Cartilage It is a modified connective tissue providing strength, support and varying degree of flexibility. Its ground substance is rubbery in consistency. It is formed of cells and fibers widely separated by extra cellular matrix. Cartilage cells a. Chondrocyte in the mature cartilage, responsible for production of ground substance and fibers. b. Chondroblasts = present at the periphery of the cartilage. Matrix It consists of chondromucoprotein chondritin sulphate and rubbery in consistency. Fibers Either collagen or elastic fibers similar in characteristic of those present in the connective tissue Depending on the type of fibers, cartilage is divided into: Hyaline cartilage. Fibro cartilage. Elastic cartilage. Perichondrium Free surfaces of both hyaline and elastic cartilage covered by dense Connective tissue called perichondrium, which consist of: *Outer fibrous layer: consists of collagenous bundles rich in blood vessels *Inner layer (cellular): formed of chondroblasts which can be changed into chondrocytes. Chondroblasts be divide and can secrete the matrix resulting in growth of cartilage from its periphery Functions Supply the cartilage with blood and nutrition. Growth of cartilage. Provide an attachment for muscle General Comments: *Cartilage is avascular (has no blood vessels), no lymphatic and no innervation of its own. *It got its O2 and nutrition through diffusion from surrounding connective tissue. *Blood vessels can pass through the cartilage in tunnels without supplying it directly. Calcification of cartilage: Matrix calcified in old age thus prevent diffusion and subsequently chondrocytes die ( chest X-ray may show calcified area in old age) Regeneration of cartilage It occurs in young cartilage only. The adult cartilage transform into scar tissue by regeneration. Regadless to the type of the cartilage, the repair of damaged cartilage occurs by formation of fibrocartilage i.e (fibrous tissue). Matrix or the ground substance LM: o Stained blue with basic dye (i.e. basophilic) o Also show metachromasia i.e stain with metachromatic stains (e.g. toludine blue) because it is very rich with chondritin sulphuric acid. o Usually appear homogenous. o The basophilia is more around the chondrocytes due to increase in concentration of glycosaminoglycan around the lacunae (territorial matrix) Chemically, it consists of proteoglycans rich in glycosaminoglycan and chondroitin sulfate. Cells of cartilage o Young chondrocytes (chondroblasts) are flat basophilic cells with oval nuclei. They are present at the periphery of the cartilage under the perichondrium (may present in the center during growth of cartilage) arrange in parallel direction. o Mature chondrocytes They are spherical cells. Stained in lacunae (spaces in the matrix). The cytoplasm of chondrocytes is basophilic with large Nucleus with on or more prominent nucleoli. EM= the cell are rich in rER, well-developed Golgi apparatus, secreoary vesicles contain material needed to maintain the matrix. Chondrocytes can divide so they may present single or in groups (isogenous groups). When many chondrocytes present in single lacunae, they form cell nest (2 or 4 or 8 cells, forming isogenous groups). If the cell die because its old or no blood supply empty lacunae. Hyaline cartilage Hyalos = glass Hyaline = glassy. In fresh state, it appears as glassy whitish – blue structure. It is the commonest type of cartilage. Covered by perichondrium Note = perichondrium is not present over the cartilage of the articular surfaces of joints. Sites: Costal cartilage in the chest. Cartilage of respiratory passages: nasal septum, nose, trachea, bronchi, large bronchi, thyroid, cricoid cartilage of larynx. Articular surfaces of the joint. Long bones in the skeleton of the foetus. LM: Homogenous matrix. Contain delicate collagen fibers (acidophilic) – type II but the basophilic property of the matrix masks its acidophilic nature matrix. (http://www.mc.ntu.edu.tw/department/anatomy/Histology/cartilage.html) Early Age processing = Lead to increase Late Process of aging collagen fibers in hyaline cartilage and formation of fibro cartilage. Calcification of the cartilage. Function Acts as shock absorber and bearing surfaces and provides the mechanism by which long bones grow in length. Elastic cartilage It is similar to hyaline cartilage but: The matrix is rich in elastic fibers. Elastic randomly distributed fewer at perichondrium. Its chondrocytes are derived from fibroblasts rather than directly from mesenchyme. Function = Provide extreme flexible support. Site: Ear pinna, External auditory tube. Medial part of the eustacian tube. Epiglottis. Cuneiform + cornicular cartilage of the larynx. Fibro cartilage It is a combination of hyaline cartilage and dense regular connective tissue. It has great tensile strength with considerable elasticity. It is characterized by the following: o Matrix is acidophilic (due rich collagen). o No perichondrium. o The cartilage cells (chondrocytes) arrange in rows or columns. o Abundancy of collagen fibers ( arrang in bundles) o chondrocytes arise from fibroblast. Site Intervertebral disc. Symphysis pubis, manubristernal joint. Acetabulum (acetabular labrum) – hip joint. Glenoid labrum (shoulder joint). Articular disc e.g. sternoclavicular, menisci of the knee. Certain tendentious in secretion. Function Shoclc absorber, functional support . Growth of the cartilage All cartilage develops from mesenchyme like other connective tissue. Growth of the cartilage occurred by two mechanisms 1- Interstitial growth The cartilage cell in the center divide to form groups and secret matrix result in growth of matrix from the center (length). 2- Appositional growth = Young chondrocytes of perichondrium transformed into mature cells which can divide and secret matrix, result in peripheral growth in width. Clinical note: Ankylosis mean: Replacement of cartilage with bone in tissue = as in a the letic foot or (joint) Rupture disk It is caused by tear in laminate of annulus fibrousus, which leads to protrusion of nucleus pulposus (gelatinous substance) It occurs commonly in the posterior part of the disk in the lumbar region. Slipped disk: lumbar region Severe pain Rupture disk