Testes

Key Features of the Testes:

• Comprise tightly packed seminiferous tubules, which house the male gametes.
• Sustentacular, aka, Sertoli, cells of the seminiferous tubules envelop the gametes as they develop into sperm.
• Outside the seminiferous tubules, interstitial, aka, Leydig, cells produce testosterone, which facilitates sperm formation.

Anatomical Overview:

• Testes are egg-shaped
• Tunica albuginea comprises the fibrous outer surface.
• Mediastinum of the testis (aka, mediastinum testes) is where the tunica albuginea forms a thickened ridge along the posterior aspect, and,
• Septa extend from the mediastinum and separate the seminiferous tubules into lobules.
• Straight tubules transport sperm from the seminiferous tubules to the rete testis, which comprises a network of tubules within the mediastinum.
• Efferent ductules converge to deliver sperm to the epididymis, which is continuous with the ductus deferens.
• Tunica vaginalis is a double-layered sac that comprises a visceral layer, which is closely adhered to the tunica albuginea of the testis, and, a parietal layer, which is in contact with the innermost layer of the scrotum and spermatic cord.
  • The cavity of the tunica vaginalis is the space between these two layers, and contains a small amount of fluid that allows for movement of the testicles within the scrotum.

Low magnification view of the testes.

• Mediastinum, which comprises vascular and supporting collagenous tissues, as well as the rete testis; though not highlighted here, myoid cells of the mediastinum contract to move spermatozoa towards the epididymis.
• Septa dividing the seminiferous tubules into lobules, and,
• Inner tunica albuginea and outer tunica vaginalis.

Seminiferous tubules.

• Lumen and basement membrane.
• Sustentacular cells are columnar with extensive cytoplasmic processes.
  • Because sustentacular cells secrete substances that facilitate spermatogenesis and nurture the developing sperms, they are also referred to as "nurse" cells.
  • Connected via tight junctions, which divides the tubule into basal and adluminal compartments.

Blood-testis barrier

-Intercellular junctions form the blood-testis barrier, which blocks toxins in the blood from the developing gametes.

• Spermatogenic series, aka, the male gametes in various stages of development
  • Spermatogonia in basal compartment undergo mitosis to create primary spermatocytes, which reside within the adluminal compartment and give rise to secondary spermatocytes.
  • Secondary spermatocytes undergo meiosis II to produce spermatids, which then form immature sperm. Notice that each successive stage moves closer to the lumen.
  • Sperm are released into the lumen, and label their heads and tails.

Histological sample feautres

• Basement membrane, and lamina propria with myofibroblasts; myofibroblasts contract and move sperm through the seminiferous tubules.
• Sustentacular cell has an oval nucleus near the basement membrane; because its cytoplasmic extensions envelop the spermatogenic series, its irregular cell borders shift to accommodate the developing gametes.
• Spermatogonia, the primordial germ cell, lies close to the basement membrane and has a spherical nucleus.
• Early and late stage sperm are visible near the lumen.
• Interstitial (aka, Leydig) cell, lies outside the seminiferous tubule; these cells produce testosterone, which facilitates sperm production.

Be aware of intertextual variation in morphological nomenclature: some texts

refer to these early sperm cells as spermatids, or late spermatids; such discrepancies reflect the difficulty of creating discrete stages and categories out of continuous processes.

Images:

Histology (Mark Braun, MD, & Indiana University: http://medsci.indiana.edu/c602web/602/c602web/toc.htm; http://www.indiana.edu/~anat215/virtualscope2/start.htm)