Formation of Bone in the Early Skeleton ENDOCHONDRAL OSSIFICATION in the fetus notes Flashcards
STEP 1: Cartilage growth occurs by two methods:
Appositional Growth
Interstitial Growth
What is Appositional Growth?
Cartilage cells on the surface of the existing
cartilage multiply and produce matrix,
causing growth of the cartilage on its surface.
What is Interstitial Growth?
Cartilage cells in the center of the existing
cartilage multiply and produce matrix, causing
growth of the cartilage from within.
STEP 2: What forms on the surface of the cartilage?
periosteum
STEP 3: What forms beneath the periosteum.
Compact bone
STEP 4: Two things occur in the center of the cartilage.
Calcification and cavitation
Why does calcification happen?
To kill the cartilage.
Hypertrophy of the chondrocytes occurs before step 4 begins.
The cartilage cells enlarge before they add calcium carbonate to the cartilage,
causing their own death and therefore creating holes (cavities) in the cartilage.
Adding calcium to the cartilage kills it so that it can be replaced with bone.
STEP 5: Primary Ossification Centers appear. What two things happen?
a. The periosteal bud invades the cavities and spongy bone forms.
b. The diaphysis elongates, thickens, and a medullary cavity forms.
What will start primary ossification?
The bud, a blood vessel, grows into the hole in the center of the cartilage, bringing along with it osteoblasts.
Primary Ossification Centers will produce spongy bone in the _______________?
Diaphysis (shaft)
What type of bone is made first and what is made second? Spongy bone or Compact Bone?
Compact bone is 1st
Spongy bone is 2nd
STEP 6: Secondary Ossification Centers appear.
Shortly before or after birth, these centers develop and turn the cartilage of
the epiphyses into spongy bone.
At birth, hyaline cartilage remains
at only two locations:
- Metaphyses as growth plates(allow growth in height)
2. Covering epiphyses(called articular cartilage; allows bones to glide on each other during movement)
