Nephron

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urinary system

urinary system, group of organs of the body concerned with excretion of urine, that is, water and the waste products of metabolism. In humans, the kidneys are two small organs situated near the vertebral column at the small of the back, the left lying somewhat higher than the right. They are bean-shaped, about 4 in. (10 cm) long and about 21-2 in. (6.4 cm) wide. Their purpose is to separate urea, mineral salts, toxins, and other waste products from the blood, and to conserve water, salts, and electrolytes. At least one kidney must function properly for life to be maintained. Each kidney contains 1.2 million filtering units called nephrons. One end of the nephron is expanded into a structure called the renal corpuscle, or glomerulus, which surrounds a cluster of blood capillaries. The remainder of the nephron consists of a very long narrow tubule, in alternately convoluted and looping sections. Blood containing waste products enters the glomerulus through an afferent arteriole from the renal artery. The cells of the glomerulus extract the water and waste products as the blood leaves through the outgoing blood vessel (the efferent arteriole) of the glomerulus, in a process called filtration. Blood leaving the glomerulus flows through the network of capillaries that surrounds each tubule; there the substances that the body still needs, such as water and certain salts, are restored to the blood. The purified blood returns to the general circulation through blood vessels leading to the renal vein. The ends of the tubules unite to form collecting tubules, which empty the urine into the kidney pelvis, a collecting chamber in the middle of the kidney. Urine from the kidney pelvis then passes into the ureters, a pair of tubes 16 to 18 in. (40–45 cm) long. Muscles in the walls of the ureters send the urine in small spurts into the bladder, a collapsible sac found on the forward part of the cavity of the bony pelvis that allows temporary storage of urine. The outlet of the bladder is controlled by a sphincter muscle. A full bladder stimulates sensory nerves in the bladder wall that relax the sphincter and allow release of the urine. However, relaxation of the sphincter is also in part a learned response under voluntary control. The released urine enters the urethra, a tube lined with mucus membrane that conveys the urine to the outside. The male urethra, about 8 in. (20 cm) long, terminates at the tip of the penis, and serves as the passage through which semen is released (see reproductive system). The female urethra is less than 2 in. (5 cm) long and opens just in front of the entrance to the vagina; it has no function other than excretion of urine. There are many types of urinary system disorders, including congenital malformation, injury, infection, presence of kidney stones, or calculi, other types of obstruction, and tumors. See cystitis; nephritis; nephrosis. Abnormal urine output may indicate other diseases, such as diabetes.

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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Nephron

 

the basic structural and functional unit of the kidneys in vertebrate animals and man. A distinction is made between aglomerular and glomerular nephrons. Aglomerular nephrons are found in certain fishes and contain cells of a single type; glomerular nephrons, found in all other vertebrates and in man, contain the Malpighian bodies and Bowman’s capsules. The renal tubules extend from Bowman’s capsules.

The cells of glomerular nephrons are highly specialized to perform the functions required in the formation of urine—filtration, reabsorption, and secretion. In embryos the nephron also includes the nephrostomes, which are the ciliated infundibuli of the tubules. The nephrostomes open into the body cavity.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

nephron

[′nef‚rän]
(anatomy)
The functional unit of a kidney, consisting of the glomerulus with its capsule and attached uriniferous tubule.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Each kidney contains about 1 million nephrons, each of which can form urine; therefore, in most cases it is not necessary to discuss the entire kidney but simply the activities of a single nephron to explain the organ's function.
Reduced nephron endowment has been proposed as playing a determinant role [10-13].
Pre-renal causes generally arise due to hypoperfusion of the nephrons due to shock, heart failure, hypotension, dehydration, hypovolvaemia or renal arterial stenosis, which all decrease renal blood flow and may trigger renal failure.
Nephron sparing surgery for appropriately selected renal cell carcinoma between 4 and 7 cm results in outcome similar to radical nephrectomy.
The fundamental structural unit of the kidney is the nephron. These high-pressure filtering mechanisms govern the removal of waste products and toxins, control blood pressure and volume, and regulate levels of electrolytes and metabolites in the blood.
Development of the human kidney as shown by microdissection, IV: development of tubular portions of nephrons. Arch Pathol.
Thus, the nephrons have the responsibility of handling this large volume of filtrate and separating that which must be conserved and that which needs to be excreted.
Damage to the nephrons from unused sugar in the blood is called diabetic nephropathy.
For the first time, researchers discovered that in the nephrons, the functional units of the kidneys, had coated a specialized part of cells called brush borders, which help reabsorb and process proteins.
When the body suffers a crushing injury, however, iron-containing heme proteins like myoglobin spill out of crushed tissue into the bloodstream, get caught in the blood-filtering nephrons in the kidney and die, releasing their iron.
The lesions were "focal," affecting some nephrons and sparing others, and "segmented," scarring one part of the nephron.2 The picture of FSGS on biopsies originally caused it to be referred to as the "flea bitten" kidney.