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Human Body Study

Testes

The paired male gonads — egg-shaped organs about 4–5 cm long, held in the scrotum outside the body. Each testis is two organs in one: a spermatogenic organ (the seminiferous tubules) that produces sperm continuously from puberty onward, and an endocrine organ (the Leydig cells of the interstitium) that produces testosterone.

Schematic of the testis A labelled diagram of the testis. The left figure is a cut-away sagittal view showing the fibrous capsule (tunica albuginea), the septa dividing the testis into lobules, the coiled seminiferous tubules within each lobule, the mediastinum testis with its rete testis, the efferent ductules leaving the testis, the epididymis draped along its posterior border (head, body, tail), the vas deferens, and the spermatic cord with its testicular artery and pampiniform venous plexus. The centre figure is a magnified cross-section of a single seminiferous tubule with adjacent interstitium, showing tall Sertoli cells spanning the tubule wall, the spermatogenic lineage maturing from basement membrane to lumen, peritubular myoid cells, and Leydig cells in the interstitial space. The testis — cut-away and tubule cross-section scrotum mediastinum head body tail testicular artery pampiniform plexus vas deferens seminiferous tubule (cross-section) lumen capillary Scrotum & spermatic cord the skin sac that holds both testes outside the body,and the cord that suspends each testis carrying itsvessels, nerves, and vas deferens. Vasculature & nerves the testicular artery and the pampiniform venousplexus that cools it; lymphatics; autonomic nerves. Tunics & lobules the tough fibrous capsule (tunica albuginea), theserous outer tunica vaginalis, and the septa carvingthe testis into ~250 wedge-shaped lobules. Seminiferous tubules the tightly coiled tubes within each lobule wheresperm are made — about 250 m of tubule per testis. Intratesticular ducts straight tubules feed the rete testis (a networkin the mediastinum), which drains via efferentductules to the head of the epididymis. Sertoli cells tall nurse cells spanning the tubule wall;their tight junctions form the blood-testis barrier. Spermatogenic cells the germ-cell lineage, base to lumen — spermatogonia→ spermatocytes → spermatids → spermatozoa. Leydig cells endocrine cells between the tubules — thesource of testosterone, driven by LH. Interstitial tissue the loose stroma between tubules — capillaries,lymphatics, macrophages, and connective tissue. Left: sagittal cut-away of one testis with its epididymis and spermatic cord. Centre: magnified seminiferous tubule and adjacent interstitium. Not to scale.

Constituent parts

Section titled “Constituent parts”

From the outside in, then by tissue compartment:

  • Tunics and lobules — the layered coverings of the testis (the serous tunica vaginalis, the tough fibrous tunica albuginea that is the capsule, and the inner vascular tunica vasculosa) together with the septa that fan inward from the capsule’s posterior thickening (the mediastinum testis), dividing the organ into roughly 250 wedge-shaped lobules.
  • Seminiferous tubules — the tightly coiled tubes packed inside each lobule (about 1–4 per lobule, ~250 m of tubule per testis in total). Their wall — the seminiferous epithelium — is where sperm are made. Two cell populations sit in this wall: somatic Sertoli cells (tall nurse cells whose tight junctions form the blood-testis barrier) and the spermatogenic cells of the germ-cell lineage (spermatogonia → spermatocytes → spermatids → spermatozoa). Outside the basement membrane sits a thin ring of contractile peritubular myoid cells that slowly squeeze sperm onward.
  • Interstitial tissue — the loose connective stroma that fills the gaps between tubules. It contains Leydig cells — the endocrine cells that make testosterone in response to LH — together with capillaries, lymphatic channels, resident macrophages, mast cells, fibroblasts, and a small population of nerves.
  • Intratesticular ducts — the outflow plumbing inside the testis: each seminiferous tubule narrows into a short straight tubule (tubulus rectus), which feeds the rete testis (an anastomosing network of channels in the mediastinum), which drains into ~12–20 efferent ductules that leave the testis and merge into the head of the epididymis.
  • Vasculature and nerves — the testicular artery (from the abdominal aorta), the pampiniform venous plexus that wraps it and acts as a countercurrent heat exchanger, lymphatic drainage to the para-aortic nodes, and a small autonomic supply.
  • Scrotum and spermatic cord — the supporting envelope and suspension: the skin sac holding both testes outside the body, its thin dartos muscle in the wall, the cremaster muscle that raises and lowers the testis, and the spermatic cord through which the vessels, nerves, and vas deferens enter and leave.

What it does

Section titled “What it does”
  • Spermatogenesis — produce sperm continuously from puberty onward at roughly 100–200 million per day, on a ~74-day cycle from stem cell to mature sperm. The seminiferous tubules are the factory.
  • Testosterone production — the Leydig cells make testosterone in response to pituitary LH; this drives male sexual development and feeds back negatively to the HPG axis.
  • Immune privilege — the blood-testis barrier walls off the developing germ cells (which carry novel antigens not present at the time the immune system learned what self is) from circulating lymphocytes.

Key idea

Section titled “Key idea”

The testis is two organs braided together. The seminiferous tubules and the Leydig cells in the interstitium share a single organ but answer to different signals (FSH and intratesticular testosterone for spermatogenesis; LH for testosterone production) and produce different outputs (sperm vs. testosterone). The whole arrangement runs a few degrees below body-core temperature — which is why the testes hang outside the body in the scrotum, and why the pampiniform plexus, dartos, and cremaster all exist as a temperature-control system.