Nephron Nephron of the kidney without juxtaglomerular apparatus Latin nephroneum Gray's subject #253 1221 Precursor Metanephric blastema (intermediate mesoderm) MeSH Nephrons
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 blood 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. In humans, a normal kidney contains 800,000 to 1.5 million nephrons.
Types of nephrons
Two general classes of nephrons are cortical nephrons and juxtamedullary nephrons, both of which are classified according to the length of their associated Loop of Henle and location of their renal corpuscle. All nephrons have their renal corpuscles in the cortex. Cortical nephrons have their Loop of Henle in the renal medulla near its junction with the renal cortex, while the Loop of Henle of juxtamedullary nephrons is located deep in the renal medulla; they are called juxtamedullary because their renal corpuscle is located near the medulla (but still in the cortex). The nomenclature for cortical nephrons varies, with some sources distinguishing between superficial cortical nephrons and midcortical nephrons, depending on where their corpuscle is located within the cortex.
The majority of nephrons are cortical. Cortical nephrons have a shorter loop of Henle compared to juxtamedullary nephrons. The longer loop of Henle in juxtamedullary nephrons create a hyperosmolar gradient that allows for the creation of concentrated urine.
Each 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.
The glomerulus is a capillary tuft that receives its blood supply from an afferent arteriole of the renal circulation. The glomerular blood pressure provides the driving force for water and solutes to be filtered out of the blood and into the space made by Bowman's capsule. The remainder of the blood (only approximately 1/5 of all plasma passing through the kidney is filtered through the glomerular wall into the Bowman's capsule) passes into the efferent arteriole.The diameter of efferent arteriole is comparatively less than that of afferent arteriole. It then moves into the vasa recta, which are only found in juxtamedullary nephrons and not cortical nephrons. The vasa recta are collecting capillaries intertwined with the convoluted tubules through the interstitial space, in which the reabsorbed substances will also enter. This then combines with efferent venules from other nephrons into the renal vein, and rejoins the main bloodstream.
The Bowman's capsule, also called the glomerular capsule, surrounds the glomerulus. It is composed of a visceral inner layer formed by specialized cells called podocytes, and a parietal outer layer composed of a single layer of flat cells called simple squamous epithelium. Fluids from blood in the glomerulus are filtered through the visceral layer of podocytes, and the resulting glomerular filtrate is further processed along the nephron to form urine.
Renal tubule Latin tubulus renalis Gray's subject #253 1223
The renal tubule is the portion of the nephron containing the tubular fluid filtered through the glomerulus. After passing through the renal tubule, the filtrate continues to the collecting duct system, which is not part of the nephron.
The components of the renal tubule are:
- Proximal convoluted tubule (lies in cortex and lined by simple cuboidal epithelium with brushed borders which help to increase the area of absorption greatly.)
- Loop of Henle (hair-pin like i.e. U-shaped and lies in medulla)
- Descending limb of loop of Henle
- Ascending limb of loop of Henle
- The ascending limb of loop of Henle is divided into 2 segments: Lower end of ascending limb is very thin and is lined by simple squamous epithelium. The distal portion of ascending limb is thick and is lined by simple cuboidal epithelium.
- Thin ascending limb of loop of Henle
- Thick ascending limb of loop of Henle (enters cortex and becomes DCT-distal convoluted tubule.)
- Distal convoluted tubule
The nephron carries out nearly all of the kidney's functions. Most of these functions concern the reabsorption and secretion of various solutes such as ions (e.g., sodium), carbohydrates (e.g., glucose), and amino acids (e.g., glutamate). Properties of the cells that line the nephron change dramatically along its length; consequently, each segment of the nephron has highly specialized functions.
The proximal tubule as a part of the nephron can be divided into an initial convoluted portion and a following straight (descending) portion. Fluid in the filtrate entering the proximal convoluted tubule is reabsorbed into the peritubular capillaries, including approximately two-thirds of the filtered salt and water and all filtered organic solutes (primarily glucose and amino acids).
The loop of Henle, also called the nephron loop, is a U-shaped tube that extends from the proximal tubule. It consists of a descending limb and ascending limb. It begins in the cortex, receiving filtrate from the proximal convoluted tubule, extends into the medulla as the descending limb, and then returns to the cortex as the ascending limb to empty into the distal convoluted tubule. The primary role of the loop of Henle is to concentrate the salt in the interstitium, the tissue surrounding the loop.
Considerable differences distinguish the descending and ascending limbs of the loop of Henle. The descending limb is permeable to water and noticeably less impermeable to salt, and thus only indirectly contributes to the concentration of the interstitium. As the filtrate descends deeper into the hypertonic interstitium of the renal medulla, water flows freely out of the descending limb by osmosis until the tonicity of the filtrate and interstitium equilibrate. Longer descending limbs allow more time for water to flow out of the filtrate, so longer limbs make the filtrate more hypertonic than shorter limbs.
Unlike the descending limb, the ascending limb of Henle's loop[disambiguation needed ] is impermeable to water, a critical feature of the countercurrent exchange mechanism employed by the loop. The ascending limb actively pumps sodium out of the filtrate, generating the hypertonic interstitium that drives countercurrent exchange. In passing through the ascending limb, the filtrate grows hypotonic since it has lost much of its sodium content. This hypotonic filtrate is passed to the distal convoluted tubule in the renal cortex.
The distal convoluted tubule has a different structure and function to that of the proximal convoluted tubule. Cells lining the tubule have numerous mitochondria to produce enough energy (ATP) for active transport to take place. Much of the ion transport taking place in the distal convoluted tubule is regulated by the endocrine system. In the presence of parathyroid hormone, the distal convoluted tubule reabsorbs more calcium and excretes more phosphate. When aldosterone is present, more sodium is reabsorbed and more potassium excreted. Atrial natriuretic peptide causes the distal convoluted tubule to excrete more sodium. In addition, the tubule also secretes hydrogen and ammonium to regulate pH.
After traveling the length of the distal convoluted tubule, only about 1% of water remains, and the remaining salt content is negligible.
Collecting duct system
Each 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). ADH affects the function of aquaporins, resulting in the reabsorption of water molecules as it passes through the collecting duct. Aquaporins are membrane proteins that selectively conduct water molecules while preventing the passage of ions and other solutes. As much as three-quarters 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 organ are also permeable to urea, allowing some of it to enter the medulla of the kidney, thus maintaining its high concentration (which is very important for the nephron).
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.
The juxtaglomerular apparatus is a specialized region of the nephron responsible for production and secretion of the enzyme renin, involved in the renin-angiotensin system. This apparatus occurs near the site of contact between the thick ascending limb and the afferent arteriole. It contains three components: the macula densa, juxtaglomerular cells, and extraglomerular mesangial cells.
Because 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.
main point and land
- ^ Maton, Anthea; Jean Hopkins, Charles William McLaughlin, Susan Johnson, Maryanna Quon Warner, David LaHart, Jill D. Wright (1993). Human Biology and Health. Englewood Cliffs, New Jersey, USA: Prentice Hall. ISBN 0-13-981176-1.
- ^ Guyton, Arthur C.; Hall, John E. (2006). Textbook of Medical Physiology. Philadelphia: Elsevier Saunders. p. 310. ISBN 0-7216-0240-1.
- ^ Physiology at MCG 7/7ch03/7ch03p16
- ^ Jameson, J. Larry & Loscalzo, Joseph (2010). Harrison's Nephrology and Acid-Base Disorders. McGraw-Hill Professional. p. 3. ISBN 9780071663397. http://books.google.com/books?id=yoeXSV8O2wUC&pg=PA3.
- ^ Ecology & Evolutionary Biology - University of Colorado at Boulder. "The Kidney Tubule I: Urine Production." URL: http://www.colorado.edu/eeb/web_resources/cartoons/nephrex1.html. Accessed on: March 6, 2007.
- ^ Walter F., PhD. Boron. Medical Physiology: A Cellular And Molecular Approaoch. Elsevier/Saunders. p. 743. ISBN 1-4160-2328-3.
Anatomy: urinary system (TA A08, TH H3.06, GA 11.1215) AbdomenLayersRenal tubuleFiltration Pelvis Urinary system, physiology: renal physiology and acid-base physiology Filtration Hormones affecting filtration Secretion/clearancePharmacokinetics · Clearance of medications · Urine flow rate Reabsorption Endocrine Assessing Renal function/
Measures of dialysis
Acid-base physiology Buffering/compensation Other
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néphron — [ nefrɔ̃ ] n. m. • 1954; du gr. nephros ♦ Physiol., anat. Unité anatomique et fonctionnelle du rein, constituée par un glomérule rénal et les tubes rénaux qui s y rattachent. Un rein humain comprend environ 1 million de néphrons. ● néphron nom… … Encyclopédie Universelle
Nephron — Nephron, als blind geschlossenes Rohr aus dem ⇒ Malpighi Körperchen und dem sich anschließenden ⇒ Nierenkanälchen zusammengesetzte anatomische und funktionelle Einheit der ⇒ Niere der Wirbeltiere. Im N. erfolgt die Bildung des ⇒ Harns. ⊙ Nephron… … Deutsch wörterbuch der biologie
nephron — (n.) 1932, from Ger. nephron (1924), from Gk. nephros kidney, from PIE *negwhro kidney (Cf. L. nefrones, O.N. nyra, Du. nier, Ger. Niere kidney ) … Etymology dictionary
nephron — [nef′rän΄, nef′rən] n. [Ger < Gr nephros: see NEPHRO ] a single urinary tubule in the vertebrate kidney … English World dictionary
Néphron — Le néphron est l unité structurale et fonctionnelle du rein. Il permet la formation d urine. Un rein humain adulte en compte entre 900 000 et 1,6 million. Sommaire 1 Embryologie 2 Structure 2.1 Le glomérule … Wikipédia en Français
Nephron — Ein Nephron (von griech. νεφρός Niere) ist die funktionelle Untereinheit der Niere. Es besteht aus: dem Nierenkörperchen (Malpighi Körperchen, benannt nach Marcello Malpighi) und dem daran angeschlossenen Nierenkanälchen (Tubulus). Jede Niere… … Deutsch Wikipedia
nephron — /nef ron/, n. Anat., Zool. the filtering and excretory unit of the kidney, consisting of the glomerulus and tubules. [1930 35; < G; alter. of Gk nephrós kidney] * * * Functional unit of the kidney that removes waste and excess substances from the … Universalium
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