Male Reproductive System

Male Reproductive System Notes

Objectives

  • Understand hormones secreted by Leydig and Sertoli cells in the testes.
  • Learn about spermatogenesis.
  • Explore mechanisms of erection and ejaculation.
  • Study the structure, biosynthesis, transport, metabolism, and actions of testosterone.
  • Discuss the regulation of testosterone secretion.

Anatomy of the Male Reproductive System

  • Components include:
    • Urinary bladder
    • Seminal vesicle
    • Prostate gland
    • Testes and epididymis
    • Vas deferens
    • Urethra
    • Penis
    • Scrotum
  • Each component has specific functions that contribute to male reproductive health.

Physiologic Anatomy of the Testes

  • Testes contain convoluted seminiferous tubules and interstitial Leydig cells.
    • Convoluted seminiferous tubules: Site of spermatogenesis where sperm are formed.
    • Leydig cells: Secrete testosterone and contain lipid granules.
  • The anatomy allows for countercurrent exchange of heat and testosterone, essential for testicular function.

Blood-Testis Barrier

  • Sertoli cells and germ cells maintain survival of spermatogenic cells through:
    • Tight junctions creating a blood-testis barrier, restricting large molecule passage.
    • Facilitates a specific composition of tubular fluid necessary for sperm development.
  • Actions of the blood-testis barrier include:
    • Protecting germ cells from pathogens.
    • Preventing autoimmune responses against germ cells.

Spermatogenesis

  • Starts with spermatogonia maturing into primary spermatocytes.
  • Primary spermatocytes undergo meiosis to form secondary spermatocytes, then spermatids which develop into spermatozoa.
  • Total transformation takes approximately 74 days.
  • The process ensures synchronization through cytoplasmic bridges among developing cells.

Structure of Spermatozoa

  • Composed of:
    • Head: Contains chromosomal material covered by acrosome rich in fertilization enzymes.
    • Midpiece: Contains mitochondria providing energy for motility.
    • Tail: Facilitates movement toward the ovum.
  • Germinal angiotensin-converting enzyme (gACE) may play roles in fertility.

Role of Sertoli Cells

  • Support spermatogenesis by:
    • Providing androgen binding protein (ABP) and inhibin.
    • Converting androgens to estrogens via aromatase.
  • Regulate fluid composition in the testes to support sperm maturation.

Hormonal Regulation

  • Testosterone and FSH are crucial for testicular function:
    • LH stimulates Leydig cells for testosterone production.
    • FSH maintains spermatogenesis via Sertoli cells.
  • Inhibin feeds back to inhibit FSH secretion, helping regulate sperm production.

Temperature Effects

  • Ideal testicular temperature is about 32°C for optimal spermatogenesis.
  • Increased temperature (e.g., hot baths, insulation) can result in reduced sperm counts.

Semen Composition

  • Avg volume per ejaculate: 2.5–3.5 mL containing about 100 million sperm/mL.
  • Semen includes secretions from seminal vesicles, prostate, and bulbo-urethral glands.
  • Prostaglandins present but functions are unclear.

Erection Mechanisms

  • Initiated by dilation of arterioles and filling of erectile tissue with blood.
  • Affected by the release of acetylcholine and nitric oxide (NO) which promote vasodilation via cGMP.
  • NO synthase inhibitors can prevent erections, while drugs like sildenafil promote prolonged erections by inhibiting breakdown of cGMP.

Ejaculation Process

  • Involves two parts: emission (movement of semen into urethra) and ejaculation (propulsion of semen out).
  • Fluid propulsion occurs due to contraction of the bulbocavernosus muscle.

Testosterone Biosynthesis

  • Testosterone is derived from cholesterol in Leydig cells and regulated by LH.
  • The synthesis involves various hydroxylation and cleavage processes.

Actions of Testosterone

  • Develops and maintains male secondary sex characteristics.
  • Influences protein synthesis and promotes growth (anabolic effects).
  • Feedback inhibition of LH secretion occurs through direct action on the anterior pituitary.

Inhibins and Activins

  • Inhibins inhibit FSH secretion, while activins stimulate it.
  • Inhibins formed by Sertoli cells and granulosa cells.

Abnormalities of Testicular Function

  • Conditions include: cryptorchidism and androgen-secreting tumors.
  • Understanding hormonal levels assist in diagnosing related conditions.