Functions of the kidneys

Urine production begins with the substances that the Mood leaves behind during its passage through the kidney—the water, salts, and other substances collected from the glomerulus in Bowman's capsule. This liquid, called glomerular filtrate, moves from Bowman'scapsule through the renal tubule. As the filtrate flows through the renal tubule, the network of Mood vessels surrounding the tubule reabsorbs much of the water, salt, and virtually all of the nutrients, especially glucose and amino acids, that were removed in the glomerulus. This important process, called tubular reabsorption, enables the body to selectively keep the substances it needs while ridding itself of wastes. Eventually, about 99 percent of the water, salt, and other nutrients is reabsorbed.

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At the same time that the kidney reabsorbs valuable nutrients from the glomerular filtrate, it carries out an opposing task, called tubular secretion. In this process, unwanted substances from the capillaries surrounding the nephron are added to the glomerular filtrate. These substances include various charged panicles called ions, including ammonium, hydrogen, and potassium ions.

Together, glomerular filtration, tubular reabsorption, and tubular secretion produce urine, which flows into collecting ducts, which guide it into the microtubules of the pyramids. The urine is then stored in the renal cavity and eventually drained into the ureters, which are long, narrow tubes leading to the Madder. From the roughly 180 liters (about 50 gallons) of blood that the kidneys filter each day, about 1.5 liters (1.3 qt) of urine are produced.

FUNCTIONS OF THE KIDNEYS

A primary function of kidneys is the removal of poisonous wastes from the blood. Chief among these wastes are the nitrogen-containing compounds urea and uric acid, which result from the breakdown of proteins and nucleic acids. Life-threatening illnesses occur when too many of these waste products accumulate in the bloodstream. Fortunately, a healthy kidney can easily rid the body of these substances.

In addition to cleaning the blood, the kidneys perform several other essential functions. One such activity is regulation of the amount of water contained in the blood. This process is influenced by antidiuretic hormone (ADH), also called vasopressin, which is produced in the hypothalamus (a part of the brain that regulates many internal functions) and stored in the nearby pituitary gland. Receptors in the brain monitor the blood's water concentration. When the amount of salt and other substances in the blood becomes too high, the pituitary gland releases ADH into the bloodstream. When it enters the kidney. ADM makes the walls of the renal tubules and collecting ducts more permeable to water, so that more water is reabsorbed into the bloodstream.

The hormone aldosterone, produced by the adrenal glands, interacts with the kidneys to regulate the blood's sodium and potassium content. High amounts of aldosterone cause the nephrons to reabsorb more sodium ions, more water, and fewer potassium ions; low levels of aldosterone have the reverse effect. The kidney's responses to aldosterone help keep the blood's salt levels within the narrow range that is best for crucial physiological activities.

Aldosterone also helps regulate blood pressure. When blood pressure starts to fall, the kidney releases an enzyme (a specialized protein) called renin, which converts a blood protein into the hormone angiotensin

This hormone causes blood vessels to constrict, resulting in a rise in blood pressure. Angiotensin then induces the adrenal glands to release aldosterone, which promotes sodium and water to be reabsorbed, further increasing blood volume and blood pressure. The kidney also adjusts the body's acid-base balance.

It helps to prevent such blood disorders as acidosis and alkalosis, both of which impair the functioning of the central nervous system. If the blood is too acidic, meaning that there is an excess of hydrogen ions, the kidney moves these ions to the urine through the process of tubular secretion. An additional function of the kidney is the processing of vitamin D): the kidney converts this vitamin to an active form that stimulates bone development.

Several hormones are produced in the kidney. One of these, erythropoietin, influences the production of red blood cells in the bone marrow. When the kidney detects that the number of red blood cells in the body is declining, it secretes erythropoietin. This hormone travels in the bloodstream to the bone marrow, stimulating the production and release of more red cells.

Дата добавления: 2015-11-16