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METABOLISM, ENDOCRINOLOGY AND HAEMATOLOGY > Parathyroid gland, calcium and phosphate regulation > Flashcards

Parathyroid gland, calcium and phosphate regulation Flashcards

1
Q

Where is calcium mostly stored?

A

Sequestered in bone

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2
Q

What form is calcium sequestered to bones?

A

Hydroxyapatite crystals

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3
Q

What is the purpose of the skeleton?

A
  • Structural support
  • Major reserve of calcium
  • Helps to buffer serum levels
  • Releasing calcium phosphate into interstitium
  • Up taking calcium phosphate
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4
Q

What is the normal serum calcium level (range)?

A

2.2-2.6 mM

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5
Q

What are the three interconvertible fractional forms of calcium in plasma?

A
  • Ionized
  • Protein bound
  • Complexed (with low-molecular-weight inorganic ions such as citrate)
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6
Q

List some uses of calcium in the body?

A
  • Build and maintain bones and teeth
  • Regulates heart rhythm
  • Assists in normal blood clotting (factor 4)
  • Help maintain proper nerve and muscle function
  • Needed for activity of some enzymes
  • Required for nerve transmission
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7
Q

What are the 3 hormones involved in the regulation of calcium serum levels?

A
  • Parathyroid hormone
  • Calcitriol (1,25(OH)2D)
  • Calcitonin
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8
Q

How much calcium does an average 70kg man contain?

A

~1000g

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9
Q

How much calcium is excreted a day for an average 70kg man?

A

~1000g (825 from faeces and 175 from urine)

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10
Q

What effect does PTH have on serum calcium levels?

A

Increases

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11
Q

What is the half life of PTH?

A

4 minutes

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12
Q

Where is PTH synthesised?

A

PTH is CONSTANTLY synthesised in chief cells of parathyroid gland (also constantly degraded)

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13
Q

What are the 3 target organs of PTH and their subsequent effect?

A
  • Bone = increased resorption
  • Intestine = activates vitamin D thus increase transcellular uptake from GI (Vit D to Calcitriol)
  • Kidneys = increased Calcium reabsorption (less lost from urine)
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14
Q

Describe the mechanism of PTH on bones

A
  • induces osteoblastic cells to activate osteoclasts and protect them from apoptosis (through cytokines)
  • PTH decreases osteoblast activity exposing bony surface to osteoclasts
  • Reabsorption of mineralized bone and released of Pi and Ca 2+ into ECF
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15
Q

List sources of vitamin D

A
  • Body (exposure to sunlight)
  • Cheese
  • Butter
  • Fortified milk and cereals
  • Fish
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16
Q

Describe how vitamin D is activated

A
  • Vitamin D3 = precursor
  • Hydroxylated in the liver
  • Hydroxylated in the kidneys
17
Q

What effect does calcitriol have on calcium serum levels?

A

Increase serum calcium by increasing absorption in the gut

18
Q

What effect does calcitonin have on calcium serum levels?

A

Decrease

19
Q

Where is calcitonin synthesised?

A

C cells in Thyroid gland

20
Q

What is severe/chronic hypercalaemia?

A

Abnormally high serum calcium levels exceeding 3mmol/L

21
Q

What are symptoms of hypercalaemia?

A
  • Renal calculi
  • Kidney damage
  • Constipation
  • Tiredness
  • Depression
22
Q

How can polyuria exacerbate hypercalaemia and what are the consequences?

A

Dehydration

  • Lethargy
  • Weakness
  • Confusion
  • Coma
  • Renal failure
23
Q

What is the usual treatment for hypercalaemia?

A

Rehydration

24
Q

What is the main aetiology for hypercalaemia?

A

Malignant OSTEOLYTIC bone metastasis

-common cancers that metastasise to bone causing lytic lesions: breast, lung, renal, thyroid

25
Q

Where are common sites for bone metastasis?

A
  • Vertebrae
  • Pelvis
  • Ribs
  • Proximal femur and humerus
  • Skull
26
Q

What is hypocalcemia?

A

Condition where serum calcium is abnormally lower than the normal range

27
Q

What does hypocalcemia lead to and what are the symptoms?

A

Hyper-excitability of neuromuscular junction
(low serum calcium causes increase Na+ entry to neurons=depolarisation)
-Pins + needles
-Tetany (muscle spasms)
-Paralysis
-Convulsions
-Carpopedal spasm

28
Q

What is hyperparathyroidism?

A

Secretion of too much parathyroid hormone

29
Q

What are the two types of hyperparathyroidism?

A
  • Primary = 1/4 glands develop an adenoma and secrete excessive PTH
  • Secondary = all 4 glands become hyperplastic (vit D deficiency)

METABOLISM, ENDOCRINOLOGY AND HAEMATOLOGY (19 decks)

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