Bone growth in length in depth

Question 1

What bones grow in length and where in the bone does this occur?

Answer 1

This happens in the long bones of the body on the Diaphysial side of the Growth plate.
This growth happens by the process of Interstitial growth.

Question 2

What are all the layers/steps to bone growth in length?

Answer 2

1: Zone of resting cartilage
2: Zone of Proliferating Cartilage
3: Zone of Hypertrophic Cartilage
4: Zone of Calcified cartilage

Question 3

What is included in the First layer/step of bone growth in length?

Answer 3

Zone of Resting Cartilage:
This layer is nearest to the Epiphysis and consist of small scattered Chondrocytes.
These cells do not function in bone growth but rather anchor the Epiphyseal plate to the Epiphysis of the bone.

Question 4

What is included in the Second layer/step of bone growth in length?

Answer 4

Zone of Proliferating Cartilage:
There is slightly larger Chondrocytes in this layer arranged like stacks of coins.
These chondrocytes undergo Interstitial growth as they divide and secret extraceullar matrix.

Question 5

What is the Epiphyseal plate made of?

Answer 5

It is a layer of Hyaline cartilage consisting of 4 Zones.

Question 6

What occurs in the Third layer/step of bone growth in length?

Answer 6

Zone of Hypertrophic Cartilage:
This layer consist of a large chondrocytes arranged in columns.
Continues to grow.

Question 7

What occurs in the Fourth layer/step of bone growth in length?

Answer 7

The final layer of the Epiphyseal plate is only a few cells thick. Consist mostly of dead chondrocytes because the extracelular matrix around it has calcified.
After capillaries and osteoblast from the Diaphysis invade the area the osteoblast lay down bone matrix replacing the cartilage in a process called Endochondral ossification.
As a result the Zone of calcification becomes the new Diaphysis.