Kidney

In humans, the kidneys are two reddish-brown bean-shaped blood-filtering organs that are a multilobar, multipapillary form of mammalian kidneys, usually without signs of external lobulation. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; blood exits into the paired renal veins. Each kidney is attached to a ureter, a tube that carries excreted urine to the bladder.

The ureters are tubes composed of smooth muscle that transport urine from the kidneys to the urinary bladder. In adult humans, the ureters are typically 20–30 centimeters long and 3–4 millimeters in diameter. They are lined with urothelial cells, a form of transitional epithelium, and feature an extra layer of smooth muscle in the lower third to aid peristalsis. The ureters can be affected by diseases including urinary tract infections and kidney stones. is the narrowing of a ureter, often caused by chronic inflammation. Congenital abnormalities can cause development of two ureters on the same

chemical compound

The mesonephros () is one of three excretory organs that develop in vertebrates. It serves as the main excretory organ of aquatic vertebrates and as a temporary kidney in reptiles, birds, and mammals. The mesonephros is also known as the Wolffian body after Caspar Friedrich Wolff who described it in 1759. (The Wolffian body is composed of: mesonephros + paramesonephrotic blastema)

Pronephros is the most basic of the three excretory organs that develop in vertebrates, corresponding to the first stage of kidney development. It is succeeded by the mesonephros, which in fish and amphibians remains as the adult kidney. In amniotes, the mesonephros is the embryonic kidney and a more complex metanephros acts as the adult kidney. Once a more advanced kidney forms, the previous version typically degenerates by apoptosis or becomes part of the male reproductive system.

cell line

incurable progressive feline disease

nerve in the abdominal region

In earlier conceptions of kidney biology, the nephrotome was a section of the mesoderm that gives rise to the pronephros and eventually to the rest of the kidney. Older texts describe the pronephros as forming through the fusion of multiple nephrotomes.