cartilage

cartilage

cartilage (kärˈtəlĭj), flexible semiopaque connective tissue without blood vessels or nerve cells. It forms part of the skeletal system in humans and in other vertebrates, and is also known as gristle. Temporary cartilage makes up the skeletal system of the fetus and the infant, forming a model for later replacement by bone as the body matures. Permanent cartilage remains throughout life, as in the external ear, nose, larynx, and windpipe (or trachea). Cartilage is also present at the joints, where it reduces friction and imparts flexibility. There are three major types of cartilage appearing in vertebrates. The most common is hyaline cartilage, which composes the pre-skeletal model and is found in adults at the joints, in the nose, and in several internal organs. Elastic cartilage is found in several parts of the ear and in the epiglottis, and is the most pliable type of cartilage. Fibrocartilage is found in the intervertebral disks, and is an extremely resilient tissue.

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Cartilage

A firm, resilient connective tissue of vertebrates and some invertebrates. Isolated pieces act to provide support and anchor muscles, or with bone to contribute its resilience and interstitial growth to skeletal functions. Cartilage comprises a firm extracellular matrix synthesized by large, ovoid cells (chondrocytes) located in holes called lacunae. The matrix elements are water bound by the high negative charge of extended proteoglycan (protein-polysaccharide) molecules, and a network of fine collagen fibrils. The elements furnish mechanical stability, give, and tensile strength, but allow the diffusion of nutrients and waste to keep the cells alive. See Bone, Collagen

Cartilage is modified in several ways. In elastic cartilage, elastic fibers in the matrix increase resilience, as in cartilages supporting the Eustachian tube, mammalian external ear, and parts of the larynx. Where cartilage joins bones tightly at certain joints with limited mobility, for example, at the pubic symphysis and between vertebrae, the matrix of fibrocartilage contains prominent collagen fibers and has less proteoglycan than the typical hyaline variety. Hyaline cartilage, named for its glassy translucence, is the major support in the airway; and throughout the embryo, pieces of it develop as a precursor to the bony skeleton, except in the face and upper skull. See Ear (vertebrate), Larynx

The primitive cartilaginous skeleton undergoes another modification, by locally calcifying its matrix. At sites of calcification, invading cells destroy the cartilage and mostly replace it by bone, leaving permanent hyaline cartilage only at the joint or articular surfaces, in some ribs, and, until maturity, at growth plates set back from the joints and perpendicular to the long axis of limb bones. The precarious physiological balance between chondrocytes and matrix materials in the heavily loaded articular cartilage breaks down in old age or in inflamed joints. See Connective tissue, Joint (anatomy)

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Cartilage

 

a connective tissue that performs a mechanical (support) function; it is found in all vertebrates, including man, and in some invertebrates, for example, cephalopod mollusks. In cartilaginous fish and cyclostomes the entire skeleton consists of cartilage; in other vertebrates the cartilaginous skeleton occurs only in embryos. In adult mammals, including man, cartilage is preserved in the joint surfaces of bones, in the thoracic ends of the ribs, in the tracheal and bronchial walls, and in the auricle of the external ear. It also is present in the nasal wall, larynx, epiglottis, and eyelids.

Cartilage is formed from the mesenchyma. It is constructed from cells known as chondrocytes and by the intercellular substance elaborated by the cells. The substance consists of collagenous fibers (chondrin) and ground substance. Three types of cartilage—hyaline, elastic, and fibrous—are distinguished according to the characteristics of the intercellular substance. Hyaline cartilage is the most common. Its large quantity of ground substance and the similar values of the refractive index of ground substance and fibrous component determine its external features: homogeneity and glassiness. Elastic cartilage differs from hyaline cartilage in that it has elastic fibers. Fibrous cartilage has bundles of collagenous fibers that can be easily observed under a light microscope.

Cartilage is covered with a membrane of connective tissue, perichondrium, which contains cells capable of changing into chondrocytes. Cartilage grows mainly by such transformation and by the division of cartilage cells (intercalary growth). Cartilage does not have blood vessels; nutrients penetrate it by diffusion.

N. G. KHRUSHCHOV

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

cartilage

[′kärd·əl·ij]

(histology)

A specialized connective tissue which is bluish, translucent, and hard but yielding.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

cartilage

a tough elastic tissue composing most of the embryonic skeleton of vertebrates. In the adults of higher vertebrates it is mostly converted into bone, remaining only on the articulating ends of bones, in the thorax, trachea, nose, and ears

Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005