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Male Reproductive Physiology

Overview of Male Reproductive Physiology

  • Focuses on hormones involved in reproductive function and sperm production.

  • Discusses processes of erection, ejaculation, and spermatogenesis.

Male Sexual Response

Erection

  • Definition: Enlargement and stiffening of the penis for female penetration.

  • Controlled by the autonomic nervous system.

    • Parasympathetic Nervous System: Responsible for erection (memory aid: "points").

      • Causes relaxation of smooth muscle in erectile tissue.

      • Vasodilation of arterioles in corpora cavernosa.

      • Increased blood flow leads to engorgement and reduces venous drainage.

    • Structures Involved:

      • Corpora Cavernosa: Tissue on sides of the penis.

      • Corpus Spongiosum: Surrounds the urethra, maintaining its openness for ejaculation.

Ejaculation

  • Definition: Propulsion of semen through the male reproductive duct system (memory aid: "shoot").

  • Controlled by the Sympathetic Nervous System:

    • Involves contraction of smooth and striated muscles before and during ejaculation.

  • Organs involved:

    • Seminiferous Tubules: Site of spermatogenesis.

    • Vas Deferens: Transports sperm after production.

    • Prostate & Seminal Vesicles: Contribute fluids to semen.

  • Internal Urethral Sphincter: Constriction occurs to prevent backflow of semen.

  • Bulbospongiosus Muscle: Contracts rapidly to propel semen (speed around 500 cm/s).

Physiological Responses During Ejaculation

  • Pleasure response increases dopamine levels.

  • Physiological changes: Increased heart rate and blood pressure.

  • Resolution Phase:

    • Relaxation of smooth muscle.

    • Sympathetic vasoconstriction of penile arterioles.

  • Refractory Period: Time post-ejaculation where further erections are impossible. Duration increases with age.

Semen Composition

  • Semen: Fluid plus sperm.

    • Typical Volume: 2 to 5 milliliters per ejaculation.

    • Sperm Count: 20 million to 150 million sperm per milliliter.

  • Components of Semen:

    • Fructose: Provides energy for sperm.

    • Alkaline Nature: Balances acidic female vaginal secretions.

    • Prostaglandins & Relaxins: Facilitate reproductive function and combat infections.

    • Clotting Factors & Fibrinolysin: Manage semen consistency for successful transport.

Spermatogenesis

  • Process of sperm development occurring in the seminiferous tubules.

  • Histological Structure:

    • Surrounded by smooth muscle and supportive cells (sustentocytes).

    • Spermatogenic Cells: Located towards the lumen, undergo differentiation.

    • Leydig Cells: Produce testosterone, located among spermatogenic cells.

Stages of Spermatogenesis

  1. Stem Cells (2N) undergo mitosis, producing daughter cells.

  2. Daughter cells differentiate into Primary Spermatocytes (2N), which undergo Meiosis I.

  3. Meiosis I results in Secondary Spermatocytes (N).

  4. Secondary Spermatocytes undergo Meiosis II, leading to Spermatids (N).

  5. Spermiogenesis: Transformation of spermatids into mature sperm, characterized by tail and acrosome formation.

  6. Overall Process: Mitosis for stem cells; meiosis for formation of haploid sperm cells.

Hormonal Regulation of Spermatogenesis

  • Gonadotropin-Releasing Hormone (GnRH): Secreted from the hypothalamus influencing the anterior pituitary.

  • FSH (Follicle-Stimulating Hormone): Initiates spermatogenesis in seminiferous tubules.

  • LH (Luteinizing Hormone): Stimulates testosterone production in Leydig cells.

Testosterone Effects

  • Integral to spermatogenesis and male secondary sexual characteristics:

    • Hair growth patterns (pubic, axillary, facial).

    • Development of Adam's apple and deepened voice.

    • Skin changes (thicker, oilier).

    • Increased bone and muscle mass during puberty.

  • Testosterone, synthesized from cholesterol, has a vital role in male reproductive health.

    • Converted to DHT, impacting male characteristics, and estradiol, affecting brain development.

Feedback Mechanisms

  • Inhibin: Released by sustentocytes to inhibit FSH release, controlling spermatogenesis.

  • Testosterone Level Regulation: Fluctuates throughout life.

    • Peaks during early development, post-birth, and puberty; decreases with age.

Summary of Male Reproductive System Physiology

  • Interplay of hormones regulates erection, ejaculation, and spermatogenesis.

  • Understanding these processes essential for grasping male reproductive health and addressing issues like hypogonadism.