculation:
- Emission: Peristalsis of ductus deferens and contraction of ampulla, prostate, and seminal vesicles.
- Expulsion: Reflexive contraction of bulbospongiosus and ischiocavernosus muscles.
- Internal urethral sphincter contracts to prevent urine and semen backflow.
Resolution:
- Relaxation post-ejaculation involves blood drainage from erectile tissues.

HPG Axis in Females:
- GnRH secretion increases during late childhood, stimulating FSH and LH production for ovarian follicle development.
- Hormones secreted: estrogen, progesterone, inhibin, and androgens.
- They require a body fat threshold (leptin signals the hypothalamus).
Puberty Changes in Females:
- Thelarche: Onset of breast development due to estrogen/progesterone.
- Pubarche: Appearance of pubic/axillary hair due to adrenal androgens.
- Menarche: First menstruation, often anovulatory initially.

Occurs monthly except during pregnancy, lasting approximately 28 days.
Consists of two subcycles:
- Ovarian Cycle: Changes in the ovaries (follicular phase, ovulation, luteal phase).
- Menstrual Cycle: Changes in the uterus (proliferative phase, secretory phase, menstrual phase).

Follicular Phase (Day 1 - 14):
- FSH stimulates growth of follicles.
- Development of a dominant follicle results in estrogen production, leading to the LH spike for ovulation.
Ovulation (Day 15):
- Follicle ruptures, releasing the oocyte into the uterine tube.
Luteal Phase (Day 16 - 28):
- The ruptured follicle transforms into the corpus luteum and produces hormones until involution occurs around Day 22.

Proliferative Phase (Day 6 - 14):
- Endometrium thickens in preparation for possible implantation, driven by estrogen.
Secretory Phase (Day 15 - 26):
- Progesterone from the corpus luteum thickens the endometrium further.
Premenstrual Phase (Day 27 - 28):
- Degeneration of endometrial tissue occurs.
Menstrual Phase (Day 1 - 5):
- Discharge of functional layer of the endometrium as menstrual fluid.

Hormonal Birth Control:
- Progesterone-only Methods: (minipill, Nexplanon) prevent ovulation by suppressing FSH.
- Combined Hormonal Methods: (Yaz, Ortho-Tri-Cyclen) also thicken cervical mucus and thin the endometrium.

Condition involves the growth of endometrium outside of the uterus, leading to symptoms like pelvic pain and abnormal bleeding. It may be due to retrograde menstruation.
- Treatments include medications, hormone therapy, or surgery, with hysterectomy for severe cases.