Figure 62

A, Electron micrograph of a rat kidney cortex, where C is the cortex. B, Schematic rendering, where the narrow interstitium is shown in black and the wide interstitium is shown by dots. The relative volume of the interstitium of the cortex is approximately 7%, consisting of about 3% interstitial cells and 4% extracellular space. The vasculature occupies another 6%; the remainder (ie, some 85% or more) is occupied by the tubules. The cortical interstitial space is unevenly distributed and has been divided into narrow and wide structural components. The tubules and peritubular capillaries either are closely apposed at several points, sometimes to the point of sharing a common basement membrane, or are separated by a very narrow space.

This space, the so-called narrow interstitium, has been estimated to occupy 0.6% of cortical volume in rats. The narrow interstitium occupies about one-half to two-thirds of the cortical peritubular capillary surface area. The remainder of the cortical interstitium consists of irregularly shaped clearly discernible larger areas, the so-called wide interstitium. The wide interstitium has been estimated to occupy 3.4% of cortical volume in rats. The capillary wall facing the narrow interstitium is significantly more fenestrated than is that facing the wide interstitium. Functional heterogeneity of these interstitial spaces has been proposed but remains to be clearly defined. (From Bohman [1]; with permission.)

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