Pre- and postglomerular arterioles of the kidney.

Characteristics of the structural organization of the afferent and efferent glomerular arterioles of the mammalian kidney, that have so far escaped adequate functional discussion, include: presence and distribution of myoendothelial junctions in afferent and efferent arterioles and their possible functional relevance as stretch receptors; distribution of smooth-muscle cells around cortical efferent arterioles and, in particular, the presence of a contractile segment at the beginning of the efferent arterioles; elaboration of a basement membrane-like material beneath the endothelium of efferent arterioles and the continuity of this material with the mesangial and extramesangial matrix material; and structural organization of the endothelium of juxtamedullary efferent arterioles, consisting of up to 30 longitudinally arranged endothelial cells, and its possible functional significance.