Bone

Question 1

Describe the function of bone as a support for the mechanical function of joints.

Answer 1

Weight baring/structural support, protection of vital organs, mineral store (Ca2+), blood formation

Question 2

Describe the development of bone

Answer 2

Endochondral ossification occurs within the cartilage and is most common particularly with long bones.
Intramembraneous ossification occurs within membranes. There is no cartilage model so is more direct. Occurs in flat bones and adult cortical bone.

Question 3

Haemopoiesis

Answer 3

The production of blood cells and platelets occuring in the bone marrow. In adults it occurs on the pelvis, cranium, vertebrae and sternum.

Question 4

Trabecular bone

Answer 4

AKA spongy bone, cancellous or diploe bone. It is less dense that cortical bone and is a network of lamellated trabeculae filled with bone marrow. The struts provide strength. The orientation of trabeculae reflects the main direction of mechanical force. The structure resembles a sponge.

Question 5

Cortical bone

Answer 5

Conpact/hard bone which is organised in circular structures known as osteons/haversion systems. It is the dense outer surface if bone that forms a protective layer around the internal cavity.

Question 6

Describe the composition of bone.

Answer 6

Cells; osteoblasts (bone forming), osteocytes (communication), osteoclasts (bone resorbing).

ECM; 45% hydroxyapatite crystals (complex form of calcium phosphate), 35% type 1 collagen (strongly cross linked with large gaps for hydroxyapatite), 20% water.

Compsite material; minerals make it stiff and able to support structured they have high strength undef conpression. Collagen has high strength under tension with some flexibilty.

Question 7

Bone renewal

Answer 7

Old bone is broken down by osteoclasts, osteoblasts rebuild to form new bone. In healthy bone removal matches formation. We have a new skeleton every 10 years.

Question 8

Osteoclasts

Answer 8

Large cells for bone resorbing/break down old bone. They are derived from the haemopoietic lineage, specifically macrophages.

Question 9

Osteoblasts

Answer 9

Small cells for bone forming/building new bone. They are derived from the osteopregenitor cells (mesenchymal stem cell) in the periosteum and endosteum.

Question 10

Osteocytes

Answer 10

They are derived from the differentiation of osteoblasts. Found in mature bone inside the lacunae and carry out numerous processes in the canaliculi and allow communication between cells. Their function is not well understood but they may maintain bone matrix and sense mechanical forces.