Microscopic unit in vertebrate kidneys that forms urine. A human kidney is composed of over a million nephrons. Each nephron consists of a knot of blood capillaries called a glomerulus, contained in the Bowman’s capsule, and a long narrow tubule enmeshed with yet more capillaries. Waste materials and water pass from the bloodstream into the tubule, and essential minerals and some water are reabsorbed from the tubule back into the bloodstream. The remaining filtrate (urine) is passed out from the body.
Any of the small tubules that are the excretory units of the vertebrate kidney; SYN. uriniferous tubule.