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BRS 4: Endocrinology > 4.6: Regulation of calcium and phosphate > Flashcards

4.6: Regulation of calcium and phosphate Flashcards

1
Q

What is the most abundant metal in the body

A

Calcium

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2
Q

Where does 99% of calcium reside in the body, what is it stored as

A

In the skeleton and teeth
Calcium hydroxyapatite crystals

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3
Q

What is Extracellular calcium

A

Calcium that is present in the bloodstream - measured during a blood test

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4
Q

Why is Extracellular calcium tightly regulated

A

Lives in circulation, often bound to albumin

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5
Q

Unbound ionised calcium is a

A

Biologically active component

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6
Q

Hormones involved in calcium control (increase)

A

Parathyroid hormone (PTH)
Vitamin D

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7
Q

What is parathyroid hormone secreted by

A

Parathyroid glands

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8
Q

How is vitamin D synthesised

A

In skin or intake via diet

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9
Q

How do Vit D and PTH regulate Ca and PO4 homeostasis

A

Via actions on kidney, bone and gut

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10
Q

What is calcitonin

A

Hormone that can reduce calcium acutely, but no negative effect if parafollicular cells are removed

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11
Q

Two types of Vitamin D

A

Ergocalciferol
Cholecalciferol

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12
Q

What is ergocalciferol derived from

A

UV irradiation of plants - consumed in vegetables

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13
Q

What is cholecalciferol derived from

A

UV irradiation of skin and certain foods (oily fish, egg yolk)

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14
Q

Vitamin D metabolism

A

1) UVB from the sun causes 7-dehydrocholesterol to convert to Pre-vitamin D3 in the skin
2) this is then converted to Vit D3 which enters the circulation
3) Vit D2 is present in the diet and absorbed from the gut
4) D3 and D2 pass into the liver (25-hydroxylase) and are hydroxylated at position 25 producing 25(OH)cholecalciferol
5) this is then hydroxylated again in the kidneys to form active vitamin D : using enzyme 1 alpha-hydroxylase

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15
Q

Active form of vitamin D is called

A

Calcitriol

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16
Q

2 Characteristics of serum 25-OH cholecalciferol

A

Biologically inactive
Good indicator of body vitamin status

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17
Q

How is Vitamin D synthesis regulated

A

1,25(OH)2cholcalciferol regulates own synthesis by decreasing transcription of 1 alpha-hydroxylase

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18
Q

Major role of calcitriol

A

Increase Ca2+ and PO4 ^3- reabsorption from the gut

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19
Q

Role of calcitriol in kidney

A

Increases Ca2+ and PO4 ^3- reabsorption, less lost in urine more in bloodstream

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20
Q

Role of 1,25(OH)2D3 in bone

A

Increased Ca2+ reabsorption from bone

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21
Q

What cells secrete PTH

A

Chief cells in parathyroid glands

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22
Q

What is PTH secreted as

A

Large precursor and cleaved to PTH

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23
Q

feedback (regulation) of PTH

A

G-protein coupled calcium sensing receptor on chief cells detect change in circulating calcium concentration

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24
Q

What is PTH secretion inversely proportional to

A

Serum calcium

25
Q

High levels of ECF (Ca2+)

A

Ca2+ binds to receptors on parathyroid cells
PTH secretion inhibited

26
Q

At low levels of ECF (Ca2+)

A

Less Ca2+ binding to receptors on parathyroid cells
PTH secreted

27
Q

When serum calcium increases, what happens to parathyroid hormone (PTH)

A

PTH decreases

28
Q

Function of osteoblast

A

Build bone

29
Q

Function of osteoclast

A

Consume bone

30
Q

PTH in bone

A

PTH binds to receptors
Osteoblast build bone
If osteoclast activating factors are present
Osteoblast turns into osteoclasts
Causing bone reabsorption

31
Q

Calcitriol action in bone depend on

A

Serum calcium

32
Q

During low serum calcium calcitriol has a ___ effect

A

Calcitriol works with PTH to increase calcium reabsorption from bone
Osteoclast > osteoblasts

33
Q

During normal serum calcium levels, calcitriol has a ___ effect

A

Calcitriol promotes bone formation
Osteoblast > osteoclasts

34
Q

2 processes of Negative feedback in PTH regulation

A

PTH increase and 1,25 (OH)2D3 synthesis
Increased plasma Ca2+ and parathyroid cell’s increased PTH

35
Q

Calcitonin is secreted from

A

Parafollicular cells of thyroid gland

36
Q

Function of calcitonin

A

Reduces serum calcium

37
Q

Calcitonin actions and regulation

A

Increased plasma Ca2+ detected by parafollicular cells of thyroid
Secretes calcitonin
Decreases osteoclast activity in bone
Increases Ca2+ excretion in kidneys
Both decrease claims Ca2+ limited effect

38
Q

What is serum phosphate regulated by

A

FGF23

39
Q

What is FGF23 secreted by

A

Bone cells

40
Q

Function of FGF23 and two ways in which this occurs

A

Promotes phosphate loss:
Blocks sodium phosphate cotransporter in kidneys
Switches off calcitriol
More phosphate into urine

41
Q

Hypercalcaemia is

A

High serum calcium

42
Q

Hypocalcaemia is

A

Low serum calcium

43
Q

Characteristics of the membrane during Hypercalcaemia

A

High Extracellular calcium, blocks Na+ influx so less membrane excitability

44
Q

Characteristics of the membrane during hypocalcaemia

A

Low Extracellular calcium, so greater Na+ influx enables, so more membrane excitability

45
Q

Signs and symptoms of hypocalcaemia (4)

A

Paraesthesia
Convolutions
Arrhythmias
Tetany
(CATs go numb)

46
Q

Process of Chvosteks sign test

A

Tap facial nerve below zygomatic arch
Positive response = twitching of facial muscles = neuromuscular irritability due to hypocalcaemia

47
Q

How to test for hypocalcaemia (2)

A

Chvosteks sign
Trousseaus sign

48
Q

Process of trousseaus sign test

A

Inflation of BP cuff for several minutes
Induces carpopedal spasm
Neuromuscular irritability due to hypocalcaemia

49
Q

2 Causes of hypocalcaemia

A

Low PTH levels = hypoparathyroidism
Vitamin D efficiency

50
Q

4 causes of hypoparathyroidism

A

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

51
Q

5 Causes of vitamin D deficiency

A

Malabsorption or dietary insufficiency
Inadequate sun exposure
Liver disease
Renal disease
Vit D receptor defects (rare)

52
Q

Consequences of vitamin D deficiency in children

A

Rickets (bowling of bones)

53
Q

Consequences of vitamin D deficiency in adults

A

Osteomalacia
(Fractures, proximal myopathy)

54
Q

Vitamin D deficiency effect on bones

A

Lack of bone mineralisation, leading to soft bones

55
Q

Signs of Hypercalcaemia

A

Reduced neuronal excitability- atonal muscles

56
Q

3 symptoms of Hypercalcaemia

A

Stones - renal effects : Nephrocalcinosis, kidney stones, renal colic
Adbominal moans - GI defects: anorexia, nausea, dyspepsia, constipation, pancreatitis
Psychic groans - CNS effects : fatigue, depression, impaired concentration, altered mentation, coma

57
Q

3 causes of Hypercalcaemia

A

Primary hyperparathyroidism
Malignancy
Vitamin D excess (rare)

58
Q

3 causes of primary hyperparathyroidism

A

Too much PTH
Parathyroid gland adenoma
No negative feedback- high PTH, but high calcium

59
Q

Cause of malignancy

A

Bony metastases produce local factors to active osteoclasts, increasing calcium reabsorption from bone

BRS 4: Endocrinology (10 decks)

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