Bone Formation and Growth Flashcards
Describe Intramembranous Ossification.
the bone formation of a bone directly on or in embryonic fibrous connective tissue membranes.
Can form flat bones of the skull, the mandible, and the clavicles.
What is the first step in Intramembranous Ossification?
When the mesenchyme cells cluster together and differentiates into osteogenic cells and then become osteoblasts and begin to form a center of ossification.
What do the osteoblasts do in intramembranous ossification step 1?
They secrete organic bone matrix until they are completely surrounded.
What is the second step in intramembranous ossification?
The matrix secretion stops; osteoblasts become osteocytes, and deposit calcium phosphate and other mineral salts until the matrix is calcified.
What is the third step of intramembranous ossification?
When there is a developments of the trabeculae from the bone matrix which fuses together and creates spongy bone.
What do the osteoclasts do in step 3 of intramembranous ossification?
they reabsorb and remodel this bone to form spaces that fill with red marrow.
What is the final step of intramembranous ossification?
the trabeculae at the surface calcifies until the spongy bone is replaced with compact bone.
the mesenchyme at the surface condenses to form the periosteum.
Describe the endochondral ossification.
the bone formation within the hyaline cartilage model.
It forms most of the bones in the skeleton, including the vertebrae, pelvis, limbs,
begins 6 weeks into embryonic development and continues until the age of 20.
What is the beginning step in endochondral ossification?
when the mesenchyme cells crowd together and differentiate into chondroblasts, that produce a matrix of hyaline cartilage.
- the perichondrium develops and produces chondrocytes to thicken cartilage.
What is the second step in the endochondral ossification?
chondrocytes in the center grow and burst and release chemicals that trigger calcification.
- some cells become osteoblasts and deposit thin shell of compact bone under perichondrium to form periosteum.
Define calcification.
Blocks nutrients from reaching the chondrocytes, so many die and leave small cavities in matrix that eventually join together into one large cavity.
What is the third step in endochondral ossification?
blood vessels with grow into deteriorating cartilage and form a primary ossification center and stem cells that give rise to osteoblasts and osteoclasts.
What do the osteoblasts do during the third step in endochonral ossification?
(bone forming cells) and they deposit bone over the cartilage to form the trabeculae of spongy bone.
What do the osteoclasts do during the third step of endochondral ossification?
(break-down bone cells) - break-down newly formed spongy bone and leave medullary cavity.
When does cartilage erosion occur in the third step of endochondral?
If occurs from the outside of a bone inward during primary ossification.
What is the fourth step during endochondral ossification?
When the cartilage of the shaft is replaced with compact bone, except for the marrow and it is filled with medullary cavity and secondary ossification center develops in both epiphyses as blood vessels in filtrate them near the time of birth.
