Capillary: Difference between revisions

Content deleted Content added

Inline

Revision as of 12:28, 9 November 2007

Capillaries are the smallest of a body's blood vessels, measuring 5-10 μm in diameter, which connect arterioles and venules, and are important for the interchange of oxygen, carbon dioxide, and other substances between blood and tissue cells.^[1]

Structure

The walls of capillaries are composed of only a single layer of cells, the endothelium. This layer is so thin that molecules such as oxygen, water and lipids can pass through them by diffusion and enter the tissues. Waste products such as carbon dioxide and urea can diffuse back into the blood to be carried away for removal from the body. Capillaries are so small the blood cells need to pass through it in a single file line.

Capillary permeability can be increased by the release of certain cytokines, such as in an immune response

Immune response

In an immune response, the endothelial cells of the capillary will upregulate receptor molecules, thus it signals the need for an immune response by the site of infection and aids extravasion of these cells into the tissue.

Capillary bed

The "capillary bed" is the network of capillaries supplying an organ. The more metabolically active the cells, the more capillaries it will require to supply nutrients.

The capillary bed usually carries no more than 25% of the amount of blood it could contain, although this amount can be increased through autoregulation by inducing relaxation of smooth muscle.

The capillaries do not possess this smooth muscle in their own walls, and so any change in their diameter is passive. Any signalling molecules they release (such as endothelin for constriction and nitric oxide for dilation) act on the smooth muscle cells in the walls of nearby, larger vessels, e.g. arterioles.

Types

Capillaries come in three types:

Continuous - Continuous capillaries have a sealed endothelium and only allow small molecules, water and ions to diffuse.
Fenestrated - Fenestrated capillaries (derived from "fenestra," the Latin word for "window") have openings that allow larger molecules to diffuse.^[2]
Sinusoidal - Sinusoidal capillaries are special forms of fenestrated capillaries that have larger openings in the epithelium allowing red blood cells and serum proteins to enter.

References

^ Template:KMLEref
^ Histology image: 22401lba – Histology Learning System at Boston University

External links

Histology image: 00903loa – Histology Learning System at Boston University

[1] Template:KMLEref

[2] Histology image: 22401lba – Histology Learning System at Boston University

[1]

[2]

@@ Line 8: / Line 8: @@
 ==Structure==
+The walls of capillaries are composed of only a single layer of [[cell (biology)|cells]], the [[endothelium]]. This layer is so thin that [[molecules]] such as [[oxygen]], [[water]] and [[lipids]] can pass through them by [[diffusion]] and enter the tissues. Waste products such as [[carbon dioxide]] and [[urea]] can diffuse back into the [[blood]] to be carried away for removal from the body. Capillaries are so small the blood cells need to pass through it in a single file line.
+Capillary [[permeability]] can be increased by the release of certain [[cytokines]], such as in an [[immune response]]
-== BEFORE EVERY THING ==
-'''KISS MY ASS'''
-The walls of capillaries are composed of only a single layer of [[cell (biology)|cells]], the [[endothelium]]. This layer is so thin that [[molecules]] such as [[oxygen]], [[water]] and [[lipids]] can pass through them by [[diffusion]] and enter the tissues. Waste products such as [[carbon dioxide]] and [[urea]] can diffuse back into the [[blood]] to be carried away for removal from the body. Capillaries are so small the blood cells need to pass through it in a single file line.
-Capillary [[permeability]] can be increased by the release of certain [[cytokines]], such as in an [[immune response]]
 ==Immune response==