Connective tissue (CT) is one of the four types of biological tissue that supports, connects or separates different types of tissues and organs in the body. It develops from the mesoderm. The other three types are epithelial, muscle, and nervous tissue. 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.
All connective tissue consists of three main components: fibers (elastic and collagenous fibers), ground substance and cells. (Not all authorities include blood or lymph as connective tissue.) Blood and lymph lack the fiber component. All are immersed in the body water.
Connective tissue can be broadly subdivided into connective tissue proper, and special connective tissue. Connective tissue proper consists of loose connective tissue and dense connective tissue (which is further subdivided into dense regular and dense irregular connective tissues.) Special connective tissue consists of reticular connective tissue, adipose tissue, cartilage, bone, and blood. Other kinds of connective tissues include fibrous, elastic, and lymphoid connective tissues. New vascularised connective tissue that forms in the process of wound healing is termed granulation tissue. 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.
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. 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.
Types of fibers:
|Collagenous fibers||Bind bones and other tissues to each other||Alpha polypeptide chains||tendon, ligament, skin, cornea, cartilage, bone, blood vessels, gut, and intervertebral disc.|
|Elastic fibers||Allow organs like arteries and lungs to recoil||Elastic microfibril and elastin||extracellular matrix|
|Reticular fibers||Form a scaffolding for other cells||Type III collagen||liver, bone marrow, and lymphatic organs|
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.:161 Elastic fibers, made from elastin and fibrillin, also provide resistance to stretch forces.:171 They are found in the walls of large blood vessels and in certain ligaments, particularly in the ligamenta flava.:173
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. Another type of relatively undifferentiated connective tissue is mucous connective tissue, found inside the umbilical cord.:160
Various type 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.: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.:161
- 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
- Van Gieson's stain
- Masson's trichrome stain
- Mallory's trichrome stain
- Aniline blue stain
- Reticulin stain
Notes and references
- "Connective Tissue Study Guide". 2 January 2013. Retrieved 26 October 2014.
- Dorland, W. A. Newman (2012). Dorland's Illustrated Medical Dictionary (32nd ed.). Elsevier. p. 1931. ISBN 978-1-4160-6257-8.
- Shostak, Stanley. "Connective Tissues". Retrieved 9 December 2012.
- Potter, Hugh. "The Connective Tissues". Retrieved 9 December 2012.
- Caceci, Thomas. "Connective Tisues". Retrieved 9 December 2012.
- King, David. "Histology Intro". Retrieved 9 December 2012.
- "Granulation Tissue Definition". Memidex. Retrieved 7 May 2016.
- Di Lullo; G. A. (2002). "Mapping the Ligand-binding Sites and Disease-associated Mutations on the Most Abundant Protein in the Human, Type I Collagen". Journal of Biological Chemistry. 277 (6): 4223–31. doi:10.1074/jbc.M110709200. PMID 11704682.
- Xu, H.; et al. (2008). "Monitoring Tissue Engineering Using Magnetic Resonance Imaging". Journal of Bioscience and Bioengineering. 106 (6): 515–527. doi:10.1263/jbb.106.515. PMID 19134545.
- Laclaustra, M.; et al. (2007). "Metabolic syndrome pathophysiology: The role of adiposetissue". Nutrition, Metabolism and Cardiovascular Diseases. 17 (2): 125–139. doi:10.1016/j.numecd.2006.10.005. PMID 17270403.
- Ross M, Pawlina W (2011). Histology: A Text and Atlas (6th ed.). Lippincott Williams & Wilkins. pp. 158–197. ISBN 978-0-7817-7200-6.
- Young B, Woodford P, O'Dowd G (2013). Wheater's Functional Histology: A Text and Colour Atlas (6th ed.). Elsevier. p. 65. ISBN 978-0702047473.
- EDS Awareness.com (2012). "EDS Awareness Ehlers-Danlos Syndrome." Acquired by (EDSawareness.com)
|Wikimedia Commons has media related to Connective tissues.|
- Encyclopaedia 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