Figure 1912

Transmission electron micrograph of a glomerular capillary and adjacent podocyte. The pedicels of the podocytes rest on the basal lamina adjacent to the capillary endothelium, and together, the three components-capillary endothelium, basal lamina, and podocyte-

form a filtration apparatus, x 5,600. Inset. The large arrows point to the fenestrations in the endothelium. On the other side of the basal lamina are the pedicels of the podocytes. Note the slit membrane (small arrows) spanning the gap between adjacent pedicels, x 12,000.

abetic nephropathy) the number of anionic sites, especially in the lamina rara externa, is significantly reduced.

The narrow slit pores formed by the pedicels and the filtration slit membranes also act as physical barriers to bulk flow and free diffusion. The glycoproteins of the filtration slit membrane and of the glycocalyx of the pedicels probably act in a manner similar to that of the glycosamino-

glycans of the laminae rarae of the GBM. Lastly, the fen-estrae of the capillary endothelium restrict the movement of blood cells and other formed elements of the blood from the capillaries. In addition to the structural barriers, the flow rate and the pressure of the blood in the glomerular capillaries also have an effect on the filtration function of the renal corpuscle.

Urinalysis is an important part of the examination of patients with suspected renal disease. Part of this analysis includes the determination of the amount of protein excreted in the urine. The excretion of excessive amounts of protein, i.e., proteinuria (albuminuria), is an important diagnostic sign of renal disease. Normally, less than 150 mg of protein is excreted in the urine each day. Although excessive excretion of protein almost always indicates renal disease, extreme exercise, such as jogging, or severe dehydration may produce increased proteinuria in individuals without renal disease.

Simple squamous epithelium constitutes the parietal layer of Bowman's capsule

The parietal layer of Bowman's capsule contains parietal epithelial cells and forms a simple squamous epithelium. At the urinary pole of the renal corpuscle, it is continuous with the cuboidal epithelium of the proximal convoluted tubule (see Figs. 19.7 and 19.8).

The space between the visceral and parietal layers of Bowman's capsule is called the urinaiy space or Bowman's space (see Fig. 19.8). It is the receptacle for the ultrafiltrate produced by the filtration apparatus of the renal corpuscle. At the urinary pole of the renal corpuscle, the urinary space is continuous with the lumen of the proximal convoluted tubule.

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