Skeletal system
functions
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Framework / support
Protection
Movement by Levers; actuated by muscles
Storehouse for calcium and phosphorus
Produce blood cells – hemopoiesis
Triglyceride storage – Yellow bone marrow
(adipose cells)
Bone classification
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BONES CLASSIFIED BY SHAPE
Flat bones – rib, skull, sternum, scapulae
Short / Cube bones – wrist, ankle
Irregular bones – vertebrae
Long bones (typical) – arms / legs
Long bone anatomy
• Compact bone – Hard and dense, main
shaft of long bone (diaphysis), outer layers
of others. Osteocytes are located in the
rings of bones around a central canal
(Haversian system)
• Spongy bone – meshwork of small boney
plates (trabeculae) filled with red marrow
and found at ends of long bones
(epiphysis), center of others
Long bone con’t
• Medullary cavity (marrow) : Red – makes
blood cells, Yellow- largely fat, adults
• Membranes: Periosteum (dense irregular)
– covers on outside; inner layer has
osteoblasts. Endosteum – lines marrow
cavity inside, single layer, bone forming
cells
• Metaphyses – end of bones, diaphysis
joins epiphyses (epiphyseal plate) , when
harden in early 20’s. A line forms on Xray
and growth stops.
Long bone
Ossification – formation
• Bones are organs that as we are babies
they start out as cartilage. During the 2/3rd
month the osteoblasts become active.
First the intercellular material has collagen
and Calcium (Ca) deposited the material.
It hardens. Now the cells are called
osteocytes. When bone is damaged,
osteoclasts reabsorb the bone fragments.
Haversian system
• Compact bone consists of closely packed
osteons or haversian systems. The osteon
consists of a central canal called the osteonic
(haversian) canal, which is surrounded by
concentric rings (lamellae) of matrix. Between
the rings of matrix, the bone cells (osteocytes)
are located in spaces called lacunae. Small
channels (canaliculi) radiate from the lacunae to
the osteonic (haversian) canal to provide
passageways through the hard matrix. Blood
vessels penetrate through transverse
Volkmann’s canals.
Haversian system
Haversian system
Bone formation
• 1) the initial formation in embryo / fetus
• 2) growth during infancy, childhood,
adolescence
• 3) remodeling of bone
• 4) repair of fractures
Initial bone formation
• Embryonic skeleton first composed of
mesenchyme (gelatin / reticular tissue shaped like bones) which provides the
template for ossification.
• Intramembranous – bone forms directly
within mesenchyme arranged in sheetlike
layers that resemble membranes
• Endochondrial – bone forms within hyaline
cartilage that develops from mesenchyme
Intramembranous
1)
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3)
4)
Ossification center
Calcifcation
Formation of trabeculae
Periosteum
Endochondrial
1) Development of the cartilage model
2) Growth of the cartilage model
3) Development of the primary ossification
center
4) Cavity formation
5) Development of secondary ossification
center
6) Formation of articular cartilage and
epiphyseal plate
Bone growth
• Appositional growth – increase the width of
new bone onto old bone
• Endochondrial growth – Chondrocytes
(epiphyseal plate) divide to align in columns.
Expansion causes the bone to elongate. Old
cartilage replaced by bone.
• Remodeling – Removal of existing bone by
osteoclast and deposition of new by osteroblast.
Outside is deposited, medullary cavity is
removed. Calcium levels maintained this way by
hormonal control
Bone fractures
• Open (compound) – bone protrudes
through the skin
• Closed (simple) – skin intact
• Complete – bones separate
• Greenstick – incomplete break on convex
side of bone curve
• Communited – more than 2 fragments
• Callus – zone of tissue repair between two
fragments
Lifestyle and bone development
• Diet - Daily intake of Calcium (Ca) form
dairy products (milk, yogurt, and
cheese),phosphorus, magnesium; vitamin
A, C, D
• Exercise (weight bearing), needed for
proper remodeling
• Hormones – Human growth hormone,
Insulin Growth factors, Thyroid hormones,
Estrogen – female, Androgens – males
“growth spurts” in teenagers
Calcium homeostasis
• Bone stores 99% of Calcium. Small
changes in blood calcium level can be
deadly too high stops heart, too low
breathing stops.
• Parathyroid hormones: blood Ca drops,
parathyroid produces cyclic Amp causing
PTH synthesis to increase, increases
osteoclasts to release Ca from bone and
decrease loss form urine
• Calcitonin – thyroid, decreases blood Ca
Bone features
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Head – enlarged rounded end
Crest – prominent ridge
Process – projection
Tubercle – lump, knob
Trochanter – Large knob found only on the
proximal femur
• Foramen – hole in bone, nerve / blood
vessel pass through
Bone features con’t
• Fossa – depression in bone
• Condyle – smooth round articular surface,
like on humerous, femur
• Shaft – main body of bone
Abnormal curvatures
• Kyphosis – hunchback – abnormal
posterial curvature of spine, upper
thoracic.
• Lordosis – abnormal anterior curvature in
spine, lumbar region
• Scoliosis – abnormal lateral curvature of
spine, C or S
Disorders
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Osteoporosis- loss of bone mass, fractures
Herniated disk –rupture of fibrocartilage
Spina bifida – laminae not unite at midline
Rickettes – vitamin D deficiency
Dwarfism – inadequate ossification at long bone,
shortness
• Gigantism –abnormal ossification of growth plate
• Paget’s disease – older, irregular thickening and
softening of bone.