Male Reproductive Anatomy & Physiology

Male Reproductive System

The male reproductive system includes:

  • Testes: Produce sperm.
  • Ducts: Store and transport sperm.
  • Accessory sex glands.
  • Supporting structures: Penis and scrotum.

Ducts of the Male Reproductive System

  • Ejaculatory duct
  • Prostatic urethra
  • Ductus (vas) deferens
  • Spongy (penile) urethra
  • Epididymis: Sperm maturation and storage.

Accessory Sex Glands

  • Seminal vesicles: Contribute ~60% of semen volume, containing viscous seminal fluid with fructose, prostaglandins, and fibrinogen.
  • Prostate: Contributes ~25% of semen volume, containing thin seminal fluid with a slightly acidic pH, proteolytic enzymes, and seminalplasmin.
  • Bulbourethral (Cowper’s) gland: Secretes a mucous-like, alkaline fluid.

Internal Anatomy of a Testis

  • Seminiferous tubules: Site of sperm production.
  • Sertoli cells: Support sperm production and development within seminiferous tubules.
  • Leydig cells: Produce testosterone, located in connective tissue between seminiferous tubules.

Spermatogenesis

  • Spermatogonia: Undifferentiated germ cells that convert into specialized, motile sperm (spermatozoa).
  • Meiosis: Two rounds of cell division yielding 4 haploid gametes; chromosome number is halved.

Spermiogenesis

  • Spermiogenesis: Differentiation of spermatids into sperm.
  • Acrosome: Facilitates penetration of the secondary oocyte.
  • Middle piece: Mitochondrial sheath provides ATP for locomotion.
  • Tail: Propels sperm through the female reproductive tract.
  • Spermiation: Release of mature spermatozoa from Sertoli cells into the lumen of the seminiferous tubule.
  • Capacitation: Final maturation of sperm within the female reproductive tract, triggered by uterine secretions.
  • Hyperactivation: Hyperactivation of the sperm tail is required to penetrate the matrix surrounding the oocyte, triggered by Ca2+Ca^{2+} influx due to increased progesterone.

Hormonal Control

  • GnRH: Stimulates LH and FSH production at puberty.
  • LH: Stimulates testosterone production by Leydig cells; testosterone stimulates spermatogenesis and inhibits LH release.
  • FSH: Acts on Sertoli cells to promote spermatogenesis by stimulating ABP production, maintaining high local testosterone levels. Sertoli cells release inhibin, reducing FSH release.