The kidneys are paired organs, which have the production of urine as their primary function. They are part of the urinary system, but have several secondary functions concerned with homeostatic functions. These include the regulation of electrolytes, acid-base balance, and blood pressure. In producing urine, the kidneys excrete wastes such as urea and ammonium; the kidneys also are responsible for the reabsorption of glucose and amino acids. Finally, the kidneys are important in the production of hormones including vitamin D, renin and erythropoietin.
Located behind the abdominal cavity in the retroperitoneum, the kidneys receive blood from the paired renal arteries, and drain into the paired renal veins. Each kidney excretes urine into a ureter, itself a paired structure that empties into the urinary bladder.
Each adult kidney weighs between 125 and 170 g in males and between 115 and 155 g in females. The left kidney is typically slightly larger than the right.
The kidneys receive blood from the renal arteries, left and right, which branch directly from the abdominal aorta. Despite their relatively small size, the kidneys receive approximately 20% of the cardiac output.