Porth's Essentials of Pathophysiology, 4e

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Structure and Function of the Kidney

C h a p t e r 2 4

the arcuate arteries, which arch across the top of the pyramids. Small intralobular arteries radiate from the arcuate arteries to supply the cortex of the kidney. The afferent arterioles that supply the glomeruli arise from the intralobular arteries. Although nearly all the blood that enters the kidney flows through the cortex, less than 10% passes into the medulla and only about 1% moves into the papillae. Under conditions of decreased perfusion or increased sympathetic nervous system stimulation, blood flow is redistributed away from the cortex toward the medulla. This redistribution of blood flow decreases glomerular filtration while maintaining the urine-concentrating ability of the kidneys, a factor that is important during conditions such as shock. The Nephron Each kidney is composed of more than 1 million tiny, closely packed functional units called nephrons, each of which is capable of producing urine (Fig. 24-4A). Each nephron consists of a glomerulus, where blood is fil- tered, and a system of tubular structures where water, electrolytes, and other substances needed to maintain the

Intralobular arteries

Arcuate artery

Renal artery

Pyramid

Interlobar artery

Ureter

FIGURE 24-3. Simplified illustration of the arterial supply of the kidney. (From Cormack DH. Ham’s Histology. 9th ed. Philadelphia, PA: J.B. Lippincott; 1987.)

supply the upper, middle, and lower parts of the kid- ney. The lobular arteries further subdivide to form the interlobular arteries at the level of the corticomedullary junction (Fig. 24-3). These arteries give off branches,

Proximal convoluted tubule Efferent arteriole

Peritubular capillary

Bowman capsule

Juxtaglomerular apparatus

Glomerulus

Afferent arteriole

Interlobular vein Interlobular artery

Distal convoluted tubule

Cortex

Cortex Medulla

Collecting tubule

Outer stripe

Outer medulla

Descending limb

Inner stripe

Vasa recta

Ascending limb

Inner medulla

Loop of Henle

A

B

To papilla

FIGURE 24-4. (A) Nephron showing the glomerular and tubular structures along with the blood supply. (B) Comparison of differences in location of tubular structures of the cortical and juxtamedullary nephrons.