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ESA1 - Metabolism > Control Of Calcium Levels > Flashcards

Control Of Calcium Levels Flashcards

1
Q

What are the main roles of calcium in the body?

A
  • Hormone secretion
  • Muscle contraction
  • Nerve conduction
  • Exocytosis
  • Activation of enzymes
  • Intracellular second messenger
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2
Q

How is calcium transported in the blood?

A
  • 45% bound to serum proteins e.g. Albumin
  • 45% free ionized form (ACTIVE)
  • 10% complexed into low molecular weight anions e.g. Citrate, oxalate
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3
Q

Where is the majority of calcium stored?

A

Hydroxyapatite crystals in bone

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4
Q

Where is calcitonin released from?

A

C cells of the thyroid gland

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5
Q

Where is PTH synthesised and secreted?

A

Chief (principal) cells of the parathyroid gland

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6
Q

Where is vitamin D obtained from?

A
  • Sunlight

- Food and supplements

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7
Q

What are the main actions of PTH?

A
  • Stimulates reabsorption of Ca2+ from bone
  • Stimulates Ca2+ reabsorption from the kidneys
  • Inhibits uptake of phosphate from kidneys
  • Stimulates hydroxylation of 25-hydroxyvitamin D3 to form Calcitriol
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8
Q

What are the main actions of Calcitriol (1,25-dihydroxycholecalciferol)?

A
  • Increased absorption of Ca2+ from GI tract
  • Increased bone reabsorption
  • Increased reabsorption of Ca2+ from kidneys
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9
Q

Where are the parathyroid glands located?

A
  • Behind the thyroid gland

- 2 superior and 2 inferior (4 in total)

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10
Q

Name 3 cell types you can identify in a histological image of the parathyroid gland

A
  • Principal (chief) cells
  • Adipocytes
  • Oxyphil cells
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11
Q

What is the half life of PTH?

A

4 mins

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12
Q

How is the secretion of PTH controlled?

A
  • NEGATIVE FEEDBACK LOOP
  • Low serum calcium levels detected by parathyroid glands
  • Increased secretion of PTH which increases calcium reabsorption from bone and kidneys, as well as activating vitamin D
  • Serum calcium levels increase
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13
Q

How do the concentrations of phosphate and magnesium ions affect PTH secretion?

A
  • Elevated phosphate INCREASES PTH secretion

- Elevated magnesium DECREASES PTH secretion

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14
Q

How does PTH increase reabsorption of calcium from bone?

A

Decreases osteoblast activity, exposing bony cavity to osteoclasts, which can break down hydroxyapatite crystals and release calcium

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15
Q

Why does PTH decrease uptake of phosphate from kidneys?

A
  • Increases reabsorption of calcium

- Decreases absorption of phosphate to prevent formation of KIDNEY STONES

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16
Q

Which two hormones are involved in increasing serum calcium levels?

A
  • Parathyroid hormone PTH

- Calcitriol (active vitamin D)

17
Q

Why must dietary vitamin D undergo hydroxylation?

A
  • Dietary vitamin D (D2 and D3) is BIOLOGICALLY INERT

- SHORT HALF LIFE so must be converted to 25-hydroxyvitamin D3 (half life of ~2 weeks)

18
Q

How is vitamin D transported in the blood?

A
  • LIPID SOLUBLE

- Bound to serum proteins CBP

19
Q

What are the actions of calcitriol on the gut?

A
  • Increases sensitivity of calcium receptors

- Increases absorption of calcium from the gut

20
Q

How does Calcitriol affect bone turnover?

A

INCREASES rate of bone turnover by osteoclasts

21
Q

What is the role of calcitonin?

A
  • Little effect
  • LOWERS SERUM CALCIUM
  • May have a role in preserving the maternal skeleton during pregnancy
22
Q

What are the signs and symptoms of hypocalcaemia?

A
  • Increased excitability of nervous system (NM junction)
  • TETANY
  • Paralysis
  • Convulsions
  • Pins and needles
23
Q

What are the signs and symptoms of chronic hypercalcaemia?

A
  • Kidney stones
  • KIDNEY DAMAGE
  • Constipation
  • Dehydration
  • Tiredness
  • Depression
24
Q

What are the classic triad of symptoms of a patient displaying hypercalcaemia?

A
  • STONES (kidney stones)
  • MOANS (depression)
  • GROANS (abdominal pain)
25
Q

How is hypercalcaemia treated?

A
  • FLUIDS as patient loses excess fluids in urine

- Removal of possible benign tumour on parathyroid gland causing PRIMARY HYPERPARATHYROIDISM

26
Q

What is PTHrp?

A
  • Parathyroid hormone related peptide
  • Secreted from TUMOURS and acts in a similar way to PTH
  • Can cause hypercalcaemia
27
Q

How does rickets occur and how is it treated?

A
  • VITAMIN D DEFICIENCY
  • Calcium is not absorbed from the gut
  • Serum calcium maintained AT THE EXPENSE OF BONE
  • Treatment involves INCREASING DIETARY VITAMIN D
28
Q

What is the relationship between control of calcium and phosphate levels?

A
  • Calcium levels are tightly regulated but phosphate levels are not
  • Vitamin D increases absorption of BOTH calcium and phosphate from the gut
  • PTH increases absorption of calcium from kidneys BUT NOT PHOSPHATE
29
Q

What are the main organs involved in controlling serum calcium levels?

A
  • Bone
  • Kidneys
  • GI tract (duodenum and jejunum)

ESA1 - Metabolism (20 decks)

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