Bone Function And Repair

Question 1

What are the types of ossification ?

Answer 1

1) endochondral ossification : from hyaline cartilage template. This makes all bones but flat bones.
2) intra-membranous ossification : formation of flat bones from mesenchymal cells. Interstitial growth.

Question 2

Outline the process of intramembranous ossification ?

Answer 2

1) mesenchymal cells aggregate.
2) mesenchymal cells transform into osteoproginators which transform into osteoblasts.
3) osteoblasts lay down osteoid.
4) osteoid mineralises to form rudimentary bone tissue called spicules. Spicules contain osteocytes , surrounded by osteoblasts.
5) spicules join together to form trabeculae ( spongy bone /cancellous) which merge to form woven bone
6) surface trabeculae filled in with bone deposition which converts trabeculae bone into compact bone. Persistence of the inner spongy bone.

Question 3

What does the Haversian canal contain ?

Answer 3

• lymphocytes
• blood vessels
• nerves

Question 4

How can the activity of osteocytes acting like osteoblasts be increased ?

Answer 4

• osestrogen and and thyroid hormone.

Question 5

What is osteocytic osteolysis?

Answer 5

This is where osteocytes can act like osteoclasts and degrade bone. This process is increased by parathyroid hormone.

Question 6

How can the activity of osteoblasts be increased ?

Answer 6

• 1) growth hormone which is released by the anterior pituitary gland , this stimulates Insulin - like growth factor 1 in the liver.
  2) vitamin A
  3) parthyroid hormone and thyroid hormones,
  4) oestrogen / testosterone
  5) calcitonin ( opposes the function of parathyroid hormone).

Question 7

How can the activity of osetoclasts be increased ?

Answer 7

• increased by parathyroid hormone which releases calcium in the blood.
  2) calcitonin blocks the action of parathyroid hormone at the parathyroid hormone receptor.

Question 8

Outline the process of bone healing

Answer 8

1) haematoma forms ( blood clot) due to blood vessels breaking.
2) inflammation occurs by granulocytes.
3) soft callus formation of granulation tissue ( containing capillaries and fibroblasts)
4) fibroblasts produce collagen , some differentiate into chondroblasts.
5) at the same time , osetoclasts begin to remove dead bone and osteoblasts begin the formation of spongy bone ( also known as trabecular bone).
6) endochondral ossification occurs which replaces all cartilage with spongy bone. Intramembranous ossification produces new cancellous bones in any gaps.
7) cancellous bone begins to be remodelled into compact bone especially in the cortical region.

Question 9

What is the cause of osteogenesis imperfecta

Answer 9

• mutation in the collagen 1 gene

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Question 10

What is the consequences Of osteogenesis imperfecta

Answer 10

• this results in incorrect production of collagen 1 fibres
• weak bones + fracture risk
• mainly affects neonates and children

Question 11

What is the cause of rickets

Answer 11

• vitamin D deficiency

- mainly affects children

Question 12

What is the consequences of rickets ?

Answer 12

• ineffective mineralisation
• bowed legs
• soft bones
• weakened bones
• painful to walk

Question 13

What is the cause of osteomalacia

Answer 13

Ineffective mineralisation causes osteomalacia and ineffective mineralisation is caused by a lack of vitamin D , calcium and phosphorus.

• lack of vitamin D could be caused by kidney disease , cannot get enough sunlight due , surgery on the stomach. These cause an increase in calcium resorption.

Question 14

What are the consequences of osteomalacia ?

Answer 14

• increased osteoids
• lower mineralisation

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Question 15

What is a differemce between osteoporosis and osteomalacia?

Answer 15

In osteoporosis ,living bone is weakened whereas in oestomalacia there are problems with bone formation or bone building processes.

Question 16

What are the two types of osteoporosis ?

Answer 16

Primary and secondary

Question 17

What are the two types of primary osteoporosis ?

Answer 17

• type 1 and type 2

Question 18

What is the cause of type 1 primary osteoporosis ?

Answer 18

• occurs in postmenopausal women
• as there is a loss of oestrogen after menopause
• this causes an increase in osteoclasts number

Question 19

What is the cause of type 2 primary osteoporosis ?

Answer 19

• occurs in men and women
• due to loss of osteoblasts function
• this is due to loss of oestrogen and androgen

Question 20

What is the cause of secondary osteoporosis ?

Answer 20

• result of drug therapy ( eg corticosteroids)
• metabolic bone diseases eg hyperparathyroidism
• these processes affect bone remodelling

Question 21

What can women do to prevent type 1 primary osteoporosis ?

Answer 21

• take calcium supplements eg 700mg/day after menopause
• exercise - as this can maintain bone mass
• reduce smoking

Question 22

What causes achondroplasia ?

Answer 22

• mutation in the FGF3 gene ( fibroblast growth factor 3)
• fibroblast growth factor promotes collagen formation from cartilage which means that endochondral ossification is affected , but intra membranous ossification is unaffected.

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Question 23

What are the consequences of achondroplasia ?

Answer 23

• results in short stature , normal sized head and torso

- long bones cannot lengthen properly