Types and Histology of Bones

Ch. 6

4 types of bones

• 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– 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 spongyor cancellous tissue

Compact bone

• 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