Porth's Essentials of Pathophysiology, 4e

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Kidney and Urinary Tract Function

U N I T 7

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Diaphragm

Gross Structure The kidney is composed of up to 18 lobes. Each lobular is in turn composed of nephrons, which are the functional units of the kidney. Two distinct regions can be identified on the bisected kidney—an outer cortex and an inner medulla (Fig. 24-2). The cortex has a reddish-brown granular appearance that is absent from the medulla. The medulla consists of light-colored, cone-shaped masses—the renal pyramids—that are divided by columns of the cortex that extend into the medulla. Each pyramid, topped by a region of cortex, forms a lobe of the kidney. The apices of the pyramids form the papillae (i.e., 8 to 18 per kidney, cor- responding to the number of lobes), which are perforated by the openings of the collecting tubules. The renal pelvis is a wide, funnel-shaped structure at the upper end of the ureter. It is made up of the calyces or cuplike structures that drain the upper and lower halves of the kidney. The kidney is sheathed in a fibrous external capsule and surrounded by a mass of fatty connective tissue, especially at its ends and borders. The adipose tissue protects the kidney from mechanical blows and assists, together with the attached blood vessels and fascia, in holding the kidney in place. Although the kidneys are relatively well protected, they may be bruised by blows to the loin or by compression between the lower ribs and the ileum. Because the kidneys are located outside the peritoneal cavity, injury and rupture do not produce the same threat of peritoneal involvement as that of other organs such as the liver or spleen. Renal Blood Supply Each kidney is supplied by a single renal artery that arises on either side of the aorta. As the renal artery approaches the kidney, it divides into segmental arteries that enter the hilus of the kidney. In the kidney, each seg- mental artery branches into several lobular arteries that

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Renal artery

Adrenal gland

Renal vein

Left kidney

Right kidney

Aorta

Inferior vena cava

Ureter

Bladder

Urethra

FIGURE 24-1. Kidneys, ureters, and bladder. (The right kidney is usually lower than the left.)

thoracic to 3rd lumbar vertebrae (Fig. 24-1). The right kid- ney normally is situated lower than the left, presumably because of the position of the liver. In the adult, each kid- ney is approximately 10 to 12 cm long, 5 to 6 cm wide, and 2.5 cm deep and weighs approximately 113 to 170 g. The medial border of the kidney is indented by a deep fis- sure called the hilus. It is here that blood vessels and nerves enter and leave the kidney. The ureters, which connect the kidneys with the bladder, also enter the kidney at the hilus.

Renal cortex

Renal blood vessel Renal medulla Renal papillae

Pyramid

Renal column (Bertin) Calyx (cut edge)

Renal pelvis

Renal artery

Calyx

Hilus

Capsule

Ureter

FIGURE 24-2. Internal structure of the kidney.