Reproductive Processes Detailed Notes

Reproductive Processes

Hormonal Regulation

• 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 and Adolescence

• 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.

Male Reproductive System

• 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.

Male Sexual Functions

• 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.

Female Reproductive System

• 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.

Female Sexual Cycle

• 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).

Ovarian Cycle Details:

• 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.

Menstrual Cycle Details:

• 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.

Birth Control Methods

• 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.

Endometriosis

• 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.