Cartilage is made up of semi-hard and elastic material called chondrin. Its matrix is composed of proteins called chondromucoid and chondralbunoid. Chondromucoid and chondralbuinoid together are called chondrin. It contains collagen, elastin, proteoglycan, chondrocytes etc. Cartilage cells are called chondrocytes. Clusters of chondrocytes are called lacunae. It is covered by perichondrium.
Where is the cartilage or orange bone: Nose, ear, head of humerus and femur, joints, trachea, periosteum, epigøtis, intervertebral disc etc.
Characteristics of cartilage or cartilage
1. Cartilage has no blood vessels or lymph.
2. It has no nerve conduction i.e. no sensation.
3. It takes longer for wounds to heal.
4. The perichondrium is covered by the mantle.
5. It contains chondroitin instead of calcium.
6. Calcium deposits in the cartilage cause the cells to die.
7. Cartilage gradually turns into bone.
8. Contains so much lubricin that acts as a lubricator.
Classification of cartilage
Cartilage is divided into 4 parts based on structure. These are-
1. Clear or Hyaline Cartilage: This cartilage matrix is transparent, firm, flexible, homogenous, bluish and elastic. It is covered by the perichondrium. It contains no fibers. It contains cavities called lacunae. Inside the lacunae are chondrocytes or chondroblasts. This cartilage is present in the nose, trachea, larynx, larynx, larynx of mammals, bones and embryos of vertebrates.
2. Biliary Cartilage: The matrix of this cartilage is opaque, elastic and light yellow in color. Yellow colored fibers are scattered in it. The fibers are branched and scattered. It is covered by the perichondrium. It contains cavities called lacunae. Inside the lacunae are chondrocytes or chondroblasts. It is present in external ear, pinna, tongue, eustachian tube, epiglottis, larynx, lymph nodes etc.
3. Whitish Cartilage: The matrix of this cartilage is opaque and colorless. It has white fibers. The fibers are unbranched and arranged parallel and in clusters. It is covered by the perichondrium. It contains cavities called lacunae. Inside the lacunae are chondrocytes or chondroblasts. It lies between the joints and vertebrae.
4. Calcified or calcareous cartilage: This cartilage matrix contains a large amount of calcium carbonate. Its matrix is rock solid. It resides in the head of the humerus and femur.
Function or importance of cartilage
1. Cartilage resists the tension and stress of various organs.
2. Gives shape to various organs.
3. Joints help join two or more bones together.
4. Protects bones from frictional injuries.
5. Helps tendons and ligaments attach to bones.
6. A glycoprotein called lubricin in cartilage acts as a lubricant.
7. Forms the embryonic skeleton of vertebrates and the endoskeleton of fishes such as chondrichthys.