Anatomy, Abdomen and Pelvis: Kidneys

Excerpt

The kidneys are bean-shaped organs, with medial concavity and lateral convexity, weighing anywhere from 150 to 200 g in males and about 120 to 135 g in females. The dimensions are usually a length of 10 to 12 cm, a width of 5 to 7 cm, and a thickness of 3 to 5 cm. Each kidney is about the size of a closed fist. They are located retroperitoneally on the posterior abdominal wall and are found between the transverse processes of T12 and L3. Both of the upper poles are usually oriented slightly medially and posteriorly relative to the lower poles. If the upper renal poles are oriented laterally, this could suggest a horseshoe kidney or a superior pole renal mass. Further, the right kidney is usually slightly more inferior in position than the left kidney, likely because of the liver.

The following are the kidneys relative to surrounding organs:

1. Superiorly, on top of each kidney and separated by renal fascia, are the suprarenal glands (adrenal glands), the right pyramidal suprarenal gland oriented apically on the right kidney and the left crescentic suprarenal gland oriented more medially on the left kidney

2. The right kidney is posterior to the ascending colon, the second part of the duodenum medially, and the liver, separated by the hepatorenal recess

3. The left kidney is posterior to the descending colon, its renal hilum lateral to the tail of the pancreas, superomedial aspect adjacent to the greater curvature of the stomach, and left upper pole adjacent to the spleen and connected by splenorenal ligaments

Posteriorly, the diaphragm rests over the upper third of each kidney with the 12th rib passing posteriorly over the upper pole. The kidneys usually sit located over the medial aspect of the psoas muscle and the lateral aspect of the quadratus lumborum. The proximal ureters will typically pass over the psoas muscle on their way to the bony pelvis.

At the medial margin of each kidney lies the renal hilum, where the renal artery enters, and the renal pelvis and vein leave the renal sinus. The renal vein is found anterior to the renal artery, which is anterior to the renal pelvis. The renal pelvis is the flattened, superior end of the ureter. It receives 2 or 3 major calyces, each of which receives 2 or 3 minor calyces. The minor calyces are indented by the renal papillae, which are the apices of the renal pyramids. A pyramid and its cortical tissue comprise a lobe.

Each kidney is covered by a two-layered capsule and is surrounded by perinephric fat, Gerota's fascia, Zuckerkandl fascia, and paranephric fat. The entire area immediately involving the kidneys is considered the retroperitoneum.