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Nutritional Physiology > Iron, Calcium & Vitamin Metabolism > Flashcards

Iron, Calcium & Vitamin Metabolism Flashcards

1
Q

What are the RDIs of iron?

A

14-18: 11 (M), 15mg/d (F)
19+: 8 (M), 18mg/d (F)
Pregnancy: 27mg/d

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2
Q

What are the reactions for the creation of oxidative oxygen species?

A

Fe2+ + H2O2 = Fe3+ + OH- + OH+

Fe3+ + H2O2 = Fe2+ + H+ + OOH-

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3
Q

Hydroxyl and hyper-oxyl radicals are……..

A

Highly reactive with proteins, lipids and DNA

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4
Q

What is transferrin?

A

Transports Fe around the body

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5
Q

What is mobilferrin?

A

Transports Fe in cells

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6
Q

What is ferritin?

A

Sequesters (stores) Fe in cells

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7
Q

Transferrin saturation is usually …. for males and …. for females

A

10-15%, 30%

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8
Q

How much iron goes in/out in a day?

A

1-2mg

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9
Q

The main storage organ for iron is the …..

A

Liver

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10
Q

Ferroxidase converts….

A

Fe2+ to Fe3+ (storage)

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11
Q

Ferroductase converts……

A

Fe3+ to Fe2+ (soluble release)

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12
Q

The liver is better at ……. iron

A

Storing

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13
Q

Haem iron

A
  • more readily absorbed
  • taken up as a Fe-porphyrin complex
  • only present in ferrous state (Fe2+)
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14
Q

Non-haem iron

A
  • either ferrous or ferric (Fe3+)

- only absorbed as ferrous

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15
Q

Only …… percent of iron is absorbed

A

10

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16
Q

Bioavailability of iron depends on….. (4)

A
  • pH
  • redox state of the metal
  • dietary complexes which enhance solubility
  • dietary complexes which diminish absorption
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17
Q

What are the complexes that increase the absorption of iron? (6)

A
  • ascorbate (vitamin C)
  • glutathione
  • lactate
  • pyruvate
  • cysteine
  • histidine
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18
Q

What are the complexes which decrease the absorption of iron? (5)

A
  • phytates (in cereals)
  • tannates (eg tannin in tea)
  • oxalates (rhubarb, parsley)
  • carbonates
  • carbonate by other minerals (Mn2+ and Zn2+)
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19
Q

What is the absorption process of iron? (Non haem iron)

A
  1. Transported by DMT1
  2. Energy derived from proton gradient
  3. H+ moved out of cell
  4. Binds to mobilferrin
  5. Transported to basal membrane
  6. IREG1 (ferroportin) transported into interstitial space
  7. During transport Fe2+ is oxidised by hephaestin (Cu dependent ferroxidase)
  8. Fe3+ moves into blood and immediately binds to plasma transferrin
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20
Q

Which enzyme reduces Fe3+ for absorption?

A

Duodenal cytochrome b

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21
Q

How is haem iron absorbed?

A
  1. Absorbed by heme carrier protein 1 (HCP1)
  2. Heme oxygenate liberates free Fe2+ from the heme group
  3. Fe2+ binds to mobilferrin
  4. Moves to basolateral membrane
  5. Transported by IREG1
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22
Q

How is iron absorbed into cells?

A
  1. Presence of transferrin receptors in plasma membrane
  2. Transferrin binds to receptors and is internalised via a vesicle
  3. Iron is released under acidic conditions and moved into the cell via DMTI
  4. It is incorporated into the haem or bound to ferritin
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23
Q

How is iron released from cells?

A
  1. IREG1
  2. Oxidation of Fe2+ by ceruloplasmin
  3. Process occurs in macrophages and liver cells
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24
Q

What happens if iron levels in cells become too high?

A

Haemosiderin deposits form - causes apoptosis

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25
Q

What happens if iron concentrations increase?

A
  • IREG1 closes
  • iron accumulates within cells and binds to ferritin
  • leads to haemosiderin deposits and apoptosis
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26
Q

What are the normal plasma iron concentrations?

A

Males: 13.4-31.3 microM
Females: 11.6-29.5 microM

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27
Q

Depending on the state of IREG1, iron will…….

A

Either be absorbed into the body or it will remain into the enterocytes

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28
Q

What is IREG1 present in?

A

Macrophages, duodenal enterocytes, hepatocytes and placenta

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29
Q

What regulates iron?

A

Helcidin, a small peptide of 25 amino acid

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30
Q

Which cells secrete hepcidin?

A

Liver cells

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31
Q

Calcium is the ….. most abundant element in the body

A

5th

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32
Q

Where is calcium found?

A

99% in Skelton

1% in soft tissue available for exchange

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33
Q

What is the adult body content of calcium?

A

M: 1200mg
F: 1000mg

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34
Q

What is the form of calcium in the body?

A

Hydroxyapatite: Ca10(PO4)6(OH)2

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35
Q

What are the processes that require calcium?

A
  • bone formation
  • blood clotting
  • muscle contraction
  • intercellular signalling
  • nervous system
  • endocrine system (exocytosis)
  • cardiovascular system
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36
Q

What are normal plasma calcium levels?

A

9mg/dL

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37
Q

What are the levels of calcium for hypercalaemia?

A

> 15mg/dL

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38
Q

What happens in hypercalaemia?

A
  • depresses neuromuscular activity
  • Ca binds to activation gate of fast Na+ channels and changes the state of the channel protein and reduces permeability to Na+
  • reduces resting membrane potential
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39
Q

What are the levels needed for hypocalaemia?

A

<6mg/dal

40
Q

What happens in hypocalaemia?

A
  • makes nerve and muscle hyperexcitable

- opposite mechanism to hypocalaemia

41
Q

Intracellular Ca2+

A
  • 1% in cells

- stored in mitochondria and ER

42
Q

Extracellular Ca2+

A
  • 0.1%

- 2.4mM = 9.4mg/del

43
Q

What is the distribution of calcium in the plasma?

A
  • 50% ionised
  • 41% protein bound
  • 9% calcium complexes to anions
44
Q

What is the active form of calcium?

A

Ionised

45
Q

What are the processes that maintain calcium levels?

A
  1. Absorption
  2. Reabsorption
  3. Resorption
46
Q
  1. Calcium absorption
A
  • intake of 1000mg
  • 350mg is absorbed
  • 250 is lost each day through secretions and sloughed cells
47
Q
  1. Calcium reabsorption
A
  • 59% of calcium is filtered (bound to protein is not)

- 90% of what is filtered is reabsorbed in the proximal tubule, loop of henle and distal tubule

48
Q
  1. Calcium resorption
A
  • 2 processes
    1. Osteocytic osteoclasts (fast: mins to hours)
    2. Slow phase
49
Q

How does osteocytic osteolysis work?

A
  • under control of parathyroid hormone

- increase in PTH causes secretion of Ca2+ in to extracellular fluid

50
Q

How does the slow calcium resorption work?

A
  • no PTH receptors
  • H+ ions secreted by osteoclasts into ECF
  • Cl- follows to form HCl
  • ECF becomes very acidic (pH=4)
  • releases Ca2+
  • osteoclasts also secrete phosphatase which digests collagen matrix and has optimal function at pH=4
51
Q

What is calcium regulated by?

A
  1. Parathyroid hormone
  2. Vitamin D3
  3. Calcitonin
52
Q

Parathyroid cells

A
  • chief cells: secrete PTH

- oxyphil hormones: unknown function

53
Q

Parathyroid calcium signalling

A
  • parathyroid glands have calcium sensing receptors (CaSR)
  • respond to increase in Ca2+ levels
  • leads to a decrease in production of PTH
54
Q

PTH

A
  • 88AAs

- half-life: 20-30mins

55
Q

What does PTH do?

A
  • increases calcium absorption in kidneys
  • activates Vit d
  • increases bone erosion
56
Q

Vitamin D3 characteristics

A
  • steroid hormone derived from cholesterol
  • generated in skin by Uv radiation
  • half-life: days-weeks
  • 2 different forms: active and inactive
57
Q

What are the steps of the biosynthesis of Vit D3?

A
  1. Dehydrocholesterol is present in the skin
  2. UV radiation forms colecaliferol (Vit D)
  3. Liver: colecaliferol is hydrolysed to form 25-hydroxy-colecaliferol (25-OHD3)
  4. Kidney: 2nd hydroxylation step to convert to active or inactive form, controlled by PTH
58
Q

Vit D active form

A

OH group is added to position 1

59
Q

Vit D inactive form

A

OH is added to position 24

60
Q

What does Vit D do for calcium maintenance?

A
  • increases calcium absorption
  • increases calcium reabsorption
  • calcification (small effect)
61
Q

Calcitonin characteristics

A
  • secretes by para follicular C cells in thyroid gland
  • small peptide, half-life=10mins
  • decreases plasma Ca
62
Q

What is the action of calcitonin?

A
  • main effect is the inhibition of calcium erosion and release in bone
  • increases Ca2+ secretion
  • not a main hormone though
63
Q

What are the causes of hypoparathyroidism?

A
  1. Autoimmune disease of parathyroid

2. Loss of parathyroids due to surgery

64
Q

What are the symptoms of hypoparathyroidism?

A
  • muscle tetany
  • fatigue and headaches
  • tingling
  • seizures
  • bronchospasms
  • cardiac arrhythmia S
65
Q

What is rickets?

A

Lack of Vit D deficiency

66
Q

What causes a lack of Vit D?

A
  1. Lack of solar exposure

2. Dietary deficiency

67
Q

What is rickets type 2?

A

Vit D receptor mutation

68
Q

What is the effect of rickets?

A

Kids: reduced longitudinal bone growth and weak bones
Adults: bone pain and fractures

69
Q

What is primary hyperparathyroidism?

A
  • tumour in parathyroid gland

- results in excess PTH secretion and excess demineralisation of bone

70
Q

What are the symptoms of primary hyperthyroidism?

A
  • depression of cns PNS
  • muscle weakness
  • constipation, kidney stones
  • coma
71
Q

What is secondary hyperparathyroidism?

A
  • high PTH in response to hypocalaemia

- can be caused by rickets

72
Q

What does hyperparathyroidism cause?

A
  • osteomalacia

- chronic renal disease

73
Q

Calcium requirements …… during pregnancy

A

Increase

74
Q

What are dietary sources of calcium?

A
  • dairy
  • meat
  • some seafood
  • spinach
  • beet greens
  • beans
  • peanuts
75
Q

Calcium from food sources is absorbed ……. percent better than supplements

A

30

76
Q

What are the diverse functions of vitamins?

A
  • hormone-like functions as regulators of mineral metabolism (Vit d)
  • regulators of cell/tissue growth and differentiation (Vit A)
  • antioxidants (Vit C, E)
  • enzyme co-factors (tightly bound to enzyme as part of prosthetic group) (Vit Bs)
77
Q

What are the criteria for vitamins?

A
  • essential for normal development and life

- required in diet (cannot be synthesised) - some exceptions

78
Q

What are the lipid-soluble vitamins?

A
  • A
  • D
  • E
  • K
79
Q

What are the water-soluble vitamins?

A
  • B vitamins (8)

- C

80
Q

……….. soluble vitamins are more likely to accumulate in the body

A

Lipid

81
Q

What is the name given to vitamin C?

A

Ascorbic acid

82
Q

What is the name given to vitamin B1?

A

Thiamin

83
Q

What is the name given to vitamin B2?

A

Riboflavin

84
Q

What is the name given to vitamin B3?

A

Niacin

85
Q

What is the name given to vitamin B5?

A

Pantothenic acid

86
Q

What is the name given to vitamin B6?

A

Pyridoxine and pyridoxamine

87
Q

What is the name given to vitamin B7?

A

Biotin

88
Q

What is the name given to vitamin B9?

A

Folic acid

89
Q

What is the name given to vitamin B12?

A

Cobalamin

90
Q

Which vitamins exhibit toxicity?

A

B6
E
K

91
Q

Which vitamins are enzyme cofactors?

A

All B vitamins

92
Q

Which vitamins are antioxidants?

A

E (tacopherol)

C

93
Q

Which vitamins are regulators and extras?

A

A (retinol/retinal/retinoic acid)
D
K (koagulation vitamin)

94
Q

What does vitamin C do?

A

Primary water-soluble antioxidants and free radical scavenger

95
Q

What is folic acid used for?

A

Essential in purine and pyrimidine synthesis (co-factor)

96
Q

What does vitamin K do?

A

Specific K dependent proteins: blood coagulation factors

Nutritional Physiology (13 decks)

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