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Chapter 6 - Skeletal System

Chapter 6 - Skeletal System - KIN 216 Applied Human Anatomy...

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Unformatted text preview: KIN 216 Applied Human Anatomy Lecture 6 Skeletal System Organs = bones (very metabolically active) 95% of body's Ca stored in skeleton (DYNAMIC Greek Osteon, Latin osseus process comes and goes) Avg. 206 bones in adult skeleton You have more bones in infancy (about 270 at birth) # of bones decreases during maturity due to some bones fusing together Cartilage Location External ear (hyaline) Nose (Hyaline) Joints (articular) (fibrocartilage) Ribs (costal attach ribs to sternum) hyaline Larynx (and epiglottis) Air tubes of respiratory system Intervertebral discs Pubis symphysis Articular discs (menisci) No nerves or blood vessels Cartilage Structure & Growth Perichondrium = irregular (dense) CT, surrounds cartilage; helps with growth, repair, pressure resistance 6080% water Hyaline, elastic, fibrocartilage refer back to chpt. 4 notes Grows in two ways READ box in p. 126 "A Closer Look" Appositional: ("from the outside") chondroblasts in perichondrium secrete matrix Interstitial: ("growth from within") chondrocytes divide and secrete matrix Bone Functions: Support (framework) Movement (with muscles, ligaments, tendons) Protection (skull<brain>, ribs <heart>) Mineral storage (Ca, P) Blood cell formation and energy storage Red marrow blood cell production Yellow marrow fat storage Classification of Bones Long Short Flat More long than wide Shaft and two ends Cubeshaped, wrist and ankle Sesamoid bone: forms within tendon (e.g., patella) Thin, flat, and often curved Various shapes (e.g., vertebrae, hip bones) Irregular Gross Anatomy Bones Compact bone dense, outer layer Trabecular (spongy) bone network of flat pieces called trabeculae Most long bones have same structure Epiphyses: bone ends Diaphysis: bone shaft Blood vessels Nutrient artery Nutrient vein Nutrient foramen (hole) Long Bones (cont'd.) Medullary (marrow) cavity Membranes Center of diaphysis, contains no bone tissue contains yellow marrow Periosteum covers entire outer surface of bone except ends of epiphyses 2 layers Dense irregular CT (superficial) Osteogenic layer (deep) Periosteum secured to underlying bone via perforating (Sharpey's) fibers Endosteum covers internal bone surfaces Osteoblasts (bone building) Osteoclasts (bone breakdown) Short, Irregular, Flat Bones Similar composition to long bones External: compact bone covered by periosteum Internal: spongy bone covered by endosteum No diaphysis Contain marrow, but not in medullary cavity (there is no medullary cavity) Diploe = internal spongy bone (flat bones) Design of Bones and Stress Each bone's anatomy designed for most common stresses Bending causes compression on one side bearing weight, muscle pull Tension = stretch; occurs on other side Microscopic Structure of Bone Compact bone Osteon/Haversian system (structural unit) Made of long cylinders parallel to axis Central canal (Haversian Group of concentric tubes (lamellae) canal) Perforating canals (Volkmann's canals) Osteocytes are found in lacunae, with "spider legs" extending into canaliculi Interstitial and circumferential lamellae also exist Microscopic Structure of Bone Spongy bone Less complex than compact bone Each trabecula has lamellae and osteocytes, but does not have osteons Osteocytes receive nourishment from capillaries in endosteum surrounding trabecula Chemical Composition of Bone Know Bone has organic (35%) and inorganic components (65%) Bone has significant amount of collagen flexibility and strength Inorganic components are mineral salts The combination of organic and inorganic components allow bone to be flexible yet strong Bone Development Osteogenesis (Ossification) Begins in embryo and lasts through adolescence Occurs in adult at slower rate 2 types Intramembranous ossification Endochondral ossification Modeled through mesenchyme Modeled through cartilage Intramembranous Ossification Form directly from mesenchyme Week 8 (embryonic): mesenchyme forms Most bones of skull, clavicles osteoblasts, secrete osteoid and form woven bone tissue No lamellae at this stage; trabeculae at ends grow thicker and form compact bone on surfaces Forms flat bones Endochondral Ossification Modeled first in hyaline cartilage, which is replaced by bone tissue Lasts from 2nd month of embryo until early adulthood Although bones grow in both length and width, textbook focuses on length, uses long bones for example 4 stages Stages of Endochondral Ossification Stage 1: Bone collar forms around diaphysis Stage 2: Cartilage calcifies in center of diaphysis Stage 3: Periosteal bud invades diaphysis, first trabeculae form Stage 4: Secondary ossification centers form in epiphyses Epiphyseal Growth Cartilage cells form tall columns Chondroblasts at top divide quickly Older chondrocytes in stack signal calcification, then die and disintegrate Bone is formed on diaphysis side Postnatal Growth Bones stop lengthening when epiphysis and diaphysis fuse, around age 18 for females and 21 for males Appositional growth (width) occurs at same time as lengthening Short bones single ossification center Irregular bones complex Long bones (short long bones) have one epiphysis Hormones regulate bone growth Bone Remodeling Continuous process, deposit and removal Remodeling units Not a uniform process Resorption: osteoclasts break down bone tissue Deposition: osteoblasts lay down osteoid, calcium salts crystallize Remodeling helps to maintain constant concentrations of Ca, PO43 (phosphate) in body fluids and helps bone respond to stresses Bone Fractures Simple fracture = bone breaks, no skin penetration Compound fracture = ends of bone penetrate skin KNOW fracture types, Table 6.1, p.138 Reduction = putting bone back together (closed or open) Bone Disorders Osteoporosis Osteomalacia (bone softening in adults) Low bone mass, deterioration Bone deposition CRITICAL in adolescence and early adulthood Rickets in children more than one disorder Paget's disease Osteosarcoma Excessive bone deposition and resorption Form of bone cancer ...
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