Kidneys

 The kidneys of most animal species are bean-shaped and located in the dorsal part of the abdominal cavity just ventral to the first few lumbar vertebrae.

The basic functional unit of the kidney is the nephron - a tiny system of tubules and blood vessels that filters the blood, reabsorbs useful substances back into the bloodstream and secretes waste products into the urine.

The blood supply to the kidneys is very large. Blood enters via the renal artery which branches into smaller vessels, until it enters the glomeruli through the afferent arterioles. The blood then leaves the glomeruli through the efferent arterioles and forms a capillary network around the tubules of the nephron. From there, blood vessels merge into venules and larger veins and eventually leave the kidney through the renal vein. The nerve supply of the kidney is mainly sympathetic - it controls blood flow through the organ. It is not essential to renal function.