FIGURE 20.6 • Diagrams and photomicrograph of an adult human kidney. The diagram in the upper left is a hemisection of the adult human kidney included for orientation. The diagram on the right represents an enlarged portion emphasizing the relationship of two nephrons and their collecting tubules and ducts ( yellow) to the cortex and medulla. The upper nephron, a midcortical nephron, extends only a short distance into the medulla and possesses a short thin segment in the loop of Henle. The lower nephron, a juxtamedullary nephron, has a long loop of Henle that extends deep into the medulla. Both nephrons drain into the collecting tubules in the medullary ray. The photomicrograph shows a section of the cortex. It is organized into a series of medullary rays containing straight tubules and collecting tubules and between them the cortical labyrinths containing the renal corpuscles and their associated proximal and distal convoluted tubules. A kidney lobule consists of a medullary ray at its center and half of the adjacent cortical labyrinth on either side. 60.
In summary, the gross appearance of the kidney parenchyma reflects the structure of the nephron. The renal corpuscle and the proximal and the distal convoluted tubules are all located in and make up the substance of the cortical labyrinths. The portions of the straight proximal and straight distal tubules and the descending thin and ascending thin limbs of the loop of Henle in the cortex are located in and make up the major portion of the medullary rays. The thin descending and thin ascending limbs of the loop of Henle are always located in the medulla. Thus, the arrangement of the nephrons (and the collecting tubules and ducts) accounts for the characteristic appearance of the cut surface of the kidney, as can be seen in Figure 20.6.
foot processes (pedicels) of podocytes parietal layer of basal lamina
FIGURE 20.7 • Structure of the renal corpuscle. a. This schematic diagram shows the organization of the renal corpuscle and the structures associated with it at the vascular and urinary poles. Mesangial cells are associated with the capillary endothelium of the glomerulus and the glomerular basement membrane. The macula densa cells of the distal tubule are shown intimately associated with the juxtaglomerular cells of the afferent arteriole and the extraglomerular mesangial cells. (Modified from Kriz W, Sakai T. Morphological aspects of glomerular function. In: Nephrology: Proceedings of the Tenth International Congress of Nephrology. London: Bailliere-Tindall, 1987.) b. Photomicrograph of an H&E–stained specimen showing a renal corpuscle. The macula densa is seen in close proximity to the vascular pole. 160.
Filtration Apparatus of the Kidney
The renal corpuscle contains the filtration apparatus of the kidney, which consists of the glomerular endothelium, underlying glomerular basement membrane, and the visceral layer of Bowman’s capsule.