Kidney Disease Overview
The kidneys are located in the abdominal cavity, on either side of the spine. Roughly the size of a fist and bean-shaped, the tops of the kidneys are protected by the lowest ribs, and are surrounded by two layers of fat.
The kidneys filter the blood, removing waste products, and excrete excess water from the blood, thereby regulating water volume and blood pressure. The artery that leads the blood to the kidneys is called the renal artery, and takes about 20% of the blood flow from the heart. Each kidney contains roughly 1 million nephrons, within which proximal convoluted tubules carry out secretion from and reabsorption to the blood. The filtrate from these tubules is ducted to a funnel called the renal pelvis, which leads to the ureter and the urinary bladder.
Another function of the kidney is a gland: it secretes erythropoietin, a hormone that regulates production of red blood cells. Atop each kidney is an adrenal gland, which helps to regulate metabolism, blood pressure, inflammation, and response to stress, and produces small amounts of sex hormones.
People are born with two kidneys, but can survive with only part of one, or none if they undergo artificial dialysis.