View source for Glomerulus

{{Infobox Anatomy |
  Name         = {{PAGENAME}} |
  Latin        = glomerulus renis |
  GraySubject  = 253 |
  GrayPage     = 1221 |
  Image        = Gray1130.jpg |
  Caption      = Glomerulus. |
  Image2       = Gray1129.jpg |
  Caption2     = Distribution of bloodvessels in cortex of kidney. |
  Precursor    = [[Metanephric blastema]] |
  System       = |
  Artery       = |
  Vein         = |
  Nerve        = |
  Lymph        = |
  MeshName     = Kidney+Glomerulus |
  MeshNumber   = A05.810.453.324.359 |
  DorlandsPre  = g_07 |
  DorlandsSuf  = 12394744  |
}}
{{SI}}
{{CMG}}

'''Associate Editor-In-Chief:''' {{CZ}}



==Overview==
A '''glomerulus''' is a [[capillary]] tuft surrounded by [[Bowman's capsule]] in [[nephron]]s of the vertebrate [[kidney]]. It receives its blood supply from an afferent arteriole of the [[renal circulation]]. Unlike most other capillary beds, the glomerulus drains into an efferent arteriole rather than a [[venule]]. The resistance of the arterioles results in high pressure in the glomerulus aiding the process of [[ultrafiltration]] where fluids and soluble materials in the blood are forced out of the capillaries and into [[Bowman's capsule]].

A glomerulus and its surrounding [[Bowman's capsule]] constitute a [[renal corpuscle]], the basic filtration unit of the kidney. The rate at which blood is filtered through all of the glomeruli is the [[glomerular filtration rate]] (GFR), measurements of which are often used to determine [[renal function]].

==Afferent circulation==
The afferent arteriole that supplies the glomerulus is a branch off of an interlobular artery in the cortex.

==Layers==
If a substance can pass through the endothelial cells, glomerular basement membrane, and podocytes, then it is known as ultrafiltrate, and it enters [[proximal tubule]]. Otherwise, it returns through the efferent circulation, discussed below.

===Endothelial cells===
The [[endothelial cell]]s of the glomerulus contain numerous pores ([[fenestrae]]) that, unlike those of other fenestrated capillaries, are not spanned by diaphragms. The cells have openings which are so large that nearly anything smaller than a [[red blood cell]] passes through that layer.

Because of this, the endothelial cells lining the glomerulus are not usually considered part of the renal filtration barrier.

===Glomerular basement membrane===
The glomerular endothelium sits on a very thick (100-200 nm) [[glomerular basement membrane]]. It is not only uncharacteristically thick compared to most other [[basement membrane]]s (40-50 nm), but it is also rich in negatively charged [[glycosaminoglycan]]s such as [[heparan sulfate]]. 

The negatively-charged basement membrane repels negatively-charged proteins from the blood, helping to prevent their passage into Bowman's space.

===Podocytes===
[[Podocyte]]s line the other side of the glomerular basement membrane and form part of the lining of Bowman's space. Podocytes form a tight interdigitating network of ''foot processes'' (pedicels) that control the filtration of proteins from the capillary lumen into Bowman's space.  

The space between adjacent podocyte foot processes is spanned by a slit diaphragm formed by several proteins including [[podocin]] and [[nephrin]]. In addition, foot processes have a negatively-charged coat ([[glycocalyx]]) that limits the filtration of negatively-charged molecules, such as [[serum albumin]].

The podocytes are sometimes considered the "visceral layer of [[Bowman's capsule]]", rather than part of the glomerulus.

===Intraglomerular mesangial cell===
[[Intraglomerular mesangial cell]]s are found in the interstitium between endothelial cells of the glomerulus. They are not part of the filtration barrier but are specialized pericytes that participate indirectly in filtration.

==Efferent circulation==
Blood is carried out of the glomerulus by an [[efferent arteriole|efferent ]]''[[efferent arteriole|arteriole]]'' instead of a ''[[venule]]'', as is observed in most other capillary systems. This provides tighter control over the bloodflow through the glomerulus, since arterioles can be dilated and constricted more readily than venules, owing to arterioles' larger [[smooth muscle]] layer ([[tunica media]]).

Efferent arterioles of [[juxtamedullary nephron]]s (ie, the 15% of nephrons closest to the medulla) send straight capillary branches that deliver isotonic blood to the renal medulla. Along with the loop of Henle, these [[vasa recta]] play a crucial role in the establishment of the nephron's [[countercurrent exchange]] system.

The [[efferent arteriole]], into which the glomerulus delivers blood, empties into an interlobular vein.

==Juxtaglomerular cells==
The walls of the afferent arteriole contain specialized [[smooth muscle]] cells that synthesize [[renin]]. These [[juxtaglomerular cell]]s play a major role in the [[renin-angiotensin system]], which helps regulate [[blood volume]] and [[blood pressure|pressure]].

==Additional images==
<gallery>
 Image:Corpuscule-malpighi.JPG|Malphigian corpuscle
 Image:Histology-kidney.jpg |1 [[Glomerulus]], 2 [[Proximal convoluted tubule|proximal tubule]], 3 [[Distal convoluted tubule|distal tubule]]
 Image:Glomerulus pas.JPG|Glomerulus.
 Image:PhysiologieGlomérulaire.jpg|Glomerulus.
 Image:Gray1132.jpg|Section of cortex of human kidney.
 Image:Glomerulum of mouse kidney in Scanning Electron Microscope, magnification 1,000x.GIF|Mouse glomerulus in the Scanning Electron  Microscope ("SEM"), magnification 1,000x
 Image:Glomerulum of mouse kidney in Scanning Electron Microscope, magnification 5,000x.GIF|Mouse glomerulus in the SEM, magnification 5,000x
 Image:Glomerulum of mouse kidney with broken capillary in Scanning Electron Microscope, magnification 10,000x.GIF|Mouse glomerulus in the SEM with one capillary broken, magnification 10,000x
 Image:Inner view of fenestrae in capillary of glomerulus in Scanning Electron Microscope, magnification 100,000x.GIF|View on the inside of broken capillary with [[fenestrae]] visible, magnification 100,000x
</gallery>

==External links==
* [http://coe.fgcu.edu/faculty/greenep/kidney/Glomerulus.html Image and article at FGCU]
* {{KansasHistology|epithel|epith02}} "Kidney (Glomerulus)"
* {{UCDavisOrganology|Urinary/mammal/cortex1/cortex1}} - "Mammal, kidney cortex (LM, Medium)" 
* {{BUHistology|16010loa}}
* {http://www.uncnephropathology.org  UNC Nephropathology}

{{kidney}}


[[Category:Kidney]]
[[Category:Nephrology]]

[[es:Glomérulo renal]]
[[it:Glomerulo]]
[[nl:Glomerulus]]
[[pt:Glomérulo]]

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