Male Reproductive System: Testes and Testosterone

Effects of Testosterone

  • Testosterone affects the testes and areas outside the testes.
  • Promotes development and maintenance of sexual structures, including accessory sexual structures.
  • Testosterone surges:
    • Neonatal surge: Occurs shortly after birth and is crucial for developing male sexual organs.
    • Puberty surge: Responsible for maturation of male sex organs.
  • Maintenance:
    • Testosterone is essential to prevent testicular atrophy.
  • Secondary sexual characteristics:
    • Testosterone influences characteristics that make males attractive.
    • Affects behavioral traits promoting successful mating.

Hypothalamic-Pituitary-Gonadal (HPG) Axis

  • GnRH (Gonadotropin-Releasing Hormone):
    • Released by the hypothalamus.
    • Stimulates the pituitary gland.
  • Pituitary gland hormones:
    • LH (Luteinizing Hormone): Primary hormone stimulating the testes.
    • FSH (Follicle-Stimulating Hormone): Supports LH function.
  • Testes:
    • Produce testosterone.
  • Negative Feedback:
    • Testosterone inhibits GnRH release in the hypothalamus.
    • Testosterone inhibits LH and FSH release in the pituitary gland.

Anatomy of the Testes

  • Seminiferous Tubules:
    • The bulk of the testes is composed of seminiferous tubules.
    • Sperm production occurs within the epithelium lining these tubules.
    • Each tubule forms a loop anchored at the rete testis.
  • Rete Testis:
    • The seminiferous tubules are anchored here.
    • Connects to the epididymis.
  • Epididymis:
    • Sperm is stored here until release.
    • The head of the epididymis connects to the vas deferens.
  • Vas Deferens:
    • A duct that leads to the urethra.
    • Transports sperm to the urethra for ejaculation.

Male Reproductive Tract and Scrotal Sac

  • Location:
    • The male reproductive tract is located in the scrotal sac, outside the body cavity.
  • Scrotal Sac:
    • The testes can be retracted towards the abdomen via muscle reflexes.
  • Temperature Regulation:
    • The testes are 2 degrees Celsius cooler than the body cavity.
    • Lower temperature is essential for normal spermatogenesis.
  • Cryptorchidism:
    • Failure of the testes to descend into the scrotum results in spermatogenesis dysfunction.
    • Testosterone production remains unaffected.
    • Hot baths can impair sperm production due to increased temperature.

Sperm and Testosterone Production in Testes

  • Compartmentalization:
    • Sperm and testosterone production occur in separate compartments within the testis.
  • Sperm Production:
    • Occurs in the seminiferous tubules, which constitute the bulk of the testicular mass.
  • Testosterone Production:
    • Occurs in the interstitial cells between the seminiferous tubules.
    • Leydig cells are responsible for testosterone production.

Testicular Blood Flow and Heat Exchange

  • Paired Arteries and Veins:
    • Testicular arteries and veins are paired and wrapped around each other.
  • Heat Exchange Mechanism:
    • Arteries carry warmer blood from the body cavity to the testis.
    • Veins carry cooler blood from the testis back to the body cavity.
    • Heat is exchanged between the arterial and venous blood.
  • Process:
    • Arterial blood is cooled by venous blood, reducing its temperature before it reaches the testis.
    • Venous blood is warmed by arterial blood before returning to systemic circulation.
  • Importance:
    • This arrangement maintains the temperature difference required for spermatogenesis.

Seminiferous Tubule Anatomy

  • Cross-Section:
    • Shows the lumen (inside space) of the tubule.
    • Leydig cells are located in the connective tissue surrounding the tubules.

Leydig Cells

  • Presence:
    • Present at birth but disappear within 5-6 months.
    • Reappear at puberty, resuming testosterone production.