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IUB ANAT-A 215 - Bone II

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1/30/15 BONE II I. OSSIFICATION (OSTEOGENESIS): the process of bone tissue formation; 2 types:A. INTRAMEMBRANOUS OSSIFICATION: pre-existing tissue is mesenchyme. Used to form primarily flat bones 1. mesenchymal cells differentiate into osteoblasts 2. woven bone (weak) and surrounding periosteum form 3. compact bone and spongy bone replace woven bone B. ENDOCHONDRAL OSSIFICATION: pre-existing tissue is a hyaline cartilage model surrounded by perichondrium. Used to form long bones 1. First, the perichondrium is invaded by blood vessels a. cells in perichondrium turn into osteoblasts b. perichondrium transformed into periosteum 2. Osteoblasts secrete osteoid onto cartilage (osteoblasts make a liquid bone—just like glue comes out as a liquid then eventually becomes stiff)a. forms bone collar (periosteal bone collar) 3. Due to the penetrating periosteal bud (blood vessels), chondrocytes enlarge w/in shaft (calcium and oxygen coming in through blood vessels)a. cartilage undergoes calcification b. chondrocytes die4. Along with the penetrating periosteal bud (blood vessels), osteoblasts and osteoclasts penetrate insidea. this forms the primary ossification center in the diaphsis 5. Processes 3. & 4. are repeated at the ends (epiphyses) of the bonea. secondary ossification centers 6. Cartilage removed, except at articular surfaces of bone and ends of diaphysisa. cartilage plate between epiphyses and diaphysis = epiphyseal plate b. responsible for lengthwise bone growth c. plate is active for 15-25 years 7. As bone develops, new bone is being laid down by osteoblasts associated with the periosteuma. osteoclasts remove bone from inside of diaphysis, creating medullary cavity APPOSITIONAL BONE GROWTH: Process of bone formation and removal = bone remodeling - Occurs throughout a person’s life- Production = removal- Means by which the diameter of the bone is maintained/renewed II. BONE FRACTURESA. Kinds of fractures (some break in a bone):1. Simple (closed): bone doesn’t break through skin 2. Compound (open): bone breaks through skin3. Comminuted: bone fragments into many pieces 4. Compression: bone is crushed5. Depressed: broken bone portion is pushed inward (spongy bone is shattered beneath compact bone) 6. Impacted: broken bone ends are forced into each other7. Spiral: ragged break due to twisting forces 8. Greenstick: bone breaks incompletely B. Fracture Repair:1. When bone breaks, a fracture hematoma forms2. a fibrocartilaginous (soft) callus is formed at site of fracture 3. Soft callus replaced with a bony (hard) callus:4. The newly repaired bone is remodeled: All of the following are part of endochondral bone formation EXCEPT:a. Perichondrium invaded by blood vesselsb. A bony callus forms ***c. Cartilage undergoes calcificationd. Medullary cavity is formede. Chondrocytes


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