Page 704 - Atlas of Histology with Functional Correlations

A higher magnification of the kidney shows greater detail of the cortex. The

renal corpuscles (5, 9) consist of a glomerulus (5a) and the glomerular
(Bowman) capsule (5b). The glomerulus (5a) is a tuft of capillaries formed from
the afferent glomerular arteriole (11), is supported by fine connective tissue,
and is surrounded by the glomerular capsule (5b).

The internal or visceral layer (9a) of the glomerular capsule (5b) surrounds

the glomerular capillaries with modified epithelial cells called podocytes (9a).
At the vascular pole (8) of the renal corpuscle (9), the epithelium of the visceral
layer (9a) turns back to form the simple squamous parietal layer (9b) of the
glomerular capsule (5b). The space between the visceral layer (9a) and the

parietal layer (9b) of the renal corpuscle (9) is the capsular space (10).

Two types of convoluted tubules, sectioned in various planes, surround the
renal corpuscles (5, 9). These are the proximal convoluted tubules (1) and
distal convoluted tubules (2, 4). The convoluted tubules are the initial and
terminal segments of the nephron. The proximal convoluted tubules (1) are

longer than the distal convoluted tubules (2, 4) and are, therefore, more
numerous in the cortex. The proximal convoluted tubules (1) exhibit a small,
uneven lumen and a single layer of cuboidal cells with eosinophilic granular

cytoplasm. A brush border (microvilli) lines the cells but is not always well
preserved in the sections. Also, the cell boundaries in the proximal convoluted
tubules (1) are not distinct because of the extensive basal and lateral cell
membrane interdigitations with the neighboring cells.

The urinary capsular space (10) in the renal corpuscle (5, 9) is continuous

with the lumen of the proximal convoluted tubule at the urinary pole (see Fig.
18.5). At the urinary pole, the squamous epithelium of the parietal layer (9b) of
the glomerular capsule (5b) changes to the cuboidal epithelium of the proximal
convoluted tubule (1).

The distal convoluted tubules (2, 4) are shorter and are fewer in number in
the cortex. The distal convoluted tubules (2, 4) also exhibit larger lumina with
smaller cuboidal cells. The cytoplasm stains less intensely than that in the
proximal convoluted tubules (1), and the brush border is not present on the cells.
Similar to the proximal convoluted tubules (1), the distal convoluted tubules (2,

4) show deep basal and lateral cell membrane infoldings and interdigitations.

Also seen in the cortex are the medullary rays. The medullary rays include
the following three types of tubules: straight (descending) segments of the
proximal tubules (14), straight (ascending) segments of the distal tubules

(6), and collecting tubules (12). The straight (descending) segments of the

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