Lecture 7 : Bone structure, growth and repair

Question 1

What are the two types of bone formation/ ossification during normal growth and development and what cells make bone

Answer 1

1. Intramembranous ossification
2. Endochondral ossification
   Osteoblasts make bone

Question 2

Describe the 4 steps of intramembranous ossification

Answer 2

1. osteoblasts secrete organic ECM (water + collagen fibres) to develop an ossification centre
2. The ECM hardens because of calcification where calcium and other mineral salts are deposited-> osteoblast becomes osteocyte
3. ECM develop into trabeculae that fuse to become spongey bone, blood vessels go through it
4. Mesenchyme on the periphery of the bone develop into periosteum.

Question 3

What 3 bones are formed from intramembranous ossification

Answer 3

clavicle, mandible and flat bones of skull

Question 4

Describe the 6 steps of endochondral ossification

Answer 4

1. Mesenchyme cells develop to chondroblasts which make cartilage model
2. chondrocytes divide, growing the model
3. In the diaphysis of bone, cartilage is replaced by bone and this makes a primary ossification centre
4. Osteoclasts break down bone to form the medullary cavity
5. Secondary ossification centre happens in epiphysis of bone
6. Articular cartilage and epiphyseal plate form out of hyaline cartilage

Question 5

How do bones grow longer

Answer 5

Epiphyseal growth plate separating dyaphysis and epiphysis has a zone of proliferating cartilage in the middle where cells start to divide and this pushes the epiphysis up.
New blood vessels come in to calcify the lower layers of cartilage from the diaphysis and therefore increases the length of the diaphysis.

Question 6

Briefly describe how bones grow wider

Answer 6

Appositional growth where the outer layer forms a new osteon around peripheral blood vessels

Question 7

What does cartilage need to calcify

Answer 7

blood and oxygen supply

Question 8

How do you tell compact and spongy bone apart on a microscope

Answer 8

compact bone has osteons with circular lines around a central bv, whereas spongy bone trabeculae are in straight lines on the border of compact bone before the medullary cavity