HISTO_LC8_CARTILAGE.pdf

UNIVERSITY OF NORTHERN PHILIPPINES HISTOLOGY LC8 CARTILAGE COLLEGE OF MEDICINE, BATCH 2026...

UNIVERSITY OF NORTHERN PHILIPPINES HISTOLOGY LC8 CARTILAGE COLLEGE OF MEDICINE, BATCH 2026 Transcribers: Gadaza, Gascon, Hierco, Lalap, Lang-ayan Dr. Modesto David A. Bolislis | Nov. 7, 2022 Editors: Gadaza, Gascon, Hierco, Lalap, Lang-ayan CARTILAGE III. Chondrocytes I. Definition Cartilage consists of cells called “chondrocytes” embedded in the ECM II. Cartilage Extracellular Matrix which unlike connective tissue proper contains no other cell types. III. Chondrocytes Chondrocytes synthesize and maintain all ECM components. It is IV. Physical properties of Cartilage located in matrix cavities which is called “lacunae” V. Organization of the Lymphatic Vascular Tree VI. Types of Cartilages VII. Hyaline Cartilage VIII. Elastic Cartilage IX. Fibrocartilage X. Cartilage Formation, Growth, and Repair XI. References I. Definition Cartilage is a tough, durable form of supporting connective tissue, characterized by an extracellular matrix (ECM) with high concentrations of GAGs and proteoglycans, interacting with collagen and elastic fibers. Structural features of its matrix make cartilage ideal for a variety of mechanical and protective roles within the adult skeleton and elsewhere. All types of cartilage lack vascular supplies (or blood supply) chondrocytes receive nutrients by diffusion in the perichondrium chondrocytes exhibit low metabolic activity cartilage lacks nerves (nerve endings) IV. Physical properties of Cartilage Physical properties of cartilage: Semi rigid consistency of the cartilage - due to the water bound to negatively charged hyaluronan and GAG chains, and these are enclosed within a dense meshwork of thin Type II collagen fibrils Shock absorber - The high content of bound water allows cartilage to serve as a shock absorber, an important functional role. The physical properties of cartilage depend on electrostatic bonds between the In this picture you can see a cross section, an example of a joint, and cartilage following: lies within the ends of the bone in majority of the human body. But the cartilage 1. Type 2 collagen fibrils - responsible for the semirigid consistency of the can be found in other body parts which we will mention in the succeeding cartilage and has a role on why the cartilage performs as a shock slides. absorber. II. Cartilage Extracellular Matrix (ECM) 2. Hyaluronan 3. Sulfated GAGs on densely packed proteoglycans Cartilage ECM has a firm consistency that allows the tissue to bear mechanical stresses without permanent distortion. V. Perichondrium Common locations of cartilage: respiratory tract, ears, nose The perichondrium is a sheath of dense connective tissue that surrounds Functions: cartilage in most places, forming an interface between the cartilage and the tissues supported by the cartilage. 1. Cartilage ECM forms framework supporting other tissues 2. Provides cushioning and sliding regions within skeletal joints and harbors the blood supply serving the cartilage and a small neural facilitates body movements. component. Articular cartilage -covers the ends of bones in movable joints -erodes in the course of arthritic degeneration - this is the one that is affected if there is an arthritic degeneration -lacks perichondrium and is sustained by the diffusion of oxygen and nutrients from the synovial fluid VI. Types of Cartilages Types of Cartilage 1. Hyaline cartilage 2. Elastic cartilage 3. Fibrocartilage One example of which, that is your knee joint. That is an example of your articular cartilage which we will discuss later. [HISTOLOGY] 1.08 CARTILAGE – Dr. Modesto David A. Bolislis VII. Hyaline Cartilage Another important component of cartilage matrix is the structural multiadhesive Hyaline cartilage, the most common of the three types, is homogeneous and glycoprotein chondronectin. semitransparent in the fresh state. Binds specifically to GAGs, collagen, and integrins, mediating the adherence of chrondrocutes to the ECM. A. LOCATION -articular surfaces of movable joints -walls of larger respiratory passages (nose, larynx, trachea, bronchi) -ventral ends of ribs, where they articulate with the sternum -epiphyseal plates of long bones where it makes possible longitudinal bone growth In embryo (developing fetus): -hyaline cartilage forms the temporary skeleton that is gradually replaced by bone - as the fetus will mature and grow up B. MATRIX In terms of matrix, the dry weight of hyaline cartilage is nearly 40% collagen embedded in a firm, hydrated gel of proteoglycans and structural glycoproteins. In routine histology preparations: -proteoglycans make the matrix basophilic and the thin collagen fibrils are barely discernible. Hyaline cartilage: Type II collagen Most of the collagen in hyaline cartilage is Type II, although small amounts of minor collagens are also present. Cells occupy relatively little of the hyaline cartilage mass. At the periphery of the cartilage, young chondrocytes or chondroblasts have an elliptic shape, with the long axes parallel to the surface Deeper in the cartilage, they are round and may appear in groups of up to eight cells that originate from mitotic divisions of a single chondroblast Image: P (Perichondrium) near the periphery and more elliptical, C (Chrondrocytes) rounder shape Picture: Thin region of hyaline cartilage P= perichondrium; M= matrix; C= chondrocytes Aggrecan is the most abundant proteoglycan of hyaline cartilage. Hundreds of these proteoglycans are bound noncovalently by link proteins to long polymers of hyaluronan Because cartilage matrix is avascular, chondrocytes respire under low-oxygen These proteoglycan complexes bind further to the surface of type II tension. collagen fibrils Hyaline cartilage cells metabolize glucose mainly by anaerobic glycolysis Nutrients from the blood diffuse to all the chondrocytes from the cartilage surface, with movements of water and solutes in the cartilage matrix promoted by intermittent tissue compression and decompression during body movements. Chondrocyte synthesis of sulfated GAGs and secretion of proteoglycans are accelerated by many hormones and growth factors. Pituitary-derived protein called growth hormone or somatotropin. o Major regulator of hyaline cartilage growth o Indirect action: promoting endocrine release from the liver > directly stimulate cells of hyaline cartilage ▪ somatomedins/insulin like growth factors All hyaline cartilage is covered by a layer of dense connective tissue, the perichondrium, which is essential for the growth and maintenance of cartilage. The outer region consists of o Collagen type I fibers o Fibroblasts [HISTOLOGY] 1.08 CARTILAGE – Dr. Modesto David A. Bolislis The inner layer of perichondrium adjoining the cartilage matrix Chondrocytes are axially arranged, and they can be seen surrounded by o Mesenchymal stem cells small amount of matrix and separated by larger regions with dense collagen and scattered fibroblasts with elongated nuclei. ▪ Provide a source for new chondroblasts that divide and differentiate into chondrocytes Chondrocytes of fibrocartilage occur singly and often in aligned isogenous aggregates, producing type II collagen and other extracellular matrix 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. Proteoglycans in the fibrocartilage are scarce which makes it more acidophilic than hyaline and elastic cartilage. No distinct of fibrocartilage surrounding perichondrium. Image: P (perichondrium) VIII. Elastic Cartilage Fibrocartilage. (C): Chondrocytes; Arrow: elongated nuclei X Cartilage Formation, Growth, and Repair All cartilage forms from embryonic mesenchyme in the process of chondrogenesis. The first indication of cell differentiation: rounding up of the mesenchymal cells > multiplying rapidly and became more dense and packed together. o Chondroblast and chondrocytes ▪ Basophilic cytoplasm: rich in RER necessary from collagen synthesis. Production of ECM encloses the cells in their lacunae and then gradually separates chondroblasts from one another. Embryonic development: cartilage differentiation takes place from the center going outward. Elastic cartilage is essentially similar to hyaline cartilage except that it contains an o More central cells have the characteristics of chondrocytes abundant network of elastic fibers in addition to a meshwork of collagen type II o Peripheral cells are typical chondroblasts: fibrils. o Superficial mesenchyme develops as the perichondrium. The darker stained is the abundant region of elastic fibers. In contrast to your In articular cartilage, cells and matrix near the articulating surface are gradually hyaline cartilage, we cannot observe this abundant network of elastic fibers. worn away and must be replaced from within, because there is no perichondrium to add cells by oppositional growth. More flexible than hyaline cartilage, elastic cartilage is found in the following: Except in young children o Damaged cartilage undergoes slow and incomplete repair, Auricle of the ear primarily dependent on cells in the perichondrium, which Walls of the external auditory canals, the auditory (Eustachian) tubes, evade the injured area and produce new cartilage. the epiglottis In adults Upper respiratory tract o In damaged areas, the perichondrium produces a scar of dense connective tissue instead of forming new cartilage. IX Fibrocartilage o The poor capacity of cartilage for repair or regeneration is due in part to its avascularity and low metabolic rate. Fibrocartilage takes various forms in different structures but is essentially a The major stages of cartilage formation or chondrogenesis (refer to the figure mingling of hyaline cartilage and dense connective tissue. below) A. LOCATION (a) Mesenchyme is the precursor for all types of cartilage. Can be found in the intervertebral discs (b) Mitosis and initial cell differentiation produces a tissue with condensation Attachments of certain ligaments of rounded cells called chondroblasts. Pubic symphysis (c) Chondroblasts are then separated from one another again by their production of the various matrix components which will collectively swell All places where it serves as very tough, yet cushioning support tissue with water and from very extensive ECM. for bone [HISTOLOGY] 1.08 CARTILAGE – Dr. Modesto David A. Bolislis (d) Multiplication of the chondroblasts within the matrix gives rise to isogenous cell aggregates surrounded by a condensation of territorial matrix. In mature cartilage, this interstitial mitotic activity ceases and all chondrocytes typically become more widely separated by their production matrix. X. REFERENCES Mescher, A. L. (2018). Junqueira's basic histology: Text and Atlas. McGraw-Hill Education.