Capillary

(Redirected from Capillary bed)
Jump to navigation Jump to search
Blood flows from digestive system heart to arteries, which narrow into arterioles, and then narrow further still into capillaries. After the tissue has been perfused, capillaries widen to become venules and then widen more to become veins, which return blood to the heart.

WikiDoc Resources for Capillary

Articles

Most recent articles on Capillary

Most cited articles on Capillary

Review articles on Capillary

Articles on Capillary in N Eng J Med, Lancet, BMJ

Media

Powerpoint slides on Capillary

Images of Capillary

Photos of Capillary

Podcasts & MP3s on Capillary

Videos on Capillary

Evidence Based Medicine

Cochrane Collaboration on Capillary

Bandolier on Capillary

TRIP on Capillary

Clinical Trials

Ongoing Trials on Capillary at Clinical Trials.gov

Trial results on Capillary

Clinical Trials on Capillary at Google

Guidelines / Policies / Govt

US National Guidelines Clearinghouse on Capillary

NICE Guidance on Capillary

NHS PRODIGY Guidance

FDA on Capillary

CDC on Capillary

Books

Books on Capillary

News

Capillary in the news

Be alerted to news on Capillary

News trends on Capillary

Commentary

Blogs on Capillary

Definitions

Definitions of Capillary

Patient Resources / Community

Patient resources on Capillary

Discussion groups on Capillary

Patient Handouts on Capillary

Directions to Hospitals Treating Capillary

Risk calculators and risk factors for Capillary

Healthcare Provider Resources

Symptoms of Capillary

Causes & Risk Factors for Capillary

Diagnostic studies for Capillary

Treatment of Capillary

Continuing Medical Education (CME)

CME Programs on Capillary

International

Capillary en Espanol

Capillary en Francais

Business

Capillary in the Marketplace

Patents on Capillary

Experimental / Informatics

List of terms related to Capillary

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]


Capillaries are the smallest of a body's blood vessels, measuring 5-10 μm, 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.

Capillary permeability can be increased by the release of certain cytokines.

Transport across endothelium

The endothelium also actively transports nutrients, messengers and other substances.

Large molecules may be too big to diffuse across endothelial cells. In some cases, vesicles contained in the capillary membrane use endocytosis and exocytosis to transport material between blood and the tissues. Blood hydrostatic pressure varies along the length of the capillar, and is roughly 40 mm Hg at the atreiolar end and 15 mm Hg at the venus end. The opposing force from outside the capillary is osmotic pressure and is 25 mm Hg. The result is an outward movement of fluid and ions at the atreiolar end, and an influx of fluid at the venus end of the capillary.

Immune response

In an immune response, the endothelial cells of the capillary will upregulate receptor molecules, thus "catching" immune cells as they pass by the site of infection and aiding extravasation 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.

See also

References

  1. Template:KMLEref
  2. Histology image: 22401lba – Histology Learning System at Boston University

External links


da:Kapillær de:Kapillare is:Háræð it:Capillare he:נים (כלי דם) lv:Kapilāri lt:Kapiliaras nl:Haarvat no:Kapillær simple:Capillary sr:Капилар fi:Hiussuoni sv:Kapillär


Template:WikiDoc Sources CME Category::Cardiology