Connective tissues, as the name implies, support and connect different tissues and organs of the body. They are widely distributed in every part of the body. They originate from the mesoderm (the middle germinal layer of the embryo).
Connective tissue is made up of a few cells present in the intercellular framework of protein fibres secreted by the cells, known as collagen or elastin. The cells also secrete a thin gel of polysaccharides, which together with fibres make matrix or ground substance.
Connective tissues contain three types of fibres: collagen, elastic and reticular
Collagen fibres are the most widespread and made up of fibrous protein, collagen. Collagen fibres are flexible and have high tensile strength (comparable to steel).
Elastic fibres form a network and can be stretched like a rubber band. They are made up of protein elastin. They retain their original shape and size once the force is removed.
Reticulate fibres consist of collagen and glycoproteins. They are thin and form a delicate network. They join connective tissues to neighbouring tissues.
There are various kinds of cells present in different types of connective tissues. They secrete different types of fibres and matrices. Fibroblasts or adipose cells are stationary and macrophages, mast cells, monocytes, lymphocytes are migrating cells.
Fibroblasts are found in developing tissues and play an important part in wound-healing. They are spindle-shaped and present between collagen fibres. They secrete tropocollagen and other substances found in the matrix.
Macrophages are also known as scavenger cells. They wander through connective tissues, clean up debris and remove bacteria and other antigens by phagocytosis.
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