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How many bones are in an adult human skeleton?
206
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Osteology
the study of bone
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What is the Skeletal System made of?
composed of bone, cartilage, and ligaments
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Ligaments
hold bone to bone at joints
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Tendons
attach muscle to bone
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Functions of the Skeleton
- Support
- Protection
- Movement
- Electrolyte balance
- pH balance
- Blood formation
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Bone (Osseous tissue)
- connective tissue with matrix hardened by calcium
- Called Mineralization or Calcification
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Flat Bones
- Curved but wide and thin
- Example: Ribs
- Function: protect soft organs
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Long Bones
- Longer than wide
- Functions: Rigid levers acted upon by muscles
- Example: Femur
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Short Bones
- Equal in length and width
- Function: glide across one another in multiple directions
- Example: carpal bones
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Irregular Bones
- Elaborate shapes that don't fit into other categories
- Example: vertabrae
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Epiphyses
Enlarged heads of long bones
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Compact Bone
- Also Dense Bone
- Outer shell of bones
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Diaphysis
- shaft of long bones
- cylinder of compact bone to provide leverage
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Spongy Bone
- also Cancellous Bone
- always covered by compact bone
- lighter and less dense than compact bone
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Articular Cartilage
layer of hyaline cartilage that covers joint surfaces
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Nutrient Foramina
Minute holes in the bone surface to allow blood vessels to penetrate
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Periosteum
- external sheath that covers bone except where the articular cartilage is
- made of dense irregular CT
- Outer fibrous layer of collagen
- perforating fibers for strong attachment
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Endosteum
Thin layer of reticular CT lining marrow cavity
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Epiphyseal Place
- Line of hyaline cartilage that separates marrow space of the epiphysis and diaphysis
- Only seen in children who are still growing
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Dipole
- Flat bone composition
- Spongy layer sandwiched in between two layers of compact bone
- Absorbs shock
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Osteogenic Cells
- Stem Cells found in periosteum, endosteum and central canals
- arise from mesenchym
- produce new osteoblasts
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Osteoblasts
- Synthesis soft organic matter matrix which hardens through calcification
- nonmitotic
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Osteocytes
- Former osteoblasts that have become trapped in matrix
- Maintain bone matrix
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Lacunae
Little cavities in bone matrix where osteocytes live
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Canaliculi
Little channels that connect lacunae
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Cytoplasmic Processes
part of the osteocyte that reach into the canaliculi
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Osteoclasts
- Bone-dissolving cell found on the bone surface
- Not a bone cell
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Remodeling
results from combined action of the bone-dissolving osteoclasts and the bone-depositing osteoblasts
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Matrix Composition
- 1/3 organic matter deposited by cells by weight
- 2/3 inorganic matter
- -85% hydroxyapatite
- -10% calcium
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Rickets
- Soft bones due to calcium salts
- Only found in children
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Osteogenesis Imperfecta
- Brittle Bone Disease
- excessively brittle bones due to lack of protein, collagen
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Ceramic Polymer Composition
- Ceramic: hydroxyapatite and calcium
- Polymer: collagen
- makes bones tough but slightly flexible so they don't break
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Perforating Canals (Volkmann)
Transverse or diagonal canals carrying blood and nerves through bones
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Central Canals
Run up and down long bones a carrying blood and nerves through bone
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Spicules
Slivers of spongy bone
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trabeculae
- Thin plates in spongy bone
- Develop along lines of stress
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Bone Marrow
soft tissue that occupies the marrow cavity of long bones and small spaces amid trabeculae of spongy bone
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Red Bone Marrow (myeloid tissue)
- Found in the skull, vertebrae, ribs, sternum, pelvic girdle, proximal heads of humerus and femur
- produces blood cells
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Yellow Bone Marrow
- Only found in adults
- Composed of adipose tissue
- No longer produces blood
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Ossification
bone formation
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Intramembranous Ossification
- Formation of Flat Bones
- 1. Condensation of mesenchyme into soft sheets permeated with blood capillaries
- 2. Deposition of osteoid tissue by osteoblasts on mesenchymal surface; entrapment of first osteocytes
- 3. Honeycomb of bony trabeculae formed by continued mineral deposition; creation of spongy bone
- 4. Surface of bone filled by bone deposition, converting spongy bone to compact bone. Spongy bone in the middle
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Endochondral Ossification
- 1. Early cartilage model consisting of perichondrium and hyaline cartilage
- 2. Formation of primary ossification center, bony collar, and periosteum
- 3. Vascular invasion, formation of primary marrow cavity and secondary ossification center
- 4. Bone at birth, with enlarged primary marrow cavity and appearance of secondary marrow cavity
- 5. Bone of a child, with epiphyseal plate at distal end
- 6. Adult bone with single marrow cavity and closed epiphyseal plate
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Metaphysis
zone of transition facing the marrow cavity
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Zones of Metaphysis
- 1. Zone of reserve cartilage
- 2. Zone of cell proliferation
- 3. Zone of cell hypertrophy
- 4. Zone of calcification
- 5. Zone of bone deposition
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Interstitial Growth
Bone growth in length from the epiphyseal line
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Appositional Growth
Bone increase in width by laying down circumferential lamellae
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Wolff's Law
Architecture of bone determined by mechanical stress placed on it and bones adapt to withstand those stresses
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Achondroplastic Dwarfism
Long bones stop growing in childhood
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Pituitary Dwarfism
- Lack of growth hormone
- Normal proportions
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Growth Hormone
stimulates protein synthesis and cell growth throughout the body
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Thyrocine
stimulates cell metabolism and increase osteoblast activity
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Estrogen and Testosterone
stimulate osteoblasts to produce bone faster causing epiphyseal plate to close
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Abnormal (Ectopic) Calcification
Bone deposition outside of bones
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Mineral Resorption
the process of dissolving bone and releasing minerals into the blood
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Hypocalcemia
- Too much calcium in the blood
- causes excessive excitability of nervous system leading to muscle spasms and tremors
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Hypercalcemia
- Too little calcium in the blood
- Sodium channels are less likely to open. depressing nervous system
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Calcitriol
- A form of Vitamin D produced from the skin, liver, and kidneys
- Allows body to absorb calcium from food
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Calcitonin
- Secreted by C ells of the thyroid gland when calcium levels in the blood are too high
- inhibits osteoclasts from dissolving bone
- increases the number of osteoblasts to deposit calcium into the skeleton
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Parathyroid Hormone (PTH)
- Secreted by the parathyroid gland when blood calcium reaches too low
- Raises blood calcium level by stimulating osteoclasts
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Stress Fracture
Break caused by abnormal trauma to a bone
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Pathological Fracture
break in a bone that has been weakened by some other disease
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Healing of fractures
- 1. Hematoma formation
- 2. Soft callus made of collagen
- 3. Hard calls formation
- 4. Bone remodeling
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Closed Reduction
Bone fragments are manipulated into their normal position without surgery
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Open Reduction
Opening a fracture surgically to put the bones back together using pins and plates
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Orthopedics
Branch of medicine that deals with prevention and correction of injuries and disorders of the bones, joints, and muscles
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Electrical Stimulation
- accelerates bone repair
- suppresses effects of parathyroid hormone
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Osteoporosis
severe loss of bone density
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