Morphology of the epididymal duct of the domestic pig (Sus scrofa domesticus)

The study provides a general overview of the morphology of the epididymal duct in pigs. Four epididymides from two sexually mature boars were dissected into 32 segments and examined histologically. Duct lumen and wall thickness were measured and relative surface area of different components was assessed by Chalkley's random hit method. The epithelial lining was characterized at X1000. Lumen diameter and wall thickness of efferent ductules averaged 177 and 30 mu m, respectively. Of the epididymal duct from caput to distal corpus the luminal diameter was 332 mu m, with a narrower section in the proximal corpus. Wall thickness averaged 70 mu m. In the cauda, luminal diameter and wall thickness increased to 717 and 751 mu m, respectively. The epithelial lining of the efferent ductules consists of a single layer of columnar cells with average height 21 mu m. The lining of the epididymal duct consists of ciliated, pseudo-stratified columnar epithelium composed of "basal cells" and "principal cells." Particularly tall principal cells (96 mu m) were found in the proximal caput. Height decreased to 40 mu m at the distal cauda. Microvilli from principal cells were 14-17 mu m long in the distal caput but decreased to 5 mu m in the distal cauda. The epithelial lining was folded in the proximal caput and more so in the distal cauda. Secretory granules (epididymosomes) were present in small amounts in efferent ductules and epididymal duct; the largest quantities occurred in the distal cauda. Leukocytes were present throughout the duct, albeit in insignificant numbers. Chalkley's random hit method showed rapid spermatozoan transport through efferent ductules and proximal caput in large amounts of fluid. Sperm concentration increased due to fluid resorption in the proximal caput, was highest from caput flexure to proximal cauda and decreased at the caudal flexure, indicating secretory activity.