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ENDOCRINOLOGY - BRS > 1b Calcium Dysregulation > Flashcards

1b Calcium Dysregulation Flashcards

1
Q

What are the two hormones which control serum calcium?

A

Vitamind D and Parathyroid hormone

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2
Q

What are the three places in which the regulators of serum calcium act?

A

Kidney, bone and the gut

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3
Q

What hormone acts to decrease serum calcium?

A

Calcitonin

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4
Q

Where is calcitonin secreted from?

A

The thyroid parafollicular cells

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5
Q

What effect does calcitonin have on serum calcium?

A

Reduces calcium acutely - however no negative effect if the parafollicular cells are removed eg thyroidectomy

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6
Q

What is tested for when a patients vitamin D levels are measured?

A

Serum 25-OH Vitamin D

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7
Q

How does calcitriol regulate its own synthesis?

A

it decreases transcription of 1-alpha hydroxylase

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8
Q

Describe how calcitriol is produced?

A

UVB from sun
7 dehydrocholesterol
Pre-vitamin D3 to Vitamin D3
D3 converted to 25 (OH) Cholecalciferol
Then to 1,25 (OH)2 cholecalciferol

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9
Q

Where is 25 hydroxylase found?

A

Liver

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10
Q

Where is 1-alpha hydroxylase found?

A

In the kidney

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11
Q

Which form of vitamin D is found in the diet?

A

D2

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12
Q

What are the effects of calcitriol on the kidneys?

A

Increased calcium and Phosphate reabsorption

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13
Q

What are the effects of calcitriol on the gut?

A

Increased phosphate and calcium absorption

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14
Q

What are the effects of calcitriol on the bone?

A

Increased osteoblast activity - bone building

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15
Q

What are the effects of PTH on the kidney?

A

Increased Calcium reabsorption and phosphate excretion and 1-alpha hydroxylase activity

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16
Q

What impact does PTH have on the gut?

A

The increased 1-alpha hydroxylase activity leads to more vitamin D, therefore more calcium and phosphate absorption

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17
Q

What is the effect of PTH on the bone?

A

Increased Calcium resorption from the bone

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18
Q

Why is the net effect on phosphate 0?

A

PTH = Excretion
Vitamin D = Reabsorption therefore overall effect is zero

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19
Q

What is the effect of FGF23?

A

Increases phosphate excretion

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20
Q

How does FGF23 work?

A

It inhibits the Na+/PO4 3- co transporter in the apical membrane of the proximal tubule, therefore more phosphate in the filtrate being excreted

21
Q

What is the effect on FGF23 on calcitriol?

A

It inhibits the effects of calcitriol, leading to less phosphate reabsorption from the gut

22
Q

What is chvosteks sign?

A

Facial paraesthesia - when tapping the zygomatic arch

23
Q

What is trousseau’s sign?

A

When inflating a blood pressure cuff, the wrist = tetany = unable to relax a contracted wrist

24
Q

What are the signs and symptoms of hypocalcaemia?

A

Convulsions
Arrhythmias
Tetany
Paraethesia

25
Q

What are the causes of hypocalcaemia?

A

Low PTH
- neck surgery
- autoimmune
- magnesium deficiency
- congenital

Low Vitamin D
- deficiency
- poor metabolism
- lack of sunshine
- renal failure

26
Q

What are the signs and symptoms of hypercalcaemia?

A

Stones, abdominal moans and psychic groans and reduced neuronal excitability
- kidney stones
- constipation, pancreatitis, nausea
- Fatigue, depression, impaired concentration, low mood

27
Q

What are the causes of hypercalcaemia?

A

Primary pyperparathyroidism
Malignancy
Vitamin D excess

28
Q

What is primary pyerparathyroidism?

A

When the patient has too much PTH, usually due to a Malignancy (parathyroid gland adenoma)

29
Q

What happens to levels of PTH and Ca2+ in primary hyperparathyroidism?

A

they both increase

30
Q

How do malignancies cause hyperparathyroidism?

A

Bony metastases produce local factors to activate osteoclasts = more bone breaking
Some cancers also secrete PTH related peptide which acts as PTH therefore higher Ca2+

31
Q

What is the normal relationship between PTH and Calcium?

A

High PTH = Lower Ca2+

32
Q

High PTH, and high Ca2+, what has happened?

A

Primary hyperparathyroidism
- Parathyroid adenoma which produced too much PTH
- Ca2+ also increases, but no negative feedback to reduce the Ca2+ therefore both are high

33
Q

What happens to phosphate in primary hyperparathyroidism?

A

Low phosphate - increased renal phosphate excretion

34
Q

What is the treatment of choice of primary hyperparathyroidism?

A

Parathyroidectomy - cut out the gland

35
Q

What are the risks of untreated primary hyperparathyroidism?

A

osteoporosis
Renal calculi
Mental function reduced, mood

36
Q

What is secondary hyperparathyroidism?

A

The normal physiological response to high PTH, so low Ca2+

37
Q

What is the most common cause of hyperparathyroidism?

A

Vitamin D deficiency, as lack of vitamin D = lower Ca2+, therefore PTH will rise to try increase Ca2+

38
Q

Why can calcitriol not be made in renal failure?

A

renal 1-alpha-hydroxylase is not made, therefore no vitamin D

39
Q

What is the treatment of choice in secondary hyperparathyroidism with patients with normal renal function?

A

Vitamin D replacement - give 25 hydroxy Vitamin D (inactive forms as the body can convert them itself)

40
Q

What are the two forms of vitamin D?

A

Ergocalciferol - D2
Cholecalciferol - D3

41
Q

What is the treatment of choice

A
42
Q

What is the treatment of choice in secondary hyperparathyroidism with patients with impaired renal function?

A

Alfacalcidol - already hydroxylaed vitamin D

43
Q

What is tertiary hyperparathyroidism?

A

a complication of chronic renal failure, leading to chronic vit d deficiency - this leads to the parathyroid gland working extra hard to produce PTH that eventually hypertrophy of the gland occurs, which can lead to autonomous secretions of PTH

44
Q

What is seen in tertiary hyperparathyroidism?

A

Initially, High PTH and low Ca2+, but overtime = Ca2+ rises

45
Q

What is the treatment for tertiary hyperparathyroidism?

A

Parathyroidectomy

46
Q

What is the normal PTH response to hypercalcaemia?

A

PTH to fall

47
Q

What happens to PTH and calcium when you have hypercalcaemia due to malignancy?

A

High Calcium
Low / suppressed PTH

48
Q

what are the differentials for hypercalcaemia with raised PTH?

A

If normal renal function - primary hyperparathyroidism

If chronic renal failure - tertiary hyperparathyroidism

49
Q

What condition does a patient have if they have low Ca2+ and high PTH?

A

Secondary hyperparathyroidism = due to vitamin d deficiency

ENDOCRINOLOGY - BRS (21 decks)

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