Difference between revisions of "Connective tissue" - New World Encyclopedia
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* Characterized largely by the traits of non-living tissue. | * Characterized largely by the traits of non-living tissue. | ||
| − | Connective tissue is composed of different types of cells (fibroblasts, plasma cells, fat cells, melanocytes, mast cells) combined with large amounts of intercellular matter. The intercellular matrix includes fibers ( | + | Connective tissue is composed of different types of cells (fibroblasts, plasma cells, fat cells, melanocytes, mast cells) combined with large amounts of intercellular matter. The intercellular matrix includes fibers (collagenous, elastic, and reticular fibers) and nonfibrillar components (the ground substance in which the cells and fibers are embedded). |
| − | The | + | There are a variety of types of connective tissues, such as Areolar or loose connective tissue, adipose tissue, dense connective tissue, and reticular connective tissue. The types of connective tissue differ in terms of the relative proportions of these various cell types and substances in the intercellular matrix. Among the variables are how many fibers there are to cells, the numbers and proportions of the different cell types in a given volume, the proportions and arrangements of the different fibers, the composition of the ground substance, and so forth. |
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| + | The three basic fiber types are: | ||
| + | * '''[[Collagenous fiber]]s'''. Collagen is the main [[protein]] of connective tissue in [[animal]]s and the most abundant protein in [[mammal]]s. Tough bundles of collagen called ''collagen fibers'' or collagenous fibers are a major component of the extracellular matrix that supports most tissues and gives cells structure from the outside. Collagen involves the harmonization of three polypeptide chains into the form of a triple helix, and is characterized by the regular arrangement of [[amino acid]]s in each of the three chains. Under tension, the triple helix coils tight, resisting stretching, and making collagen valuable for structure and support, while giving [[bone]]s some elasticity. Collagen is common in loose connective tissue, dense connective tissue, reticular connective tissue, [[bone]], and [[cartilage]]. | ||
| + | * '''[[Elastic fiber]]s'''. Elastic fibers, or yellow fibers, are bundles of [[protein]]s ([[elastin]]) found in connective tissue and produced by [[fibroblast]]s and smooth [[muscle]] cells in [[artery|arteries]]. These fibers can stretch up to 1.5 times their length, and snap back to their original length when relaxed. Elastin is a protein in elastic fibers that is elastic and allows many tissues in the body to resume their shape after stretching or contracting. | ||
| + | * '''[[Reticular fiber]]s'''. Reticular fibers or reticulin is a type of structural fibers in some connective tissues that involves fine meshwork (reticulim) of glycosylated collagen III and other components. Networks of these fibers make up stroma of [[lymphatic]] and hemopoietic tissues, such as the [[thymus]], [[lymph node]]s, [[spleen]], [[bone marrow]] and [[adipose tissue]], and also parenchyma of [[liver]], [[testis]] and [[lung]]. | ||
==Classification== | ==Classification== | ||
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===Connective tissue proper=== | ===Connective tissue proper=== | ||
[[Image:Illu connective tissues 1.jpg|thumb|400px|Connective tissue proper]] | [[Image:Illu connective tissues 1.jpg|thumb|400px|Connective tissue proper]] | ||
| − | * [[Areolar connective tissue|Areolar (or loose) connective tissue]] holds organs and epithelia in place, and has a variety of [[protein]]aceous | + | * '''[[Areolar connective tissue|Areolar (or loose) connective tissue]]''' holds organs and epithelia in place, and has a variety of [[protein]]aceous fibers, including [[collagen]] and [[elastin]]. Areolar connective tissue is the most widely distributed connective tissue type in vertebrates. It is a pliable, mesh-like [[Biological tissue|tissue]] with a fluid matrix and functions to cushion and protect body organs. Cells called [[fibroblast]]s are widely dispered in this tissue; they are irregular branching cells that secrete strong fibrous [[protein]]s 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 Areolar connective tissue can be found in the [[skin]] as well as in places that connect [[epithelium]] to other tissues. The areolar tissue is found beneath the [[epidermis|dermis]] layer and is also underneath the epithelial tissue of all the organ systems that have external openings. It is a component of [[mucus membrane]]s found in the [[digestive]], [[respiratory]], [[reproductive]], and [[urinary]] systems, and surrounds the [[blood vessel]]s and [[nerve]]s. |
| − | * [[Adipose tissue]] contains [[adipocyte]]s, used for cushioning, | + | * '''[[Adipose tissue]]''' contains [[adipocyte]]s. Its main role is to store [[energy]] in the form of [[fat]], although it also is used for cushioning, thermal insulation, and lubrication (primarily in the [[pericardium]]. |
| − | * [[Dense connective tissue]] (or, less commonly, [[ | + | * '''[[Dense connective tissue]]''' (or, less commonly, fibrous connective tissue) has [[collagen]] fibers as its main matrix element. Crowded between the collagen fibers are rows of [[fibroblast]]s, fiber-forming cells, that manufacture the fibers. Dense connective tissue forms strong, rope-like structures such as [[tendon]]s and [[ligament]]s. Tendons attach [[skeletal muscle]]s to [[bone]]s; ligaments connect bones to bones at joints. Ligaments are more stretchy and contain more elastic fibers than tendons. Dense connective tissue also make up the lower layers of the [[skin]] (dermis), where it is arranged in sheets. |
| − | * [[Reticular connective tissue]] is a network of reticular | + | * '''[[Reticular connective tissue]]''' is a network of reticular fibers (fine collagen, type III) that form a soft skeleton to support the [[lymphoid]] organs ([[lymph nodes]], [[bone marrow]], [[thymus]], and [[spleen]].) Reticular fibers are synthesized by special [[fibroblasts]] called reticular cells. The fibers are thin branching structures. Adipose tissue is held together by reticular fibers. Reticular connective tissue resembles areolar connective tissue, but the only fibers in its matrix are reticular fibers, which form a delicate network along which fibroblasts called reticular cells lie scattered. Although reticular fibers are widely distributed in the body, reticular tissue is limited to certain sites. |
===Specialized connective tissues=== | ===Specialized connective tissues=== | ||
[[Image:Illu connective tissues 2.jpg|thumb|400px|Specialized connective tissues]] | [[Image:Illu connective tissues 2.jpg|thumb|400px|Specialized connective tissues]] | ||
| − | * [[Blood]] functions in transport. Its extracellular matrix is | + | * [[Blood]] functions in transport. Its extracellular matrix is blood plasma, which transports dissolved [[nutrient]]s, [[hormone]]s, and [[carbon dioxide]] in the form of bicarbonate. The main cellular component is [[red blood cell]]s. |
| − | * [[Bone]] makes up virtually the entire skeleton in adult | + | * [[Bone]] makes up virtually the entire skeleton in adult [[vertebrate]]s. |
* [[Cartilage]] makes up virtually the entire skeleton in [[chondrichthyes]]. In most other [[vertebrate]]s, it is found primarily in [[joint]]s, where it provides cushioning. The extracellular matrix of cartilage is composed primarily of [[collagen]]. | * [[Cartilage]] makes up virtually the entire skeleton in [[chondrichthyes]]. In most other [[vertebrate]]s, it is found primarily in [[joint]]s, where it provides cushioning. The extracellular matrix of cartilage is composed primarily of [[collagen]]. | ||
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* [[Mesenchyme|Mesenchymal connective tissue]] | * [[Mesenchyme|Mesenchymal connective tissue]] | ||
* [[Mucous connective tissue]] | * [[Mucous connective tissue]] | ||
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== Disorders of connective tissue == | == Disorders of connective tissue == | ||
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{{Biological tissue}} | {{Biological tissue}} | ||
| − | {{credit|120780335}} | + | {{credit|Connective_tissue|120780335|Elastic_fiber|113049351|Reticular_fiber|116306111|Areolar_connective_tissue|115234172|Adipose_tissue|119932648|Dense_connective_tissue|118710140|Reticular_connective_tissue|117859111}} |
[[Category:Life sciences}} | [[Category:Life sciences}} | ||
Revision as of 19:55, 7 April 2007
Connective tissue is one of the four types of tissue in traditional classifications (the others being epithelial, muscle, and nervous tissue.) It is characterized by abundant extracellular matter (intercellular substances and fibers) encasing relatively few cells. The various combinations of the elements in this intercellular matrix give the tissue its character, resulting in different kinds of connective tissue.
As the name implies, connective tissues provide structure and support of the body. These tissues provide integrity to the organs and the major environment of most cells, protect the body, act as a storehouse of minerals and fats, and allow motion through such tissues as bones, cartilage, tendons, ligaments, and so forth.
Blood, cartilage, and bone are usually considered connective tissue, but because they differ so substantially from the other tissues in this class, the phrase "connective tissue proper" is commonly used to exclude those three. There is also variation in the classification of embryonic connective tissues; on this page they will be treated as a third and separate category.
Overview
Connective tissue is largely a category of exclusion rather than one with a precise definition, but all or most tissues in this category are similarly:
- Involved in structure and support.
- Derived from embryonic mesoderm, usually.
- Characterized largely by the traits of non-living tissue.
Connective tissue is composed of different types of cells (fibroblasts, plasma cells, fat cells, melanocytes, mast cells) combined with large amounts of intercellular matter. The intercellular matrix includes fibers (collagenous, elastic, and reticular fibers) and nonfibrillar components (the ground substance in which the cells and fibers are embedded).
There are a variety of types of connective tissues, such as Areolar or loose connective tissue, adipose tissue, dense connective tissue, and reticular connective tissue. The types of connective tissue differ in terms of the relative proportions of these various cell types and substances in the intercellular matrix. Among the variables are how many fibers there are to cells, the numbers and proportions of the different cell types in a given volume, the proportions and arrangements of the different fibers, the composition of the ground substance, and so forth.
The three basic fiber types are:
- Collagenous fibers. Collagen is the main protein of connective tissue in animals and the most abundant protein in mammals. Tough bundles of collagen called collagen fibers or collagenous fibers are a major component of the extracellular matrix that supports most tissues and gives cells structure from the outside. Collagen involves the harmonization of three polypeptide chains into the form of a triple helix, and is characterized by the regular arrangement of amino acids in each of the three chains. Under tension, the triple helix coils tight, resisting stretching, and making collagen valuable for structure and support, while giving bones some elasticity. Collagen is common in loose connective tissue, dense connective tissue, reticular connective tissue, bone, and cartilage.
- Elastic fibers. Elastic fibers, or yellow fibers, are bundles of proteins (elastin) found in connective tissue and produced by fibroblasts and smooth muscle cells in arteries. These fibers can stretch up to 1.5 times their length, and snap back to their original length when relaxed. Elastin is a protein in elastic fibers that is elastic and allows many tissues in the body to resume their shape after stretching or contracting.
- Reticular fibers. Reticular fibers or reticulin is a type of structural fibers in some connective tissues that involves fine meshwork (reticulim) of glycosylated collagen III and other components. Networks of these fibers make up stroma of lymphatic and hemopoietic tissues, such as the thymus, lymph nodes, spleen, bone marrow and adipose tissue, and also parenchyma of liver, testis and lung.
Classification
Connective tissue proper
- Areolar (or loose) connective tissue holds organs and epithelia in place, and has a variety of proteinaceous fibers, including collagen and elastin. Areolar connective tissue is the most widely distributed connective tissue type in vertebrates. It is a pliable, mesh-like tissue with a fluid matrix and functions to cushion and protect body organs. Cells called fibroblasts are widely dispered 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 Areolar connective tissue can be found in the skin as well as in places that connect epithelium to other tissues. The areolar tissue is found beneath the dermis layer and is also underneath the epithelial tissue of all the organ systems that have external openings. It is a component of mucus membranes found in the digestive, respiratory, reproductive, and urinary systems, and surrounds the blood vessels and nerves.
- Adipose tissue contains adipocytes. Its main role is to store energy in the form of fat, although it also is used for cushioning, thermal insulation, and lubrication (primarily in the pericardium.
- Dense connective tissue (or, less commonly, fibrous connective tissue) has collagen fibers as its main matrix element. Crowded between the collagen fibers are rows of fibroblasts, fiber-forming cells, that manufacture the fibers. Dense connective tissue forms strong, rope-like structures such as tendons and ligaments. Tendons attach skeletal muscles to bones; ligaments connect bones to bones at joints. Ligaments are more stretchy and contain more elastic fibers than tendons. Dense connective tissue also make up the lower layers of the skin (dermis), where it is arranged in sheets.
- Reticular connective tissue is a network of reticular fibers (fine collagen, type III) that form a soft skeleton to support the lymphoid organs (lymph nodes, bone marrow, thymus, and spleen.) Reticular fibers are synthesized by special fibroblasts called reticular cells. The fibers are thin branching structures. Adipose tissue is held together by reticular fibers. Reticular connective tissue resembles areolar connective tissue, but the only fibers in its matrix are reticular fibers, which form a delicate network along which fibroblasts called reticular cells lie scattered. Although reticular fibers are widely distributed in the body, reticular tissue is limited to certain sites.
Specialized connective tissues
- Blood functions in transport. Its extracellular matrix is blood plasma, which transports dissolved nutrients, hormones, and carbon dioxide in the form of bicarbonate. The main cellular component is red blood cells.
- Bone makes up virtually the entire skeleton in adult vertebrates.
- Cartilage makes up virtually the entire skeleton in chondrichthyes. In most other vertebrates, it is found primarily in joints, where it provides cushioning. The extracellular matrix of cartilage is composed primarily of collagen.
Embryonic connective tissues
- Mesenchymal connective tissue
- Mucous connective tissue
Disorders of connective tissue
Various connective tissue conditions have been identified; these can be both inherited and environmental.
- Marfan syndrome - a genetic disease causing abnormal fibrillin.
- Scurvy - caused by a dietary deficiency in vitamin C, leading to abnormal collagen.
- Ehlers-Danlos syndrome - deficient type III collagen- a genetic disease causing progressive deterioration of collagens, with different EDS types affecting different sites in the body, such as joints, heart valves, organ walls, arterial walls, etc.
- Loeys-Dietz syndrome - a genetic disease related to Marfan syndrome, with an emphasis on vascular deterioration.
- Osteogenesis imperfecta (brittle bone disease) - caused by insufficient production of good quality collagen to produce healthy, strong bones.
- Fibrodysplasia ossificans progressiva - disease of the connective tissue, caused by a defective gene which turns connective tissue into bone.
- Spontaneous pneumothorax - collapsed lung, believed to be related to subtle abnormalities in connective tissue.
- Sarcoma - a neoplastic process originating within connective tissue.
Staining of connective tissue
For microscopic viewing, the majority of the connective tissue staining techniques color tissue fibers in contrasting shades. Collagen may be differentially stained by any of the following techniques:
- Van Gieson's stain
- Masson's Trichrome stain
- Mallory's Aniline Blue stain
- Azocarmine stain
- Krajian's Aniline Blue stain
See also
- Zootomy
External links
- Template:EMedicineDictionary
- Template:Dorlands
- Overview at kumc.edu
- Template:UIUCHistologySubject
- Connective tissue atlas at uiowa.edu
Animals : Epithelium - Connective - Muscular - Nervous
Plants : Dermal - Vascular - Ground - Meristematic
Credits
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- Connective_tissue history
- Elastic_fiber history
- Reticular_fiber history
- Areolar_connective_tissue history
- Adipose_tissue history
- Dense_connective_tissue history
- Reticular_connective_tissue history
The history of this article since it was imported to New World Encyclopedia:
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[[Category:Life sciences}}
