a. The kidneys (figure 2-2) are a pair of bean-shaped organs about four inches
long, two inches wide, one-inch thick, and weighing four to six ounces each.
b. One kidney is located on each side of the body. They are pressed against
the posterior abdominal wall at about the level of the first lumbar vertebrae.
c. The medial side of each kidney is concave and has a central notch called the
hilum. Here, the renal artery enters the kidney, and the renal vein and ureter exit the
kidney. Nerves and lymphatic vessels also pass through the hilum.
d. The kidneys are enclosed by the renal capsule. Directly beneath the capsule
lies a reddish area called the renal cortex. The cortex contains millions of microscopic
filtration plants called nephrons. Nephrons are the functional units of the kidney.
Figure 2-2. The kidney.