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Unit 5: The Skeletal System
Ch. 7
General Organization
206 bones*

Axial Skeleton – down the
center
 Skull
 Cranium – 8
 Facial – 14
 Middle Ear - 6
 Vertebral Column
 Cervical – 7
 Thoracic – 12
 Lumbar – 5
 Sacrum, Coccyx
 Thoracic Cage
 12 pairs
 7 true ribs
 5 False Ribs
 2
floating
ribs

Appendicular Skeleton – the appendages
 Pectoral Girdle
 Scapula – 2
 Clavicle – 2
 Upper Limbs
 Humerus – 2
 Radius – 2
 Ulna – 2
 Carpals – 16
 Metacarpals – 10
 Phalanges – 28
 Pelvic Girdle
 Coxal – 2
 Lower Limbs
 Femur – 2
 Patella – 2
 Tibia – 2
 Fibula – 2
 Tarsals – 14
 Metatarsal 10
 Phalanges - 28
Types of Bones

Long – cartoon bone

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Short – boxy or cube-like

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Vertebrae, many facial bones
Sesamoid – found in joints for stability

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Ribs, scapula, sternum
Irregular – variety of shapes

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Carpals, tarsals
Flat – platelike
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Expanded ends
Longer than wide
Humerus, femur, finger bones
Patella (knee cap)
Wormian (sutural) – extra bones in skull where cranial
bones meet
Bone Structure:


Macroscopic Structure – Long bone
 Epiphyses – expanded ends
 Articular Cartilge – hyaline; protection in joints
 Diaphysis – shaft
 Medullary Cavity – hollow portion containing marrow
 Periosteum – outer covering
 Endosteum – inner covering
Types of bone
 Compact – dense for strength
 outer
 Osteons
 Spongy – light, airy
 inner
 Reduce weight
 Trabeculae
Bone Structure:

Microscopic – Compact

Osteon – Repeating unit

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Osteonic (Haversion Canal)

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Central
Blood vessels, nerves
Lamellae – concentric circles of matrix
Osteocytes – mature bone cells

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Bullseye
Lacunae
Canaliculi
Transverse (perforating/ Volkmann’s) Canal

Connects osteonic canals
Bone Structure:

Spongy - cancellous

Trabeculae – bony plates

Osteocytes found here
Bone Growth and Development


Skeletal Formation Animation
Ossification – formation of bone

Osteoblast – deposit solid mineral matrix

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Turn into osteoclasts – mature bone cells
Endochondral Bone Formation


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Most common; arise from hyaline cartilage
Periosteum forms; deposit bone underneath –
outside of bone first
Primary ossification center – center of diaphysis

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Ossification moves towards ends
Secondary Ossification Center – Epiphyses

Mainly spongy bone develops
Bone Growth and Development

Epiphyseal Disk – growth plate



Area between the two ossification centers that
remains cartilage
Does not ossifiy until adulthood
4 layers of cells


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Cartilage cells continue to divide, mature, ossify and die
Move toward ends of bone
Intramembranous Ossification – bone formation
between two sheets of connective tissue

Generally in flat bones of skull
Factors Affecting Bone Growth

Diet – what you eat

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Minerals such as calcium, phosphates
Vitamin D – needed for proper absorption of calcium

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Rickets/ osteomalacia – lack of vit. D; soft bones
Dehydrocholesterol – inactive form; activated by sunlight in the skin
Vitamin A & C

Vit. A – bone resorption


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Vit. C – collagen synthesis
Hormones – chemical messengers from glands

Human Growth Hormone – pituitary; stimulates growth of epiphyseal
disk

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Lack causes retardation in development
Dwarfism, gigantism, achondroplasia, acromegaly
Thyroid hormone – thyroid; replace cartilage with bone
Male and Female Sex Hormones
Physical Stress – exercise

Tug of tendons cause bones to thicken and strengthen
Skeletal Functions:


Support and Protection
Body Movement – lever actions

1st class – EF, F, RF

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2nd class – F, RF, EF

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Mandible
3rd Class – F, EF, RF

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Triceps
Bicep
Blood Cell Formation – Hematopoiesis

Marrow – hematopoietic tissue



Found in medullary cavity of long bones (young); spongy
bone spaces (older)
Red – blood cell formation
Yellow – fat storage

Can be converted back and forth as needed
Skeletal Functions:

Hemocytoblast – blood stem cell

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Erythrocyte – red blood cell
Leukocyte – white blood cell
Thrombocyte – platelet
Inorganic Salt Storage

Electrolytes needed for a variety of physiological
functions


Ca++ needed for nerve impulse conduction, skeletal muscle
contraction
Negative Feedback


Blood Ca levels too high: Thyroid releases Calcitonin 
osteoblast activity; deposit calcium in bone
Blood Ca levels too low: Parathyroid release parathyroid
hormone  Osteoclast activity; dissolve bone, release
minerals into blood
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