Cartilage

Cartilage. The resistant yet elastic substance known as gristle or cartilage, plays an important part in animal structure. In the first place many bones are developed from cartilage. Cartilage which undergoes subsequent development into bone is called temporary cartilage. Secondly, cartilage is found as a permanent tissue occurring in the fully-developed body. Such permanent cartilage is of wide distribution; it covers the joint surfaces of bones, it serves as a connecting link between bone and bone, it forms the basis of such structures as the external ear and larynx, and constitutes the supporting framework of open tubes like the trachea and Eustachian tube. Cartilage when examined microscopically is found to be made up of cells imbedded in a supporting substance called the matrix. The permanent cartilage of the human body is divided into three varieties according to the characters of this matrix. In Hyaline cartilage, the first variety, the matrix is of uniform structure, and when examined in the fresh condition presents a ground-glass-like appearance. The costal and nasal cartilages, and the cartilage investing the ends of bones, and that found in parts of the larynx, and in the trachea and bronchi, are of the hyaline variety. In yellow elastic cartilage (found in the external ear, Eustachian tube, and epiglottis) the matrix is made up of fibres resembling the yellow elastic connective tissue fibres. In the third variety, white fibro-cartilage, the matrix is composed of fibres resembling white fibrous connective tissue fibres. This kind of cartilage occurs in the intervertebral discs, in sesamoid cartilage, and in the fibro-cartilages of the knee-joint. Cartilage is a non-vascular tissue, i.e. it contains no blood-vessels of its own, but derives nutrient materials from adjoining tissues. Its chief chemical constituent is a body called chondrin, closely allied to gelatin. Cartilage may be affected by inflammation, and is involved in many morbid processes.

The deposit of urate of soda in cartilage, which occurs in gouty persons, is a curious phenomenon, and cartilage undergoes important changes in rheumatoid arthritis (q.v.).