Bone Physiology

Question 1

Differentiate between cortical (compact) bone and cancellous (trabecular/spongy) bone.

Answer 1

Cortical bone: - 80% of skeleton mass - Forms hard exterior of bones - Made of packed osteons Cancellous bone: - Loose network Forms internal bone tissue Porous (has marrow)

Question 2

Briefly describe the process of bone deposition

Answer 2

Initially, woven bone is formed (weak, irregular collagen weave) Over time, it is remodelled into lamellar bone (regular structure of collagen sheets, strong)

Question 3

What are osteoprogenitor cells?

Answer 3

BOne cell precursors - stem cells that differentiate into osteoblasts.

Question 4

What are osteoblasts?

Answer 4

Located on bone surface. Synthesize organic components of bone matrix. Produce and secrete collagen, which forms osteoid. Osteoid becomes ossified to form hydroxyapatite. Osteoblasts become trapped in bone.

Question 5

What are osteocytes?

Answer 5

Differentiate from trapped osteoblasts. Reside in lacunae. Osteocytes regulate bone maintenance.

Question 6

What are osteoclasts?

Answer 6

Resorb bone. Haematopoietic origin. Secrete HCL and collagenase.

Question 7

Describe the process of intramembranous ossification.

Answer 7

Occurs in flat bones of mandible, skull and clavicles.

• Mesenchymal cells condense to form bone template.
• DIffernentation into osteoblasts.
• Osteoblasts secrete bone matrix and deposit calcium

Question 8

Describe the process of endochondral ossification.

Answer 8

Occurs in all bones in the body, except flat bones (mandible, skull, clavicles).

• Chondrocytes form hyaline cartilage
• BLood vessels invade cavities
• Osteoblasts calcify, and osteoclasts modify into spongy bone
• Osteoclasts create marrow cavity
• Hyaline cartilage is at epiphyseal plates, responsible for length growth of long bones.

Question 9

How is calcium regulated?

Answer 9

Plasma Ca2+ is regulated by calciotropic hormones

1. Parathyroid hormone (parathyroid gland)
2. Calcitriol (kidney)
3. Calcitonin (thyroid)

TOO much calcium: Release calcitonin:

• Reduced osteoclast activity
• Increased osteoblast acitivty
• Plasma [Ca2+] falls.

TOO little calcium: Release PTH

• Increased osteoclast activity
• Reduced osteoblast activity
• Plasma [Ca2+] rises