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Areolar tissue (a type of "loose connective tissue") exhibits loosely organized fibers, abundant blood vessels, and a lot of seemingly empty space. Its fiber run in random directions and are mostly collagenous, but elastic and reticular fibers are also present. Areolar tissue is highly variable in appearance. In many serous membranes, it appears as a loose arrangement of collagenous and elastic fibers, scattered cells of various types; abundant ground substance; numerous blood vessels. In the skin and mucous membranes, it is more compact and sometimes difficult to distinguish from dense irregular connective tissue. It is the most widely distributed connective tissue type in vertebrates.
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Location
It can be found in tissue sections from almost every part of the body. It surrounds blood vessels and nerves and penetrates with them even into the small spaces of muscles, tendons, and other tissues. Nearly every epithelium rests on a layer of areolar tissue, whose blood vessels provide the epithelium with nutrition, waste removal, and a ready supply of infection-fighting leukocytes in times of need. Beause the abundance of open, fluid-filled space, leukocytes can move about freely in areolar tissue and can easily find and destroy pathogens.
The areolar tissue is found beneath the dermis layer and is also underneath the epithelial tissue of all the body systems that have external openings.
It is also a component of mucus membranes found in the digestive, respiratory, reproductive, and urinary systems.
It also surrounds the blood vessels and nerves.
Composition
It is a pliable, mesh-like tissue with a fluid matrix and functions to cushion and protect body organs.
Cells called fibroblasts are widely dispersed in this tissue; they are irregular branching cells that secrete strong fibrous proteins and proteoglycans as an extracellular matrix.
The cells of this type of tissue are generally separated by quite some distance by a gel-like gelatinous substance primarily made up of collagenous and elastic fibers.
Function
Areolar connective tissue holds organs in place and attaches epithelial tissue to other underlying tissues. It also serves as a reservoir of water and salts for surrounding tissues. Almost all cells obtain their nutrients from and release their wastes into areolar connective tissue.
Classification
Loose connective tissue is named based on the "weave" and type of its constituent fibers. There are three main types:
- Collagenous fibers: collagenous fibers are made of collagen and consist of bundles of fibrils that are coils of collagen molecules.
- Elastic fibers: elastic fibers are made of elastin and are "stretchable."
- Reticular fibers: reticular fibers consist of one or more types of very thin collagen fibers. They join connective tissues to other tissues.
Additional images
 Section of the human esophagus. Moderately magnified. |
External links
- areolar+tissue at eMedicine Dictionary
- Bioweb at UWLAX Zoolab
- Histology at OU 43_07 - "Skin"
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Wikipedia content modification information:
- This page was last modified on 6 October 2008, at 01:05.
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