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Year 2 Endo > Calcium Dysregulation > Flashcards

Flashcards in Calcium Dysregulation Deck (45)
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1
Q

What can increase Calcium in the body?

A

Vitamin D

Parathyroid hormone

2
Q

What can decrease Calcium in the body?

A

Calcitonin

Not sure of physiological role

3
Q

What is Calcitonin secreted by?

A

Thyroid parafollicular cells

4
Q

What are the main steps of Vitamin D metabolism

A

UVB shines on the skin
Converts 7-dehydrocholesterol to Pre-Vitamin D3
Converts to Vitamin D3

In the liver 25-hydroxylase converts it to 25(OH)cholecalciferol

In the Kidney 1-alpha-hydroxylase converts to 1,25(OH)2 cholecalciferol

5
Q

What is the active form of Vitamin D?

A

1,25(OH)2 cholecalciferol

aka Calcitriol

Cannot be measured

6
Q

What do you measure for Vitamin D?

A

Good marker for how much Vitamin D someone has

25(OH)cholecalciferol

7
Q

What does effect does Calcitriol have on 1-alpha hydroxylase?

A

Negative feedback

8
Q

What are the effects of Calcitriol?

A

Absorb phosphates and calcium in the gut

Increased osteoblast activity

9
Q

What are the effects of PTH?

A

Increased calcium and phosphate reabsorption in the gut by increasing the synthesis of Calcitriol
(Increases 1-alpha hydroxylase activity)

Increases reabsorption of calcium and excretion of phosphate in kidney

PTH stimulates osteoclasts to reabsorb calcium from bone

10
Q

What is the net effect of PTH?

A

Increases synthesis of Calcitriol

Increase Ca mobilisation from bone

Increases plasma Calcium

11
Q

How does PTH and FGF23 regulate serum phosphate?

A

Via sodium/phosphate co-transporter

PTH inhibits this channel

Stops phosphate from being reabsorbed increasing excretion

FGF23 inhibits calcitriol

12
Q

What is FGF23?

A

Factor that is important in the regulation in phosphate

Role is to reduce serum phopsphate

  • inhibits calcitriol
  • inhibits sodium/phosphate co-transporter
13
Q

What are the signs of Hypocalcaemia?

A

Paraesthesia
Convulsions
Arrhythmias
Tetany

CATS go numb

14
Q

What are the two signs that are present with hypocalcaemia?

A

Chvosteks’ sign

Trousseau’s sign

15
Q

What causes low PTH levels?

A

Surgical - neck surgery
Auto-immune
Magnesium deficiency
Congenital (agenesis, rare)

16
Q

What causes low Vitamin D?

A

Deficiency - diet, UV light, malabsorption, impaired production (renal failure)

17
Q

What are the signs of hypercalcaemia?

A

Stones
Abdominal moans
Psychic groans

18
Q

What are stones?

A

Renal effects

Nephrocalcinosis- kidney stones, renal colic

19
Q

What are abdominal moans?

A
Anorexia
Nausea
Dyspepsia
Constipation
Pancreatitis
20
Q

What are psychic groans?

A

CNS effects

Fatigue, depression, impaired concentration, altered mentation, coma (usually >3mmol/L)

21
Q

What is the cause of hyper calcaemia?

A

Primary hyperparathyroidism

Malignancy

Vitamin D excess (rare)

22
Q

What are the features of primary hyperparathyroidism?

A

Too much PTH
Usually due to a parathyroid gland adenoma
No negative feedback - high PTH, but high calcium

23
Q

What are the features of malignancy causing hypercalcaemia?

A
Bony metastases produce local factors to activate osteoclasts
Certain cancers (eg squamous cell carcinomas) secrete PTH-related peptide that acts at PTH receptors
24
Q

What happens when serum calcium falls?

A

Feedback to parathyroid gland

Calcium sensor receptor senses this and stimulates PTH production

25
Q

What happens when serum calcium is high?

A

Feedback to parathyroid gland

Calcium sensor receptor senses this and inhibits PTH production

26
Q

What is an adenoma?

A

benign tumour of a endocrine gland

27
Q

What would a parathyroid adenoma result in?

A

Over production of PTH
Increases serum calcium
Tumour does not respond to negative feedback

Primary hyperparathyroidism

28
Q

What is the biochemistry of primary hyperparathyroidism?

A

High calcium

Low phosphate - increased renal phosphate excretion (inhibition of Na/Phosphate transporter in kidney)

High PTH

29
Q

What is the treatment of primary hyperparathyroidism?

A

Parathyroidectomy is treatment of choice for primary hyperparathyroidism

30
Q

What are the risks of untreated hyperparathyroidism?

A
Osteoporosis
Renal calculi (stones)
Psychological impact of hypercalcaemia – mental function, mood
31
Q

How does secondary hyperparathyroidism occur?

A

Calcium is low

Sensed and PTH is stimulated

32
Q

How are 1ry and 2ry hyperparathyroidism different?

A

In 1ry calcium is high

33
Q

What is the most common form of secondary hyperparathyroidism?

A

Vitamin D deficiency

34
Q

What causes Vitamin D deficiency?

A

Commonly- diet, reduced sunlight

Less common cause is renal failure (can’t make 1-alpha hydroxylase)

35
Q

How do you treat secondary hyperparathyroidism?

A

Vitamin D replacement

Give 25 hydroxy vitamin D

Patient converts this to 1,25 dihydroxy vitamin D via 1a hydroxylase

Ergocalciferol 25 hydroxy vitamin D2

Cholecalciferol 25 hydroxy vitamin D3

36
Q

How do you treat secondary hyperparathyroidism in those with renal failure?

A

inadequate 1a hydroxylation, so can’t activate 25 hydroxy vitamin D preparations
Give Alfacalcidol - 1a hydroxycholecalciferol

37
Q

What causes tertiary hyperparathyroidism?

A

Chronic kidney disease
Chronic Vitamin D deficiency
Chronic low calcium

Increase in PTH to try and restore Ca to normal

Parathyroid glad become autonomous and overactive

Eventual excess of calcium

38
Q

How do you treat tertiary hyperparathyroidism?

A

Parathyroidectomy

39
Q

Summarise primary hyperparathyroidism?

A

Parathyroid adenoma, makes too much PTH

Calcium increases, but PTH stays high (no negative feedback)

40
Q

Summarise secondary hyperparathyroidism?

A

Normal physiological response to low calcium (commonly caused by low vitamin D)
Calcium low/low-normal, PTH high

41
Q

Summarise tertiary hyperparathyroidism?

A

Complication of chronic renal failure and prolonged calcitriol deficiency
Initially calcium falls and PTH rises (secondary hyperparathyroidism), but over a long period high PTH drive by enlarged parathyroid glands increases calcium

42
Q

How do you diagnose hypercalcaemia?

A

Always look at the PTH

43
Q

How will hypercalcaemia caused by malignancy present?

A

Normal PTH response to hypercalcaemia is for PTH to fall
Hypercalcaemia due to malignancy
High calcium (hypercalcaemia)
Low/suppressed PTH

44
Q

If PTH is high how do decide which form of hyperparathyroidism it is?

A

Primary hyperparathyroidism if renal function is normal (eg parathyroid adenoma)

Tertiary hyperparathyroidism (all 4 glands enlarged – hyperplastic) if chronic renal failure

45
Q

How do you diagnose Vitamin D deficiency?

A

Calcium will be low or low/normal

PTH will be high (hyperparathyroidism) secondary to the low calcium

Vitamin D is measured as 25 (OH) vitamin D

Calcitriol (1,25 dihydroxy vitamin D) is very difficult to measure