6-1 Chapter 6 Skeletal System

6-2 Functions Support Protection Movement Storage Blood cell production

6-3 Components Bone Cartilage

6-4 Hyaline Cartilage Cells –Chondroblasts –Chondrocytes: surrounded by matrix in lacunae Matrix. Collagen fibers for strength Perichondrium. Double-layered C.T. sheath; Covers cartilage –Inner –Outer Articular cartilage. Covers bones at joints; no perichondrium Growth –Appositional –Interstitial

6-5 Bone Shapes Long Short Flat Irregular

6-6 Long Bone Structure Diaphysis –Shaft –Compact bone Epiphysis –End of the bone –Cancellous bone Epiphyseal plate: growth plate –Hyaline cartilage; present until growth stops; becomes epiphyseal line Medullary cavity –Red marrow –Yellow marrow

6-7 Con’t. Bone membranes: Periosteum (outside) –Outer is fibrous –Inner is single layer of bone cells –Continuous with tendon Endosteum (inside) –Lines all internal spaces

6-8 Other Bone Structure Flat Bones Short and Irregular Bone Some bones of skull have sinuses

6-9 Bone Histology Bone matrix –Organic: collagen –Inorganic: hydroxyapetite. CaPO 4 crystals Bone cells –Osteoblasts –Osteocytes –Osteoclasts –Stem cells (osteochondral progenitor cells)

6-10 Bone Cells Osteoblasts –Collagen produced by E.R. and golgi –Ossification: formation of bone

6-11 Con’t. Osteocytes. Mature bone cells surrounded by matrix –Lacunae: space occupied by osteocyte –Canaliculi: canals for cell extensions –Nutrients diffuse through liquid surrounding cell; transfer nutrients through gap junctions.

6-12 Con’t Osteoclasts. Resorption of bone –H ions pumped across membrane, acid forms, eats away bone. –Release enzymes that digest the bone.

6-13 Con’t Stem Cells. (Osteochondral Progenitor Cells) become chondroblasts or osteoblasts.

6-14 Bone Types Woven bone Lamellar bone Cancellous bone Compact bone

6-15 Woven and Lamellar Bone Woven bone. Collagen fibers randomly oriented. –Formed During fetal development During fracture repair Remodeling –Removing old bone and adding new –Woven bone is remodeled into lamellar bone Lamellar bone. Collagen fibers parallel

6-16 Cancellous (Spongy) Bone Trabeculae: interconnecting rods or plates of bone. –Spaces filled with marrow. –Covered with endosteum. –Oriented along stress lines

6-17 Compact Bone Osteons – unit of compact bone –Haversian canal –Lamellae –Lacunae and canaliculi contain osteocytes and fluid –Volkmann’s canal

6-18 Bone Development: 2 Types Intramembranous ossification –Takes place in CT membrane Endochondral ossification –Takes place in cartilage Both methods produce woven bone that is then remodeled into lamellar

6-19 Intramembranous Ossification Process: 1.Embryonic mesenchyme forms a CT membrane and periosteum 2.Stem cells become osteoblasts which form bone matrix 3.Osteoblasts become osteocytes 4.Bone is remodeled Centers of ossification Fontanels

6-20 Intramembranous Ossification

6-21 Endochondral Ossification Process: 1.Embryonic mesenchyme forms chondroblasts, surrounded by perichondrium 2.Hyaline cartilage forms model of bone 3.Cartilage breaks down 4.Stem cells become osteoblasts; perichondrium become periosteum 5.Bone is remodeled Primary ossification center in diaphysis Secondary ossification centers in epiphyses

6-22 Endochondral Ossification

6-23 Growth in Bone Length Interstitial growth within cartilage in epiphysis (secondary ossification center) Articular cartilage: does not ossify, and persists through life

6-24 Zones of the Epiphyseal Plate

6-25 Growth in Bone Length

6-26 Growth in Bone Width Appositional growth

6-27 Factors Affecting Bone Growth Genetics Nutrition –Lack of calcium, protein and other nutrients –Vitamin D –Vitamin C Hormones –Growth hormone (GH) –Thyroid hormone –Estrogen and testosterone

6-28 Bone Repair 1.Hematoma forms 2.Callus forms –Internal –External

Callus ossification 4. Bone remodeling

6-30 Bone Remodeling Involved in bone growth, changes in bone shape, adjustments in bone due to stress, bone repair, and Ca ion regulation

6-31 Calcium Homeostasis Bone stores Ca 2+ Level of Ca ions in the blood depends upon its movement into or out of bone –Hormones: Parathyroid hormone (PTH) secreted if blood Ca levels are too low; cause increase in number of osteoclasts Calcitonin secreted if blood Ca levels are high; decreases osteoclast activity

6-32 Calcium Homeostasis

6-33 Effects of Aging on Skeletal System Bone matrix decreases. More brittle due to lack of collagen; but also less hydroxyapetite. Bone mass decreases. Highest around 30. Men denser due to testosterone and greater weight. African Americans and Hispanics have higher bone masses than Caucasians and Asians. Rate of bone loss increases 10 fold after menopause. Cancellous bone lost first, then compact. Increased bone fractures Bone loss causes deformity, loss of height, pain, stiffness –Stooped posture –Loss of teeth

6-34 Bone Fractures Open (compound)- bone break with open wound. Bone may be sticking out of wound. Closed (simple)- Skin not perforated. Incomplete- doesn’t extend across the bone. Complete- does Greenstick: incomplete fracture that occurs on the convex side of the curve of a bone Hairline: incomplete where two sections of bone do not separate. Common in skull fractures Comminuted fractures: complete with break into more than two pieces

6-35 Bone Fractures, cont. Impacted fractures: one fragment is driven into the cancellous portion of the other fragment. Classified on basis of direction of fracture Linear Transverse Spiral Oblique Dentate: rough, toothed, broken ends Stellate radiating out from a central point.