Kidney

Definition
noun, plural: kidneys
(anatomy) Either of a pair of two bean-shaped organs located at the back of the abdominal cavity in vertebrates, and functions primarily by filtering blood of wastes to be eliminated from the body in the form of urine, and regulating the level of certain chemicals for proper fluid balance in the body
(zoology) An excretory organ in certain invertebrates
Supplement
The kidney is an organ whose function is primarily for excretion of extra fluids as wastes. In vertebrates, including humans, the kidneys are a pair of bean-shaped structures that filter blood and produce urine. The kidneys lie at the back of the abdominal cavity where each of the pair is on either side of the vertebral column.
Each kidney is surrounded by renal capsule, and, in turn is surrounded by adipose capsule, renal fascia, and pararenal fat. The functional (filtering and excretory) unit of kidney is called a nephron. Filtration at the site of the glomerulus in the Bowmans Capsule while the loops of Henle are responsible for ‘sucking up’ waste material to be excreted by the organism. Much of the water that is used in our bodies has already been reabsorbed at least once by our kidney.
The kidneys filter the blood and control the level of certain chemicals in the blood such as hydrogen, sodium, potassium, and phosphate. Thus, they are important in osmoregulation. And they are involved as well in waste elimination by forming urine. Urine passes out of the kidney via the ureters into the bladder. The bladder stores the urine until it is released during urination.
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