L. Gabriel Navar

The Regulation of Glomerular Filtration Rate in Mammalian Kidneys

During organogenesis of the kidney, small S-shaped metanephric vesicles form from the undifferentiated metanephric mesoderm. The cephalic part of each primitive renal tubule invaginates to form a cleft within which mesenchymal cells, destined to become the mesangium, accumulate. The formation of a continuous basement membrane serves to separate the intracleftal mesenchymal cells from the tubular cells. As the mesenchymal cells increase in number, vascular tissue enters the cleft to form the capillaries of the glomerular tuft. Eventually, the spherical glomerular capsule is formed and encloses the capillaries, leaving the afferent and efferent arterioles to maintain continuity with the vascular system.

MACULA DENSA FEEDBACK REGULATION OF RENAL HEMODYNAMICS AND RENAL AUTOREGULATION

Publisher Summary This chapter explains that the unique morphological arrangement of the structures that comprise the macula densa–juxtaglomerular complex has encouraged many physiological investigations regarding its functional role. In each nephrovascular unit, there is an invariant intimacy between the macula densa segment of the distal tubule and the vascular and mesangial elements of the glomerulus. Thus, the hypothesis is developed that this macula densa structure has the capability of sensing some component of the fluid as it flows out of the ascending loop of Henle into the distal tubule and, in turn, initiating signals to the vascular elements to provide a steady state influence on renal hemodynamics and glomerular filtration rate. The application of in vivo nephron microperfusion techniques has allowed investigation of several specific issues associated with the macula densa feedback hypothesis.