HISTOLOGY OF CARTILAGE & BONE Cartilage • Is a firm and flexible type of connective tissue in which the extracellular matrix has a firm consistency Cartilage • Modified Connective tissue. • Firm, not rigid • Embryologically derived from Mesenchyme. • Cells are widely separated by intercellular substance. • Firmness of Cartilage and the hardness of bone is because of the nature of ground substance in them. • Fetal Skeleton- predominantly cartilaginous. Functions • Forms the skeletal framework • Supports regions of the body which require varying degree of flexibility • Provides gliding area for the joint, facilitating movements (in Hyaline Cartilage) • Essential for the growth of long bones (In Hyaline Cartilage) Cartilage • Avascular • Nourished by diffusion • Limited ability for regeneration • Defects replaced by fibrous tissue • No nerves • No lymphatics • Covered by dense connective tissue sheath -Perichondrium Types of cartilage • Depending on the Number and Variety of fibres in the matrix, classified • 1 Hyaline cartilage • 2 Fibrocartilage • 3 Elastic Cartilage Perichondrium • Mesenchymal cells surrounding the developing cartilage form- Perichondrium • Special form of dense irregular connective tissue • Covers the free surface of the cartilage • Rich in fibres, fibroblasts and blood vessels • Since hyaline cartilage is avascular, it gets its nutrition from the perichondrium by simple diffusion • Perichondrium: 2 layers: Outer – Fibrous, InnerCellular-chondrogenic cells,undifferentiated flat cells, proliferating and differentiating into chondroblasts Components • Cells : Chondrogenic cells, Chondroblasts & Chondrocytes • Fibres: Collagen and Elastic • Ground Substance: Acid Mucopolysaccharides (Chondroitin Sulphate) Cells • Embryonically Cartilage cells- Chondroblasts derived from mesenchymal cells, lie very close to the perichondrium, rich in cell organellae • Chondroblasts- intercellular matrix & Collagen fibres • Chondrocytes are mature chondroblasts – imprisoned within the matrix, seen away from the perichondrium • Old cells are incapable of multiplication, but secrete an enzyme , Alkaline phosphatase, resulting in calcification of cartilage in old age. • Fibres: Collagen and elastic • Ground Substance: basophilic, metachromatic and PAS positive. Chemically: Mucopolysaccharides, Collagen Type II, electrolytes and Water • Examples: • • • • • • • • • Hyaline Cartilage Costal Cartilage Tracheal and Bronchial Rings Thyroid and Cricoid Cartilages Articular Cartilage Epiphyseal plates Parts of nasal Septum Parts of Lateral wall of nose Skeletal framework of fetus Articular surface of sesamoid bones ARTICULAR CARTILAGES ARE NOT COVERED BY PERICHONDRIUM Hyaline Cartilage Hyaline Cartilage • Hyalos=glass like • Transparent, homogeneous • H/E: Bluish, basophilic matrix • Chondrocytes: large & in isogenous groups • Territorial matrix • Interstitial matrix • Rich in Type II Collagen fibres Hyaline Cartilage • Chondroblasts: short, small, elongated cells, rich in all cell organellae, usually occuring singly, covered by asac like structure known as Lacunae • Chondrocytes: matured cells , large, less cell organellae, in isogenous groups, seen away from the perichondrium Hyaline Cartilage Hyaline Cartilage Matrix appears Homogeneous : WHY? • Collagen fibrils present in the matrix have same refractive index as that of the ground substance. Elastic cartilage(Yellow Elastic Cartilage) • Similar to Hyaline Cartilage • Matrix rich in Elastic fibres hence the name Elastic Cartilage • H/E: elastic fibres difficult to see. • Clearly visualized on special staining • Surface covered by Perichondrium • Better flexibility than hyaline cartilage, readily recovers its shape Sites of Elastic Cartilage • Pinna • Lateral part of External Auditory meatus • Medial part of Auditory tube • Epiglottis • Corniculate & Cunneiforms • Apical part of arytenoid • ALL THE SITES MENTIONED ARE CONCERNED EITHER WITH PRODUCTION OR PERCEPTION OF SOUND Branching Elastic fibres give FLEXIBILITY & SUPPORT Fibrocartilage(White Fibrocartilage) Great Tensile strength with considersable elasticity • Numerous dense collagen bundles oriented in the direction of functional stress with some fibroblastsn • No perichondrium • Type I Collagen Fibrocatilage Sites of Fibrocartilage • Intervertebral discs • Symphysis pubis • Manubriosternal joints • Articular discs in temporo-mandibular joints ,Sterno-clavicular joints & Menisci of Knee joints • Glenoidal labrum & Acetabular labrum • Deep groves of bone, where tendons ru. MCQ • A section of Hyaline cartilage can be identified by the presence of • 1.Homogenous matrix • 2.Elastic fibres • 3.Collagen fibres • 4.Chondrocytes arranged in row MCQ • Hyaline cartilage is present in • 1.Tracheal ring • 2.Epiglottis • 3.Intervertebral disc • 4.Glenoidal Labrum MCQ • Perichondrium is absent in • 1.Elastic and Hyaline Cartilage • 2.Hyaline Cartilage • 3.Fibrocartilage and articular cartilage • Costal Cartilage and Ear Pinna MCQ • Which of the following features is NOT TRUE about cartilage? • 1.Firm and flexible • 2.Highly vascular • 3.Insensitive • 4.Poor in regeneration Histology of Bone Bone • Is a rigid form of scleral connective tissue in which the extracellular matrix is impregnated with inorganic salts mainly calcium, phosphate and carbonate, providing hardness Rigidity and hardness is provided by the matrix which is impregnated with inorganic salts Functions • Attachment to muscles • Serves as lever for muscular actions • Bears body weight • Protects vital organs • Stores calcium, phoshate and other ions • Contains hemopoietic tissue, the bone marrow Types of Bones • Morphologically: • Compact Bone • Spongy or cancellous Bone Bone Membranes • Periosteum • Endosteum Bone Composition • Cells • Fibres and Ground substance– – organic – inorganic Compact and Spongy bone Cancellous or Spongy Bone • Slender bony trabeculae that branch and anastomose with one another. • Enclose irregular marrow spaces containing blood vessels and haemopoietic tissue that give rise to new blood vessels. • They receive nutrition from blood vessels in the bone marrow Compact Bone Compact Bone Endochondral ossification Intramembranous ossfication BONE FRACTURE REPAIR SUMMARY OF BONE TYPE AND ORGANIZATION
