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equipment designed to serve a specific function (同)setup
(anatomy) a group of body parts that work together to perform a given function; "the breathing apparatus"

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〈U〉〈C〉(一式の)『器具』;装置 / 《集合的に》(ある機能を営む一系統の身体の)器官 / 〈U〉〈C〉(ある目的のための)道具立て
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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/12/30 19:33:26」(JST)

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Schematic depicting how the RAAS works. Here, activation of the RAAS is initiated by a low perfusion pressure in the juxtaglomerular apparatus

Renal corpuscle:The structure on the left in blue and pink is the renal corpuscle. The structure on the right is the renal tubule. The blue structure (A) is the Bowman's capsule (2 and 3). The pink structure is the glomerulus with its capillaries. At the left, blood flows from the afferent areteriole (9), through the capillaries (10), and out the efferent arteriole (11). The mesangium is the pink structure inside the glomerulus between the capillaries (5a) and extending outside the glomerulus (5b). Juxtaglomerular apparatus is "D".

The juxtaglomerular apparatus is a microscopic structure in the kidney that regulates the function of each nephron. The juxtaglomerular apparatus is named for its proximity to the glomerulus: It is found between the vascular pole of the renal corpuscle and the returning distal convoluted tubule of the same nephron. This location is critical to its function in regulating renal blood flow and glomerular filtration rate. The three cellular components of the apparatus are the macula densa of the distal convoluted tubule, smooth muscle cells of the afferent arteriole known as juxtaglomerular cells, and extraglomerular mesangial cells.

Structure

The juxtaglomerular apparatus consists of: (1) the juxtaglomerular cells, (2) the macula densa, (3) the Lacis cells or agranular cells.^[1]

Juxtaglomerular Cells (Granular Cells)

Juxtaglomerular cells are specialized smooth muscle cells of glomerular arterioles. They produce and secrete renin.

Macula Densa Cells

Macula densa cells are columnar epithelium thickening of the distal tubule. The macula densa senses any increase in the sodium chloride concentration in the distal tubule of the kidney and secretes a locally active (paracrine) vasopressor, which acts on the adjacent afferent arteriole to decrease glomerular filtration rate (GFR), as part of the tubuloglomerular feedback loop.

To be specific, excessive filtration at the glomerulus or inadequate sodium uptake in the proximal tubule/thick ascending loop of Henle brings to the distal convoluted tubule fluid that has an abnormally high concentration of sodium. Apical Na-K-2Cl cotransporters move sodium into the cells of the macula densa. The macula densa cells do not have enough basolateral Na/K ATPases to excrete this added sodium, so the cell's osmolarity increases. Water flows into the cell along the osmotic gradient, causing the cell to swell. When the cell swells, a stretch-activated non-selective anion channel is opened on the basolateral surface. ATP escapes through this channel and is subsequently converted to adenosine. Adenosine vasoconstricts the afferent arteriole via A1 receptors and vasodilates (to a lesser degree) efferent arterioles via A2 receptors, which decreases GFR. Also, adenosine inhibits renin release in JG cells via A1 receptors on JG cells using a Gi pathway.

In addition, when macula densa cells detect higher concentrations of Na and Cl, they inhibit nitric oxide synthetase (decreasing renin release) by an unknown pathway.

A decrease in GFR means less solute in the tubular lumen. As the filtrate reaches the macula densa, less NaCl is reabsorbed. The macula densa cells detect lower concentrations of Na and Cl and upregulate nitric oxide synthetase (NOS). NOS creates NO, which catalyses the formation of prostaglandins. These prostaglandins diffuse to the granular cells and activate a prostaglandin-specific Gs receptor. This receptor activates adenylate cyclase, which increases levels of cAMP. cAMP augments renin release. Prostaglandins and NO also vasodilate the afferent arterioles. Efferent arterioles are spared from this effect by renin release.

Function

The juxtaglomerular cells secrete renin in response to:

Beta-1 adrenergic stimulation
Decrease in renal perfusion pressure (detected directly by the granular cells)
Decrease in NaCl concentration at the macula densa, often due to a decrease in glomerular filtration rate, resulting in slower filtrate movement through the proximal tubule and, thus, more time for reabsorption.

Clinical significance

Elevated renin due to renal artery stenosis or a very rare renin-producing juxtaglomerular cell tumor of the kidney can produce secondary hyperaldosteronism (as opposed to primary hyperaldosteronism aka Conn syndrome, usually due to a functional adrenal adenoma).

Hyperactivity of the renin-angiotensin-aldosterone system is manifested by hypertension with hypervolemia, which is severe and not responsive (or minimally responsive) to medications/lifestyle modifications that would usually control essential hypertension. In addition, patients with hyperaldosteronism will have hypernatremia, hypokalemia, and metabolic alkalosis.

References

^ Robbins and Cotran Pathologic Basis of Disease 7E

External links

Electron micrograph
Diagram

UpToDate Contents

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1. バーター症候群およびギテルマン症候群 bartter and gitelman syndromes
2. 先天性腎尿路異常（CAKUT）の概要 overview of congenital anomalies of the kidney and urinary tract cakut

English Journal

Olfactory receptor responding to gut microbiota-derived signals plays a role in renin secretion and blood pressure regulation.

Pluznick JL, Protzko RJ, Gevorgyan H, Peterlin Z, Sipos A, Han J, Brunet I, Wan LX, Rey F, Wang T, Firestein SJ, Yanagisawa M, Gordon JI, Eichmann A, Peti-Peterdi J, Caplan MJ.SourceDepartment of Physiology, The Johns Hopkins University School of Medicine, Baltimore, MD 21205.
Proceedings of the National Academy of Sciences of the United States of America.Proc Natl Acad Sci U S A.2013 Feb 11. [Epub ahead of print]
Olfactory receptors are G protein-coupled receptors that mediate olfactory chemosensation and serve as chemosensors in other tissues. We find that Olfr78, an olfactory receptor expressed in the kidney, responds to short chain fatty acids (SCFAs). Olfr78 is expressed in the renal juxtaglomerular appa
PMID 23401498

Tubuloglomerular feedback and renal function in mice with targeted deletion of the type 1 equilibrative nucleoside transporter.

Li L, Mizel D, Huang Y, Eisner C, Hoerl M, Thiel M, Schnermann J.SourceNational Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bldg. 10, Rm. 4D51, 10 Center Drive-MSC 1370, Bethesda, MD 20892. jurgens@intra.niddk.nih.gov.
American journal of physiology. Renal physiology.Am J Physiol Renal Physiol.2013 Feb;304(4):F382-9. doi: 10.1152/ajprenal.00581.2012. Epub 2012 Dec 26.
A(1) adenosine receptors (A1AR) are required for the modulation of afferent arteriolar tone by changes in luminal NaCl concentration implying that extracellular adenosine concentrations need to change in synchrony with NaCl. The present experiments were performed in mice with a null mutation in the
PMID 23269643

Endothelium-derived nitric oxide supports Renin cell recruitment through the nitric oxide-sensitive guanylate cyclase pathway.

Neubauer B, Machura K, Kettl R, Lopez ML, Friebe A, Kurtz A.SourceInstitut für Physiologie, Universität Regensburg, D-93053 Regensburg, Germany. bjoern.neubauer@vkl.uni-regensburg.de.
Hypertension.Hypertension.2013 Feb;61(2):400-7. doi: 10.1161/HYPERTENSIONAHA.111.00221. Epub 2013 Jan 7.
Chronic challenge of renin-angiotensin causes recruitment of renin-producing cells in the kidney along the media layer of afferent arterioles and hypertrophy of cells in the juxtaglomerular apparatus. This study aimed to define the role of nitric oxide (NO) with regard to the recruitment pattern of
PMID 23297374

Japanese Journal

Visualisation of cellular Ca concentration change in association with tubulo-glomerular feedback

生体医工学 52(Supplement), O-273-O-274, 2014
… Renal blood flow is regulated within an appropriate range, in which Glomerular efferent arteriolar diameter is controlled by the juxtaglomerular apparatus as tubulo-glomerular feedback. …
NAID 130004948183

Pressure induces intracellular calcium changes in juxtaglomerular cells in perfused afferent arterioles

LAI En Yin,WANG Yibing,PERSSON Anders Erik Gosta,MANNING Roy Davis Jr,LIU Ruisheng
Hypertension research : clinical and experimental : official journal of the Japanese Society of Hypertension 34(8), 942-948, 2011-08-01
NAID 10030275576

Angiotensin II and IGF-I May Interact to Regulate Tubulointerstitial Cell Kinetics and Phenotypic Changes in Hypertensive Rats.

, , , ,
Hypertension Research 25(2), 257-269, 2002
… Renin expression in the juxtaglomerular apparatus was markedly suppressed in the Nx group, although <I>de novo</I> …
NAID 130004436975