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MBBS III Sem II > Calcium Physiology > Flashcards

Calcium Physiology Flashcards

Understand the basic calcium physiology

1
Q

What is the normal calcium concentration

A

2.4mmol/L

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2
Q

Why is calcium so tightly controlled

A

It is critical for electrical impulses of the neuronal, muscular contractions

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3
Q

Effect of hypercalcaemia on the nervous system

A

Depression

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4
Q

Effect of Hypocalcaemia on the nervous system

A

Hyperexcitation

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5
Q

Outline the distribution of calcium in the body

A

0.1% in the blood, 99% is in the bones and 1% in he ells

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6
Q

Outline the 3 methods of carrying calcium

A 
Protein bound (40%)
Anion bound (10%)
Free circulating ions (50%)
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7
Q

What is calcium complexed with in the blood

A

Phosphorous ions

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8
Q

What intracellular actions does calcium affect

A

Enzyme, cell division and exocytosis

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9
Q

Describe th changes in the plasma membrane potentiation with hypocalcaemia

A

Increases the electrical gradient, which increases Na permeability –> spontaneous excitaiton

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10
Q

Describe the changes in the plasma membrane potentiation with hypercalcaemia

A

Decreases membrane electrical gradient, reduces Na permeability, reduces electrical activity

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11
Q

What proportion of Calcium from diet is absorbed

A

10%

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12
Q

Describe the limitations of calcium absorption

A

Only 350mg of 1g are absorbed by the enterocytes, then 250mg of this remains in the cytoplasm and therefore is lost during sloughing

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13
Q

What forms of calcium can be excreted?

A

Anion bound and serum free calcium

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14
Q

Describe the composition of bone

A

Bone is organic matrix and calcium salts

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15
Q

Describe the organic matrix in bone

A

Colalgen fibers and ground substance

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16
Q

What is the role of collagen fibres in the organic matrix of bone?

A

For tensile strength

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17
Q

What is the composition of ground substance in organic matrix of bone

A

Formed of proteoglycans and chondroitin sulphate + hyaluronic acid

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18
Q

What is the constituents and use of hydroxyapatitie

A

Calcium and phosphate for compressional strength

19
Q

What prevents the formation of hydroxyapatite in the blood?

A

Pyrphosphate

20
Q

Illustrate the process of bone calcification

A

Osteoblasts secrete collagen molecules and ground substance to which calcium slats can bind

21
Q

Illustrate the changes in serum calcium following an injection

A

Within 30minutes it is restored, as bone calcium is highly exchangeable

22
Q

Effect of PTH on serum calcium and phosphate

A

Increases serum calcium, decreases serum phosphate

23
Q

Effect of calcitriol o serum calcium and phosphate

A

Increases both

24
Q

Effect of calcitonin on serum calcium andphosphate

A

Decreases both

25
Q

Effect of PTH on the goes gut and kidneys

A

Bones: osteoclast resorption
kidneys: Calcium ion resorption and phosphate excretion

26
Q

Effect of calcitiol on the gut

A

Increases calcium and phosphate resorption

27
Q

Effect of calcitonin on the bone and kidneys

A

Inhibits osteoclast resorption and promotes calcium excretion from kidneys

28
Q

Structure of vitamin d

A

Fat-soluble steroid

29
Q

What is the overall effect of vitamin D

A

Increases total calcium, magnesium and phosphate

30
Q

How is vitamin D transported?

A

Bound to the Bit D binding protein

31
Q

What are the 2 major sites of vitamin D action?

A

Gut and bone, where it increases absorption

32
Q

What is the mechanism of action of vitamin D on the Kidneys

A

Increases Calcium and phosphate absorption by the epithelial cells

33
Q

How does Vitamin D promote bone absorption of calcium

A

Potentiates the effects of PTH to increase bone absorption

34
Q

How does Vitamin D promote intestinal calcium absorption

A

1,25-Dihydroxycholecalciferol acts as a hormone to increase Ca-binding protein in the intestinal epithelium

35
Q

What stimulates PTH release

A

Low serum Calcium and high serum PO4

36
Q

What inhibits PTH release

A

Low serum Mg, high serum Ca

37
Q

What stimulates Calcitriol rlease

A

Low serum PO4 or PTH

38
Q

what is the rate limiting step and therefore the modulator of calcitriol production

A

Calcitriol production in the kidneys

39
Q

What are th major sites of PTH action?

A

Osteoclasts (resorption), Intestines (Absorption), Kidneys (increase Vitamin production and renal tubular reabsorption and excrete phosphate)

40
Q

Describe the Ca sensing receptor

A

Case is a GPCR on the PTH chief cells, thyroidal cC cells and Loop of Henle

41
Q

When can CaSR be mutated

A

Familial Benign Hypocaciuric Hypercaclaemia

Neonatal severe hyperparathyroidism

42
Q

How do mutations in the CaSR lead to high calcium

A

Parathyroid gland: can stop secreting PTH

Kidneys; can’t stop reabsorbing the calcium

43
Q

What is the plasma membrane calcium gradient

A

Difference of 10^7 (ECF = 10^7 higher concentration than ICF)

MBBS III Sem II (16 decks)

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