cartilage

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cartilage

(kär`təlĭj), flexible semiopaque connective tissueconnective tissue,
supportive tissue widely distributed in the body, characterized by large amounts of intercellular substance and relatively few cells. The intercellular material, or matrix, is produced by the cells and gives the tissue its particular character.
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 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 bonebone,
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.
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 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 jointsjoint,
in anatomy, juncture between two bones. Some joints are immovable, e.g., those that connect the bones of the skull, which are separated merely by short, tough fibers of cartilage. Movable joints are found for the most part in the limbs.
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, 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.

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)

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

cartilage

[′kärd·əl·ij]
(histology)
A specialized connective tissue which is bluish, translucent, and hard but yielding.

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