Bone

Question 1

What are the four main types of bone?

Answer 1

Long bones - greater length than width, curved for strength (femur, tibia, fibula, humerus, radius, ulna, phalanges)

Short bones - cube shaped (wrist and ankle bones)

Flat bones - Thin, afford protection and a large surface for muscle attachment (cranial bones, sternum, ribs, scapulae)

Irregular bones - Complex shape (vertebrae, facial bones)

Question 2

Describe cortical and trabecular bone within bone structure.

Answer 2

Cortical bone forms an external layer over all bones, with a structure organised around osteons. Lacunae are arranged in concentric circles around canals, containing osteocytes. Cortical bone provides protection and support, and resists stresses produced by weight and movement.

Trabecular bone do not contain osteons. Lacunae are arranged irregularly, spaces filled with red bone marrow. This type of bone makes up most of short, flat and irregular bones and epiphyses (end) of long bones.

Question 3

What are the 4 main bone cells?

Answer 3

Osteoblasts - These synthesise and secrete ECM proteins and produce factors required for the mineralisation of the ECM.

Osteocytes - Mature bone cells that maintain the metabolism of bone (exchange nutrients and waste with blood)

Osteoclasts - Large multinucleated cells that are involved in normal growth, maintenance and repair of bone

Osteoprogenitor cells - A mesenchymal stem cell that can proliferate and differentiate into an osteoblast.

Question 4

What is the composition of bone ECM?

Answer 4

Type I collagen is the principal component.
Type III and V are minor collagens.

There are proteoglycans, such as decorin which binds with TGF beta, and also versican and biglycan. Hyaluronan is interactive with proteoglycans.

There are also noncollagenous proteins:
* Osteocalcin - remodelling
* Osteonectin - links mineral to matrix
* Fibronectin, vitronectin - cell adhesion
* Bone sialoprotein - modulator of mineralisation

Question 5

What is bone remodelling, and what does normal bone metabolism depend on?

Answer 5

Bone remodelling is the ongoing replacement of old bone tissue with new. It removes worn and injured bone replacing it with new tissue. It relies on a balance between osteoblast and osteoclast activity.

Metabolism depends on:
* Adequate calcium phosphorus and magnesium
* Vitamins A, C and D
* Several hormones
* Weight bearing exercise