Connective Tissue Cartilage and Bone Cartilage Develops from

Connective Tissue Cartilage and Bone

Cartilage Develops from chondroblasts Elaborate support tissue composed mainly of GAG’s and collagen (type II) Major GAG’s – hyaluronic acid, chondroitin and keratan sulfate Stains blue with hematoxylin

Cartilage Perichondrium – contains chondroblasts Cartilage growth therefore occurs by- interstitial growth (within) - appositional growth (periphery)

Cartilage Most devoid of blood vessels Depends on diffusion thru ground substance Limits thickness Thicker →cartilage canals eg. costal

Cartilage 3 types – hyaline, fibrocartilage, elastic Hyaline – type II collagen only - temporary skeleton in fetus, articular surface in joints, respiratory passage, sternal end of ribs

Cartilage Fibrocartilage – type I & II collagen - intervertebral discs, tendon attachments, junctions between flat bones of pelvis

Cartilage Elastic cartilage – type II collagen + elastic fibers Auricle of ear, walls of external auditory canal & Eustachian tubes, epiglottis

Bone

Bone 3 main functions - metabolic - mechanical - hematopoietic Continuously remodeling

Bone - classification Gross & microscopic: compact cancellous Histological: - woven (irregular ) – - lamellar (regular)

Bone Woven bone – haphazard organization of collagen fibers; weak Lamellar bone – parallel alignment of collagen into sheets (lamellae); strong Woven laid down in fetus and when osteoid is produced rapidly

Bone Mainly type I collagen (30%) + hydroxyapatite (60%), type V collagen (1. 5%) Type III collagen found in pathological conditions

Bone Formed from osteoblasts → osteoid → calcifies → bone Osteoid : type I collagen, GAG’s, chondroitin & keratan sulfate; osteocalcin binds calcium Osteocytes inactive Osteoclasts remodel

Bone Osteoblasts & osteocytes derived from osteoprogenitor cells Osteoclasts – thought to be derived from blood monocytes

Bone Architecture – outer cortex (compact) & inner trabecular (spongy) zone Spaces between trabeculae → bone marrow Basic unit = osteon

Bone Cells Osteoprogenitor cells – spindleshaped cells on surface Osteoblasts Osteocytes – in lacunae in mature bone Osteoclasts – multinucleated; found in Howship’s lacunae

Bone In fetus, formation may be intramembranous or endochondral Intramembranous – formation of flat bones eg. in skull - primitive mesenchymal cells → osteoblasts

Bone Endochondral ossification – hyaline cartilage deposited in the shape of the required bone then → bone by osteoid deposition

Bone An actively proliferating plate of cartilage ( epiphyseal plate) remains at the junction of the epiphysis and diaphysis → growth Activity ceases after puberty

Joints 2 main groups – limited movement free movement Limited movement – connected by fibrocollagenous tissue - flat bones of skull joined by fibrous tissue (syndesmoses) - ribs joined by cartilage (synchondroses)

Joints Free movement : synovial joints Internal lining of joint by synovial membrane → synovial fluid (lubricant) Bone end coated with friction free layer of hyaline cartilage Ligaments stabilize joints