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ENDOCRINOLOGY - BRS > 1a Calcium And Phosphate Regulation > Flashcards

1a Calcium And Phosphate Regulation Flashcards

1
Q

What is the recommended adult intake of calcium per day?

A

1 gram

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2
Q

Where is the majority of the bodies calcium stored?

A

In the skeleton

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3
Q

What does calcium reside as in the bones?

A

Calcium hydroxyapatite crystals

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4
Q

What is the concentration of calcium in the plasma?

A

2.5 mmol/L

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5
Q

Why is calcium important? - 5 (HIMIN)

A

Hormone stimulus
Intracellular 2nd messenger systems
Muscle contraction and bone strength
Intracellular coenzyme
Neuromuscular excitability

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6
Q

What is the relationship between extracellular calcium and phosphate?

A

They are inversely proportional

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7
Q

What is phosphate an essential component of? - 3

A

ATP, Second messengers and DNA

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8
Q

What proportion of serum calcium is found in the unbound state?

A

50%

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9
Q

What is the serum calcium bound to?

A

Plasma proteins

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10
Q

What two things work to increase calcium?

A

Vitamin D and parathyroid hormone

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11
Q

What are the three places which the main regulators of calcium act on?

A

Bone, kidney and gut

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12
Q

What secretes calcitonin?

A

The parafollicular cells of the thyroid gland

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13
Q

What effect does calcitonin have on the serum levels of calcium?

A

Decreases them

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14
Q

What happens to the serum calcium levels when the thyroid glands are removed?

A

There is no effect - calcitonin is secreted from the parafollicular cells of the thyroid gland, however when the thyroid gland is removed Ca2+ levels remain fine

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15
Q

Which is the active form of vitamin D called?

A

Calcitriol

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16
Q

How does calcitriol regulate its own synthesis?

A

Decreases the transcription of 1-alpha hydroxylase

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17
Q

What are the two types of vitamin D?

A

D2 = ergocalciferol and D3 = cholecalciferol

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18
Q

Describe the synthesis of Calcitriol?

A

UVB absorbed by skin
7-dehydrocholesterol = cholesterol precursor
Makes pre-vitamin D
Which makes vitamin D3, enters blood stream
Taken to liver where is it hydroxylated by 25-hydroxylase into 25 (OH) cholecalciferol
Then taken to kidney where it is hydroxylated again by 1-alpha-hydroxylase into Calcitriol

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19
Q

Is 25(OH) cholecalciferol active or inactive?

A

Inactive

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20
Q

What is the other name for calcitriol?

A

1,25(OH)calciferol

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21
Q

How many hydroxylated reactions for vitamin D3 undergo to make Calcitriol?

A

Two

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22
Q

Where does 25-hydroxylase work?

A

LIVER

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23
Q

Where does vitamin D2 come from?

A

Diet

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24
Q

What affect does Vitamin D have on PTH?

A

inhibits

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25
Q

What affect does calcitriol have on the blood calcium levels?

A

Increases

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26
Q

How does calcitriol affect calcium levels via the bone?

A

Stimulates the release of calcium from the bone by increasing osteocytes which chomp up the bone and therefore release calcium into the blood

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27
Q

What affect does calcitriol have on the gastrointestinal tract?

A

Increases the absorption of dietary calcium

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28
Q

What affect does calcitriol have on the kidney?

A

Increases the reabsorption of calcium from the kidney tubules into the blood, thus reducing the loss of calcium from the urine

29
Q

What effect does calcitriol have on calcitonin?

A

Inhibits calcitonin, which means there is less inhibition of calcium production, so more calcium

30
Q

What affect does calcitriol have on phosphate?

A

Increases the absorption of it in the gut and kidneys

31
Q

What are the two types of cells in the parathyroid gland?

A

Chief and oxyphil cells

32
Q

Where are the parathyroid glands located?

A

Embedded in the capsule of the thyroid gland

33
Q

What do the chief cells secrete?

A

Parathyroid hormone

34
Q

What is PTH secreted as initially?

A

Pre-pro-parathyroid hormone

35
Q

What happens to calcium levels when PTH is high?

A

Calcium levels are low

36
Q

What happens when the calcium levels in the blood are high?

A

Ca2+ binds to receptors on parathyroid cells, and PTH secretion is inhibited

37
Q

What type of receptors are calcium sensing receptors?

A

G protein coupled receptors

38
Q

What happens when the blood calcium levels are low?

A

Less Ca2+ binding to receptors on parathyroid cells, meaning, PTH is secreted

39
Q

How does PTH work on the bone?

A

Binds to osteoblasts which then differentiate into osteoclasts, which are then degraded and the calcium stored within them is released

40
Q

Why does PTH work indirectly on the bone?

A

Osteoclasts do not have a PTH receptor

41
Q

What effect does PTH have on the kidney? - 3

A
  1. Upregulates production of 1 alpha hydroxylase (converts vitamin D into the active form = calcitriol)
  2. Increases Ca2+ reabsorption, so less in urine
  3. Increases phosphate excretion
42
Q

What effect does PTH have on the gut?

A

Increases the uptake of calcium and phosphate from the gut into the blood

43
Q

When is calcitonin released?

A

secreted from the parafollicular cells of the thyroid gland when plasma ca2+ is high

44
Q

What affect does calcitonin have on serum calcium levels?

A

Reduces serum calcium levels

45
Q

How does calcitonin decrease serum calcium levels?

A

Increases Ca2+ excretion in the kidneys and decreases osteoclast activity

46
Q

What is fibroblast growth factor 23?

A

A protein responsible for phosphate and vitamin D metabolism

47
Q

What secretes Fibroblast growth factor 23?

A

Osteocytes

48
Q

What effect does fibroblast growth factor have on the kidneys?

A

Decreases the expression of a sodium-phosphate co-transporter in the proximal tubule

49
Q

What effect does fibroblast growth factor 23 have on the reabsorption of phosphate from the gut?

50
Q

What effect does fibroblast growth factor 23 have on the excretion of phosphate from the gut?

51
Q

What is hypocalcaemia?

A

Low serum calcium levels

52
Q

What happens to membrane excitability in hypocalcaemia and why?

A

There is a larger influx of Na+ as less Ca2+, which means more membrane excitability due to more action potentials triggering

53
Q

What are some signs of hypocalcaemia? - 4

A

Convulsions
Arrhythmia
Tetany
Paraesthesia

54
Q

What is tetany?

A

Spasms of muscle contractions where you cannot relax

55
Q

Where is the most common place to get tetany?

A

Hands and wrist

56
Q

What is Chvosteks sign indicate?

A

Hypocalcaemia

57
Q

What is Chvosteks sign?

A

Facial twitching when you touch the facial artery just below the zygomatic arch

58
Q

What do Chvosteks sign and Trouseau’s sign both indicate?

A

Neuromuscular irritability due to hypocalcaemia

59
Q

What is Trousseau’s sign?

A

Tetany of hand after inflating blood pressure cuff for several minutes

60
Q

What are some causes of hypocalcaemia? - 4

A
  • Vitamin D deficiency
  • Surgery, eg thyroidectory which damages parathyroid glands
  • Auto-immune conditions => hypoparathyroidism
  • Low PTH levels = hypoparathyroidism
61
Q

What causes a vitamin D deficiency? - 3

A
  • Lack of sunlight
  • Renal / liver disease
  • Dietary insufficiency
62
Q

What is a consequence of vitamin D deficiency in children?

63
Q

What condition arises in adults from a vitamin D deficiency?

A

Osteomalacia

64
Q

What is hypercalcaemia?

A

Too high serum calcium levels

65
Q

What happens membrane excitability during hypercalcaemia?

A

Membrane excitability decreases

66
Q

What are the signs and symptoms of hypercalcemia?

A

Stones, Abdominal Moans and Psychic Groans

Nephrocalcinosis - kidney stones
Renal problems like anorexia, nausea, constipation, pancreatitis
Brain effects = fatigue, depression, impaired concentration, coma, altered mentation

67
Q

What are the causes of primary hyperparathyroidism which can lead to hypercalcemia?

A

Parathyroid adenoma

68
Q

What is a cancerous cause of hypercalcaemia?

A

Malignancy activates osteoclasts , and certain cancers secrete PTH-related peptides which act as PTH receptors

69
Q

STATE the 2 enzymes involved in D3 => calcitriol synthesis

A
  1. 25 Hydroxylase
  2. 1-alpha hydroxylase

ENDOCRINOLOGY - BRS (21 decks)

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