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SKELETAL TISSUE

Hard internal framework of body, originated from mesoderm and giving support to various organs and body is called endoskeleton. It is made up of two types of tissues: one is cartilage and other is bone.

CARTILAGE

Other names for cartilage are chondros and gristle. Cartilage is a connective tissue composed of cells (chondrocyte) and fibres (collagen or yellow elastic) embedded in a firm gel like matrix which is rich in mucopolysaccharide. It is much more elastic than bone.

General characters:

(1) Intercellular matrix is called chondrin which is composed of collagen fibres and amorphous ground substance.

(2) Ground substance is composed of chondroitin sulphate and a mucoprotein.

(3) Cartilage has no blood vessel or lymphatics. The nutrition of cells diffuses through the matrix.

(4) It has no nerves, therefore it is Msensitive.

(5) The chondrocytes lies in lacunae.

Generally single chondrocyte in a lacunae is present.

(6) Multiplication of chondrocyte causes internal or interstitial growth while secretion of chondroitin around them causes appositional or perichondrial growth.

(7) All except a few cartilages have dense fibrous sheath surrounding them called perichondrium. Articular cartilaqes have no perichondrium.

(8) When cartilage calcifies, the chondrocyte dies and cartilage is replaced by the bone.

Types of cartilage: They are of four basic types:

(1) Hyaline cartilage [haulos - transparent stone]: It is prototype cartilage. It is bluish and transparent due to fine collagen fibres. It forms cushions or pads upon articular surfaces at the joints of long bones. Fibres have three dimensional orientation. This cartilage has tendency to calcify after 40 years of age. All cartilage bones are preformed hyaline cartilage. e.g. embryonic cartilage, articular cartilage, costal cartilage, bronchial cartilage, cartilage of nose and larynx.

(2) Fibro cartilage: It is white and opaque due to abundance of dense collagen fibres. Wherever fibrous tissue is subjected to great pressure, it is transformed into fibro cartilage. It is tough, strong and resilient. Perichondrium is absent. e.g. inter-vertebral disc, mansci and labra etc.

(3) Elastic cartilage: It is composed of numerous yellow elastic fibres. It is more pliable. Perichondrium is present. e.g. epiglottiS, cartilage of ear pinnae etc.

(4) Calcified cartilage: They are originally hyaline cartilage but in later course, they get calcified. Calcification reduces elasticity and makes it more rigid. e.g. suprascapula of mammalian pectoral girdle.