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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.