Branching and confluence pattern of glomerular arterioles in the rat

In addition to the usual division of the glomerular tuft into lobules, a subdivision into an afferent and an efferent capillary domain is made. Immediately after entering the glomerulus the afferent arteriole splits into superficially located branches which supply the lobules. The capillaries of each lobule first run towards the urinary pole; these parts of each lobule establish the afferent domain. The capillaries of each lobule running back towards the vascular pole establish the efferent domain. The afferent domain represents the major part of the tuft; it has the shape of an incomplete globe with a deep depression on one side within which the efferent domain is situated. The efferent arteriole is established inside the glomerular tuft within the efferent capillary domain. Generally tributaries from each lobule converge to form the intraglomerular segment of the efferent arteriole, which leaves the tuft by passing through the mesangium of the glomerular stalk. At this site the intraglomerular segment of the efferent arteriole is fully surrounded by the mesangium; consequently, it is exposed to the intramesangial pressure.