..... Click the link for more information. it is firm but flexible. The intercellular substance of bone bone, hard tissue that forms the skeleton of the body in vertebrate animals. In the very young, the skeleton is composed largely of cartilage and is therefore pliable, reducing the incidence of bone fracture and breakage in childhood.
..... Click the link for more information. , which is high in mineral salts, is rigid. Blood blood, fluid pumped by the heart that circulates throughout the body via the arteries, veins, and capillaries (see circulatory system ; heart ). An adult male of average size normally has about 6 quarts (5.6 liters) of blood.
..... Click the link for more information. and lymph have a fluid matrix. Three kinds of fibers generally form the supportive material in connective tissue proper. White, or collagenous, fibers vary in size and are composed of fine, parallel fibrils; reticular fibers are small, branching fibers that take on a meshlike pattern; yellow, or elastic, fibers are highly flexible and are capable of branching and anastomosing (or opening) directly into one another. Loose, or areolar, connective tissue is composed of all three of the above fibers; it supports most of the organs in the body and is widely distributed under the skin. The type of connective tissue that forms tendons tendon, tough cord composed of closely packed white fibers of connective tissue that serves to attach muscles to internal structures such as bones or other muscles.
..... Click the link for more information. , ligaments ligament (lĭg`əmənt)
..... Click the link for more information. , and fascia fascia (făsh`ēə), fibrous tissue network located between the skin and the underlying structure of muscle and bone.
..... Click the link for more information. is composed mainly of collagenous fibers. It is known as compact tissue. Reticular connective tissue forms the bone marrow and the framework for lymphoid tissue. Adipose, or fat, tissue serves as a cushion for various organs and as a fat reservoir. The colored area of the eye, or iris, is composed of pigmented connective tissue.
connective tissue
Tissue in the body that maintains the form of the body and its organs and provides cohesion and internal support, including bone, ligaments, tendons, cartilage, adipose tissue, and aponeuroses. Its major components are different kinds of cells and extracellular fibres and ground substance, which varies in consistency from thin gel to rigid structure. Various combinations of these elements make up the different kinds of connective tissue. Connective tissue diseases are either genetic disorders, attacking one of its elements (e.g., Marfan syndrome), or acquired inflammatory or immune-system diseases (e.g., rheumatoid arthritis, osteoarthritis, systemic lupus erythematosus, and rheumatic fever).
connective tissue
connective tissue [kə′nek·tiv ′tish·ü]
Connective tissue
One of the four primary tissues of the body. It differs from the other three tissues in that the extracellular components (fibers and intercellular substances) are abundant. It cannot be sharply delimited from the blood, whose cells may give rise to connective tissue cells, and whose plasma components continually interchange with and augment the ground substance of connective tissue. Bone and cartilage are special kinds of connective tissue.
The functions of connective tissues are varied. They are largely responsible for the cohesion of the body as an organism, of organs as functioning units, and of tissues as structural systems. The connective tissues are essential for the protection of the body both in the elaborate defense mechanisms against infection and in repair from chemical or physical injuries. Nutrition of nearly all cells of the body and the removal of their waste products are both mediated through the connective tissues. Connective tissues are important in the development and growth of many structures. Constituting the major environment of most cells, they are probably the major contributor to the homeostatic mechanisms of the body so far as salts and water are concerned. They act as the great storehouse for the body of salts and minerals, as well as of fat. The connective tissues determine in most cases the pigmentation of the body. Finally, the skeletal system (cartilage and bones) plus other kinds of connective tissue (tendons, ligaments, fasciae, and others) make motion possible.
The connective tissues consist of cells and extracellular or intercellular substance (see illustration). The cells include many varieties, of which the following are the most important: fibroblasts, macrophages (histiocytes), mast cells, plasma cells, melanocytes, and fat cells. Most of the cells of the connective tissue are developmentally related even in the adult; for example, fibroblasts may be developed from histiocytes or from undifferentiated mesenchymal cells.
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The extracellular components of connective tissues may be fibrillar or nonfibrillar. The fibrillar components are reticular fibers, collagenous fibers, and elastic fibers. The nonfibrillar component of connective tissues appears amorphous with the light microscope and is the matrix in which cells and fibers are embedded. It consists of two groups of substances: (1) those probably derived from secretory activity of connective tissue cells including mucoproteins, protein-polysaccharide complexes, tropocollagen, and antibodies; and (2) those probably derived from the blood plasma, including albumin, globulins, inorganic and organic anions and cations, and water. In addition, the ground substance contains metabolites derived from, or destined for, the blood.
All the manifold varieties of connective tissue may contain all the cells and fibers discussed above in addition to ground substance. They differ from each other in the relative occurrence of one or another cell type, in the relative proportions of cells and fibers, in the preponderance and arrangement of one or another fiber, and in the relative amount and chemical composition of ground substance. They are classified as:
1. Irregularly arranged connective tissue—which may be loose (subcutaneous connective tissue) or dense (dermis). The dominant fiber type is collagen.
2. Regularly arranged connective tissue—primarily collagenous—with the fibers arranged in certain patterns depending on whether they occur in tendons or as membranes (dura mater, capsules, fasciae, aponeuroses, or ligaments).
3. Mucous connective tissue—ground substance especially prominent (umbilical cord).
4. Elastic connective tissue—predominance of elastic fibers or bands (ligamentum nuchae) or lamellae (aorta).
5. Reticular connective tissue—fibers mostly reticular, moderately rich in ground substance, frequently numerous undifferentiated mesenchymal cells.
6. Adipose connective tissue—yellow or brown fat cells constituting chief cell type, reticular fibers most numerous.
7. Pigment tissue—melanocytes numerous.
8. Cartilage—cells exclusively of one type, derived from mesenchymal cells.
9. Bone—cells are predominantly osteocytes, but also include fibroblasts, mesenchymal cells, endothelial cells, and osteoclasts.
See Blood, Bone, Cartilage, Collagen, Histology, Ligament, Tendon
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