Macula densa 674713 201517349 2008-03-28T06:05:14Z Franamax 5177550 /* Histology */ un-redundify In the [[kidney]], the '''macula densa''' is an area of closely packed specialized [[cell (biology)|cells]] lining the wall of the [[distal convoluted tubule]] (DCT) at the point of return of the nephron to the vascular pole of its parent glomerulus [[glomerulus (kidney)|glomerular]] [[vascular pole]]. The cells of the macula densa are sensitive to the ionic content and water volume of the fluid in the DCT, producing molecular signals that promote [[renin]] secretion by other cells of the [[juxtaglomerular apparatus]].<ref>{{cite book |last=Junqueira |first= Luiz C. |coauthors= Jose Carneiro |title= Basic Histology|year= 2003|publisher= McGraw-Hill|id= ISBN 0071378294 }}</ref> The release of renin is an essential component of the [[renin-angiotensin-aldosterone system]] (''RAAS''), which regulates [[blood pressure]] and volume. ==Histology== <!--Macula densa cell redirects here--> The cells of the macula densa are taller and have more prominent [[cell nucleus|nuclei]] than surrounding cells of the distal convoluted tubule. The close proximity and prominence of the nuclei cause this segment of the DCT wall to appear darker in microscopic preparations<ref>{{BUHistology|16010loa}}</ref>, hence the name ''macula densa''. ==Function== [[Image:Renin-angiotensin-aldosterone system.png|thumb|400px|Schematic depicting how the RAAS works. Here, activation of the RAAS is initiated by a low perfusion pressure in the juxtaglomerular apparatus]] A decrease in [[blood pressure]] results in a decreased concentration of sodium and chloride ions at the macula densa. (This is due to reduced filtration by the glomerulus: less filtrate is expelled into [[Bowman's space]] and the [[proximal convoluted tubule]]; the resulting fluid reaching the macula will have a lower sodium chloride concentration after the sodium chloride is removed along the thick ascending limb of Henle.) In response, the macula densa cells release [[prostaglandins]], which triggers granular [[juxtaglomerular cells]] lining the [[afferent arterioles]] to release [[renin]] into the bloodstream. (The juxtaglomerular cells can also release renin independently of the macula densa, as they are also triggered by [[baroreceptors]] lining the arterioles, and release renin if a fall in blood pressure in the arterioles is detected.) Furthermore, activation of the sympathetic nervous system stimulates renin release through activation of beta-1 receptors. ==References== <references/> ==External links== * {{UCDavisOrganology|Urinary/mammal/cortex1/cortex5}} - "Mammal, kidney cortex (LM, Medium)" * {{GeorgiaPhysiology|7/7ch03/7ch03p17}} - "The Nephron: Juxtaglomerular Apparatus" {{kidney}} [[Category:Kidney]] {{anatomy-stub}} [[de:Macula densa]] [[es:Macula densa]]