Cartilage is characterized by an extracellular matrix enriched with glycosaminoglycans and proteoglycans, macromolecules that interact with collagen and elastic fibers.
FUNCTION OF CARTILAGE:
1:firm consistency of the extracellular matrix allows the tissue to bear mechanical stresses without permanent distortion.
2:support soft tissues.
3:Because it is smooth surfaced and resilient, cartilage is a shock-absorbing and sliding area for joints and facilitates bone movements.
4:Cartilage is also essential for the development and growth of long bones both before and after birth
As a consequence of various functional requirements, THREE forms of cartilage have evolved, depending on variations in matrix composition.
- HYALINE CARTILAGE
- ELASTIC CARTILAGE
In all three forms, cartilage is AVASCULAR and is nourished by the diffusion of nutrients from capillaries in adjacent connective tissue (perichondrium) or by synovial fluid from joint cavities. In some instances, blood vessels traverse cartilage to nourish other tissues, but these vessels do not supply nutrients to the cartilage. As might be expected of cells in an avascular tissue, chondrocytes exhibit low metabolic activity. Cartilage has no lymphatic vessels or nerves.
- Hyaline cartilage is the most common and best studied of the three forms. Fresh hyaline cartilage is BLUISH-WHITE and TRANSLUCENT. In the embryo, it serves as a temporary skeleton until it is gradually replaced by bone.
- In adult , hyaline cartilage is located in the
- articular surfaces of the movable joints,
- in the walls of larger respiratory passages (nose, larynx, trachea, bronchi),
- in the ventral ends of ribs, where they articulate with the sternum,
- and in the epiphyseal plate, where it is responsible for the longitudinal growth of bone .
- Hyaline cartilage contains primarily TYPE II COLLAGEN .
Elastic cartilage is found in the auricle of the ear, the walls of the external auditory canals, the auditory (eustachian) tubes, the epiglottis, and the cuneiform cartilage in the larynx.
Elastic cartilage is essentially identical to hyaline cartilage except that it contains an abundant network of fine elastic fibers in addition to collagen type II fibrils. Fresh elastic cartilage has a yellowish color owing to the presence of elastin in the elastic fibers. .
- Fibrocartilage is a tissue intermediate between dense connective tissue and hyaline cartilage. It is found in intervertebral disks, in attachments of certain ligaments to the cartilaginous surface of bones, and in the symphysis pubis. Fibrocartilage is always associated with dense connective tissue.
- it is rich in Collagen type I.
As we know connective tissue contain
In Cartilage also the arrangement is same .
Photomicrograph of HYALINE CARTILAGE. Chondrocytes are located in matrix lacunae, and most belong to isogenous groups. The upper and lower parts of the figure show the perichondrium stained pink. Note the gradual differentiation of cells from the perichondrium into chondrocytes.
Photo-micrograph of elastic cartilage, stained for elastic fibers. Cells are not stained.
Photomicrograph of FIBROCARTILAGE. Note the rows of chondrocytes separated by collagen fibers. Fibrocartilage is frequently found in the insertion of tendons on the epiphyseal hyaline cartilage.
Except in the articular cartilage of joints, all hyaline cartilage is covered by a layer of dense connective tissue, the perichondrium, which is essential for the growth and maintenance of cartilage. It is rich in COLLAGEN TYPE I fibers and contains numerous FIBROBLASTS. Although cells in the INNER LAYER of the perichondrium resemble fibroblasts, they are CHONDROBLASTS and easily differentiate into chondrocytes.