Connective tissue facts for kids

Section of epididymis. Connective tissue (blue) is seen supporting the epithelium (purple)

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 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.

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

Structure

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

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:

Tissue	Purpose	Components	Location
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

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.

Clinical significance

Main pages: Connective tissue disease and Connective tissue neoplasm

It is estimated that 1 in 10 people have a connective tissue disorder. Diseases of connective tissue include:

• 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