KINS 1223 Unit 3 Lecture 2 Study Guide Ossification Producing hardened bone from 1 Fibrous CT membranes 2 Cartilage 3 At fetal 6 weeks skeleton either fibrous CT or hyaline cartilage bones begin to develop Bone development process 1 Matrix is secreted 2 Mineral salts deposited into matrix 3 Soft CT fibrous cartilage becomes hard CT bone Ossification extends from 6th fetal week to 25 years Types of ossification 1 Intramembranous ossification within membranes flat skull clavicles a Bone formed by hardening of fibrous CT membranes b Process i Primitive CT cells arrange around blood vessels differentiate into osteoblasts ii Osteoblasts secrete organic bone matrix Osteoid around CT to appear iii Minerals deposited into osteoid trabecular structure begins iv Osteoid now mineralized true hardened bone 1 Osteoblasts trapped in lacunae mature into osteocytes 2 Outside fibrous CT differentiates into double 3 layered periosteum Inner layer of periosteum contains osteoblasts from cortical bone around cancellous bone 2 Endochondral ossification within cartilage Long short irregular bones a Bone formed by hardening hyaline cartilage i Primary ossification center formed at center of diaphysis ii In response to vascularization of perichondrium 1 Cells differentiate into osteoblasts 2 Vascularized perichondrium becomes periosteum iii Osteoblasts secrete osteoid organic matrix against hyaline cartilage shaft 1 Creates bony collar splint 2 Hyaline cartilage in center of shaft calcifies 3 Chondrocytes die due to lack of nutrients iv Matrix deteriorates opening cavities inside shaft v Cavities invaded by periosteal bud artery vein lymphatics osteoblasts osteoclasts etc 1 Osteoblasts secrete matrix around cartilage fragments forming spongy bone 2 Osteoclasts break down new cancellous bone to form medullary cavity 3 Secondary center around time of birth vi Cartilage in epiphyses calcifies and deteriorates 1 Allows entry of periosteal bud 2 Proximal center first distal center later 3 Secondary centers appear at varying times st year a Humeral head 1 b Capitulum 2 nd year th year c Lesser Tubercle 5 d Lateral epicondyle 13 th 14 th year Bone growth Bone growth in length During ossification remaining cartilage continues to grow Ossification appears to chase cartilage formation along shaft At birth long bones have bony diaphysis cartilage epiphyses Growth continues where cartilage is present Cartilaginous region eventually reduced to a disk or plate o Epiphyseal disk o Epiphyseal cartilage o Growth plate Epiphyseal Closure o Cartilage becomes all hardened bone can no loner grow o Closure leaves a ridge or line epiphyseal line o Time of closure varies x ray MRI CAT scan detect if epiphyses are closed Distal end later Female before male Olecranon process 16yrs Distal ulna 20yrs Distal femur 20yrs o Implications Before closure Growth interrupted or stopped Severe or repeated blows Problem contralateral limb continues to grow Healthy limb longer o Injuries sports Ossification not complete until age 25 children in contact Child sprains need careful evaluation Epiphyses less strong than CT around joints Accidents cause most epiphyseal injuries not sports Little League Elbow epiphyseal injury o Medial epicondyle to strong elbow extension of humeurs separates due Bone growth in diameter Appositional growth becomes larger stronger Osteoblasts secrete matrix on external bone surface Simultaneously osteoclasts destroy bone bone o Usually less osteoclast activity bone diameter increases stronger o If less osteoblast activity more osteoclast activity bone is eroded Factors affecting bone growth Reduced mechanical stress osteoblast activity reduced osteoclasts dominate Bone material is lost o Bone in cast bedridden patients space travel Weightlessness Gemini 4 4days 12 demineralization Gemini 5 8days 20 demineralization Increased stress stimulates osteoblast o More bone produced o Fractures stimulate bone production Nutrition o Vitamin D Absorption of Calcium Bone inadequately mineralized soft bend easily Children rickets bones easily deformed Adults osteomalacia bones soft fracture easily Synthesized in skin need UV rays Can be ingested Eggs Liver Milk o Vitamin C Normal collagen synthesis matrix mineralization Deficiency Growth retarded in young Elderly osteoporosis bone brittle fracture easily o Osteoporosis Bones lose mass become brittle loss of organic matrix and minerals Complications pneumonia blood clotting Postmenopausal white women at greatest risk 30 of bone lost by age 70 Estrogen maintains density in both sexes inhibits resorption Testes adrenals produce estrogen in men Rapid loss after menopause if body fat too low or with disuse during immobilization Treatment ERT o Slows bone resorption o Increased risk of breast cancer stroke and heart disease PTH o Slows bone loss o May promote bone cancer Prevention best treatment o Exercise o Calcium intake 1000mg day between ages 25 40 Hormones very important factor o Defer to endocrine system Ligaments Bands of dense regular CT only slightly elastic Bone ends attach to bone Functions 1 Hold bundles of muscle tendons in place a Ankle wrist regions muscle bodies in leg forearm b Attach to metatarsals metacarpals and or phalanges c Retinaculum d Transverse humeral ligament holds long head of biceps in bicipital groove 2 Holds joints together make them more stable Intrinsic or capsular ligaments thickened part of capsule a b Extracapsular outside the capsule c Intracapsular deep to capsule cruciates of knee 3 Limit ROM range of motion of joints a Prevent dislocation other tissue damage
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