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BSMS 204- Theme 3 > Lecture 3- Physiology of bone repair > Flashcards

Lecture 3- Physiology of bone repair Flashcards

1
Q

What conditions result as imbalance of bone resorption?

A

Osteoprosis
Osteopenia
Rickets

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2
Q

what conditions result as imbalance of bone formation?

A

OsteoPETrosis

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3
Q

Name the two classifications of bone?

A
  • Long bone

- Flat bone

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4
Q

Name the macroscopic features of different bones?

A
  • Cortical Bone

- Cancellous bone –>has spicules and trabeculae

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5
Q

Name the microscopic features of different bones?

A
  • Lamellar- osteons

- Woven- immature and disorganised

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6
Q

Name the three principle cell types of bone?

A
  1. Osteoclasts- degradation and remodelling of bones
  2. Osteoblasts- formation of new bone
  3. Osteocytes- maintenance and detection of environmental changes
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7
Q

Name the functions of the three principle cell types?

A
  • Osteoblasts – on surface bone, produce protein component acellular matrix – regulate bone growth and degradation
  • Osteocytes – quiescent mature cells embedded in bone matrix. They maintain bone.
  • Osteoclasts – responsible for bone degradation and remodelling
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8
Q

What is the purpose of haversian system(Aka osteon) in lamellar bone?

A

-Communication system between cells immobilised in bone matrix

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9
Q

What do the osteocyte arise from?

A

Osteoblasts

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10
Q

describe the process osteocyte formation?

A

-From mesenchyme- precursor cells in bone marrow stroma

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11
Q

where are the osteocytes found?

A

inside the lacuna (spicules)

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12
Q

Describe the function of osteoclasts?

A

Resorption of bone

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13
Q

Describe the structure of osteoclasts?

A
  • Multi-nucleate
  • 40-100 micrometer in diameter
  • 15-20 closely packed oval shaped nuclei
  • can proliferate
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14
Q

what are osteoclasts same precursors as?

A

monocytes- haematopoietic stem

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15
Q

How do osteoclasts act?

A
  • Phagocytose (bone and matrix)
  • Secrete acids
  • Secrete proteolytic enzymes from lysosomes
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16
Q

What does ruffled border show?

A

-Where bone resorption occurs

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17
Q

Describe the bone constituents?

A

Extracellular matrix=70% minerals

proteins and sparse cells

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18
Q

what are the acellular elements of bone?

A
  • collagen fibres- protein, flexible but strong
  • Hydroxyapatite- mineral- provides rigidity
  • Calcium/phosphate >50%
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19
Q

what is the extracellular matrix of bones includes?

A

Glycosaminoglycans-

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20
Q

Describe the structure of glycosaminoglycans?

A
  • Long polysaccharides
  • Highly negative
  • attract water
  • Repel each other
  • resist compression
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21
Q

Where are the growth factors found?

A

suspended in matrix

22
Q

How are the growth factors revealed?

A

osteoclast action-proliferation and mineralisation

23
Q

What is meant by bone remodelling?

A

Bone turnover- the activation-resorption -formation sequence

24
Q

how do bone cells remodel bone?

A
  1. Osteoclasts resorb bone in Howship lacuna
  2. Osteoblasts deposit bone-onto pre-existing bone
  3. active process
  4. bone is layed down in different direction
25
Q

What two types of bones are formed and by which mechanism?

A

Compact or cancellous

by either intramembranous or endochondral bone formation

26
Q

what are the two major factors that govern bone remodelling?

A

recurrent mechanical stress

Calcium homeostasis

27
Q

what does mechanical stress do to the bone?

A

strengthens bone

28
Q

How does the mechanical stress strengthen bone?

A
  1. Inhibits bone resorption and promotes deposition
29
Q

What two factors cause bones to weaken?

A

Bed rest

lack of gravity

30
Q

Name one treatment option for osteoprosis and mechanism?

A
  • Bisphosphonates- alendronate

- works by inhibiting osteoclast mediated bone resorption

31
Q

What other drugs can be used for osteoprosis?

A

Teriparatide- encourage osteoblast formation of bone

-recombinat form Human parathyroid hormone

32
Q

What other drugs can be used for osteoprosis?

A

Denosumab- prevents osteoclast maturation

-monoclonal antibody that targets RANK-ligand

33
Q

Explain OsteoPETrosis?

A
  • Autosomal recessive-

- Rare

34
Q

Define the molecular mechanism of OsteoPETrosis?

A
  • osteoclasts can not remodel bone

- defective vacuolar proton pump or defective chloride channel

35
Q

Explain the consequences of OsteoPETrosis?

A

Brittle bones
Blindness
deafness
severe anaemia

36
Q

what are the 4 phases of fracture healing?

A
  1. Reactive phase: haematoma and inflammation
  2. soft callous formation
  3. hard callous formation
  4. Hard callous formation
37
Q

How long does bone take to heal in the upper body and lower body?

A

Upper . 2-3 weeks

Lower >4 weeks

38
Q

Name the hormones of calcium regulation?

A
  1. PTH
  2. Vitamin D
  3. Calcitonin
39
Q

Briefly explain the function of PTH in calcium regulation?

A

PTH- Parathormone- secreted by parathyroid chief cell –> increases plasma Ca2+

40
Q

Briefly explain the function of Vitamin D in calcium regulation?

A

-Made in stages- skin>Liver>Kidney

Increases plasma Ca2+

41
Q

Briefly explain the function of Calcitonin in calcium regulation?

A
  • Made by thyroid C cells

- Tones down blood calcium>calcium goes into bones- used as treatment for osteoprosis

42
Q

Describe the pathway of Vitamin D production and activation

A

Skin- absorbs vit D3
Liver- converts it to 25-OH cholecalciferol
Kidneys- convert it to 1, 25-di-OH cholecalciferol (calcitriol)
Gut- Calbindin- increases intestinal absorption of Ca2+
AND Ca2+ reabsorption in kidneys

RESULT - Increased plasma Ca2+

43
Q

Describe the function of Vitamin D in calcium homeostasis?

A
  1. Increases intestinal Ca2+ absorption-increases calbindin
  2. Stimulates kidneys to reabsorb calcium
  3. stimulates osteoclasts indirectly- via osteblasts
  4. Facilitates bone remodelling- thus increases serum Ca2+
44
Q

what are the possible causes of low calcium?

A 
1. Loss- pregnanacy and lactation
Kidney dysfunction
2. Low intake - 
Insufficent ingestion of calcium
Rickets
3. Parathyroid dysfucntion
45
Q

What does chronic hypocalcaemia result in?

A
  1. skeletal deformaties
  2. Increased bone fractures
  3. impaired grwoth
  4. short stature
  5. dental deformaties
46
Q

What are the signs of acute hypocalcaemia?

A

C-convulsions
A- arrhythmia
T-tetany

47
Q

Name two clincal signs used to detect hypocalcaemia?

A

Chovestek’s sign-Tapping masseter leads to twitch on same side of face

Trousseau sign-Hand spasm after 3 minutes with blood pressure cuff in place (above systolic pressure)

48
Q

What does low calcium do the membrane excitabilty?

A

More excitable: Na is more able to leak through- explains tetany

49
Q

What is the effect of hypercalcaemia on membrane excitabilty?

A

Makes membrane more stable

50
Q

What are the signs and symptoms of hypercalcaemia?

A
  • Can be asymptomatic
  • Reduced excitability- constipation and depression
  • Abnormal heart rhythms
51
Q

What are the consequences of severe hypercalcaemia?

A

Coma

Cardiac arrest

BSMS 204- Theme 3 (5 decks)

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