Connective Tissue - Biology Encyclopedia - cells, body, function, human, animal, system, organs, blood, types
Connective Tissue - Biology Encyclopedia
Connective Tissue
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The human body is composed of just four basic kinds of tissue: nervous,       muscular, epithelial, and connective tissue. Connective tissue is the most       abundant, widely distributed, and varied type. It includes fibrous       tissues, fat, cartilage, bone, bone marrow, and blood. As the name       implies, connective tissues often bind other organs together, hold organs       in place, cushion them, and fill space.
Connective tissue is distinguished from the other types in that the       extracellular material (matrix) usually occupies more space than the cells       do, and the cells are relatively far apart. Fat is an exception, having       cells in close contact with each other; but with large, nonliving, intracellular lipid droplets, fat contains much more nonliving material than living material.
The matrix of connective tissue typically consists of fibers and a featureless       ground substance. The most abundant fiber in connective tissues is a tough protein called collagen. Tendons, ligaments, and the white stringy tissue       (fascia) seen in some cuts of meat are composed almost entirely of       collagen, as is leather, which consists of the connective tissue layer       (dermis) of animal skins. Collagen also strengthens bone and cartilage.       Elastic and reticular fibers are less abundant connective tissue proteins with a more limited       distribution.
The ground substance may be liquid, as in blood; gelatinous, as in areolar tissue; rubbery, as in cartilage; or calcified and stony, as in bone. It       consists mainly of water and small dissolved ions and organic molecules, but the gelatinous to rubbery consistency of some tissues       results from enormous protein-carbohydrate complexes in the ground       substance. The hard consistency of bone results mainly from calcium       phosphate salts in the ground substance.
Some of the cells of connective tissue are fibroblasts (which produce collagen fibers and are the only cell type in tendons and       ligaments); adipocytes (fat cells); leukocytes (white blood cells, also       found outside the
Connective tissue type and characteristics
Functions
Locations
Areolar (loose) connective tissue. Loose array of random fibers with a wide variety of cell types
Nourishes and cushions epithelia, provides arena for immune defense             against infection, binds organs together, allows passage for nerves             and blood vessels through other tissues
Under all epithelia; outer coverings of blood vessels, nerves,             esophagus, and other organs; fascia between muscles; pleural and             pericardial sacs
Adipose tissue (fat). Large fat-filled adipocytes and scanty extracellular matrix.
Stores energy, conserves body heat, cushions and protects many             organs, fills space, shapes body
Beneath skin; around kidneys, heart, and eyes; breast; abdominal             membranes (mesenteries)
Dense irregular connective tissue. Densely spaced, randomly arranged fibers and fibroblasts.
Toughness; protects organs from injury; provides protective             capsules around many organs
Dermis of skin; capsules around liver, spleen, and other organs;             fibrous sheath around bones
Dense regular connective tissue. Densely spaced, parallel collagen fibers and fibroblasts.
Binds bones together and attaches muscle to bone; transfers force             from muscle to bone
Tendons and ligaments
Cartilage (gristle). Widely spaced cells in small cavities (lacunae); rubbery matrix.
Eases joint movements; resists compression at joints; holds airway             open; shapes outer ear; moves vocal cords; forerunner of fetal             skeleton; growth zone of children's bones
External ear, larynx, rings around trachea, joint surfaces and             growth zones of bones, between ribs and sternum, intervertebral             discs
Bone (osseous tissue). Widely spaced cells in lacunae; much of matrix in concentric             onionlike layers; hard mineralized matrix.
Physically supports body, provides movement, encloses and protects             soft organs, stores and releases calcium and phosphorus
  Skeleton
Blood. Erythrocytes, leukocytes, and platelets in
Transports nutrients, gases, wastes, hormones,
Circulates in cardiovascular system
bloodstream in fibrous connective tissues); macrophages (large phagocytic       cells descended from certain leukocytes); erythrocytes (red blood cells,       found only in the blood and bone marrow); chondrocytes (cartilage cells);       and osteocytes (bone cells).
The table above lists representative locations and functions of the major       types of connective tissue. Further details on connective tissue can be       found in textbooks of histology and human anatomy.
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