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 spongy or 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