Bowman's capsule
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| Bowman's capsule | |
|---|---|
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| Glomerulus. (Bowman's capsule not labeled, but visible at top.) | |
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| Glomerulus is red; Bowman's capsule is green. | |
| Latin | capsula glomeruli |
| Gray's | subject #253 1222 |
| Precursor | Metanephric blastema |
| MeSH | Bowman+Capsule |
| Dorlands/Elsevier | c_07/12211408 |
The Bowman's capsule is a blind sac at the beginning of a the tubular component of a nephron in the mammalian kidney. A glomerulus is enclosed in the sac. Fluids from blood in the glomerulus are collected in the Bowman's capsule (i.e., glomerular filtrate) and further processed along the nephron to form urine.
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[edit] Anatomy
There are two "poles", or sides to Bowman's capusle:
- The vascular pole is the side with the afferent arteriole and efferent arteriole, as well as the distal convoluted tubule.
- the urinary pole is the side with the proximal convoluted tubule.
The barrier between the blood and the lumen of the nephron here is formed of the following layers, from external to internal:
| basal lamina | Covers intraglomerular mesangial cells |
| parietal layer | A single layer of simple squamous epithelium. Does not function in filtration. |
| Bowman's space (or "urinary space", or "capsular space") | Between the visceral and parietal layers, into which the filtrate enters after passing through the podocytes' filtration slits. [1] |
| visceral layer | Lies just beneath the thickened glomerular basement membrane and is made of podocytes which send primary foot processes and secondary processes ("pedicels") over the length of the glomerulus. Foot processes interdigitate with one another forming filtration slits. In addition, foot processes have a negatively-charged coat (glycocalyx) that limits the filtration of negatively-charged molecules, such as albumin. The endothelial cells have openings which are so large, that nearly anything smaller than a red blood cell passes through that layer. |
Beneath the visceral layer lie the capillaries of the glomerulus.
The barriers are 'leaky' in the sense that some large molecules can pass through unfiltered, while others are blocked. Below are the layers of the basal lamina:
| lamina rara externa | by heparan sulfate | blocks by charge |
| lamina densa | by type 4 collagen | blocks by size |
| lamina rara interna | heparan sulfate | blocks by charge |
[edit] Physiology
The process of filtration of the blood in the Bowman's capsule is ultrafiltration (or glomerular filtration), and the normal rate of filtration is 125 ml/min, equivalent to ten times the blood volume daily.
Any proteins under roughly 30 kilodaltons can pass freely through the membrane, although there is some extra hindrance for negatively charged molecules due to the negative charge of the basement membrane and the podocytes.
Any small molecules such as water, glucose, salt (NaCl), amino acids, and urea pass freely into Bowman's space, but cells, platelets and large proteins do not.
As a result, the filtrate leaving the Bowman's capsule is very similar to blood plasma in composition as it passes into the proximal convoluted tubule.
[edit] Clinical significance
Measuring the glomerular filtration rate (GFR) is a diagnostic test of kidney function.
A decreased GFR may be a sign of renal failure.
[edit] Eponym
Bowman's capsule is named after Sir William Bowman (1816-1892), a British surgeon and anatomist.
Together with the glomerulus it is known as a renal corpuscle, or a Malpighian corpuscle, named after Marcello Malpighi (1628-1694), an Italian physician and biologist. This name is not used widely anymore, probably to avoid confusion with a Malpighian corpuscle in the spleen.
[edit] See also
[edit] Additional images
 Distribution of blood vessels in cortex of kidney. |
 Glomerulus. |
[edit] References
[edit] External links
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