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Endocrinology > Endo 12 - Endocrine Bone Disorders > Flashcards

Endo 12 - Endocrine Bone Disorders Flashcards

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1
Q

What is the common name given to the most important vitamin D metabolite?

A

Calcitriol

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2
Q

What is the chemical name of calcitriol?

A

1, 25-dihydroxycholecalciferol

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3
Q

What is the principle effect of calcitriol?

A

increases calcium, magnesium and phosphate absorption in the small intestine

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4
Q

What are the other effects of calcitriol?

A
  • increases calcium and phosphate reabsorption from the kidneys
  • stimulates osteoclast formation
  • stimulates osteoblasts to make osteoclast activating factors
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5
Q

What does Vitamin D deficiency cause?

A
  • lack of bone mineralisation
  • softening of bone - bowing of legs
  • bone deformities
  • bone pain
  • severe proximal myopathy
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6
Q

What is vitamin D deficiency called in children?

A

rickets

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7
Q

What is Vitamin D deficiency called in adults?

A

Osteomalacia

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8
Q

Name 4 causes of vitamin D deficiency?

A
  • diet
  • lack of sunlight
  • GI malabsorption
  • renal failure
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9
Q

Which step in vitamin D metabolism requires UV light?

A

conversion of 7-dehydrocholesterol in the skin to form cholecalciferol

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10
Q

How many hydroxylation reactions are there in vitamin D metabolism?

A

2

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11
Q

Describe the 2 hydroxylation reactions in vitamin d metabolism?

A
  1. cholecalciferol hydroxylated to form 25-hydroxycholecalciferol in the liver
  2. hydroxylated by 1-hydroxylase to form 1,25 dihydroxycholecalciferol (calcitriol)
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12
Q

What can stimulate 1-hydroxylase in the kidneys?

A

Parathyroid hormone

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13
Q

How can lack of sunlight cause vitamin D deficiency?

A

will mean less 7-dehydrocholesterol gets converted into cholecalciferol in skin

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14
Q

How can liver disease cause vitamin D deficiency?

A

liver is where the first hydroxylation takes place

where 25-hydroxycholecalciferol is stored

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15
Q

How can renal failure cause vitamin D deficiency?

A

where 2nd hydroxylation takes place

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16
Q

What is measured to gage the level of calcitriol?

A

25-Hydroxycholecalciferol

can only be used if normal renal function

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17
Q

How would you diagnose vitamin d deficiency?

A 
Plasma 25-hydroxycholecalciferol = low
plasma calcium = low
plasma PTH = high
plasma phosphate = low
radiology = widened osteoid seams
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18
Q

What would the level of phosphate be in someone with renal failure?

A

High

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19
Q

What would plasma calcium be in someone with renal failure?

A

Low - as not producing calcitriol

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20
Q

What is the consequence of hypocalcaemia caused by renal failure?

A

decrease in bone mineralisation
increase in bone resorption

= osteitis fibrosa cystica

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21
Q

What can vitamin d excess lead to?

A

Hypercalcaemia and hypercalciuria

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22
Q

What does PTH do to bone?

A

Breaks it done in order to restore blood calcium level

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23
Q

What can excess vitamin D result from?

A

excessive treatment

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24
Q

What is Paget’s disease?

Study These Flashcards
A

Very active, increased localised but disorganised bone metabolism
increased bone breakdown and formation

25
What is Paget's disease characterised by?
Abnormal large osteoclasts
26
State some of the symptoms of Paget's disease?
``` - increased warmth over bones increased osteoblast/osteoclast activity - first osteoclast breaks bone down - then osteoblast builds bone back up - pelvis and femur most commonly affected - increased chance of fracture ```
27
Describe how you would diagnose Paget's disease?
plasma calcium - normal plasma ALP - high radiology - spongy bone, increased bone density
28
What are the two components of bone where 95% of body's calcium is stored?
1. Inorganic mineral component - 65% | 2. Organic component - 35%
29
What is the normal plasma calcium range?
2.2-2.6mmol/L
30
State 2 hormones which increase plasma calcium?
PTH | Calcitriol
31
Name a hormone that reduces plasma calcium?
Calcitonin
32
What are the 2 direct effects of PTH?
- Calcium mobilisation from bone | - increased calcium reabsorption in kidneys
33
What are the 2 direct effects of calcitriol?
- increased calcium absorption in small intestine | - increased mobilisation of calcium in bone
34
What stimulates PTH release?
hypocalcaemia
35
State 4 signs of hypocalcaemia?
1. parasthesia 2. arrhythmias 3. convulsions 4. tetany
36
What effect does hypocalcaemia have on excitable tissue?
sensitises excitable tissue
37
State 2 clinical signs of neuromuscular irritability due to hypocalcaemia?
1. Chvostek's sign - tap facial nerve just below zygomatic arch, twitching = positive response 2. Trousseau's sign = Pump blood pressure cuff for several minutes - +ve = carpopedal spasm
38
State 4 causes of hypocalcaemia?
- Hypoparathyroidism - vitamin d deficiency - pseudohypoparathyroidism - renal failure - imparied 1 hydroxylase
39
Describe the effect of hypercalcaemia on neuronal excitability?
reduces neuronal excitability
40
What are the signs of hypercalcaemia?
- stones, groans and moans - stones - renal effects - polyuria and thirst - abdominal moans - anorexia, nausea, constipation - psychic groans - fatigue, depression, coma
41
What are the 2 main causes of hypercalcaemia?
- Primary hyperparathyroidism - e.g. adenoma | - Malignancy - bone tumours causing increased bone turnover
42
How would you differentiate between primary hyperparthyroidism and malignancy?
Primary HPT would have no negative feedback so PTH will be high along with plasma calcium Malignancy - plasma calcium high but PTH low
43
Describe the treatment of vitamin D deficiency if normal renal function?
Give 25-hydroxy vitamin D | - patient can convert this to calcitriol using 1-hydroxylase
44
Name the 2 types of supplements for vitamin D deficiency in normal renal function?
- ergocalciferol | - cholecalciferol
45
What is the treatment for vitamin D deficiency in patients with renal failure?
Alfacalcidol - 1-hydroxycholecalciferol
46
What do osteocytes produce?
Type 1 collagen
47
What is RANK ligand?
osteoclast activating factor stimulates the maturation of osteoclast from precursors so more bone resorption
48
Define osteoporosis
Having a bone mineral density that is 2.5 standard deviations or more below the average for young healthy adults
49
How is BMD measured?
DEXA scan
50
State some pre-disposing conditions for osteoporosis?
- post menopausal women - endocrine disease - hypogonadism in young people
51
What are the advantages and disadvantages of estrogen replacement to prevent osteoporosis in post menopausal women?
adv - anti-resorptive effect in bone so prevents bone loss dis - must be given with progesterone otherwise endometrial carcinoma also breast cancer VTE
52
Name 2 oestrogen receptor modulators and their effects
- Tamoxifen - oestrogenic in bone and anti-oestrogenic in breast and uterus SERM - Raloxifene - SERM - but causes stroke and VTE
53
What is the 1st, 2nd and 3rd line treatment for osteoporosis?
1. Bisphosphonates 2. Denusomab 3. Teriparatide
54
What are bisphosphonates analogues of?
Pyrophosphate
55
How do bisphosphonates work?
impairs ability of osteoclast to resorp bone decreases maturation of osteoclasts promotes osteoclast apoptosis
56
State some uses of bisphosphonates?
Osteoporosis malignanacy paget's
57
State some of the unwanted effects of bisphosphonates
oesophagitis | flu like symptoms
58
What is denusomab?
human monoclonal antibody binds to RANKL and inhibits osteoclast formation given every 6-12 months
59
What is teriparatide?
recombinant PTH | INCREASES BONE RESORPTION and formation

Endocrinology (18 decks)

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