Microscopic Anatomy of Bone

osteoprogenitor cells

stem cell, destined to be bone cells, but have not differentiated yet

osteoblasts

secrete osteoid, forming bone matrix

osteoid

hardens and becomes bone tissue

osteocytes

mature bone cells; osteoblasts that have been buried in bone tissue

osteoclasts

cells that dissolve/break down bone; could be from low bone calcium levels or because the bone isn’t being used very often

osteon

aka Haversian system; cylindrical structures that make up the basic unit of compact bone; run parallel to the diaphysis; provides lots of strength

central canal of osteon

contains blood vessels and nerves

lamellae

thin layers in osteon rings

canaliculi

little canals in the lamellae that osteocytes run through

perforating canals

canals that contain blood vessels and nerves; run perpendicular to central canals

spongy bone

lacks osteons; trabeculae contains parallel lamellae; distributes stress from mechanical forces across framework

ossification

formation of bone connective tissue

intramembranous ossification

produces flat bones of the skull, some facial bones, mandible, and central portion of the clavicle; bones develop from mesenchyme membrane

intramembranous ossification

calcification entraps osteoblasts within lacunae in bone matrix (now osteocytes)

endochondral ossification

formation of most bones in skeleton: limbs, pelvis, vertebrae, ends of clavicles; bones develop from hyaline cartilage model

periosteal bone collar

fetal hyaline cartilage after it calcifies

primary ossification center

first area bone begins to form

secondary ossification center

the area of ossification that appears after the primary ossification center has already appeared

epiphysial lines

ridge on a bone that marks where a growth plate once was (adult bones)

interstitial growth

a long bone’s growth in length

appositional growth

a long bone’s growth in diameter

epiphysisial plate

site of interstitial growth; consists of 5 microscopic zones

effects of exercise

the more active a person is, the greater the size and mineralization of bones