Nephron, structural and functional unit of the kidney, formation of urine. The nephron is made up of a renal corpuscle, the glomerulus, and a tubular system. The glomerulus, located in the renal cortex, contains a cluster of capillaries. It produces the primary urine by filtering the blood. The uriniferous tube passes through the cortex and the medulla. It makes the final urine from the primary urine. It is subdivided into 4 segments: the proximal convoluted tube, which follows the glomerulus, the loop of Henle, the distal convoluted tube then the collecting tube (or canal). The latter opens at the bottom of the small calyces (ducts flowing into the large calyxes, which discharge urine into the pelvis) in an area called the renal papilla. Each of these segments has a precise physiological function, which involves both reabsorption phenomena (recovery of part of the water, sodium, etc.). But it also involves secretion phenomena, to transform the primary urine, formed in the glomerulus, into final urine. The amount and composition of final urine varies so that the internal environment of the body remains constant.