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BRS Y1 > Week 4- Regulation of Calcium & Phosphate > Flashcards

Week 4- Regulation of Calcium & Phosphate Flashcards

1
Q

What is the recommended adult intake of calcium?

A

1000mg per day

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2
Q

What are the 3 key hormones in calcium regulation? Do they increase or decrease calcium?

A 
Parathyroid hormone (increases calcium)
Vitamin D (increases calcium)
Calcitonin (decreases calcium)
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3
Q

Where is parathyroid hormone secreted?

A

Parathyroid glands

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4
Q

Where is vitamin D synthesised?

A

In the skin (or intaken via diet)

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5
Q

Where is calcitonin secreted?

A

Thyroids parafollicular cells

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6
Q

What are the 2 sources of vitamin D?

A

Ergocalciferol ie D2 (intaken via diet)

Cholecalciferol ie D3 (made in skin with sunshine)

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7
Q

When measuring Vit D levels what do we measure?

A

25 (OH) cholecalciferol ie unactive form

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8
Q

What 3 areas does calcitriol work on and what does it do?

A

Increases calcium absorbtion and phosphate reabsorbtion in the kidney

It works on the small intestine increasing phosphate and calcium absorbtion

Increases reabsorbtion of calcium in bones and stimulates osteoblasts (important for bone health)

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9
Q

How many parathyroid glands are there and where are they located?

A

4- located at the back of the thyroid

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10
Q

What is the precursor for parathyroid hormone?

A

Pre-pro-PTH

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11
Q

What does PTH do?

A

Drives calcium to increase, when it does PTH switches off

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12
Q

What happens when there is high extracellular calcium?

A

Binding of calcium to receptors on parathyroid gland cells inhibits PTH

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13
Q

What happens when there is low extracellular calcium?

A

Less binding of calcium to receptors of parathyroid gland cells stimulates PTH secretion

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14
Q

What 3 main areas does PTH effect and what does it do?

A

Kidney- increases calcium absorption and stimulates loss of phosphate. Stimulates action of 1 alpha hydroxylase allowing more active vit D (calcitriol) formation

Bone- stimulates calcium reabsorbtion

Gut- increases reabsorbtion of calcium and phosphate

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15
Q

What do osteoblasts do?

A

Build bone

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16
Q

What do osteoclasts do?

A

Consume bone

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17
Q

How are osteoblasts converted to osteoclasts?

A

Binding of PTH to receptors causes osteoclast activating factors to be expressed turning the osteoblasts to clasts

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18
Q

What are the 2 ways PTH regulated?

A

Increased serum calcium reduces PTH secretion

As PTH stimulates production of calcitriol, the calcitriol negatively feeds back onto parathyroid cells

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19
Q

What does calcitonin do? What is special about it

A

It reduces serum calcium but it is possible to live without it

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20
Q

What are the 2 mechanisms by which calcitonin works?

A

Increases calcium excretion from kidney

Lowers osteoclast activity on the bone

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21
Q

What are the 2 mechanisms by which FGF23 inhibits phosphate reabsorbtion?

A

1- directly inhibits the cotransporter that reabsorbs phosphate that would otherwise be urinated

2- indirectly by inhibiting calcitrol production

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22
Q

What happens to membrane excitability in hypercalcaemia?

A

Blocks Na influx so less excitability

23
Q

What happens to membrane excitability in hypocalcaemia?

A

Enables greater Na influx so more membrane excitability

24
Q

What are symptoms of hypocalcaemia? What mnemonic do we use to remember them?

A

Parasthesia (pins and needles) around lips, hands, mouths

Convulsions

Arrhythmia

Tetany (muscles contract then cant relax)

Cats go numb

25
Q

What is Chvostek’s sign and why is it used?

A

Tap the facial nerve (just below zygomatic arch) and facial muscle will twitch

Indicates hypocalcaemia

26
Q

What is Trousseaus sign and why is it used?

A

Inflation of the BP cuff for several mins induces a carpopedal spasm

Indicates hypocalcaemia

27
Q

What is it called when PTH levels are low?

A

Hypoparathyroidism

28
Q

What are the 2 main causes of hypocalcaemia and how do they arise?

A

Low PTH levels (due to neck surgery, autoimmunity, magnesium deficiency, congenital)

Vit D deficiency

29
Q

What are the 5 causes of Vit D deficiency?

A 
Dietary insufficiency
Inadequate sun exposure
Liver disease
Renal disease
Vit D receptor defects (rare)
30
Q

What is vit D deficiency called in children and in adults? What are the symptoms in each

A

Children- rickets (soft bones that bow)

Adults- osteomalacia (fractures, proximal myopathy)

31
Q

What is the phrase we use to describe the symptoms of hypercalcaemia? Describe the symptoms

A

Stones, abdominal moans and psychic groans

Reduced neuronal excitability

Stones- renal effects ie kidney stones, renal colic
Abdominal moans- GI effects ie nausea, dyspepsia, constipation
Psychic groans- CNS effects ie coma, fatigue, depression

32
Q

What are the causes of hypercalcaemia?

A

Primary hyperparathyroidism (too much PTH)

Malignancy (bone metastases activate osteoclasts and some cancers secrete peptides that act at PTH receptors)

Vit D excess (rare)

33
Q

How is calcium distributed in the body?

A

99% in the skeleton and teeth

Very small amount of extracellular calcium that is tightly regulated

34
Q

Why is calcium important in the body?

A

Muscle contraction
Bone strength
Intracellular 2nd messenger and coenzyme
Blood coagulation

35
Q

Why are phosphates required in the body?

A

They are essential components of high energy compounds eg ATP, 2nd messengers and fundamental molecules eg RNA/DNA

36
Q

What is the link between extracellular calcium and phosphate?

A

Their levels are inversely proportional to each other and they are regulated by the same hormones

37
Q

What 2 forms does serum calcium exist as?

A

Unbound (ie free/ionised) and bound

38
Q

What is the normal serum calcium level for unbound calcium and how much of total serum calcium is found unbound?

A

Normal level: 1.25mM

% of total serum calcium: 50%

39
Q

What is the normal serum calcium level for bound calcium and how much of total serum calcium is found bound?

A

Normal level: 1.13 mM

% of total serum calcium: 45%

40
Q

What is the other name by which vitamin D2 is known?

A

Ergocalciferol

41
Q

What is the other name by which vitamin D3 is known?

A

Cholecalciferol

42
Q

How do we gain vitamin D2?

A

Via diet

43
Q

How do we gain vitamin D3?

A

Make it from sunshine in the skin

44
Q

Describe the general process by which vitamin D is metabolised

A

Skin cells absorb UVB light from the sun

This triggers conversion of 7 dehydrocholesterol to pre vitamin D3 which is converted to vit D3

Vit D3 alongside vit D2 from diet is transported to the liver and hydroxylated at position 25 to form 25 hydroxylase which is not active

The enzyme 1 alpha hydroxylase carries out the 2nd hydroxylation step forming calcitriol, the active form of vitamin D

45
Q

What type of sunlight does the skin absorb?

A

UVB

46
Q

What 2 molecules are synthesised before vit D3 is made in the skin?

A

7 dehydrocholesterol and pre vitamin D3

47
Q

Where is the first hydroxylation step of vit D metabolisation carried out?

A

Liver

48
Q

Where is the second hydroxylation step of vit D metabolisation carried out?

A

Kidney

49
Q

What is the name of the enzyme that carries out the second hydroxylation step during vitamin D metabolisation?

A

1 alpha hydroxylase

50
Q

What is the active form of vitamin D known as?

A

Calcitriol

51
Q

What type of receptor detects changes in calcium and where is it found?

A

G protein coupled receptors in parathyroid glands

52
Q

What is the relationship between PTH secretion and serum calcium?

A

PTH secretion is inversely proportional to serum calcium levels

53
Q

Where is calcitonin secreted from?

A

Parafollicular cells of the thyroid gland

BRS Y1 (52 decks)

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