Biological Chemistry - Berezov T. T., Korovkin B. F. 1998

Kidneys and Urine
Structural features of the kidneys

The combined mass of both Kidneys in an adult human is approximately 300 g. The kidneys are vital Organs whose primary function is to maintain the Homeostasis of the body's internal environment. They are the body's principal secretory organs, producing urine from Blood Plasma components.

The kidneys are involved in The regulation of Water and Electrolyte balance, maintenance of acid-base equilibrium, excretion of nitrogenous wastes, regulation of body fluid osmotic pressure, Blood Pressure Regulation, stimulation of erythropoiesis, and other critical Functions.

The renal tissue comprises two distinct layers: an outer cortex and an inner medulla. The nephron serves as the primary Structural and functional unit of the renal parenchyma. There are approximately 2 million nephrons in both human kidneys, 62,000 in a rat, and 816,000 in a dog.

The mammalian nephron (Fig. 18.1) consists of a renal (Malpighian) corpuscle—comprising a glomerulus and a double-walled glomerular capsule (Bowman's capsule)*—along with a system of renal tubules. Extending from the glomerular capsule is the renal tubule, which in the cortex forms the proximal convoluted tubule that leads into the Loop of Henle (nephric loop). The loop consists of descending and ascending limbs. The latter continues into the Distal convoluted tubule, which empties into the collecting ducts. Several collecting ducts converge to form papillary ducts that open into the renal calyces.

Two Types of nephrons are distinguished in the mammalian Kidney: cortical nephrons (85%), whose renal corpuscles are located within the cortex, and juxtamedullary nephrons (15%), whose glomeruli are situated near the cortico-medullary junction, with their loops—comprising descending and ascending limbs—extending deep into the medulla.

* The vascular glomerulus was discovered by the Russian scientist A.V. Shumlyansky, and the surrounding capsule was first described in 1842 by W. Bowman.