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Block 5 ellen > Bone metabolism L5 > Flashcards

Bone metabolism L5 Flashcards

1
Q

What percentage of the bone is organic

A

40%

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2
Q

Organic components of bone (2)

A

Type 1 collagen

non-collagenous proteins

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3
Q

Inorganic components of bone (1)

A

calcium hydroxyapatite

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4
Q

What percentage of bone is inorganic

A

60%

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5
Q

other word for trabecular bone

A

cancellous bone/ spongy bone

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6
Q

osteoclasts have multiple

A

nuclei

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7
Q

Osteoclasts formed from

A

fusion of monocytes haematopoietic

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8
Q

Where do osteoclasts sit

A

Adhere strongly on the bone surface

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9
Q

Osteoblasts have how many nuclei

A

1

mononuclear cell

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10
Q

What are they called when osteoblasts burry themselves alive in the new bone matrix they form

A

osteocytes

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11
Q

How is new bone first laid down

A

non-mineralised osteoid

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12
Q

If formation is equal to resorption –>

A

coupled remodelling

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13
Q

osteoid=

A

type 1 collagen and proteins

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14
Q

How much bone do we lose in space per month

A

1%

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15
Q

Mechanisms involved in bone growth and remodelling

A

PTH
Vitamin D3
Calcitonin

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16
Q

approx how much calcium in the body

A

1000g

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17
Q

recommended daily calicum intake

A

1000mg

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18
Q

percentage of calcium in skeleton

A

99%

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19
Q

Serum conc of calcium

A

2.25-2.6

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20
Q

Three fractions of calcium in serum

A 
ionised (50%)
Protein bound (40%)
Complexed calcium (10%)
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21
Q

Ca2+ levels maintained by

A

PTH
Vitamin D
Calcitonin

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22
Q

Approx how much phosphate in human body

A

600g

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23
Q

Percentage phosphate in skeleton

A

85%

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24
Q

major ionic species of phosphate in serum

A

HPO4-2

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25
Q

three fractions of inorganic phosphate

A 
ionised (55%)
Protein bound (10%)
Complexed phosphate (35%)
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26
Q

What is phosphate primarily regulated by

A

PTH

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27
Q

Main route of Vitamin D into body

A

7-dehydrocholesterol by UV light

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28
Q

1st activation of vitamin D

A

25-hydroxylation in the liver produces 25(OH)D3

29
Q

what is 25(OH)D3 ?

A

The main circulating metabolite of vitamin D with little biological activity

30
Q

2nd activation of vitamin D

A

1-hydroxylation in the kidney produces 1,25 (OH)2 vitamin D3

31
Q

What is 1,25(OH2)vitamin D3

A

the principal hormonal form of vitamin D and is responsible for most of its biological actions

32
Q

What does PTH do in regards to vitamin D

A

it stimulates and regulates 1,25(OH2) vitamin D3 production

33
Q

What inhibits vitamin D

A

elevated serum Ca and P

34
Q

(3) actions of 1,25 (OH2) vitamin D3

A
  • increases calcium and phosphate absorption from the intestines
  • Mobilises calcium and phosphate from bone
  • Induces marrow monocytes to differentiate into osteoclasts to stimulate bone resorption.
35
Q

what does 24-hydroxylation effect

A

25(OH)D3 and 1,25(OH2)D3 catabolism

36
Q

what is PTH

A

parathyroid hormone

37
Q

What structure does PTH have

A

small polypeptide

84 amino acids

38
Q

Where and why is PTH secreted?

A

by the parathyroid gland in response to low plasma Ca2+ levels

39
Q

Effect of high PTH levels

A

osteoclastic bone resorption

mobilising calcium

40
Q

effect of Intermediate-low PTH levels

A

osteoblastic bone formation

41
Q

What is the main way through which PTH communicates its effect

A

predominatly through osteoblasts which communicate with osteoclasts

42
Q

Other general effects of PTH (3)

A
  1. decreased renal calcium excretion
  2. Increases renal production of 1,25(OH2) D3
  3. increases blood calcium
43
Q

What is PTHrp

A

parathyroid hormone- related protein

44
Q

What is increased PTHrp production linked with

A

malignant tumours

45
Q

What does PTHrp do?

A

major mediator of hypercalcaemia (raised calcium)

46
Q

Calcitonin–>

A

Reduces bone resorption by activating calcitonin receptors expressed by osteoclasts.

47
Q

Decreased Ca2+ induces–>

A

PTH secretion

48
Q

Increased Ca2+ induces

A

Calcitonin secretion

49
Q

Oestrogen–>

A

reduces bone resorption by inhibiting osteoclastogenesis and inhibiting osteoclast function

50
Q

What expresses oestrogen receptors

A

osteoblasts and osteoclasts

51
Q

Androgen–>

A

decreases bone resorption by directly targeting osteoclasts

52
Q

Is Androgen used in men or women

A

Both

53
Q

Hypercalcaemia=

A

elevated calcium in circulation

54
Q

Causes of hypercalcaemia

A 
primary hyperparathyroidism 
Malignancy 
Hyperthyroidism
immobilisation
vitamin D toxicity
55
Q

Primary hyperparathyroidism=

A

hypercalcaemic state caused by excessive secretion of PTH

Main cause= solitary adenoma

56
Q

Symptoms of hyperparathyroidism

A

at skeletal sites osteitis fibres cystica

57
Q

What is osteitis fibres cystica

A

replacement of bone with fibrous tissue

58
Q

What area of skeleton does hyperparathyroidism effect most (2)

A

Skull and phalanges

59
Q

causes of hypocalcaemia

A

renal failure
vitamin D deficiency
prematurity

60
Q

what is secondary hyperparathyroidism

A

physiological response to hypocalcaemia

61
Q

Cause of osteomalacia and rickets

A

vitamin D deficiency
malabsorption
renal disease
Lack of sunlight

62
Q

Features of osteomalacia

A 
diffuse bone pain
localised bone pain around hips
Muscle weakness
Decreased mineralisation  
ect
63
Q

Osteoporosis =

A

net loss of bone mass resorption> formation.

64
Q

Osteoporosis most common in

A

post-menopausal women

65
Q

Osteoporosis treatment

A 
Calcium supplementation 
hormone replacement therapy 
bisphosphonates 
calcitonin 
Selective estrogen-receptors modulators (SERMs)
66
Q

Three bisphosphonates

A

Alendronate, residronate, etridronate

67
Q

What cells secret calcium

A

C cells in thyroid

68
Q

What cells secret PTH

A

Chief cells

69
Q

PTH increases calcium travelling to blood from

A

intestine
bone
kidney

Block 5 ellen (17 decks)

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