Structure of Testes

Overview

Anatomy

• Tunica albuginea
  • an unusually thick, dense connective tissue capsule that covers each testis
• Lobules
  • incomplete connective tissue septa that projects from tunica albuginea divides each testis into lobules
• Seminiferous tubules
  • lobules consist of seminiferous tubules
  • spermatogenesis occurs in seminiferous tubules
  • seminiferous tubule epithelium contains spermatogenic cells and Sertoli cells

Spermatogenic Cells

• Found within the seminiferous tubules
• Spermatogenic cells are organized in poorly defined layers of progressive development between adjacent Sertoli cells
  • most immature spermatogenic cells, spermatogonia, rest on basal lamina 
  • most mature spermatogenic cells, spermatids, attach to apical portion of Sertoli cells and border lumen of seminiferous tubules
• dividing spermatogenic cells form daughter cells that remain joined by cytoplasmic bridges

Sertoli Cells 

• Function to synthesize and secrete hormones including 
  • anti-Müllerian hormone (AMH)
    • released during embryogenesis and inhibits development of Müllerian (paramesonephric) ducts
  •  androgen-binding protein (ABP)
    • released into luminal space of seminiferous tubules, near developing spermatogonia
    • ABP binds testosterone and maintains high local testosterone levels, necessary for spermatogenesis
  • inhibin  
    • provides negative-feedback on hypothalamic-pituitary axis and inhibits GnRH, LH, and FSH
    • has more of an effect inhibiting FSH than GnRH or LH
  • other products
    • other products that support developing spermatogonia and support spermatogenesis
• Sertoli cell junctional complexes 
  • extensive tight junctions bind adjacent Sertoli cells
  • junctional complexes establish 2 epithelial compartments 
    • basal compartment
      • occupies space between basal lamina and Sertoli cell – Sertoli cell junctional complexes
      • contains spermatogonia
    • luminal compartment
      • occupies space above Sertoli cell – Sertoli cell junctional complexes
      • contains primary spermatocytes, secondary spermatocytes, spermatids, and spermatozoa
  •  blood-testis barrier
    • established by junctional complexes
    • spermatogenic cells differ antigenically from somatic cells;therefore, a blood-testis barrier is required to prevent spermatogenic cell exposure to immune system and a resulting autoimmune response