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. The other three types are epithelial, muscle, and nervous tissue. Connective tissue is found in between other tissues everywhere in the body, including the central nervous system. The outer membranes covering the brain and spinal cord are the meninges composed of connective tissue.
All connective tissue apart from blood and lymph 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.
Structure
Connective tissue can be broadly subdivided into connective tissue proper, special connective tissue, and series of other, less classifiable types of connective tissues. 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.
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
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 bodywater 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 our 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:
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. Elastic fibers, made from elastin and fibrillin, also provide resistance to stretch forces. They are found in the walls of large blood vessels and in certain ligaments, particularly in the ligamenta flava.
In hematopoietic and lymphatic tissues, reticular fibers made by reticular cells provide the stromaâ€"or structural supportâ€"for the parenchymaâ€"or functional partâ€"of the organ.
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.
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. 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.
Clinical significance
It is estimated that 1 in 10 people have a connective tissue disorder.
There are several connective tissue neoplasms including sarcomas such as - hemangiopericytoma, and malignant peripheral nerve sheath tumor in the 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
Scurvy is caused by a vitamin C deficiency which is necessary for the synthesis of collagen.
Staining of connective tissue
For microscopic viewing, most of the connective tissue staining-techniques, color 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
See also
- Fascia
- Connective tissue in skeletal muscle
Notes and references
External links
- 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
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