Cartilage PDF

Cartilage Histology department Faculty of medicine It is a specialized type of connective tissue which is a tough to perform its function General characters Consists of cells and extracellular matrix (ground substance & fibers). The cells are present in spaces called lacunae. General characters Cart...

Cartilage Histology department Faculty of medicine It is a specialized type of connective tissue which is a tough to perform its function General characters Consists of cells and extracellular matrix (ground substance & fibers). The cells are present in spaces called lacunae. General characters Cartilage has a plastic appearance and can bear a certain amount of weight. It can bend easily but does not stretch. The free surface of cartilage is smooth and lubricated thus allowing the gliding of two or more cartilage surfaces on each other as in Joints. General characters Cartilage is avascular; it is nourished by diffusion from blood vessels in the perichondrium Function: 1. Form skeleton of the fetus. 2. Support soft tissue (trachea – contain hyaline cartilage) 3. Essential for the growth of the long bone. (epiphyseal cartilaginous plate) 4. Facilitate bone movement Types of cartilage According to the types of fibers in the matrix, there are three types of cartilage: Hyaline, elastic and fibrocartilage Hyaline cartilage It is called hyaline because in the fresh condition it has a white glassy translucent appearance, when examined with the naked eye. Sites of hyaline cartilage In prenatal life, most of the skeleton is formed of hyaline cartilage In adult life it is present in articular surfaces of joints, epiphyseal plate of long bones (until its growth is completed), nose, larynx, trachea and bronchi. Microscopic appearance of Hyaline Cartilage perichondrium: A layer of dense connective tissue The outer layers of the perichondrium consist of fibrous layers of type I collagen with a small number of fibroblasts embedded among them and blood capillaries. The innermost layers of the perichondrium contain relatively undifferentiated mesenchymal cells, which can differentiate into new fibroblasts of the outer perichondrium or into chondroprogenitor cells that differentiate further into chondroblasts,. Cartilage cells Chondroblasts Chondrocytes LM They have rounded nuclei and vacuolated cytoplasm.. A single lacuna may contain one chondrocyte or more. If it contains more than one chondrocyte it is called a nest. Cartilage cells (chondrocytes By L/M: ❑Matrix that are in contact with the lacuna often stain darker than the adjacent matrix, giving another impression, namely, that the chondrocyte has a “capsule.. E/M : Active euchromatic nucleus well developed RER welldeveloped Golgi body. The outline of the cell is irregular due to the presence of cytoplasmic processes like microvilli. Function : responsible for the production of collagen and the extracellular matrix that will lead to the maintenance of cartilaginous tissue *Matrix of Hyaline cartilage It is composed of 1- Fibers 2- Ground substance The fibrous part is collagenic fibers (type II) and fibrils. Ground substance 1-proteoglycan (aggrecan)+Hylourinic acid 2- Glycoprotein 3- Water 60-80% Ground substance 1-proteoglycan (aggrecan)+Hylourinic acid 2- Glycoprotein 3- Water 60-80% Elastic cartilage: In fresh state: yellowish in colour It is present in tissues that need stiffness and also elasticity ear pinna( auricle) external auditory meatus Eustachian tube and epiglottis It is similar to hyaline cartilage but it differs in that it contains great amounts of elastic fibers in the extracellular matrix C-White fibrocartilage Sites: Symphysis pubis, intervertebral discs, semilunar cartilage of knee joint It is characterized by the presence of groups of chondrocytes arranged in rows separated by bundles of collagenic fibers and fibrocytes. It is not covered by perichondrium Cartilage formation Formed from the embryo mesenchyme Mesenchymal cells proliferate, differentiate, and secrete cartilage matrix molecules Growth of cartilage: 1-Interstitial growth: Immature chondrocytes have the divide and lay down matrix around them. By this method cartilage increases in size. 2-Appositional growth: new cartilage is laid down at one of its surfaces. This occurs by the inner chondrogenic layer of the perichondrium in which the cells divide and differentiate into chondroblasts and chondrocytes which form intercellular substance. Cartilage repair:Regeneration of cartilage occurs in young cartilage only. In adults, cartilage damage results in connective tissue scar. Thank you