Connective tissue

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 (reticular, collagenous, elastic fibers) and nonfibrillar components (the ground substance in which the cells and fibers are embedded).

The various types of connective tissue differ in terms the relative proportions of these various elements, such as how many fibers relative to cells, the proportions and numbers of the different cell types in a given volume, the proportions, numbers and arrangements of the different fibers, the composiiton of the ground substance and so forth.

Classification

Connective tissue proper

Connective tissue proper

• Areolar (or loose) connective tissue holds organs and epithelia in place, and has a variety of proteinaceous fibres, including collagen and elastin. It is also important in inflammation.
• Adipose tissue contains adipocytes, used for cushioning, thermal insulation, lubrication (primarily in the pericardium) and energy storage. [fat]
• Dense connective tissue (or, less commonly, fibrous connective tissue) forms ligaments and tendons. Its densely packed collagen fibres have great tensile strength.
• Reticular connective tissue is a network of reticular fibres (fine collagen, type III) that form a soft skeleton to support the lymphoid organs (lymph nodes, bone marrow, and spleen.)

Specialized connective tissues

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

Fiber types

Fiber types as follows:

• collagenous fibers
• elastic fibers
• reticular fibers

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

Biological tissue

Animals : Epithelium - Connective - Muscular - Nervous

Plants : Dermal - Vascular - Ground - Meristematic

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