Structure of the germinal epithelium
The epithelium consists of Sertoli's sustentacular cells and the spermatogenic cells. The Sertoli's cells form a single-layered lamina and extend from the basal lamina to the tubule lumen. With their labyrinthine cellular processes they surround the individual types of germ cells more or less completely. Spermatogenesis is thus accomplished in close contact with the Sertoli's cells, which not only have supportive and nourishing functions, but also secrete hormones and phagocytize cell fragments. Somewhat above the basal lamina they are bound to each other through complicated occluding junctional complexes (tight junctions), so that 2 separated compartments are present in the epithelium: a basal one, in which the spermatogonia are lined up, and a luminal one, in which all the other stages of spermatogenesis are found.
- 1
- Peritubular cells
- 2
- Basal membrane
- 3
- Spermatogonia
- 4
- Tight junction
- 5
- Spermatocyte I
- 6
- Spermatocyte II
- 7a
- Spermatids
- 7b
- Spermatids
- 8
- Acrosome
- 9
- Residual bodies
- 10
- Spermatozoas
- 11
- Cell nucleus of sustentacular cells (Sertoli)
- A
- Basal zone
- B
- Adluminal zone
Schema of the germinal epithelium: The supportive (Sertoli) cells sit on the basal membrane. Towards the lumen of the spermatogonia (lowest row of cells) the Sertoli cells are connected with each other by the occluding junctional complexes (tight junctions). This seal gives rise to the blood-testicle barrier. The cytoplasm of these supportive cells gets formed into complicated processes because they surround all of the cells involved with spermatogenesis.
Through the occluding junctional complexes of the Sertoli's cells a "blood/testicle" barrier is created in the tubule. This means that outside this barrier, in the tubular periphery, cells, substances and hormones from the blood have unhindered access.
On the other hand, the inner compartment of the tubule is protected by the barrier, which is selectively permeable and serves as an entry check. This is of practical importance because haploid cells in the inner part of the tubule exhibit surface antigenic properties, different from all other body cells. They must thus be kept secluded from the immune system of the organism by the "blood/testicle" barrier.