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| Loose connective tissue | |
|---|---|
 Section of dermis. The papillary dermis consists of loose connective tissue. | |
| Details | |
| Identifiers | |
| Latin | textus connectivus laxus |
| TA98 | A04.5.02.020 A16.0.03.006 |
| TA2 | 7089 |
| TH | H2.00.03.1.00002 |
| FMA | 19783 |
| Anatomical terminology | |
Loose connective tissue, also known asareolar tissue, is a cellularconnective tissue with thin and relatively sparsecollagen fibers. They have a semi-fluid matrix with lesser proportions of fibers. Itsground substance occupies more volume than the fibers do. It has a viscous to gel-like consistency and plays an important role in the diffusion of oxygen and nutrients from the capillaries that course through this connective tissue as well as in the diffusion of carbon dioxide andmetabolic wastes back to the vessels. Moreover, loose connective tissue is primarily located beneath theepithelia that cover the body surfaces and line the internal surfaces of the body. It is also associated with the epithelium of glands and surrounds the smallest blood vessels. This tissue is thus the initial site where pathogenic agents, such as bacteria that have breached an epithelial surface, are challenged and destroyed by cells of the immune system.[1]
In the past, the designations areolar tissue,adipose tissue, andreticular tissue have been listed as subsets of loose connective tissue. However, they are no longer considered subsets of loose connective tissue. Loose connective tissue is a subset ofconnective tissue proper. Furthermore, areolar tissue is the same as loose connective tissue, adipose tissue is a subset of specialized connective tissue, and reticular tissue is the presence of reticular fibers and reticular cells together forming the stroma of hemopoietic tissue (specifically the red bone marrow) and lymphatic tissue organs (lymph nodes and spleen but not the thymus).[1]
Most cell types in loose connective tissue are transient wandering cells that migrate from local blood vessels in response to specific stimuli. Loose connective tissue, therefore, is a site of inflammatory and immune reactions. In areas of the body where foreign substances are continually present, large populations of immune cells are maintained. For example, the lamina propria, the loose connective tissue of mucous membranes, such as those of the respiratory and alimentary systems, contains large numbers of these cells.[1]
It is a pliable, mesh-liketissue with a fluidmatrix and functions to cushion and protect bodyorgans.
Fibroblasts are widely dispersed in this tissue; they are irregular branching cells that secrete strong fibrousproteins andproteoglycans as an extracellular matrix.
The cells of this type of tissue are generally connected by a gelatinous substance known asground substance primarily made up of collagenous and elastic fibers.
It may 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. It may likewise be present in the mediastinal extremities. 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 when needed. Because of 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 theepidermis layer and is also underneath theepithelial tissue of all thebody systems that have external openings.it makes the skin elastic and helps it to withstand pulling pain. It is also a component of thelamina propria of thedigestive andrespiratory tracts, themucous membranes ofreproductive andurinary systems, thestroma of glands, and thehypodermis of the skin.It is also found in themesentery which is surrounding the intestine.
Loose connective tissue is named based on the "weave" and type of its constituent fibers. There are three main types:
Areolar tissue (/əˈriːələr/ or/ˌɛəriˈoʊlər,ˌær-/[2][3]) is a common type of loose connective tissue (and the most widely distributed type ofconnective tissue in vertebrates). It is so-named because its fibers are far enough apart to leave ample open space forinterstitial fluid in between (areola is Latin for a "little open space"). It is strong enough to bind different tissue types together, yet soft enough to provide flexibility and cushioning. It exhibits interlacing,[4] loosely organized fibers,[citation needed] abundant blood vessels, and significant empty space filled with interstitial fluid. Many adjacentepithelial tissues (which are avascular) get their nutrients from the interstitial fluid of areolar tissue; thelamina propria is areolar in many body locations. Its fibers run in random directions and are mostly collagenous, but elastic and reticular fibers are also present. Areolar tissue is highly variable in appearance. In manyserous membranes, it appears as a loose arrangement of collagenous and elastic fibers, scattered cells of various types; abundantground substance; numerous blood vessels. In the skin and mucous membranes, it is more compact and sometimes difficult to distinguish fromdense irregular connective tissue.
Areolar connective tissue holdsorgans in place and attachesepithelial 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.
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Organs that are rich in loose connective tissue (such as the eyelids) are usually sites that undergo oedema, indicatingkidney failure or nephrotic syndrome. Therefore, periorbital swelling is one characteristic finding in severe kidney disease.
