Biology » The Excretory System » The Kidneys and Osmoregulatory Organs

Kidneys: the Main Osmoregulatory Organ

Although the kidneys are the major osmoregulatory organ, the skin and lungs also play a role in the process. Water and electrolytes are lost through sweat glands in the skin, which helps moisturize and cool the skin surface, while the lungs expel a small amount of water in the form of mucous secretions and via evaporation of water vapor.

Kidneys: The Main Osmoregulatory Organ

The kidneys, illustrated in the figure below, are a pair of bean-shaped structures that are located just below and posterior to the liver in the peritoneal cavity. The adrenal glands sit on top of each kidney and are also called the suprarenal glands. Kidneys filter blood and purify it. All the blood in the human body is filtered many times a day by the kidneys; these organs use up almost 25 percent of the oxygen absorbed through the lungs to perform this function. Oxygen allows the kidney cells to efficiently manufacture chemical energy in the form of ATP through aerobic respiration. The filtrate coming out of the kidneys is called urine.

Illustration shows the placement of the kidneys and bladder in a human man. The two kidneys face one another and are located on the posterior side, about halfway up the back. A renal artery and a renal vein extend from the inside middle of each kidney, toward a major blood vessel that runs up the middle of the body. A ureter runs down from each kidney to the bladder, a sac that sits just above the pelvis. The urethra runs down from the bottom of the bladder and through the penis. The adrenal glands are lumpy masses that sit on top of the kidneys.

Kidneys filter the blood, producing urine that is stored in the bladder prior to elimination through the urethra. (credit: modification of work by NCI)

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