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Connective tissue
Section of epididymis. Connective tissue (blue) is seen supporting the epithelium (purple)
Identifiers
MeSH	D003238
FMA	9640
Anatomical terminology [edit on Wikidata]

Connective tissue (CT) is one of the four basic types of animal tissue, along with epithelial tissue, muscle tissue, and nervous tissue. It develops from the mesoderm. Connective tissue is found in between other tissues everywhere in the body, including the nervous system. In the central nervous system, the three outer membranes (the meninges) that envelop the brain and spinal cord are composed of connective tissue. They support and protect the body.
All connective tissue consists of three main components: fibers (elastic and collagenous fibers),^[1]ground substance and cells. Not all authorities include blood^[2] or lymph as connective tissue because they lack the fiber component. All are immersed in the body water.

The cells of connective tissue include fibroblasts, adipocytes, macrophages, mast cells and leucocytes.

The term "connective tissue" (in German, Bindegewebe) was introduced in 1830 by Johannes Peter Müller. The tissue was already recognized as a distinct class in the 18th century.^[3][4]

Types

Connective tissue can be broadly subdivided into connective tissue proper, and special connective tissue.^[5][6] Connective tissue proper consists of loose connective tissue and dense connective tissue (which is further subdivided into dense regular and dense irregular connective tissues.)^[7] Loose and dense connective tissue are distinguished by the ratio of ground substance to fibrous tissue. Loose connective tissue has much more ground substance and a relative lack of fibrous tissue, while the reverse is true of dense connective tissue. Dense regular connective tissue, found in structures such as tendons and ligaments, is characterized by collagen fibers arranged in an orderly parallel fashion, giving it tensile strength in one direction. Dense irregular connective tissue provides strength in multiple directions by its dense bundles of fibers arranged in all directions.

Special connective tissue consists of reticular connective tissue, adipose tissue, cartilage, bone, and blood.^[8] Other kinds of connective tissues include fibrous, elastic, and lymphoid connective tissues.^[9] Fibroareolar tissue is a mix of fibrous and areolar tissue.^[10] New vascularised connective tissue that forms in the process of wound healing is termed granulation tissue.^[11]Fibroblasts are the cells responsible for the production of some CT.

Type I collagen is present in many forms of connective tissue, and makes up about 25% of the total protein content of the mammalian body.^[12]

Characteristics

Characteristics of CT:

• Cells are spread through an extracellular fluid.


• Ground substance - A clear, colorless, and viscous fluid containing glycosaminoglycans and proteoglycans to fix the body water and the collagen fibers in the intercellular spaces. Ground substance slows the spread of pathogens.


• 
  Fibers. Not all types of CT are fibrous. Examples of non-fibrous CT include adipose tissue and blood. Adipose tissue gives "mechanical cushioning" to the body, among other functions.^[13][14] Although there is no dense collagen network in adipose tissue, groups of adipose cells are kept together by collagen fibers and collagen sheets in order to keep fat tissue under compression in place (for example, the sole of the foot). The matrix of blood is plasma.


• Both the ground substance and proteins (fibers) create the matrix for CT. Connective tissues are derived from the mesenchyme.

Function

Connective tissue has a wide variety of functions that depend on the types of cells and the different classes of fibers involved. Loose and dense irregular connective tissue, formed mainly by fibroblasts and collagen fibers, have an important role in providing a medium for oxygen and nutrients to diffuse from capillaries to cells, and carbon dioxide and waste substances to diffuse from cells back into circulation. They also allow organs to resist stretching and tearing forces. Dense regular connective tissue, which forms organized structures, is a major functional component of tendons, ligaments and aponeuroses, and is also found in highly specialized organs such as the cornea.^[15]:161Elastic fibers, made from elastin and fibrillin, also provide resistance to stretch forces.^[15]:171 They are found in the walls of large blood vessels and in certain ligaments, particularly in the ligamenta flava.^[15]:173

In hematopoietic and lymphatic tissues, reticular fibers made by reticular cells provide the stroma—or structural support—for the parenchyma—or functional part—of the organ.^[15]:171

Mesenchyme is a type of connective tissue found in developing organs of embryos that is capable of differentiation into all types of mature connective tissue.^[16] Another type of relatively undifferentiated connective tissue is mucous connective tissue, found inside the umbilical cord.^[15]:160

Various types of specialized tissues and cells are classified under the spectrum of connective tissue, and are as diverse as brown and white adipose tissue, blood, cartilage and bone.^[15]:158 Cells of the immune system, such as macrophages, mast cells, plasma cells and eosinophils are found scattered in loose connective tissue, providing the ground for starting inflammatory and immune responses upon the detection of antigens.^[15]:161

Clinical significance

There are many types of connective tissue disorders, such as:

• 
  Connective tissue neoplasms including sarcomas such as hemangiopericytoma and malignant peripheral nerve sheath tumor in nervous tissue.


• 
  Congenital diseases include Marfan syndrome and Ehlers-Danlos Syndrome.


• 
  Myxomatous degeneration – a pathological weakening of connective tissue.


• 
  Mixed connective tissue disease – a disease of the autoimmune system, also undifferentiated connective tissue disease.


• 
  Systemic lupus erythematosus (SLE) – a major autoimmune disease of connective tissue


• 
  Scurvy, caused by a deficiency of vitamin C which is necessary for the synthesis of collagen.

Staining of connective tissue

For microscopic viewing, most of the connective tissue staining-techniques, colour tissue fibers in contrasting shades. Collagen may be differentially stained by any of the following:

• 
  Van Gieson's stain


• Masson's trichrome stain


• Mallory's trichrome stain


• 
  Aniline blue stain


• Eosin


• Reticulin stain

See also

• Endometrium


• Fascia


• Parametrium

Notes and references

External links

Wikimedia Commons has media related to Connective tissues.

• Encyclopædia Britannica, Connective Tissue


• Overview at kumc.edu


• 
  UIUC Histology Subject 230
  


• Connective tissue atlas at uiowa.edu


• 
  Questions and Answers about Heritable Disorders of Connective Tissue - US National Institute of Arthritis and Musculoskeletal and Skin Diseases


• Connective Tissue Photomicrographs