Kidney

Article By:

Schmidt-Neilsen, Bodil Department of Zoology, Duke University, Durham, North Carolina.

Last reviewed:November 2019

DOI:https://doi.org/10.1036/1097-8542.364000

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• Kidney, published June 2014:Download PDF Get Adobe Acrobat Reader

Either of a pair of vertebrate organs involved with the elimination of water and waste products from the body. In vertebrates, the kidneys are paired organs located close to the spine, dorsal to the body cavity, and are covered ventrally by the coelomic epithelium. They consist of a number of smaller functional units, which are called urinary tubules or nephrons. The nephrons open to larger ducts—the collecting ducts—which open into a ureter. The two ureters run backward to open into the cloaca or into a urinary bladder. The shape and the location of the kidneys vary in different animals. In fish, the kidneys are extremely elongated and may reach forward almost to the pericardium. In reptiles, the kidneys are smaller and are located in the pelvic region. In mammals, the kidneys are bean-shaped (Fig. 1) and found between the thorax and the pelvis. The number, structure, and function of the nephrons vary with evolution and, in certain significant ways, with the adaptation of the animals to their various habitats. Disorders of the kidney are classified by their etiology and their anatomic location along the nephron. See also: Adaptation (biology); Animal evolution; Evolution; Excretion; Kidney disorders; Urinary bladder; Urinary system; Urogenital system

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