The blood vasculature as the forming element of the uterus of the estrous donkey (Equus asinus)

Light, scanning electron microscopy of endometrial surface and vascular cas ts were used to study the vascular architecture of the donkey uterus during estrous. The arterial blood supply of the uterus comes from three arteries : the uterine branch of the ovarian artery, the uterine artery of the exter nal iliac artery, and the uterine branch of the urogenital artery. All arte ries enter the uterus at its mesometrial border and divide into smaller one s. Segmentally constricted arteries are seen to circumscribe large veins at the perimetrium which become highly convoluted in the intermuscular vascul ar layer of the myometrium. Small arteries and arterioles originate at the borderline between the myometrium and the endometrium and radiate to the su rface of the endometrium to constitute a system of numerous ridges and groo ves by a widely meshed plexus of subepithelial capillary network. The post- capillary venules of the endometrium arise from the subepithelial capillary plexus to form slightly larger veins than the concurrent arteries which jo in up to the large tortuous veins in the intermuscular vascular layer of th e uterus. This arrangement of blood vessels in the donkey uterus and partic ularly in the endometrium provides the requirement for instant blood flow o n the arterial side and for the slow flow rate on the venous side to amelio rate the process of substances exchange.