Aqaba Medical Sciences University Lecture 15 on Cartilage PDF

General Histology Course number: 2110104 Lecture 15 Cartilage Tarek Hamdy Abd-Elhamid, MBBCh. MSc. PhD. Department of Basic Medical Sciences Faculty of Medicine Aqaba Medical Sciences University Aqaba Jordan ...

General Histology Course number: 2110104 Lecture 15 Cartilage Tarek Hamdy Abd-Elhamid, MBBCh. MSc. PhD. Department of Basic Medical Sciences Faculty of Medicine Aqaba Medical Sciences University Aqaba Jordan  Objectives 1. Recognize the general features of cartilage. 2. List the different histological types of cartilage. 3. Demonstrate main features of different cartilage types. 4. Give example of body’s sites where each type can be found. 5. Describe detailed structure of chondrocytes 6. Explain the structure of perichondrium & cartilage matrix. 7. Recognize cartilage development, methods of growth & repair.  Cartilage General characters: A special type of connective tissue functioning as a supporting or weight-bearing tissue Cartilage is completely avascular and chondrocytes receive nutrients by diffusion from capillaries in surrounding connective tissue (the perichondrium).. Composed of cells embedded in extracellular matrix with high concentrations of GAGs and proteoglycans, interacting with collagen type II fibrils and sometimes elastic fibers. Cartilage cells, called chondrocytes, are located in matrix cavities called lacunae Cartilage ECM has a firm consistency that allows the tissue to bear mechanical stresses without permanent deformation. The perichondrium is a fibrous connective tissue sheath surround or enclose most cartilage with two notable exceptions, articular cartilage and fibrocartilage, neither of which has a perichondrium.  Functions of cartilage 1. Forms the framework supporting soft tissue as in respiratory tract (nose, larynx and traches). 2. Facilitate smooth movement of bones at joints. 3. Mediate development and growth of long bones, both before and after birth.  The perichondrium Definition: Perichondrium is a sheath of dense irregular connective tissue that surrounds cartilage in most places, forming an interface between the cartilage and the tissues supported by the cartilage. Perichondrium has blood supply serving the cartilage and a small neural component. Perichondrium encloses most cartilages except fibrocartilage and articular cartilage of the joint, which do not have perichondrium Articular cartilage is nourished by diffusion of oxygen and nutrients from the synovial fluid.  The perichondrium Has two layers: The outer fibrous layer of the perichondrium contains collagen type I fibers, fibroblasts, and blood vessels through which nutrients access the matrix by diffusion. The inner cellular layer of the perichondrium consists of chondrogenic cells, which can differentiate into chondroblasts, so perichondrium is important for the growth (appositional (Atlas of Histology with Functional and Clinical Correlations, 1E (2010)) growth) and maintenance of cartilage  Cartilage cells The main types of cells in cartilage are chondrogenic cells, chondroblasts, and chondrocytes. 1. Chondrogenic cells are in the inner cellular layer of the perichondrium and differentiate into chondroblasts, 2. Chondroblasts are young chondrocytes, which derive from chondrogenic cells, and can actively manufacture the matrix of cartilage. The chondroblasts have RER- rich basophilic cytoplasm. They synthesize and deposit cartilage matrix around themselves. The cells become entrapped in small individual compartments called lacunae and are then referred to as chondrocytes.  Cartilage cells 3. Chondrocytes: Found deeper in the matrix. These are mature chondroblasts that are embedded in matrix cavities called lacunae of the matrix. Chondrocytes retain the ability to divide and often present as an isogenous group, two or more chondrocytes arranged in a groups of up to eight cells that originate from mitotic divisions of a single progenitor cell. (Atlas of Histology with Functional and Clinical Correlations, 1E (2010))  Cartilage cells 3. Chondrocytes: L.M. In H&E-stained preparations, chondrocytes may shrink slightly during routine histologic preparation, resulting in both the irregular shape of the chondrocytes and their retraction from the matrix. In living tissue, chondrocytes fill their lacunae completely. In sections with well-preserved chondrocytes, the cytoplasm is basophilic. The clear areas (arrows) represent sites of the Golgi apparatus. The nucleus of the chondrocyte is eccentrically located, vesicular with prominent nucleoli. (Ross Histology Text and Atlas, 2011)  Cartilage Cells 3. Chondrocytes: E.M. Chondrocyte cytoplasm displays numerous RER, Golgi apparatus (G), and mitochondria (M). The large amount of RER and the extensive Golgi apparatus indicate that the cell is actively engaged in the production of cartilage matrix. The numerous dark particles in the matrix contain proteoglycans. The large particles adjacent to the cell are located in the region of the matrix that is identified as territorial matrix. (Ross Histology Text and Atlas, 2011)  Cartilage matrix (Aggrecan) Consists of fibers and ground substance. Fibers: Mainly type II collagen fibrils (although some cartilage may also contain type I or elastic fibers) Ground substances include glycosaminoglycans (GAGs), proteoglycans, and glycoproteins. Collagen type II fibrils is bound to hyaluronan, and the sulfated GAGs on densely packed proteoglycans. The semi-rigid consistency of cartilage is due to water bound to negatively charged hyaluronan and GAGs in the proteoglycans allows cartilage to resist compression and return to its original shape. Aggrecan: is the most abundant proteoglycan of hyaline cartilage and composed of GAG side chains of chondroitin sulfate and keratan sulfate, Hundreds of these proteoglycans are bound non-covalently by link proteins to the hyaluronic acid (Junqueira’s basic histology, 2018) Chondronectin, a multiadhesive glycoprotein, binds to GAGs, collagen type II, and integrins, mediating the adherence of chondrocytes to the ECM.  Cartilage matrix The matrix of cartilage surrounding each chondrocyte, or immediately adjacent to chondrocytes of isogenous groups, is called territorial matrix. This newly produced matrix has abundant proteoglycans and less collagen. In H&E- stained preparations, the proteoglycans make the matrix generally basophilic and the thin collagen fibrils are barely visible. Another type of matrix, which surrounds the regions of territorial matrix and fills the rest of the space, is called interterritorial matrix. This type of matrix is richer in collagen and may be less basophilic than does the territorial matrix. (Junqueira’s basic histology, 2018)  Cartilage matrix The matrix of cartilage surrounding each chondrocyte, or immediately adjacent to chondrocytes of isogenous groups, is called territorial matrix. This newly produced matrix has abundant proteoglycans and less collagen. In H&E-stained preparations, the proteoglycans make the matrix generally basophilic and the thin collagen fibrils are barely visible. Another type of matrix, which surrounds the regions of territorial matrix and fills the rest of the space, is called interterritorial matrix. (Atlas of Histology with Functional and Clinical This type of matrix is richer in collagen and Correlations, 1E (2010)) may be less basophilic than does the territorial matrix.  Types of cartilage According to the variation in matrix composition, there are 3 types of cartilage: 1. Hyaline cartilage 2. Elastic cartilage 3. Fibrocartilage All three types of cartilage contain type II collagen fibrils; in addition, some types contain type I collagen or elastic fibers in the extracellular (Junqueira’s basic histology, 2018) matrix  Hyaline cartilage It is the most common type of cartilage Sites: Articular ends of long bones, wall of respiratory passages (nose, larynx, trachea, bronchi), the distal ends of ribs (costal cartilage); and in the epiphyseal plates of long bones Structure: Covered by perichondrium, except at the articular cartilage. Matrix: glassy, homogeneous matrix that contains type II collagen. Collagen embedded in a firm, hydrated gel of proteoglycans and structural glycoproteins. Aggrecan is the most abundant proteoglycan of hyaline cartilage. The structural multi-adhesive glycoprotein chondronectin mediate the adherence of chondrocytes to the ECM (Junqueira’s basic histology, 2018)  Function Hyaline cartilage covers the smooth surface of joints, providing free movement, and is also involved in bone formation and long bone growth. The high content of bound water allows cartilage to serve as a shock absorber, a role of major functional importance.  Elastic cartilage L.M: similar to the hyaline cartilage but contains abundant network of elastic fibers in the matrix in addition to a meshwork of collagen type II fibrils Elastic fibers are demonstrated by orcein stain. The elastic material gives the cartilage elastic properties in addition to the resilience and pliability that are characteristic of hyaline cartilage. Sites: It is present in tissues that need stiffness and also elasticity as auricles of the ear, wall of the external auditory canals, Eustachian tube, and epiglottis (Atlas of Histology with Functional and Clinical Correlations, 1E (2010))  Elastic cartilage L.M: similar to the hyaline cartilage but contains abundant network of elastic fibers in the matrix in addition to a meshwork of collagen type II fibrils Elastic fibers are demonstrated by orcein stain. The elastic material gives the cartilage elastic properties in addition to the resilience and pliability that are characteristic of hyaline cartilage. Sites: It is present in tissues that need stiffness and also elasticity as auricles of the ear, wall of the external auditory canals, Eustachian tube, and epiglottis (Junqueira’s basic histology, 2018)  Fibrocartilage A combination of dense regular connective tissue and hyaline cartilage. Found in the pubic symphysis, intervertebral disks, and attachment of ligaments. Structure: The chondrocytes of fibrocartilage are dispersed among the collagen fibers singularly, in rows, and in aligned isogenous groups producing type II collagen and other ECM components. Areas with chondrocytes and hyaline matrix are separated by other regions with fibroblasts and dense bundles of type I collagen which confer extra tensile (Atlas of Histology with Functional and Clinical Correlations, 1E (2010)) strength to this tissue (There is no distinct surrounding perichondrium in fibrocartilage.  Fibrocartilage A combination of dense regular connective tissue and hyaline cartilage. Found in the pubic symphysis, intervertebral disks, and attachment of ligaments. Structure: The chondrocytes of fibrocartilage are dispersed among the collagen fibers singularly, in rows, and in aligned isogenous groups producing type II collagen and other ECM components. Areas with chondrocytes and hyaline matrix are separated by other regions with fibroblasts and dense bundles of type I collagen which confer extra tensile strength to this tissue There is no distinct surrounding perichondrium in fibrocartilage. (Junqueira’s basic histology, 2018)  Cartilage development All cartilages formed from mesenchyme through a process called chondrogenesis. Mesenchymal cells retract their processes and rounding up. They proliferate and differentiate into chondroblasts. Chondroblasts are then separated from one another by their production of the various matrix components. Multiplication of chondroblasts within the matrix gives rise to isogenous cell aggregates surrounded by a condensation of territorial matrix.  Cartilage growth Appositional growth A process that forms new cartilage at the surface of an existing cartilage Growth begins with the chondrogenic cells that differentiate from mesenchymal stem cells in the perichondrium. These chondrogenic cells differentiate into chondroblasts and these cells start to elaborate a new layer of matrix at the surface (periphery) region of the cartilage near the perichondrium. Most cartilage growth in the body is appositional growth (Atlas of Histology with Functional and Clinical Correlations, 1E (2010))  Cartilage growth Interstitial growth A process that forms new cartilage within an existing cartilage mass. It begins with the cell division of pre- existing chondrocytes. Interstitial growth increases the tissue size by expanding the cartilage matrix from within. Fibrocartilage lacks a perichondrium, so it grows only by interstitial growth. In the epiphyseal plates of long bones, interstitial growth serves to lengthen the bone. (Atlas of Histology with Functional and Clinical Correlations, 1E (2010))  Cartilage repair Regeneration of cartilage occurs in young cartilage only In adults , damaged cartilage undergoes slow and often incomplete repair, by activity of cells in the perichondrium, which invade the injured area and produce new cartilage. In extensively damaged areas, the perichondrium produces a scar of dense connective tissue The poor capacity of cartilage for repair or regeneration is due to the avascularity of this tissue  References Cui, D., 2011. “Atlas of histology with functional and clinical correlations.” Lippincott Williams & Wilkins. Mescher, A.L., 2018. Junqueira’s Basic Histology: Text and Atlas, 15th Ed. McGraw Hill. Ross MH, Pawlina W. 2015. Histology: A Text and Atlas: with Correlated Cell and Molecular Biology: Lippincott Williams & Wilkins. Thank you