Types and Histology of Bones
Ch. 6
4 types of bones
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Long
Short
Flat
Irregular
4 types of bone
• Long bone
– Cylindrical
– Longer than they are wide
– Ex: femur, humerus
4 types of bone
• Short bones
– As long as they are wide
– Sometimes have cuboidal shape
4 types of bone
• Flat bones
– When bone tissue
invades and
hardens fibrous
membranes
– They are sheet-like
in shape
– Usually curved
rather than flat
4 types of bone
• Irregular
– Complex in shape
– Do not fit into other
categories
2 types of skeletons
• Axial – 80 bones
– Central axis of skeleton
– 28 are skull bones
– 26 vertebrae
– 25 rib cage bones
– 1 unattached hyoid bone
2 types of skeletons
• Appendicular skeleton
– 126 nonaxial bones
– Includes bones of
extremities
– 64 bones in upper
extremities
– 62 bones in lower
extremities
Bone Histology
• Made up of matrix of
– 25% water
– 25% protein
– 50% mineral salts
• 4 types of cells
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Osteoprogenitor cells
Osteoblasts
Osteocytes
Osteoclasts
4 types of cells
• Osteoprogenitor cells
– Osteo = bone, pro = precursor, gen = to produce
– Unspecialized cells
– Undergo mitosis and develop into osteoblasts
– Found in: inner periosteum, endosteum, and in
canals
4 types of cells
• Osteoblasts
– Cells that form bone
– Lost ability to divide
– Secretes collagen which helps build bones
– Found on surface of bones
4 types of cells
• Osteoclasts
– Develop from circulating
monocytes (WBC)
– Settles on surface of
bone
– Function is bone
resorption (destroying
matrix)
– Helps development,
growth, maintenance
and repair of bone
4 types of cells
• Osteocytes
– Mature bone cells from
osteoblasts
– Principal cells of bone
tissue
– Can’t divide
– Maintains cellular activity
• Exchange of nutrients and
waste with blood
• Calcium absorption
2 regions of bone
• Compact and spongy
or cancellous tissue
Compact bone
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External layers of bone
Protection and support
Helps long bones resist stress of weight on them
Tensile strength – resistance to being stretched
apart
• Haversian canals – openings for blood vessels
• Volkmann’s canals – opening for blood vessels
that are perpendicular to Haversian canals
Compact bone
Spongy bone
• No true osteons
• Makes up epiphysis of long bones
• In hips, ribs, sternum, spine, skull and end of
bones
• Sites of red bone marrow storage
• Trabeculae – thin plates of lamellae
Spongy bone