Kidneys

Kidneys are a pair of organs located in the rear of the abdomen that perform several essential regulatory roles in vertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and regulation of blood pressure. They serve the body as a natural filter of the blood, and remove wastes which are diverted to the urinary bladder. In producing urine, the kidneys excrete wastes such as urea and ammonium. They are also responsible for the reabsorption of water, glucose, and amino acids. The kidneys also produce hormones including calcitriol, erythropoietin, and the enzyme renin.

Anatomy

The kidneys are bean-shaped with the convex side of each organ located laterally and the concave side medial. The hilum of the kidney is the entry and exit site for structures servicing the kidneys: vessels, nerves, lymphatics, and ureters. The renal arteries form directly from the descending aorta, while the renal veins return cleansed blood directly to the inferior vena cava. The ureter carries urine from the kidneys to the urinary bladder.

Function

The kidneys excrete a variety of waste products produced by metabolism into the urine. These include the nitrogenous wastes urea, from protein catabolism, and uric acid, from nucleic acid metabolism. The ability of mammals and some birds to concentrate wastes into a volume of urine much smaller than the volume of blood from which the wastes were extracted is dependent on an elaborate countercurrent multiplication mechanism. This requires several independent nephron characteristics to operate: a tight hairpin configuration of the tubules, water and ion permeability in the descending limb of the loop, water impermeability in the ascending loop, and active ion transport out of most of the ascending limb. In addition, passive countercurrent exchange by the vessels carrying the blood supply to the nephron is essential for enabling this function.

Diseases

Kidney diseases are normally investigated and treated by nephrologists, while the specialty of urology deals with problems in the other organs of the urinary system. Renal pathology is a specialty that deals with diseases that affect the kidneys. Some of the renal diseases include renal failure, polycystic kidney disease, and nephrotic syndrome. Kidney diseases can be serious, but early detection and good management can increase the life of your kidneys.

See also

• Nephrology
• Renal physiology
• Kidney disease
• Kidney transplantation
• Renal failure
• Dialysis

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