Physiology Topics
Connective tissue is the most abundant and widely distributed tissue in the body. It consists of cells and a matrix. The matrix consists of fibers and a ground substance, and it may be fluid, semifluid, gelatinous, fibrous or calcified. It is highly vascular and has a nerve supply, except in cartilage. The types of cells present depend on the type of tissue and include fibroblasts, macrophages, plasma cells, mast cells, adipocytes and white blood cells. Fibroblasts are present in all conective tissue and usually are the most numerous conective tissue cells. They migrate through the connective tissue, secreting the fibers and ground substance of the matrix.
Ground substance is an assortment of large molecules, many of which are complex combinations of polysaccharides and proteins: hyaluronic acid, chondroitin sulfate, dermatase sulfate and keratane sulfate. Fibers in the matrix strengthen and support connective tissue and include collagen, elastic fibers and reticular fibers.
In loose connective tissue the fibers are loosely woven and many cells are present. Loose conective tissue may be areolar, adipose or reticular. Areolar connective tissue is one of the most widely distributed throughtout the body and, combined with adipose tissue, forms the subcutaneous layer (attaches the skin to underlying tissues and organs). Adipose tissue is a loose connective tissue with specialized cells for the storage of triacylglycerols called adipocytes. Reticular connective tissue consist of fine interlacing reticular fibers and reticular cells (cells that are connected to each other forming a network). Reticular connective tissue forms the supporting framework of some organs.
Dense connective tissue contains more numerous, thicker and denser fibers but considerably fewer cells than loose connective tissue. In dense regular connective tissue bundles of collagen fibers are regularly arranged in parallel patterns that confer great strength, and its found in tendons and ligaments. Dense irregular connective tissue contains collagen fibers irregularly arranged and is found where pulling forces are excepted in various directions. It occurs usually in sheets such as the dermis. Freely branching elastic fibers predominate in elastic connective tissue, which is quite strong and can recoil to its original shape after being stretched. It is found in lung tissue and arteries.
Cartilage consists of a dense network of collagen fibers and elastic fibers firmly embedded in chondroitin sulfate. Three kinds of cartilage are recognized: hyaline, fibrocartilage and elastic. Hyaline cartilage is the most abundant and provides flexibility and support (trachea), reduces friction (joints) and absorbs shock. Fibrocartilage is the strongest, found in tendons and backbone disks. Elastic cartilage provides strength and elasticity and maintains the shape of structures such as the external ear.
Bones are organs composed of several different connective tissues, including bone tissue. Blood is a connective tissue with a liquid matrix called plasma. Lymph is a connective tissue that consists of clear fluid similar to plasma but with much less protein.
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