A&P Chapter 6 Flashcards
Functions of the Skeletal System
Support - Weight bearing Protection - Encases organs Movement - Muscle attachment Storage - Minerals
Cartilage (3 types)
Hyaline Cartilage associated with bones - Development, lengthening, and repair. Specialized cells - Chondroblasts - Chondrocytes
2 types of cartilage growth
Apositional
- Chondroblasts in perichondrium add matrix to outside of existing cartilage.
Interstitial
- Chondrocytes within tissue divide and matrix between existing cells.
Bone Matrix
- 35% organic material
- 65 inorganic material
- collagen gives flexibility
- loss of collagen causes brittle bones
- minerals give strength
- loss of minerals causes “bendy” bones
Bone Histology
Bone cells - osteoblasts, osteocytes, osteoclasts Woven bone: collagen fibers randomly oriented Lamellar bone: mature bone in sheets Spongy: trabeculae Compact bone: dense
Origin of bone cells
Mesenchymal cells give rise to osteochindral progenitor cells Osteochondral progenitors cells -Innner perichondrium & periosteum -Give rise to osteoblasts Osteoblasts -Develop into osteocytes
Bone Cells
Osteoblasts
- Formation of bone through ossification or osteogenesis. Collagen produced by E.R. and golgi. Released by exocytosis. Precursors of hydroxyapetite stored in vesicles, then released by exocytosis.
- Ossification: formation of bone by osteoblasts. Osteoblasts communicate through gap junctions. Cells surround themselves by matrix.
Bone Cells
Osteocytes. Mature bone cells. Surrounded by matrix, but can make small amounts of matrix to maintain it.
- Lacunae: spaces occupied by osteocyte cell body
- Canaliculi: canals occupied by osteocyte cell processes
- Nutrients diffuse through tiny amount of liquid surrounding cell and filling lacunae and canaliculi. Then can transfer nutrients from one cell to the next through gap junctions.
Bone Cells
Osteoclasts. Resorption of bone
- Ruffled border: where cell membrane borders bone and resorption is taking place.
- H ions pumped across membrane, acid forms, eats away bone.
- Release enzymes that digest the bone.
- Derived from monocytes (which are formed from stem cells in red bone marrow)
- Multinucleated and probably arise from fusion of a number of cells
Woven and Lamellar Bone
Woven bone
- Collagen fibers randomly oriented
- Formed during embryonic development and fracture repair
- Replaced with lamellar bone over time
Lamellar bone
- Mature bone with organized collagen fibers
- Arranged in thin sheets called lamellae
Spongy Bone
- Contains interconnected plates called trabeculae
- Bone marrow and blood vessels fill spaces between trabeculae
- Trabeculae are oriented along lines of stress
- Trabeculae can rearrange if stress changes
Compact Bone
- Denser than spongy bone
- Central canal contain blood vessel
- Concentric lamella surround central canal
- Osteon is central canal, lamella, & osteocytes
- Circumferential lamella form outer surface
- Blood vessels enter bone by perforating canals
Shape of Bones
Long bones - Upper and lower limb Short bones - Ankle and wrist Flat bones - Skull, ribs, sternum, shoulder blades Irregular bones - Vertebrae and facial bones
Structure of Long Bones
Diaphysis - Long axis or shaft of bone Articular cartilage - Covers the end of long bones Epiphysis - End of bones Epiphyseal plate - Separates epiphysis from diaphysis
Structures of Bone
Medullary cavity - Internal cavities filled with marrow Periosteum - Covers outside of bone has blood - Outer layer of vascularized connective tissue -Fibers of tendons become continuous with fibers of periosteum. Endosteum - Covers internal space of bone
Bone Shapes
Long - Ex. Upper and lower limbs Short - Ex. Carpals and tarsals Flat - Ex. Ribs, sternum, skull, scapulae Irregular - Ex. Vertebrae, facial
Structure of flat, short, and irregular bones
Flat Bones
- No diaphyses, epiphyses
- Sandwich of cancellous between compact bone
Short and Irregular Bone
- Compact bone that surrounds cancellous bone center; similar to structure of epiphyses of long bones
- No diaphyses and not elongated
Some flat and irregular bones of skull have sinuses lined by mucous membranes.
Bone Formation
Intramembranous ossification
- Takes place in connective tissue membrane
Endochondral ossification
- Takes place in cartilage
Both methods of ossification
- Produce woven bone that is then remodeled
- After remodeling, formation cannot be distinguished as one or other
Intramembranous Ossification
- Takes place in connective tissue membrane formed from embryonic mesenchyme
- Forms many skull bones, part of mandible, diaphyses of clavicles
- When remodeled, indistinguishable from endochondral bone.
- Centers of ossification: locations in membrane where ossification begins
- Fontanels: large membrane-covered spaces between developing skull bones; unossified
Intramembranous Ossification
- Osteoblasts develop from mesenchymal cells & produce bone matrix
- Trabeculae develop
- Osteoblasts enlarge trabeculae to form spongy bone
- Specialized cells form red marrow
- Periosteum develops
- Compact bone develops from periosteum osteoblasts
Endochondral Ossification
- Bones of the base of the skull, part of the mandible, epiphyses of the clavicles, and most of remaining bones of skeletal system
- Cartilage formation begins at end of fourth week of development
- Some ossification beginning at about week eight; some does not begin until 18-20 years of age
Endochondral Ossification
- Mesenchyme derived osteochondral progenitor cells become chondroblasts
- Chondroblasts produce hyaline cartilage
- Perichondrium surrounds cartilage
- Blood vessels invade perichondrium
- Perichondrium become periosteum
- Osteoblasts produce compact bone on surface of cartilage to form bone collar
Endochondral Ossification
- Chondrocytes absorb matrix and enlarge
- Chondrocytes calcify forming hydroxyapatite
- Osetoblasts form bone on surface of calcified cartilage to form spongy bone (primary ossification site)
- Osteoclasts form medulla cavity
- In mature bone epiphyseal line becomes epiphyseal plate
Bone Growth
Increase due to growth at epiphyseal plate Zone of epiphyseal plate Zone of resting cartilage Zone of proliferation Zone of hypertrophy Zone of decalcification
Epiphyseal growth
Zone of resting cartilage - Nearest epiphysis Zone of proliferation - Produce new cartilage via interstitial growth Zone of hypertrophy - Cartilage matures and enlarges Zone of decalcification - Cartilage dies and osteoblasts deposit bone
Growth at Articular Cartilage
- Increases size of bones with no epiphyses:
e. g., short bones - Chondrocytes near the surface of the articular cartilage similar to those in zone of resting cartilage
Growth in Width
- Due to apositional growth beneath periosteum
- Osteoblasts lay down ridges
- Periosteum and blood vessels line ridges
- Osteobasts produce bone until ridge becomes a tunnel
- Osteoblasts lay down lamella to fill tunnel
Nutrition
Vitamin D - Absorption of calcium - Ricketts, bowed bones and inflamed joints Vitamin C - Collagen synthesis - Slow growth - Scurvy - Lose of teeth due to compromised ligaments
Hormones
Growth hormone - Apositional and interstitial growth - Gigantism and dwarfism Thyroid hormone - Normal tissue growth Sex hormones - Estrogen and testosterone - Stimulate bone growth
Bone Remodeling
Old bone must be replaced with new Converts woven bone to lamellar bone Bone growth Changes in bone shape Stress adjustments Bone repair Calcium ion regulation Entire skeleton renewed every 10 years
Mechanical Stress
Stress can modify bone’s strength Increased stress increases osteoblasts Pressure increases osteoblasts activity Reduced stress reduced osteoblasts - Astronauts and the bedridden Osteoclasts activity remains constant
Bone Repair
- Blood released from damaged vessel forms a clot
- A callus containing cartilage and collagen forms
- Cartilage callus replaced with woven bone via endochondral ossification
- Remodeling replaces spongy bone with compact bone
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
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.
Calcium Homeostasis
Circulating calcium required for muscle contractions & membrane potentials Bone is major site for calcium storage Osteoblasts - remove calcium from blood Osteoclasts - add calcium to blood from bone
Calcium Homeostasis
Parathyroid hormone
- Major regulator of blood calcium levels
- Stimulates osteoclast activity when calcium levels are low
Calcitonin (thyroid)
- Decreases osteoclast activity when calcium levels are high
Osteoprotegerin
- Inhibits osteoclast production
Aging on the Skeleton
- Peak bone mass at 30 years
- Decreased collagen causes brittle bones
- Decreased matrix formation
- Increased likelihood of fractures
- Curvature of the spine
