Renal Corpuscle

General Description

A renal corpuscle is the invaginated blind end of a renal tubule called Bowman's capsule. The capsule is composed of a simple squamous epithelium referred to as the parietal layer. Internally (the visceral layer) is a capillary tuft, the glomerulus, and specialized cells (refer to R-P, Fig. 20.7 & Pls. 71 & 72) that are intimately associated with the capillary tuft. These cells are the podocytes. In H&E stained sections the podocytes are difficult to see but have pale cytoplasm, and lightly stained, slightly larger, oval nuclei. The podocytes extend finger-like processes (pedicels) that wrap around the capillaries. Between the pedicels are basal lamina-covered slits that act as a filter, allowing fluid from the blood to enter the corpuscle. In the electron microscope, podocytes are seen to consist of a central cell body and numerous foot processes applied to the basal lamina of the capillary. Note the pores between the foot processes and fenestrations in the capillary wall (R-P, Figs. 20.8 & 20.11). The other major cell type within the corpuscle is the mesangial cell. These cells are difficult to distinguish from endothelial cells. Between the visceral and parietal layers of Bowman's capsule is Bowman's space, which fills up with the filtrate.

The corpuscle is a polarized structure with a vascular pole and a urinary pole (RP, Fig. 20.7). At the vascular pole, the vessel bringing blood to the glomerulus is called the afferent arteriole, and the vessel taking blood away is called the efferent arteriole. These vessels anchor the glomerulus to the wall of Bowman's capsule.

Identifications

Study a section of the kidney, referring to R-P, Figs. 20.1, 20.3, 20.6 & Pl. 70. In the cortex, locate a renal (Malpighian) corpuscle (slide B-67, H&E [2.5x-labeled, 10x, 20x, 40x]; B-68, PAS [2.5x, 10x, 20x, 40x-labeled]; B-69, PAS [2.5x, 10x, 20x, 40x]; B-70, carmine [2.5x-labeled, 10x, 20x, 40x-labeled]; B-71, H&E [2.5x, 10x, 20x, 40x]).

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