Intramembranous Bone Ossification
What is the precursor for bone in this process?
Embryonic connective tissue
What is the precursor for bone in this process?
Hyaline cartilage
Division of which cells is responsible for longitudinal growth?
Condrocytes
Where in bone does appositional growth take place?
In between bone surface and periosteum
Osteoblasts ________ bone, osteocytes _______ new bone, osteoclasts ________ bone
What bones undergo this development?
Skull and clavicles (flat bones)
What is unique about long bones undergoing this process?
They have secondary ossification centers at their epiphyses
Between ages 12-15 the zone of ________ takes over the the zones of ________ & _________ until ossification is complete between ages 18-21
Does appostionial bone growth stop at the same time as longitudinal growth? Yes/No
No, it can continue depending on hormone levels and lifestyle habits
What are some reasons bone remodeling occurs?
Replacing primary bone w/ secondary bone, maintaining Ca ion concentration, replacing old brittle bones, repairing injured bone, adapting to stress and tension
______ bone ossifies first, creating the _______________
Spongy; primary ossification center
Which bone cell type is responsible for creating an opening for blood vessels and enlarging the medullary cavity?
Osteocytes
Which bone undergoes longitudinal growth and where in the bone does it occur?
Long bones, epiphyseal plate
Do new or old layers of lamellae become osteons in appositional bone growth?
Old layers of lamellae
How do osteoclasts breakdown bone?
Secrete hydrogen ions and enzymes into bone ECM; inorganic matrix degrades in acidic environment and enzymes breakdown organic molecules (ex: proteoglycans)
Osteoblasts scerete salts that begin the process of __________ and form __________
Calcification; trabeculae
Two processes occur at the same time in endochondral ossification. What are they?
Osteoblasts create bone collar on external surface; condrocytes begin to die as calcification of internal cartilage cuts off blood supply
What is the purpose of the zone of reserve cartilage?
Which zone is key to continuing the process of bone growth?
Zone of proliferation; Bone growth will only continue as long as mitosis occurs at this level
When PTH is released into the blood, it causes.... Why?
Osteoclasts to reabsorb bone, kidneys to retain Ca+2, and the intestines to absorb more Ca+2. To increase plasma levels of calcium
What additional structure must be synthesized along with spongy and compact bone? How is this accomplished?
________ replace calcified cartilage with bone. What areas of the skeletal system retain cartilage into adulthood?
Osteoblasts; at epiphyseal plates and places where bone articulates at joints
Osteoblasts are responsible for laying down primary bone. What do osteoclasts do to primary bone eventually?
Osteoclasts absorb primary bone (and calcified cartilage) and lay down mature bone
Summarize the 5 zones of longitudinal bone growth.
Reserve cartilage: condrocytes sit and wait to be recruited for division
Proliferation: condrocytes divide near epiphyseal plate
Hypertrophy/Maturation: condrocytes grow and mature in large lacunae
Calcification: condrocytes die and cartilage undergoes calcification via osteoblasts
Ossification: osteocytes lay down new bone through ossification
Osteoblasts...