Connective tissue

Connective tissue is biological tissue that is found in between other tissues in the body. Most types of connective tissue consists of three main components: elastic and collagen fibers, ground substance, and cells.

It is one of the four primary types of animal tissue along with epithelial tissue, muscle tissue, and nervous tissue. It develops mostly from the mesenchyme, derived from the mesoderm, the middle embryonic germ layer.

The three meninges, membranes that envelop the brain and spinal cord, are composed of connective tissue. Blood and lymph are classed as specialized fluid connective tissues that do not contain fiber. All are immersed in the body water. The cells of connective tissue include fibroblasts, adipocytes, macrophages, mast cells and leukocytes.

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.

Connective tissue can be broadly classified into connective tissue proper (including loose connective tissue and dense connective tissue) and special connective tissue (including supportive connective tissue and fluid connective tissue).

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.

Loose connective tissue includes reticular connective tissue, and adipose tissue.

Dense connective tissue is subdivided into dense regular and dense irregular 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.^{[citation needed]}