Block 2: Skeletal System - Lecture 2.5 Flashcards
What are the two types of Postnatal bone growth?
Longitudinal Growth: length
Appositional Growth: width
How long does bone growth occur?
Until about ages 14-24
- when Epiphyseal (growth) plates close
On an X-Ray, how can you tell if growth plates are open or closed?
Epiphyseal plates will still be composed of cartilage until growth period is over
- cartilage DOES NOT show on X-Ray panels, meaning that is cartilage is still present, growth is not done
Where does longitudinal bone growth occur and what does it replace?
Occurs at epiphyseal plates in zones
- very similar steps to endochondral ossification
Hyaline cartilage is replaced by bone
What is the first zone of Epiphyseal Plate Cartilage?
Zone of Reserve or Resting Cartilage
- looks like typical hyaline cartilage
- no signs of ossification
What is the second zone of Epiphyseal Plate Cartilage?
Zone of Cell Proliferation
- proliferating cartilage
- chondrocytes go through mitotic division and arrange themselves in columns to increase epiphyseal cartilage tissue and bone length
What is the third zone of Epiphyseal Plate Cartilage?
Zone of Cell Hypertrophy
- chondrocytes stop dividing and grow in size
- calcium accumulation begins
about the same process as step two of endochondral ossification
What is the fourth zone of Epiphyseal Plate Cartilage?
Zone of Calcification
- cartilage calcifies which means no diffusion of nutrients
- minerals deposited between lacunae
- chondrocytes die leaving behind large empty cavities
about the same process as step two of endochondral ossification
What is the fifth zone of Epiphyseal Plate Cartilage?
Zone of Bone Deposition
- blood vessels invade cavities to bring in nutrients and bone cells
- bone remodeling by osteoclasts & osteoblasts
As bone grows, what happens to the thickness of the Epiphyseal plate?
The thickness does not change while the Epiphysis and Diaphysis lengthen
What happens when the Epiphyseal Plate closes?
Epiphyseal cartilage cells stop dividing and are replaced by bone to create the Epiphyseal line
- triggered by shift of hormones
In the overall Epiphyseal plate, what are the order and names of all the zones?
Epiphysis
5: Zone of Bone Deposition
4: Zone of Calcification
3: Zone of Cell Hypertrophy
2: Zone of Cell Proliferation
1: Zone of Reserve Cartilage
2: Zone of Cell Proliferation
3: Zone of Cell Hypertrophy
4: Zone of Calcification
5: Zone of Bone Deposition
Diaphysis
What is Appositional Bone Growth?
Growth in the width of the bone
- most similar to intramembranous ossification
What is the overall process of appositional bone growth?
Osteoclasts resorb inside layer
- increases size of medullary cavity
- decreases weight of bone
Osteoblasts deposit bone onto outside layer
