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Encyclopedia > Nephron
Nephron
Nephron of the kidney without juxtaglomerular apparatus
Nephron. Diagram is labeled in Polish, but flow can still be identified.
Gray's subject #253 1221
Precursor Metanephric blastema
MeSH Nephrons

A nephron is the basic structural and functional unit of the kidney. Its chief function is to regulate water and soluble substances by filtering the blood, reabsorbing what is needed and excreting the rest as urine. Nephrons eliminate wastes from the body, regulate blood volume and pressure, control levels of electrolytes and metabolites, and regulate 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. Image File history File links Gray1128. ... The juxtaglomerular apparatus is a renal structure consisting of the macula densa, mesangial cells, and juxtaglomerular cells. ... Image File history File links Nefron. ... This article or section is in need of attention from an expert on the subject. ... The Metanephric blastema (or metanephric mesenchyme) is one of the two embryological structures that give rise to the kidney (the other is the ureteric bud. ... Medical Subject Headings (MeSH) is a huge controlled vocabulary (or metadata system) for the purpose of indexing journal articles and books in the life sciences. ... It has been suggested that Renal anomalies and Renal plasma threshold be merged into this article or section. ... Impact of a drop of water. ... Human blood smear: a - erythrocytes; b - neutrophil; c - eosinophil; d - lymphocyte. ... This article or section is in need of attention from an expert on the subject. ... Blood volume is a term describing the amout of blood (including both red blood cells and plasma) in a persons circulatory system. ... A sphygmomanometer, a device used for measuring blood pressure. ... An electrolyte is a substance containing free ions which behaves as an electrically conductive medium. ... A metabolite is the product of metabolism. ... The correct title of this article is . ... This article or section does not cite its references or sources. ... Norepinephrine A hormone (from Greek όρμή - to set in motion) is a chemical messenger from one cell (or group of cells) to another. ... Antidiuretic hormone (ADH), or arginine vasopressin (AVP), is a peptide hormone produced by the hypothalamus, and stored in the posterior part of the pituitary gland. ... Aldosterone is a steroid hormone synthesized from cholesterol by the enzyme aldosterone synthase. ... Parathyroid hormone (PTH) is secreted by the parathyroid glands as a polypeptide containing 84 amino acids. ...

Contents

Types of nephrons

Most of the concentration of urine in the kidney is performed by juxtamedullary nephron, which are at a relatively deep position in the kidney[1]. The nomenclature for more shallow nephrons varies, with some sources distinguishing between "Superficial cortical nephrons" and "Mid cortical nephrons"[2] while other sources simply call all non-juxtamedullary nephrons "superficial nephrons".[1]. We can say that cortical nephrons (85 % of all nephrons) mainly perform excretory and regulatory functions, while juxtamedullary nephrons (15 % of nephrons) concentrate and dilute urine. Nephron of the kidney A nephron is the basic structural and functional unit of the kidney. ...


Anatomy

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.


Renal corpuscle

Composed 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. The glomerulus is a capillary bed found surrounded by the Bowmans capsule of the nephron in the vertebrate kidney. ... The Bowmans capsule is a blind sac at the beginning of a the tubular component of a nephron in the mammalian kidney. ... A renal corpuscle is the initial filtering component of a nephron in the kidney. ...

glomerulus 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, basically the blood plasma, not filtered into the glomerulus passes into the narrower efferent arteriole. It then moves into the vasa recta, which are collecting capillaries intertwined with the convoluted tubules through the interstitial space, and 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.
Bowman's capsule Bowman's capsule (also called the glomerular capsule) surrounds the glomerulus and is composed of a visceral inner layer and a parietal outer layer, both formed by simple squamous epithelial cells. Fluids from blood in the glomerulus are collected in the Bowman's capsule (i.e., glomerular filtrate) and further processed along the nephron to form urine.

The glomerulus is a capillary bed found surrounded by the Bowmans capsule of the nephron in the vertebrate kidney. ... The word capillary is used to describe any very narrow tube or channel through which a fluid can pass. ... An arteriole is a blood vessel that extends and branches out from an artery and leads to capillaries. ... Grays Fig. ... The Bowmans capsule is a blind sac at the beginning of a the tubular component of a nephron in the mammalian kidney. ... The Bowmans capsule is a blind sac at the beginning of a the tubular component of a nephron in the mammalian kidney. ... This article or section is in need of attention from an expert on the subject. ...

Renal tubule

The flow of the renal tubule is as follows:

Name Description
Proximal tubule 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).
loop of Henle The loop of Henle (sometimes known as the nephron loop) is a U-shaped tube that consists of a descending limb and ascending limb. It begins in the cortex, receiving filtrate from the proximal convoluted tubule, extends into the medulla, and then returns to the cortex to empty into the distal convoluted tubule. Its primary role is to concentrate the salt in the interstitium, the tissue surrounding the loop.
It is divided into descending and ascending limbs:
descending limb Its descending limb is permeable to water but completely 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.
ascending limb Unlike the descending limb, the ascending limb of Henle's loop 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.
Distal convoluted tubule The distal convoluted tubule is not similar to the proximal convoluted tubule in structure and function. 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 3% of water remains, and the remaining salt content is negligible. In the biology of the kidney, the proximal convoluted tubule is the segment of the renal tubule that drains Bowmans capsule. ... Benzene is the simplest of the arenes, a family of organic compounds An organic compound is any member of a large class of chemical compounds whose molecules contain carbon and hydrogen; therefore, carbides, carbonates, carbon oxides and elementary carbon are not organic (see below for more on the definition controversy... Glucose (Glc), a monosaccharide (or simple sugar), is the most important carbohydrate in biology. ... Phenylalanine is one of the standard amino acids. ... In the kidney, the loop of Henle is the portion of the nephron that leads from the proximal convoluted tubule to the distal convoluted tubule. ... The descending limb of loop of Henle is the portion of the renal tubule constituting the first part of the loop of Henle. ... It has been suggested that Hyperosmotic be merged into this article or section. ... Osmosis is the net movement of water molecules across a semipermeable membrane from a region of low solute potential to an area of high solute potential (or equivalently, from a region of high solvent potential to a region of low solvent potential). ... Ascending limb of Henles loop can refer to: Thin ascending limb of loop of Henle Thick ascending limb of loop of Henle (this is more frequently what is meant) Category: ... Countercurrent exchange is a mechanism used to transfer some component of a fluid from one flowing current of fluid to another across a permeable barrier between them. ... Kidney nephron The distal convoluted tubule (DCT) is a portion of kidney nephron between the loop of Henle and the collecting duct system. ... Kidney nephron The distal convoluted tubule (DCT) is a portion of kidney nephron between the loop of Henle and the collecting duct system. ... In cell biology, a mitochondrion is an organelle found in the cells of most eukaryotes. ... Adenosine 5-triphosphate (ATP) is a multifunctional nucleotide that is most important as a molecular currency of intracellular energy transfer. ... Active transport is the mediated transport of biochemicals, and other atomic/molecular substances, across membranes. ... This article or section does not cite its references or sources. ... Parathyroid hormone (PTH) is secreted by the parathyroid glands as a polypeptide containing 84 amino acids. ... Aldosterone is a steroid hormone synthesized from cholesterol by the enzyme aldosterone synthase. ... Atrial natriuretic factor (ANF), atrial natriuretic peptide (ANP) or atriopeptin, is a polypeptide hormone involved in the homeostatic control of body water and sodium. ... This article is about the chemistry of hydrogen. ... A ball-and-stick model of the ammonium cation Fumes from hydrochloric acid and ammonia forming a white cloud of ammonium chloride Ammonium is also an old name for the Siwa Oasis in western Egypt. ... The correct title of this article is . ...


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. The collecting duct system of the kidney consists of: The connecting tubule The cortical collecting duct The medullary collecting duct Categories: | ... The collecting duct system of the kidney consists of: The connecting tubule The cortical collecting duct The medullary collecting duct Categories: | ... In the kidney, the collecting tubule (CNT, or junctional tubule, or arcuate renal tubule) is a tubular segment of the renal collecting duct system that connects the distal convoluted tubule to the cortical collecting duct. ... Countercurrent exchange is a mechanism used to transfer some property of a fluid from one flowing current of fluid to another across a semipermeable barrier between them. ...


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. Dehydration results in an increase in ADH, while water sufficiency results in low ADH allowing for diluted urine. Antidiuretic hormone (ADH), or arginine vasopressin (AVP), is a peptide hormone produced by the hypothalamus, and stored in the posterior part of the pituitary gland. ... Dehydration (hypohydration) is the removal of water (hydro in ancient Greek) from an object. ...


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). Urea is an organic compound of carbon, nitrogen, oxygen and hydrogen, with the formula CON2H4 or (NH2)2CO. Urea is also known as carbamide, especially in the recommended International Non-proprietary Names (rINN) in use in Europe. ... It has been suggested that Renal anomalies and Renal plasma threshold be merged into this article or section. ...


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. In the kidney, the renal papilla is the location where the papillary ducts converge at a minor calyx. ... Calyx can refer to: Minor calyx Major calyx Category: ... The renal pelvis represents the dilated proximal part of the ureter. ... In anatomy, the urinary bladder is a hollow, muscular, and distensible (or elastic) organ that sits on the pelvic floor in mammals. ... Transverse section of ureter. ...


Because it has a different embryonic origin than the rest of the nephron, the collecting duct is sometimes not considered a part of the nephron.


Juxtaglomerular apparatus

The juxtaglomerular apparatus occurs near the site of contact between the thick ascending limb and the afferent arteriole. It contains three components: The juxtaglomerular apparatus is a renal structure consisting of the macula densa, mesangial cells, and juxtaglomerular cells. ...

the macula densa a tightly-packed area with diverse population of cells, including the renin granular cells
juxtaglomerular cells specialized smooth muscle cells in the wall of the afferent arteriole
extraglomerular mesangial cells couple to arterioles

Juxtaglomerular cells are the site of renin synthesis and secretion and thus play a critical role in the renin-angiotensin system. In the kidney, the macula densa is an area of closely packed specialized cells lining the distal convoluted tubule where it lies next to the glomerular vascular pole. ... The juxtaglomerular cells are specialized cells that stimulate the secretion of the adrenal hormone aldosterone and play a major role in renal autoregulation, the kidneys self-governance. ... Cultured Smooth muscle of the aorta. ... The afferent arterioles are a group of blood vessels that supply the nephrons in many excretory systems. ... Extraglomerular mesangial cells (or lacis cells) are light-staining cells in the kidney found outside the glomerulus, near the vascular pole and macula densa. ... An arteriole is a blood vessel that extends and branchs out from an artery and leads to capillaries. ... Renin, also known as angiotensinogenase, is a circulating enzyme (EC 3. ... Schematic depicting how the RAAS works. ...


Clinical relevance

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. A sphygmomanometer, a device used for measuring blood pressure. ... Edema (American English) or oedema (British English), formerly known as dropsy or hydropsy, is swelling of any organ or tissue due to accumulation of excess lymph fluid, without an increase of the number of cells in the affected tissue. ... A diuretic (colloquially called a water pill) is any drug or herb that elevates the rate of bodily urine excretion (diuresis). ...


References

  1. ^ a b http://sprojects.mmi.mcgill.ca/nephrology/presentation/presentation1.htm
  2. ^ Physiology at MCG 7/7ch03/7ch03p16,

In 1828 the Medical Academy of Georgia was chartered by the state of Georgia with plans to offer a single course of lectures leading to a bachelors degree. ...

Additional images

See also

Nephrology is the branch of internal medicine dealing with the study of the function and diseases of the kidney. ... Urology is the field of medicine that focuses on the urinary tracts of males and females, and on the reproductive system of males. ... Hyperchloremic acidosis is a form of Metabolic acidosis associated with a normal anion gap, a decrease in bicarbonate, and in increase in chloride. ...

External links

  • Science aid: Kidney Nephron About the kidney nephron for teen understanding.

  Results from FactBites:
 
Highbeam Encyclopedia - Search Results for Nephron (1132 words)
nephron One of the units in the vertebrate kidney that extracts metabolic wastes which are discharged as urine.
The fluid in the Bowman capsule at the start of each nephron is essentially plasma without the large molecules (e.g., proteins).
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.
Nephron - Wikipedia, the free encyclopedia (1385 words)
A nephron is the basic structural and functional unit of the kidney.
Each nephron is composed of an initial filtering component (the renal corpuscle) and a tubule specialized for reabsorption and excretion (the renal tubule).
The loop of Henle is a U-shaped tube that consists of a descending limb and ascending limb.
  More results at FactBites »

 
 

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