Bone Formation ( Ossification)------- A. Intramembranous Ossification

Question 1

What tissue is grudually turned into bone in this process?

Answer 1

Mesenchyme, a fetal (embryonic) tissue.

Question 2

What is this tissue made of? What adult connective tissue is it similar to?

Answer 2

Collagen. Mesenchyme is similar to dense or fibrous c.t.

Question 3

Which bones of the skeleton are made?

Answer 3

The flat bones of the skull and the clavicles.

Question 4

What are the 4 main events of intramembranous ossification

Answer 4

1. Spongy bone forms ( by ossification centers in the center of mesenchyme)
2. Periosteum forms ( on surface of mesenchyme)
3. Compact bone forms (under the periosteum)
4. Red bone marrow forms

Question 5

What type of bone is made first?

Answer 5

spongy bone

Question 6

What type of bone is made second?

Answer 6

Compact bone

Question 7

What must happen before the 2nd type of the bone can be made?

Answer 7

The periosteum must form before the compact bone can be made because there are no osteoblasts on the surface of the mesenchyme(where compact bone needs to be made). When the periosteum forms it puts a layer of osteoblasts on the surface of the mesenchyme so that compact bone can be made on the surface of the fetal tissue.

Question 8

At what age is intramembranous ossification complete?

Answer 8

Around age 2

Question 9

Why is the process important in the formation of the skull?

Answer 9

It allows the skull to grow as the brain grows.

Question 10

How are fontanels of a baby’s skull related to this process?

Answer 10

The fontanels (“soft spots”) show that intramembranous ossification is still taking place. The fontanels are pieces of mesenchyme that have not turned into bone yet.