Epididymis

The epididymis is a highly coiled, tubular structure that plays an important role in sperm maturation, storage and transport. The epididymal ducts are surrounded by concentric layers of fibromuscular tissue rich in smooth muscle cells with blood vessels and nerves in the adjacent supporting stroma. The duct of the epididymis is lined with pseudostratified columnar epithelial cells called principal cells. The principal cells are the major cell type and they have straight non-motile stereocilia that enable extensive absorptive and secretory functions. Together with the peristaltic movement of the smooth muscle, the duct cells facilitate flow of sperm through the epididymis to the vas deferens and connecting excretory tubes. In addition to the principal cells, the epididymal duct also consists of several other types of epithelial cells called clear cells, narrow cells, basal cells, halo cells, and the mitochondria rich apical cells. However, the functions of these cells are poorly understood. A few scattered macrophages and lymphocytes can also be present in the stromal compartment.