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Nephron
A nephron (from Greek νεφρός (nephros) meaning "kidney") is the basic structural and functional unit of the kidney. Its chief function is to regulate the concentration of water and soluble substances like sodium salts by filtering the blood, reabsorbing what is needed and excreting the rest as urine. A nephron eliminates wastes from the body, regulates blood volume and pressure, controls levels of electrolytes and metabolites, and regulates blood pH. Its functions are vital to life and are regulated by the endocrine system by hormones such as antidiuretic hormone, aldosterone, and parathyroid hormone. Additional recommended knowledge
Types of nephronsTwo general classes of nephrons are cortical nephrons and juxtamedullary nephrons, both of which are classified according to the location of their associated renal corpuscle. Cortical nephrons have their renal corpuscle in the superficial renal cortex, while the renal corpuscles of juxtamedullary nephrons are located near the renal medulla. The nomenclature for cortical nephrons varies, with some sources distinguishing between superficial cortical nephrons and midcortical nephrons;[1] other sources simply call all non-juxtamedullary nephrons superficial nephrons.[2] Functionally, cortical and juxtamedullary nephrons have distinct roles. Cortical nephrons (85% of all nephrons) mainly perform excretory and regulatory functions, while juxtamedullary nephrons (15% of nephrons) concentrate and dilute urine.[2] AnatomyEach nephron is composed of an initial filtering component (the "renal corpuscle") and a tubule specialized for reabsorption and secretion (the "renal tubule"). The renal corpuscle filters out large solutes from the blood, delivering water and small solutes to the renal tubule for modification. Renal corpuscleComposed of a glomerulus and Bowman's capsule, the renal corpuscle (or "Malphigian corpuscle") is the beginning of the nephron. It is the nephron's initial filtering component.
Renal tubule
The kidney tubule, also renal tubule, is the portion of the nephron of the kidney containing the tubular fluid filtered through the glomerulus.[3] After passing the tubule, the filtrate continues to the collecting duct system. The components of the kidney tubule are:
After traveling the length of the distal convoluted tubule, only about 1% of water remains, and the remaining salt content is negligible. Collecting duct systemEach distal convoluted tubule delivers its filtrate to a system of collecting ducts, the first segment of which is the collecting tubule. The collecting duct system begins in the renal cortex and extends deep into the medulla. As the urine travels down the collecting duct system, it passes by the medullary interstitium which has a high sodium concentration as a result of the loop of Henle's countercurrent multiplier system. Though the collecting duct is normally impermeable to water, it becomes permeable in the presence of antidiuretic hormone (ADH). As much as three-fourths of the water from urine can be reabsorbed as it leaves the collecting duct by osmosis. Thus the levels of ADH determine whether urine will be concentrated or diluted. An increase in ADH is an indication of dehydration, while water sufficiency results in low ADH allowing for diluted urine. Lower portions of the collecting duct are also permeable to urea, allowing some of it to enter the medulla of the kidney, thus maintaining its high ion concentration (which is very important for the nephron). Urine leaves the medullary collecting ducts through the renal papilla, emptying into the renal calyces, the renal pelvis, and finally into the bladder via the ureter. Because it has a different origin during the development of the urinary and reproductive organs than the rest of the nephron, the collecting duct is sometimes not considered a part of the nephron. Instead of originating from the metanephrogenic blastema, the collecting duct originates from the ureteric bud. Juxtaglomerular apparatusThe juxtaglomerular apparatus occurs near the site of contact between the thick ascending limb and the afferent arteriole. It contains three components:
Juxtaglomerular cells are the site of renin synthesis and secretion and thus play a critical role in the renin-angiotensin system. Clinical relevanceBecause of its importance in body fluid regulation, the nephron is a common target of drugs that treat high blood pressure and edema. These drugs, called diuretics, inhibit the ability of the nephron to retain water, thereby increasing the amount of urine produced. References
Additional imagesSee also
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This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Nephron". A list of authors is available in Wikipedia. |