Microvasculature of the corpus epididymis of canis familiaris. A scanning electron microscopic study of microvascular corrosion casts.

The microvasculature of the corpus epididymis of adult domestic dogs (Canis familiaris) was studied using the technique of scanning electron microscopy of microvascular corrosion casts. The vascularization of the dog's corpus epididymis is accomplished by small arteries that course in the upper border of the organ. From these vessels arise first order arterioles (200-101 microm) which cross the surface of the epididymis and often show some coiling. The latter vessels supply second order arterioles (100-31 microm) which vascularize segments of the epididymal duct. The coiled and tight course of this duct is responsible for its peculiar microvascular arrangement. This is characterized by a 'bicycle-wheel' pattern and it is provided with precapillary or terminal arterioles (30-11 microm) nourishing a rich periductal network, mostly formed by anastomosing capillaries (10-3 microm). The periductal capillary network drains into postcapillary (11-30 microm), second order (31-100 microm) and first order (101-200 microm) venules, which empty into small calibre veins that course in the upper border of the epididymis. Anastomoses between vessels of the same type are often found. These are arteriovenous anastomoses mainly located at the periductal network. This study demonstrates that the epididymal microvasculature can be subdivided into a distribution microvascular network (DMN), formed by first and second order arterioles and venules, which presents a behaviour independent of the epididymal duct's sinuosities and a nutrition microvascular network (NMN), formed by precapillary arterioles, capillaries and post-capillary venules, characterised by the close relationship of the vessels with the loops of the epididymal duct.