Kidney : An excretory organ.

In humans, kidneys are the primary excretory organ. A pair of dark red, bean-shaped kidneys are present in the dorsal surface of the abdominal cavity; one on either side of the vertebral column. Each kidney extends from 12th thoracic up to 3rd lumbar vertebrae. It is about 150gm in weight, 10cm long, 5cm wide and 3cm thick. Kidneys are retroperitoneal organs.

Kidney is externally covered by thin whitish fibrous membrane known as renal capsule. Outer to it lies layer of fat known as adipose capsule which is externally covered by whitish fibrous membrane known as renal fascia.