The body’s packing material has a 1830 name
Connective tissue fills the gaps between other tissues, usually mixing collagen and elastic fibers, ground substance, and cells. It is one of four animal primary tissues beside epithelium, muscle, and nerve, mostly born from mesenchyme of the mesoderm. Johannes Peter Müller coined Bindegewebe in 1830.
Broad classes split into connective tissue proper—loose or dense—and special forms such as supportive bone and cartilage or fluid blood and lymph. Fibroblasts, adipocytes, macrophages and kin populate the matrix. The three meninges wrapping brain and cord are connective sheets; blood and lymph count as fiber-free fluid connective tissues bathed in body water.
Eighteenth-century anatomists already treated the stuff as distinct; Müller’s German label simply stuck. Developmentally it is the mesoderm’s packing foam—cells that secrete extracellular scaffolding instead of forming tight linings or contractile fibers.
Loose and dense types differ in their balance of ground substance and fibre: loose tissue, which includes reticular tissue and fat, is mostly ground substance, while dense tissue is packed with fibres. Dense regular tissue in tendons and ligaments lines its collagen up in parallel, so it resists pulling in one direction, whereas dense irregular tissue weaves fibres to withstand force from many sides. Bone and cartilage form the supportive branch, and blood and lymph are sometimes described as liquid fascia. The matrix holds three fibre types, collagen, elastic and reticular, set in a clear, viscous ground substance rich in glycosaminoglycans and proteoglycans. Type I collagen alone accounts for about a quarter of all protein in a mammal's body. Fat cushions the body mechanically, loose and dense irregular tissue give oxygen, nutrients and wastes a medium to diffuse between capillaries and cells, and the fresh vascular tissue that fills a healing wound is called granulation tissue. Synovial membranes lining the joints are connective tissue too, while mucous and serous membranes are epithelium resting on a loose connective layer.
Source: Connective tissue
