Difference between revisions of "Macula densa"

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In the [[kidney]], the '''macula densa''' is an area of closely packed specialized [[cell (biology)|cells]] lining the region of the [[distal convoluted tubule]] (DCT) lying next to the [[glomerulus (kidney)|glomerular]] [[vascular pole]].  
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In the [[kidney]], the '''macula densa''' is an area of closely packed specialized [[cell (biology)|cells]] lining the wall of the thick ascending limb of Henle (TALH) 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.
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The cells of the macula densa are sensitive to the ionic content and water volume of the fluid in the TALH, 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==
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==Histology== <!--Macula densa cell redirects here-->
The cells of the macula densa cells are taller and have more prominent [[cell nucleus|nuclei]] than surrounding cells of the distal convoluted tubule.  
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The cells of the macula densa cells are taller and have more prominent [[cell nucleus|nuclei]] than surrounding cells of the thick ascending limb of Henle.  
  
The close proximity and prominence of the nuclei cause this segment of the DCT's wall to appear darker in microscopic preparations<ref>{{BUHistology|16010loa}}</ref>, hence the name ''macula densa''.
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The close proximity and prominence of the nuclei cause this segment of the TALH wall to appear darker in microscopic preparations<ref>{{BUHistology|16010loa}}</ref>, hence the name ''macula densa''.
  
 
==Function==
 
==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]]
 
[[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 ions in the distal convoluted tubule. (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 distal convoluted tubule will have a lower sodium concentration after the water is removed.)  
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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 juxtoglomerular 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.)
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In response, the macula densa cells release [[prostaglandins]], which triggers granular [[juxtaglomerular cells]] lining the [[afferent arterioles]] to release [[renin]] into the bloodstream.  (The juxtoglomerular 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==
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[[de:Macula densa]]
 
[[es:Macula densa]]
 
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Revision as of 11:36, 16 December 2007

In the kidney, the macula densa is an area of closely packed specialized cells lining the wall of the thick ascending limb of Henle (TALH) at the point of return of the nephron to the vascular pole of its parent glomerulus glomerular vascular pole.

The cells of the macula densa are sensitive to the ionic content and water volume of the fluid in the TALH, producing molecular signals that promote renin secretion by other cells of the juxtaglomerular apparatus.[1] The release of renin is an essential component of the renin-angiotensin-aldosterone system (RAAS), which regulates blood pressure and volume.

Histology

The cells of the macula densa cells are taller and have more prominent nuclei than surrounding cells of the thick ascending limb of Henle.

The close proximity and prominence of the nuclei cause this segment of the TALH wall to appear darker in microscopic preparations[2], hence the name macula densa.

Function

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 juxtoglomerular 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

  1. Junqueira, Luiz C. (2003). Basic Histology. McGraw-Hill. ISBN 0071378294. Unknown parameter |coauthors= ignored (help)
  2. Histology image: 16010loa – Histology Learning System at Boston University

External links


de:Macula densa


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