Cartilage Tissue PDF

Cartilaginous tissue • Specialized connective tissue • Firm but flexible matrix, resistant to mechanical forces • Its main cells are chondrocytes, which occupy small cavities in the matrix called lacunae • It does not have blood vessels (avascular) or nerves. The cells are nourished by diff...

Cartilaginous tissue • Specialized connective tissue • Firm but flexible matrix, resistant to mechanical forces • Its main cells are chondrocytes, which occupy small cavities in the matrix called lacunae • It does not have blood vessels (avascular) or nerves. The cells are nourished by diffusion through the matrix. Only in very large pieces of cartilage there will be channels for vessels and nerves to circulate to the deeper areas of the cartilage • The matrix is made of GAG and proteoglycans, such as in the connective tissue, but its fibers are collagen type II and, in some cases, also elastic fibers • Surrounding almost all the cartilage, there is a sheath of connective tissue called perichondrium. It consists of two layers: the outer layer is fibrous (collagen type I, fibroblasts, vascularized) and the inner layer is cellular (with chondroblasts that secrete matrix) Lacunae Chondrocytes Extracellular matrix •Ground substance: proteoglycans • GAG: Chondroitinsulphate, keratansulphate •Collagen type II and elastic fibers •Adhesion glycoproteins: chondronectin Formation of cartilage During the embryonic development, in the place where the cartilage will appear, the mesenchymal stem cells retract their extensions, round off and group together to form the chondrification centers. Under the influence of certain stimuli, these cells differentiate into chondroblasts that begin to secrete matrix. When they are completely surrounded by matrix, they become chondrocytes. The chondrocytes still retain the ability to divide and can form groups of several cells within the same lacuna, which are called an isogenic group. As the cells of the isogenic group secrete matrix, they will separate forming individual lacunae and thus grow the cartilage from within. This is called interstitial cartilage growth. Interstitial cartilage growth Mesenchymal stem cells Chondrification centers Apositional cartilage growth The mesenchymal cells that surround the cartilage differentiate into fibroblasts that will originate the connective tissue that forms the perichondrium. The outer fibrous layer of the perichondrium is irregular dense connective tissue. The inner chondrogenic layer contains chondroblasts that can add new layers of cartilage in its periphery, making it grow in thickness. This is what is called apositional growth. Interstitial growth Apositional growth Cartilage types Types of cartilage based on differences in fiber composition: • Hyaline cartilage - type II collagen • Elastic cartilage - elastic fibers and type II collagen • Fibrocartilage - type I and II collagen Hyaline cartilage • It is the most abundant • Flexible, semi-translucent, bluish gray color • Uniform and very resistant to tensile and compression forces • Precursor of long bones during embryonic development • Nasal cartilages, laryngeal, tracheobronchial, costal and articular surfaces Chondroblasts Chondrocytes Elastic cartilage • Same composition as the hyaline cartilage, but also contains abundant elastic fibers in its matrix • More flexible than hyaline cartilage • Chondrocytes more abundant and larger • Yellowish color and more opaque than hyaline cartilage • Auricular pavilion, internal and external auditory canals, epiglottis and some laryngeal cartilages Fibrocartilage • Intermediate structure between cartilage and dense connective tissue • Scarce matrix formed by type I and II collagen and low concentration of water and proteoglycans • Chondrocytes aligned in parallel rows • Great tensile strength • Without perichondrium • Intervertebral discs, symphysis of the pubis, tendons and ligaments insertions in the bone