Cartilage and Bone Tissue PDF

The Cartilage and Bone Tissue Roland Oswald A. Banta, RMT, MD General Physician-Primary Care - Philippine Pharmaceutical Directory (PPD) Clinic Program Head - College of Medical Technology, WCC-QC Cartilage  The Cartilage Tough durable form of connective ti...

The Cartilage and Bone Tissue Roland Oswald A. Banta, RMT, MD General Physician-Primary Care - Philippine Pharmaceutical Directory (PPD) Clinic Program Head - College of Medical Technology, WCC-QC Cartilage  The Cartilage Tough durable form of connective tissue characterized by an extracellular matrix (ECM) with high concentration of Glycosaminoglycans and Proteoglycans, interacting with collagen and elastic fibers. Cartilage ECM has a firm consistency that allows the tissue to bear mechanical stresses without permanent distortion. Provides cushioning and sliding regions, within skeletal joints. Cartilage guides development and growth of long bones, both before and after birth. Chondrocytes The cartilage consists of cells called chondrocytes embedded in the ECM The Chondrocytes synthesize and maintain all ECM components and are located in matrix cavities called lacunae. Young chondrocytes are called Chondroblasts. Blood Supply All types of cartilage lack vascular supplies and chondrocytes receive nutrients by diffusion from capillaries in surrounding connective tissue (called the Perichondrium) Cartilage lacks nerves Perichondrium Sheath of dense connective tissue that surrounds cartilage in most places, forming an interface between the cartilage and the tissues supported by the cartilage. The perichondrium shelters the blood supply. ○ Serving the cartilage and a small neural component Articular Cartilage ○ Covers the ends of bones in movable joints and which erodes in the course of arthritic degeneration. Lacks perichondrium and is sustained by the diffusion of oxygen and nutrients from the synovial fluid. Three Main Types of Cartilage  Hyaline Cartilage Most common of the 3 types of cartilage Homogenous and semitransparent in the fresh state In adults, hyaline cartilage is located in: ○ 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 → longitudinal bone growth Hyaline Cartilage In the embryo, hyaline cartilage forms the temporary skeleton that is gradually replaced by bone Hyaline cartilage cells metabolize glucose mainly by: ○ Anaerobic glycolysis  Elastic Cartilage Similar to hyaline cartilage except that it contains an abundant network of elastic fibers. Elastic cartilage is found in the: ○ Auricle of the ear ○ Walls of the external auditory canal ○ Epiglottis ○ Upper respiratory tract Elastic cartilage is more flexible than hyaline cartilage  Fibrocartilage The interaction of hyaline cartilage and dense connective tissue. Fibrocartilage is found in: ○ Intervertebral discs ○ Attachments of certain ligaments ○ Pubic symphysis Serves as very tough, yet cushioning support tissue for bone There is no distinct surrounding perichondrium in fibrocartilage. Bone Bone Tissue Specialized connective tissue composed of calcified extracellular bone matrix Main function → for mechanical and metabolic functions and provides solid support for the body. Protection of vital organs (ex. cranial and thoracic cavities) Encloses internal (medullary) cavities containing bone marrow where blood cells are produced. Reservoir of calcium, phosphate, and other ions. Participates in skeletal muscle contraction and bodily movements. Provide solid support for the body. Components of Bone Canaliculi: a very thin cylindrical space to facilitate the exchanges between osteocytes and blood capillaries. Endosteum: Layers of connective tissue containing osteogenic cells on the internal surface. Periosteum: Layers of connective tissue containing osteogenic cells on the external surface. Bone Cells Osteoblasts From mesenchymal stem cells Produces the organic components of bone matrix: ○ Type 1 Collagen FIbers ○ Proteoglycans ○ Osteonectin → matricellular glycoprotein Deposition of the inorganic components Differentiate as osteocytes Forming a single layer of cuboidal cells Osteocytes Most abundant cells in bone Detect mechanical load Detect stress or fatigue-induced microdamage Osteoclasts Very large, MULTINUCLEATED, motile cells Essential for matrix resorption during bone growth and remodeling Bone marrow-derived monocytes At the resorption lacunae is the Howship lacunae. Bone Matrix Inorganic Bone Matrix Organic Bone Matrix About 50% of the dry weight of 90% Type I Collagen bone matrix are INORGANIC With small proteoglycans materials With Osteonectin – Contains Hydroxyapatite multiadhesive glycoproteins (most abundant) With Osteocalcin → Calcium With bicarbonate, citrate, binding proteins magnesium, potassium, and With Phosphatases → from sodium ions matrix vesicles which With non-crystalline calcium promotes calcification phosphate Compact versus Cancellous Bone Compact Bone Cancellous Bone “Cortical Bone” “Trabecular Bone”, “Spongy Dense area near the surface Bone” 80% of the total bone mass Deeper areas with numerous interconnecting cavities Comprises 20% of the total bone mass Woven versus Lamellar Bone Woven Bone Lamellar Bone Also known as immature bone, Also known as Mature Bone / primary bone, and bundle Secondary Bone bone Remodeled from woven bone Newly calcified All normal regions of adult bone Osteogenesis Intramembranous Endochondral Ossification Ossification Osteoblasts differentiate Pre-existing matrix of hyaline directly from condensed cartilage is eroded and sheets (“membranes”) of invaded by osteoblasts, embryonic mesenchymal which then begin osteoid tissue and begin secreting production. osteoid. Osteon (Haversian System) Refers to the complex of concentric lamellae surrounding a central canal that contains small blood vessels, nerves, and endosteum Constitute most of the compact bone Epiphyseal Growth Plate Also called epiphyseal cartilage Responsible for the growth in length of the bone and disappears upon completion of bone development at adulthood Obvious in pediatric patients  Epiphyseal Plates (5 Different Zones) Zone of Reserve Cartilage Normal or typical hyaline cartilage Zone of Proliferation Cartilage cells divide repeatedly and secrete more Type II collagen and proteoglycans Where chondroblasts are proliferated. Zone of Hypertrophy Cells are hypertrophic and the matrix appears condensed With swollen, terminally differentiated chondrocytes which compress the matrix into aligned spicules and stiffen it by secretion of Type X collagen. Unique to the hypertrophic chondrocytes in developing or fractured bone. Promotes vascularization from the adjacent primary ossification center. Zone of Calcified Cartilage An important layer where chondrocytes disappear Chondrocytes about to undergo apoptosis release matrix vesicles and osteocalcin to begin matrix calcification by the formation of hydroxyapatite crystals. Zone of Ossification Where blood vessels and osteoblasts infiltrate Capillaries and osteoprogenitor cells invade the now vacant chondrocyte lacunae, then merge to form the initial marrow cavity. Osteoblasts settle in a layer over the spicules of calcified cartilage matrix and secrete osteoid which becomes woven bone, then remodeled as lamellar bone. Joints Joints Joints are places where bones meet, or articulate, allowing at least the potential for bending or movement in that portion of the skeleton. Joints with very limited or no movement are classified collectively as synarthroses and freely mobile joints are called diarthroses. Joints Intervertebral discs are synarthroses in the vertebral column which cushion adjacent vertebrae. Each intervertebral disc consists of a thick outer layer of fibrocartilage forming a tough annulus fibrosus and a shock-absorbing inner, gel-like core, the nucleus pulposus. Joints Diarthroses have a joint cavity filled with lubricant synovial fluid, enclosed within a tough, fibrous articular capsule; ends of the bones involved are covered with hyaline articular cartilage. Specialized connective tissue of the synovial membrane lines the capsule, with folds extended into some areas of the joint cavity. References Mescher, Anthony L. (2024). Junqueira's Basic Histology: Text & Atlas, 17th International ed. New York:McGraw Hill. Esteban and Gonzales' Textbook of Histology 6th edition. Eduardo G. Gonzales. C & E Publishing, Inc. 2022.