Chapter 18 Urinary section 1

The kidneys lie against the posterior abdominal wall underneath the 12th rib, behind the peritoneum (retroperitoneal)

The ribs help protect the kidneys, as does a heavy cushion of fat encasing each organ.

•Each kidney measures about 4 inches (10 cm) long, 2 inches (5 cm) wide, and 1 inch (2.5 cm) thick; they extend from the level of the T12 vertebra to the L3 vertebra. The right kidney sits a little lower than the left because of the liver, which occupies the space above it.

Structures (such as blood vessels, the ureters, and nerves) enter and leave the kidney through a slit called the hilum—located in a concave notch on the medial side

A tough, fibrous capsule surrounds each kidney. 

•The interior consists of the renal cortex and renal medulla; the renal cortex forms the outer region and the renal medulla forms the inner region.

Extensions from the renal cortex, called renal columns, divide the interior into cone-shaped sections called renal pyramids. The base of each pyramid faces outward toward the cortex; the point of the pyramid, called the renal papilla, faces the hilum.

•The renal papilla extends into a cup called a minor calyx. The calyx collects urine leaving the papilla. Two or three minor calyces join together to form a major calyx.

•The major calyces converge to form the renal pelvis, which receives urine from the major calyces. The renal pelvis continues as the ureter, which channels urine to the urinary bladder.

The renal artery (which branches off the abdominal aorta) brings blood to the kidney. As it enters the kidney, it divides into smaller and smaller arteries. The arteries pass through the renal columns and into the renal cortex. 

•Blood leaves the kidney through the renal vein, which empties into the inferior vena cava.