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Bone and Skeletal Tissues The Skeletal system is composed of cartilage and bone.

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I. Cartilage

A. Contains water, but no nerves B. There are 3 basic types.

     1. Hyaline - smooth, glassy, highly collagenic           a.articular - joints           b. costal - ribs           c. respiratory           d. laryngeal - larynx           e. nasal

     2. Elastic           a. external ear           b. epiglottis

     3. Fibrocartilage           a. intervertebral discs           b. knee joints

C. Cartilage grows in two ways

1. Interstitial growth - new cells are produced internally 2. Appositional growth - new cells are produced at the surface

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II. Bones

A. Functions of bones

     1. Support      2. Protection      3. Movement      4. Mineral storage      5. Blood cell formation

B. Classification of bones

1. Bones are made of two types of structure a. dense, compact bone - found on the surface of bones and throughout the diaphysis of long bones           b. spongy, cancellous bone - found at the ends of long bones and inside flat, irregular, and short bones

2. Bones can be classified into 4 shapes           a. Long - most arm and leg bones           b. Short - like wrist and ankle bones           c. Flat - like the ribs and the skull bones           d. Irregular - such as the pelvis (hip) and vertebrae

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C. Bone structure

1. Long bones           a. diaphysis                i. the central section                ii. it is made of dense bone around a medullary cavity (containing red and yellow marrow)                iii. covered externally by a membrane known as the periosteum                iv. medullary cavity lined (internally) by the endosteum           b. epiphysis - the ends of the bone; filled with spongy bone           c. the diaphysis and epiphysis are separated by epiphyseal lines2. Short, flat, and irregular bones           a. thin outer covering of dense bone          b. inside is composed of spongy bone

      3. Microscopic structure           a. the basic unit is the osteon (composed of a central, Haversion canal surrounded by layers of concentric                   lamellae bone matrix)          b. osteocytes, embedded in spaces called lacunae, are connected to each other and the central canal by                   tubes called canaliculi

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C. Bone structure

4. Chemical composition           a. living cells                i. osteoblasts                ii. osteocytes                iii. osteoclasts           b. matrix                i. organic substances, secreted by osteoblasts, that give the bone tensile strength                ii. inorganic substances, like calcium salts, to make the bone hard

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D. Bone markings      

1. Projections           a. tuberosity - rounded, possible roughened, projection           b. crest - narrow ridge           c. trochanter - large process; found only on the femur           d. line - narrow ridge; less prominent than a crest           e. tubercle - small projection           f. epicondyle - raised area on or above a condyle           g. spine - slender, pointed projection           h. head - bone expansion "above" a narrow neck           i. facet - flat articular surface           j. condyle - rounded articular projection           k. ramus - armlike bar of bone

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D. Bone markings

2. Depressions & openings           a. meatus - canal-like tunnel           b. sinus - cavity within a bone           c. fossa - shallow depression in a bone           d. groove - furrow           e. fissure - narrow slit           f. foramen - round or oval opening

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E. Bone development - osteogenesis or ossification

     1. Intramembranous ossification           a. occurs in most skull bones and in the clavicles           b. ground substance is trapped in the collagen fibers and fibrous membrane to form a spongy bone layer;                   then compact bone covers the surfaces

     2. Endochondral ossification           a. most common type of bone formation           b. osteoblasts beneath the periosteum create bone cells that for a bone collar (bony cylinder just under the                   periosteum           c. bone grows inward from the bone collar as cartilage dies away; the bone cells gradually replace the                   cartilage

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F. Bone Growth

     1. Interstitial growth - new cells are produced internally, at the epiphyseal plate, and can make the bone               longer      2. Appositional growth - new cells are produced at the surface and make the bone thicker

G. Types of fractures

      1. simple - clean break; bone is still fairly in its proper place      2. compound - bone breaks and protrudes through the skin      3. comminuted - bone is broken into several fragments      4. compression - bone is crushed      5. depressed - a piece of the bone is protruding inwardly      6. impacted - bone ends are forced together      7. spiral - bone is broken by twisting forces      8. green stick - incomplete break; most common in young bones

(i.e. children)

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H. Repair of fractures       1. Hematoma (large blood clot) forms

     2. Fibrocartilagenous callus forms      3. Bony callus forms      4. Remodelling; spongy bone callus is compacted

I. Homeostatic imbalances of bone

     1. Osteoporosis - calcium is extracted from the bone, making it porous and weak; most common in older  women      2. Osteomalacia - occurs when bone is not adequately mineralized; the bone becomes soft and can be deformed; caused by not enough calcium or vitamin D in the diet      3. Rickets - a type of osteomalacia particularly affecting kids, whose bones are still growing      4. Paget's disease - a disease of unknown origin that causes excessive and abnormal bone growth.

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