Bone

Question 1

What are the six functions of bone?

Answer 1

1. Mechanical Support
2. Protection
3. Facilitates Movement
4. Mineral Storage and Release (calcium and phosphorus in the bone matrix)
5. Produce blood cells (red marrow makes RBC, Wbc, and platelets
6. Energy storage (yellow marrow is made up of adipose tissues)

Question 2

What is the cellular composition of bone?

Answer 2

1. 30% organic (collagen)
2. 70% inorganic (hydroxyapatite)

Question 3

What is Wolff’s Law?

Answer 3

Bone will be laid down where needed and reabsorbed where not needed

Question 4

What is the piezoelectric effect of bone?

Answer 4

High enough stress can cause the collagen fibers of bone to slip past one another and this generates and electrical potential

Question 5

How does bone remodeling occur?

Answer 5

Bone remodeling is carried out by the osteoblasts and osteoclasts. The osteoclasts absorb the bone and the osteoblasts deposit new bone. The way they do this is explained by Wolff’s Law, which states bone will be laid down where it is need and reabsorbed where it is not. The areas that are under higher stress will have bone laid there and low stress areas will have bone reabsorbed. The stress causes the collagen fibers in bone to slip past each other and this causes an electric potential, known as a piezoelectric effect. This is how the body knows where the high and low stress areas are.

Question 6

What is an example of how bone stress is influenced by muscle activity?

Answer 6

When the triceps surae contract they can cause a tensile stress on the calcaneus as it inserts there and is pulling on it. However for the tibia they result in a net compressive stress on it due to it originating on the femur and inserting on the calcaneus, causing the tibia between these bone to be compressed.

Question 7

What is stress?

Answer 7

Stress is the normalized load. This is the force on the bone distributed over the area of the bone.

Question 8

What is strain?

Answer 8

Strain is the normalized deformation. This is a measure of the change in length of the the bone compared to original length.

Question 9

What does this graphic indicate about the Stress-Strain relationship of bone under different conditions?

Answer 9

The slope of these graphs represent the stiffness of the bone. In the tension graph there is a high stress but low strain in the elastic region showing high stiffness, and the area of high stress and strain in the plastic region shows low stiffness. The high strain in the plastic region shows that the bone has been deformed and will be unable to return to its original length. This continues until the maximal stress and strain is reached and the bone breaks. For the bone under compression the strain is higher under lower stress, showing a lower stiffness. This continues until the strain starts to increase more rapidly and the maximal stress is reached and the bone crushes and deforms.