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Functions of Skeletal System
1. Support
2. Storage of lipids
3. Storage of minerals
4. Protection
5. Blood cell production
6. Leverage
Classification of Bone
1. Shape
2. internal tissue organization
3. Bone markings
Long Bones
1. Long, thin
2. Arms, legs, hands, feet, fingers, toes
Flat Bones
1. Thin with parallel surface
2. Skull, sternum, ribs, and scapulae
Sutural Bones
1. Small, irregular bones
2. between flat bones of skull
Irregular bones
1. Complex shapes
2. Spinal vertebrae and pelvic bones
Sesamoid Bones
1. Small and flat
2. In tendons near joint of knees, hands, and feet
Bone Markings
1. Depression or grooves: along surface
2. Projections: tendons and ligaments attach
3. Tunnels: Where blood and nerves enter bone
Diaphysis
1. Shaft
2. heavy wall of compact bone/dense bone
3. Medullar cavity=central space
Epiphysis
1. Wide part at each end
2. articulation with other bone
3. Spongy bone
4. covered with compact bone
Metaphysis
Where diaphysis and epiphysis meet
Osseous Tissue
1. Dense, supportive CT
2. specialized cells
3. produce solid matrix of calcium salts
4. Around collagen fibers
Characteristic of Bone tissue
1. Dense matrix w/ calcium salts and osteocytes in lacunae around blood vessels
2. Canaliculi: exchange waste and nutrients
3. Periosteum: outer fibrous and inner cellular layers
Matrix materials
2/3 Ca3(PO4)2
reacts with calcium hydroxide to form crystals of hydroxyapetite
incorporates ither calcium salts and ions
Matrix proteins: 1/3 Collagen
Osteocytes
1. Mature bone cells
2. In lacunae
3. between lamellae of matrix
4. Do not divide
5. Connect through canaliculi
Function:
1. maintain protein/mineral content of matrix
2. help repair damaged bone
Osteoblasts
1. Immature bone cells
2. secrete matrix cmpds (osteogenesis)
3. osteoid: matrix produced by osteoblasts not yet calcified to form bone
4. Surround bone to become osteocytes
Osteoprogenitor cells
1. Mesenchymal cells that produce osteoblasts
2. in endosteum
3. assist in fracture repair.
Osteoclasts
1. Secrete acids and protein digesting enzymes
2. giant, multinucleate cells
3. dissolve bone matrix and release stored minerals (osteolysis)
4. Derived from stem cells that produce macrophages
Homeostasis
Bone building=bone recycling

breakdown>building=weak

weight bearing exercise cause osteoblasts to build bone.
Compact bone
1. Osteon: basic unit
2. osteocytes in concentric lamellae around central canal containing blood vessels
perforating canals:
perpendicular to central canal
carry bv into bone and marrow

Circumferential lamellae:
lamellae wrapped around long bone
bind osteons together.


Spongy Bone
1. No osteons
2. matrix forms trabeculae
3. trabeculae=no bv
4. space between trabeculae filled w/ red marrow
-has bv
-forms rbc
-supplies nutrients to osteocytes
5. yellow marrow: stores fat

Periosteum
1. covers all bone except parts enclosed in joint capsules
2. made up of outer, fibrous layer and inner cellular layer
Perforating fibers
1. Collagen fibers of periosteum
2. connect w/ collagen fibers in bone
3. and with fibers of joint capsules; attach tendons and ligaments
Periosteum Functions
1. Isolates bone from surrounding tissues
2. provide route for circulatory and nervous supply
3. participates in bone growth and repair
endosteum
1. incomplete cellular layer
2. lines medullary cavity
3. covers trabeculae of spongy bone
4. lines central canals
5. contain, osteoblasts, osteoprogenitor cells, and osteoclasts
6. Active in bone growth and repair
Osteogenesis
Bone formation
Ossification
Process of replating other tissues w/bone
Calcification
Process of depositing calcium salts
during ossification and in other tissues
Endochondrial ossification
Ossifies bone that originates as hyaline cartilage
1. Cartilage enlarge, chondrocytes near center of shaft. Inc in size. Matrix dec. that begin to calcify. chondrocytes die/ disintegrate leaving cavities.
2. Blood vessels grow around edge of catilage & cells of perichondrium convert to osteoblasts.
3. BV penetrate cartilage & invade central region. Fibroblasts in BV differentiate into osteoblasts & produce spongy bone. Bone formation spreads along shaft towards both ends
4. remodeling occurs creating marrows. Bone of shaft thicker & cartilage near epiphysis replaced by shaft. Inc length + size.
5. Capillaries + osteoblasts migrate into epiphyses creating secondary ossification centers.
6. Epiphysis filled w/ spongy bone. Articular cartilage remains exposed to joint cavity. Overtime will be reduced to superficial layer. At ea. metaphysis an epiphyseal cartilage separates epiphysis from diaphysis.
Appositional Growth
Compact bone thickens and strengthens long bone w/ layers of circumferential lamellae.
Dermal Ossification (intramembranous ossification)
1. In dermis
2. Produces dermal bones (mandible, clavicle)
Steps:
1. Mesenchymal cells aggregate, differentiate, & begin ossification. Bone expands as a series of spicules that spread to surrounding tissue.
2. As spicules connect they trap bv in bone.
3. overtime bone assume structure of spongy bone. Areas of spongy bone may later be removed creating marrow cavities. through remodeling, spongy bone formed in this way can be converted to compact bone.
Nutrient Artery and Vein
1. Single pair of large bv
2. enter diaphysis through nutrient foramen
3. femur has more than 1 pair
Metaphyseal Vessels
1. Supply the epiphyseal cartliage
2. where bone growth occurs
Periosteal Vessels
1. Blood to superficial osteons
2. secondary ossification centers
Remodeling
1. maintain itself
2. replace mineral reserves
3. recycles and renews bone matrix
4. osteocytes, osteoblasts, and osteoclasts
Turnover rate:
deposition>removal=stronger
removal>depositio=weaker
Hormones
1. Vit C: collagen synthesis and stimulation of osteoblast differentiation
2. Vit A: stim osteoblast activity
3. Vit K & B12: synthesize bone proteins
4. GH & thyroxine: stim bone growth
5. Estrogens/Androgens: stim osteoblasts
6. Calcitonin & PTH: reg calcium and phosphate levels.
Parathyroid hormone
1. Inc calcium levels
2. Stim osteoclasts
3. dec calcium excretion
4. inc intestinal absorption of calcium
Calcitonin
1. Secreted C cells in thyroid
2. inhibit osteoclast activity
3. inc calcium excretion at kidneys
Fractures
1. Bleeding
Produce clot (fracture hematoma)
establish fibrous network
Bone cells in area die
2. Cells of endosteum and periosteum divide and migrate into fracture zone
calluses stabilize break
external callus: cartilage and bone surround break
internal callus: develop in medullary cavity
3. Osteoblasts replace central cartilage of external callus with spongy bone
4. Osteoblasts and osteocytes remodel the fracture for up to a yr. reduce bone calluses.
Pituitary Dwarfism
Head and arms proportional to body
Hyposectretion of GH
Gigantism
Hypersecretion of GH
Acromegaly
Epiphyseal plates ossified
grow wider and dermal thickening
furrowed eyebrows and wrinkles
Types of fractures
1. Colles: Elderly. arm
2. Greenstick: kids. 1 side fracture
3. epiphyseal: child/teen. along epiphyseal plate.
Osteoporosis
Severe bone loss
affect normal function
>age 45
29% women
18% men
Osteosarcoma
Tumor on bone
Osteoclasia
Bone infection
staph/ strep
Acondroplasia Dwarfism
small growth plates
short stubby arms and legs
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