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GERR > Calcium metabolism > Flashcards

Calcium metabolism Flashcards

1
Q

Where does calcium enter and exit body and how is it stored?

A
  • Absorbed by GIT
  • excreted in kidneys through urine and some calcium intake excreted instead of absorbed in faeces
  • constant exchange of calcium between ECF and bone through bone remodelling (moves back and forth)
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2
Q

Where is the total body calcium stores found?

A

Skeleton

+ small amount in intracellular and extracellular fluid

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3
Q

How is calcium transported in the blood?

A
  • most remains as free calcium
  • also lots fo albumin bound and less but some globulin bound
  • some anion bound also
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4
Q

What factors effect the proportion of each calcium transport in the blood?

A
  • Albumin concentration (if elevated falsely high calcium can be reported and less free calcium as binds to albumin)
  • PH, the lower the PH the more free calcium as hydrogen binds to albumin binding sites instead of calcium
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5
Q

Name some of the functions of calcium?

A
  • Nerve and cardiac excitability
  • Muscle contraction
  • Cell differentiation
  • Gene regulation
  • Neurotransmitter release
  • Enzyme and allosteric protein modulation
  • Co-factor in coagulation cascade
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6
Q

What are the three hormones which regulate calcium?

A

1) Parathyroid hormone
2) Vitamin D
3) Calcitonin

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7
Q

What are the other two names of vitamin D

A

Calcitriol

1,25-dihydroxycholecalciferol (active form of Vitamin D)

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8
Q

What are the cells in the parathyroid which release parathyroid hormone?

A

Chief cells which are able to sense calcium levels and manufacture and release parathyroid hormone accordingly

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9
Q

What are the factors regulate the chief cells?

A

Release PTH when:

  • Low calcium
  • Low Magnesium
  • High phosphate
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10
Q

What effect does parathyroid hormone have on bone?

A

Bone:
short term - calcium from bone pool moves into ECF
long term - Osteoclasts breakdown bone to release calcium

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11
Q

What effect does parathyroid hormone have on Kidneys?

A
  • reabsorbs more calcium
  • excretes more phosphate
  • forms more active Vit D (1,25-dihydroxycholecalciferol)
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12
Q

What effect does parathyroid hormone have on Intestines?

A

Increases calcium absorption

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13
Q

Where is negative feedback loop in PTH secretion?

A

Normal calcium levels in ECF will switch off release of PTH

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14
Q

Why do phosphate levels decrease when calcium levels increase?

A
  • The product of calcium and phosphate is insoluble so can precipitate in tissues
  • to prevent this when there’s an increase in one body decreases other
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15
Q

Where can you get vitamin D?

A

Synthesised in skin

Diet: Dairy, oily fish, mushrooms and liver

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16
Q

What external factor is needed for synthesis of Vit D in the skin?

A

UV light needed

17
Q

What reaction occurs in the skin?

A

7-dehydrocholesterol > cholecalciferol (Vit D3)

18
Q

What is cholecalciferol converted to in the liver?

A

24-dehydroxycholecalciferol

which then inhibits further conversion of cholecalciferol to itself

19
Q

Where is the Vit D then activated, what hormone stimulates this and what enzyme is required?

A
  • proximal tubule kidneys
  • PTH
  • 1-Alpha-hydroxylase
20
Q

What does Vitamin D achieve?

A

increased intestinal absorption of calcium which increases calcium levels in plasma
(inc plasma calcium inhibits PTH)

21
Q

What two factors will affect activation of Vit K?

A
  • PTH activates it

- Low phosphate levels will increase Vit K activation

22
Q

How does Vit K increase intestinal absorption of calcium?

A

(acts on nuclear receptor to increase gene transcription of these and binds to Vitamin D receptor to initiate non-genomic effects)

  • increase calcium binding proteins (calcitonin, transports calcium across cell)
  • increases calcium stimulated ATPase (transporter protein from intestinal cell into blood)
  • increase alkaline phosphatase
23
Q

What condition is caused by lack of active vitamin K?

A

Rickets (children)

also called Osteomalacia (adults)

24
Q

What are the causes of Rickets?

A
  • Lack of dietary Vit K or sunlight
  • malabsorption of fats (vit K fat soluble
  • failure to form calciferol (usually due to CKD)
  • mutation in 1alpha-hydroxylase
  • mutation in Vit K receptor
25
Q

What is the difference between rickets and osteoporosis?

A

In rickets get very soft bone as it is not mineralised

In Osteoporosis bone is mineralised but there is just very low bone density

26
Q

Who is more at risk of Vit D deficiency?

A
  • elderly (poor diet and indoors more)
  • those who are house bound
  • those who cover up and wear lots of sunscreen
  • Ethnic groups with darker skin (melanin makes it harder for UV light to penetrate skin)
27
Q

What hormone can act to decrease calcium levels and through what mechanism is this achieved?

A
  • Calcitonin released from parafollicular cells of thyroid
  • inhibits osteoclastic activity so less bone resorption (broken down) and less calcium released
  • increases calcium excretion in kidneys
28
Q

What other hormones will influence bones?

A

1) Oestrogen and Testosterone - dec resorption
2) Glucocorticoids - increase bone resorption and dec bone synthesis
3) Inflammatory cytokines - increase bone resorption
4) Prolactin - inc Ca renal reabsorption + 1alpha-hydroxylase activity
5) GH and IGF - increase bone synthesis and growth
6) Thyroid hormone - increases bone turnover

29
Q

Why does bone mass decrease faster in women than men over 50?

A

Decreases in Oestrogen in women result in bone loss so oestrogen replacement can help treat

30
Q

Causes of hypocalcaemia?

A
  • Hypoparathyroidism (usually due to removal of thyroid gland)
  • pseudohypoparathyroidism (PTH secreted by problem with G-protein linked receptor so has no effects on body)
  • Vit D deficiency
31
Q

Causes of hyperparathyroidism?

A

Primary - problem within gland usually PTH secreting adenoma
Secondary - usually as a result of CKD which then causes low calcium and so increase PTH secretion
Tertiary - result of chronic secondary hyperparathyroidism, PTH constantly secreted even after calcium levels rise

32
Q

What is the major problem of hypocalcaemia and what causes this?

A
  • Neuromuscular excitability followed by tetany
  • Normally calcium blocks sodium from entering cells
  • If low calcium then more sodium can enter cells faster
  • means easier for cell depolarisation which leads to tetany
33
Q

What are the two clinical signs of hypocalcaemia?

A

1) Chvostek’s sign - tap on face anterior to ear & below Zygomatic bone will cause twitching
2) Trousseau’s sign - inflation of BP cuff will cause flexion of wrist and metacarpophalangeal joints, hyperextension of fingers and flexion of the thumb

34
Q

Symptoms of hyperparathyroidism?

A
  • Bone pain
  • Kidney stones
  • GI disruption (constipation, low appetite, abdominal pain)
  • CNS disturbance (muscle weakness, lethargy)

GERR (49 decks)

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