- Macula densa
In the
kidney , the macula densa is an area of closely packed specialized cells lining the wall of thedistal convoluted tubule (DCT) at the point of return of the nephron to the vascular pole of its parent glomerulus glomerularvascular 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 thejuxtaglomerular apparatus . [cite book |last=Junqueira |first= Luiz C. |coauthors= Jose Carneiro |title= Basic Histology|year= 2003|publisher= McGraw-Hill|id= ISBN 0071378294 ] The release of renin is an essential component of therenin-angiotensin-aldosterone system ("RAAS"), which regulatesblood pressure and volume.Histology
The cells of the macula densa are taller and have more prominent 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 [BUHistology|16010loa] , hence the name "macula densa".
Function
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 intoBowman's space and theproximal 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 granularjuxtaglomerular cells lining theafferent arterioles to releaserenin into the bloodstream. (The juxtaglomerular cells can also release renin independently of the macula densa, as they are also triggered bybaroreceptors 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
External links
* - "Mammal, kidney cortex (LM, Medium)"
* - "The Nephron: Juxtaglomerular Apparatus"
Wikimedia Foundation. 2010.
