Bone Maintenance

Question 1

general

Answer 1

• Bone continually remodels, recycles, + replaces
  Turnover rate varies:
• If deposition is greater than removal, bones get stronger
• If removal is faster than replacement, bones get weaker

Question 2

Process of remodelling

Answer 2

The adult skeleton:

• Maintains itself
• Replaces mineral reserves
• Recycles + renews bone matrix (5-7% per week!)
• Involves activity of osteocytes, osteoblasts, + osteoclasts

Question 3

Exercise, Hormones and Nutrition

Answer 3

• Up to one third of bone mass can be lost in a few weeks of inactivity

Effect of hormones on bone

• Calcitriol is made in the kidneys, helps absorb Ca + P from the digestive tract. Synthesis of calcitrol requires Vit D3
• Growth hormone + thyroxine stimulate bone growth
• Estrogens + androgens stimulate osteoblasts
• Calcitonin + parathyroid hormone regulate calcium + phosphate levels

Effects of diet on bone

• A dietary source of calcium + phosphate salts + small amounts of magnesium, fluoride, iron, and manganese
• Vitamin C is required for collagen synthesis, + stimulation of osteoblast differentiation
• Vitamin A stimulates osteoblast activity
• Vitamin K2 – helps to bind calcium

Effects of exercise on bone

• Mineral recycling allows bones to adapt to stress
• Heavily stressed bones become thicker + stronger

Question 4

Fractures

Answer 4

• Fracture is the medical term for a “broken” bone.
• They are caused by physical stress which can be acute or prolonged (stress fracture)

Fracture Repair

1. Bleeding, producing a clot
2. Cells of the endosteum + periosteum move into fracture zone
   - Osteoblasts form spongy bone
   - Osteoblasts, osteocytes + osteoclasts remodel the fracture for up to a year

Question 5

Bone Healing

Answer 5

• Bleeding produces a clot (fracture hematoma)
• Establishes a fibrous network
• Bone cells in the area die

Cells of the endosteum + periosteum

• Divide + migrate into fracture zone
• Calluses stabilise the break
• External callus of cartilage + bone surrounds break
• Internal callus develops in medullary cavity

Osteoblasts

• Replace central cartilage of external callus
• With spongy bone
• Osteoblasts + osteocytes remodel the fracture for up to a year
• Reducing bone calluses

Question 6

Repair of a fracture (steps)

Answer 6

1. Immediately after the fracture, extensive bleeding occurs. Over a period of several hours, a large blood clot or fracture hematoma develops
2. An internal callus forms as a network of spongy bone unties the inner edges and an external callus of cartilage and bone stabilises the outer edges
3. The cartilage of the external callus has been replaced by bone and struts of spongy bone now untied the broken ends. Fragments of dead bone and the areas of bone closest to the break have been removed and replaced
4. A swelling initially marks the location of the fracture. Over time, this region will be remodelled, and little evidence of the fracture will remain