Kidney

Function
The kidney is responsible for two primary functions. First, the kidneys work by extracting water, urea, mineral salts, toxins, and other waste products from the blood with filtering units called nephrons. Secondly, the kidneys regulate the production of red blood cells, blood pressure, blood volume, blood composition and pH of the blood. The functional unit of the kidney is called the nephron. From the nephrons, the collected urine passes through thick-walled tubes called ureters.

Structure and Location
The kidney is one of a pair of small bean-shaped organs of the urinary system, located near the spine. They lie on either side of the spinal column in a depression high on the posterior wall of the abdominal cavity, and are positioned behind the parietal peritoneum, called the retroperitoneum, against the deep muscles of the back. The nephron consists of a renal corpuscle made up of a glomerulus and Bowman's capsule, and a renal tubule made up of a proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct. The kidney contains a hollow chamber, called the renal sinus. Through the renal sinus passes various blood vessels, nerves, lymphatic vessels and the ureter. The superior end of the ureter is expanded to form a funnel-shaped sac called the renal pelvis, which is located inside the renal sinus. The renal pelvis is subdivided into several tubules, or major calyces. The major calyces are then subdivided into minor calyces.