Cartilage and bone provide strong supporting framework

Cartilage and bone provide strong supporting framework

1. Cartilage

   • cartilage matrix is a firm gel that has polysaccharide derivatives, chondroitin sulfates — which form complexes with protein in ground substance — creating proteoglycans
   • chondrocytes (cartilage cells) — only cells in cartilage matrix — which is surrounded by chambers, lacunae
   • cartilage = avascular — exchange of nutrients and waste products must occur by diffusion through matrix
   • antiangiogensis factor (produced via chondrocytes)— chemical inhibitor that prevents blood vessels from turning into cartilage
   • blood vessels in perichondrium provide OXYGEN and NUTRIENTS to chondrcytes
   • perichondrium — fibrous — separates cartilage from surrounding tissues — TWO types: outer (fibrous) layer — provides support and protection, attaches cartilage together inner (cellular) layer — growth and maintenance of cartilage
   • Cartilage growth
     • interstitial growth — enlarges cartilage from within via division of chondrocytes in matrix most important during development begins early in embryonic development and continues through adolescence
     • appositional growth — adds new layer of cartilage to the surface by gradually increasing outer layer cells of inner layer of perichondrium divide and become chondroblasts (immature chondrocytes) these cells begin producing cartilage matrix — as they become surrounded by and embedded in new matrix, they differentiate into mature chondrocytes do not usually occur in adults — but it is possible if cartilage is damaged or if there is an overstimulation of growth hormone via pituitary gland
     • both growth periods take place during development these do not occur in adults severed injured cartilage will be replaced by a fibrous patch
   • Types of cartilage
     • Hyaline cartilage — most common dense perichondrium surrounds cartilage except inside joint cavities reduces friction between bones tough, but flexible bc matrix is made of packed collagen fibers ex. connection b/w ribs and sternum, nasal cartilage, trachea
     • Elastic cartilage resilient and flexible bc of elastic fibers yellow colour forms external flap of ear (auricle/pinna), epiglottis, small cartilages in larynx
     • Fibrocartilage — durable bc of little ground substance and interwoven collagen fibers resists compression absorbs shocks prevents bone-to-bone contact limits movement found b/w pubic bones and intervertebral discs pads knee joints

2. BONE

   • bone/ osseous tissue little ground substance bone matrix has mixture of calcium salts (calcium phosphate, calcium carbonate) AND collagen fibers calcium salts = hard, brittle collagen fibers = strong, flexible
   • lacunae in matrix have osteocytes (bone cells) Arranged around central canals within matrix canaliculi — slender passageway in matrix that has cytoplasmic extensions that allow for osteocytes to communicate with blood vessels
   • periosteum — fibrous covering that covers the bone (except in joint cavities) helps to attach bone to surrounding tissue, tendons and ligaments cellular layer undergoes appositional growth and repairs after injury