The Skeletal System
Bone as a Living Tissue
Functions of Bones
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1.
2.
3.
4.
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Support
Protection
Movement
Storage
(Minerals, medullary cavity stores marrow)
5. Blood cell formation
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Hematopoiesis
Bone Composition
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Cortical bone – dense outer layer; looks
smooth & solid
Trabecular (Spongy) bone – inner
framework of small needle-like/flat pieces
of bone (trabeculae) that have spaces in
between
Spaces between filled with red or
yellow bone marrow
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Spongy
Bone
Shape Categories of Bones
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1. Long bones
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All limb bones (except kneecap, wrist, & ankle
bones) are long bones
Long Bone Structure
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1. Diaphysis – shaft of bone; cortical bone and
medullary cavity with yellow bone marrow (fat)
2. Epiphyses – bone ends; covered in layer of
articular cartilage, red bone marrow
3. Membranes –
 a. periosteum – double-layered membrane that
covers external surface of bone
 b. endosteum – lines medullary cavity
Shape Categories of Bones
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2. Short bones – cube shaped
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Wrist and ankle bones
3. Flat bones – thin, somewhat curved
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Ribs, scapula
Shape Categories of Bones
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4. Irregular bones – have complicated
shape that does not fit in other 3
categories
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Vertebrae, hip bones are irregular
Short Bone
Composition of Bone
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Osteocyte= mature bone cell
Osteon (aka Haversian system) – column parallel to
long axis of bone
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Haversian canal – run length of bone; osteocytes here
Lamella – hollow tubes of bone matrix; make up
osteons; like rings on tree trunk
Microscopic Anatomy of Compact
Bone
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Lacunae – small cavities in bones
Volkmann’s canal – perforating canal; runs
sideways, connects blood/nerve to central
canals
Canaliculi – small sideways canals connecting
lacunae and central canal; tie all osteocytes in
an osteon
Osteon
Bone Growth & Development
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Bone deposition, build bone – osteoblasts
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Remove/remodel – osteoclast
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Epiphyseal plate = growth plate
Ossification – Bone Development
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Aka osteogenesis
1. Formation of bony skeleton
2. Bone growth
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length
width (with stress)
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Hypertrophy vs. atrophy
3. Remodeling
Ossification
Factors Affecting Bone
Development, Growth & Repair
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Deficiency of Vitamins:
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Vitamin A - slows bone development, Vita C – fragile
bones, Vita D – rickets
Insufficient or Excessive GH: dwarfism or Gigantism
Sex Hormones – promote bone formation;
stimulate ossification of epiphyseal plates
Physical Stress – stimulates bone growth
Axial Skeleton