Regional Structural and Functional–Morphological Differences in the Epididymis of the Adult Domestic Cat ( Felis catus ): Light and Scanning Electron Microscopic Study

The current study aimed to characterize the regional histological, histometric and ultrastructural features of the epididymis in adult domestic cats (Felis catus) using light and scanning electron microscopy (SEM). Eight adult cat epididymis samples (2 for SEM, 6 for light microscopy) were used as tissue material in this study. Epididymal samples were subdivided into six regions and examined following routine histological, histochemical and ultrastructural procedures. Histometric measurements included tubular diameter, luminal diameter, epithelial height, stereocilium height and smooth muscle wall thickness. Tubular and luminal diameters, as well as smooth muscle wall thickness, were significantly greater in region VI, whereas stereocilium height was highest in region I and epithelial height was lowest in region VI (p < 0.05). The tubules were lined with pseudostratified columnar epithelium with stereocilia. Basal, principal, narrow and apical cells were identified in the epithelial layer. Intraepithelial glands were identified in regions IV, V and VI. Spermatozoa were present in the lumen of all regions, with a greater visual accumulation in the distal segments. Secretory vesicles and macrophages were also detected in the lumen. Luminal macrophages were more abundant in regions IV, V and VI. Spermatozoa were observed to be embedded within stereocilia, and this morphological pattern was more frequently detected in region VI. PAS staining demonstrated positivity in stereocilia, narrow cells and secretion-filled intraepithelial glands. As a result, the findings demonstrate distinct region-specific morphological and histometric characteristics along the cat epididymis. These structural differences among epididymal regions may reflect variations in regional activity along the epididymal duct.