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Human Body Study

Tunics and Lobules

The coverings and internal partitioning of the testis — its capsule, the inward partitions that carve it into wedges, and the lobules those wedges define.

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.

Parts

Section titled “Parts”

From outside in:

  • Tunica vaginalis — a thin, two-layered serous sac, the leftover pouch the testis took with it as it descended through the abdominal wall during fetal life (it is a piece of peritoneum). A parietal layer lines the inside of the scrotum and a visceral layer hugs the testis itself; a film of serous fluid between the two lets the testis glide. Excess fluid here is a hydrocele.
  • Tunica albuginea — the testis’s true capsule: a thick, glistening, off-white sheet of dense fibrous connective tissue. It gives the testis its firm feel, contains the organ under modest pressure, and projects fibrous partitions inward.
  • Mediastinum testis — a posterior thickening of the tunica albuginea that hangs into the testis like a wedge. It is where the rete testis is housed and where the vessels, nerves, and lymphatics enter and leave.
  • Septa testis — fibrous partitions fanning from the mediastinum out to the inner surface of the tunica albuginea, dividing the organ radially.
  • Lobuli testis (lobules) — the ~250 wedge-shaped compartments carved out by the septa. Each lobule contains 1–4 seminiferous tubules along with the interstitial tissue between them.
  • Tunica vasculosa — a thin, vessel-rich layer lining the inside of the tunica albuginea (and the surfaces of the septa). The first plane the testicular artery’s branches reach as they spread over the organ.

What it does

Section titled “What it does”
  • Contains and shapes — the tunica albuginea bears the internal pressure of the lobules and gives the testis its egg shape.
  • Compartmentalises — the septa divide the testis so each block of seminiferous tubules drains tidily to its own slice of the rete testis.
  • Conducts vessels — the tunica vasculosa carries the capillary network that feeds tubules and interstitium; the mediastinum is the door through which everything enters and leaves.
  • Lubricates and isolates — the tunica vaginalis lets the testis move freely inside the scrotum and provides a serous plane that limits the spread of inflammation.

Key idea

Section titled “Key idea”

The capsule and septa are the testis’s architecture — passive structural tissue that organises the active tissue (tubules and interstitium) into a tidy, drainable, well-vascularised whole. Without the septa, the 250 m of seminiferous tubule packed into each testis could not be sorted into outflow lanes.