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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
What happens if iron concentrations increase?
- IREG1 closes - iron accumulates within cells and binds to ferritin - leads to haemosiderin deposits and apoptosis
26
What are the normal plasma iron concentrations?
Males: 13.4-31.3 microM Females: 11.6-29.5 microM
27
Depending on the state of IREG1, iron will.......
Either be absorbed into the body or it will remain into the enterocytes
28
What is IREG1 present in?
Macrophages, duodenal enterocytes, hepatocytes and placenta
29
What regulates iron?
Helcidin, a small peptide of 25 amino acid
30
Which cells secrete hepcidin?
Liver cells
31
Calcium is the ..... most abundant element in the body
5th
32
Where is calcium found?
99% in Skelton | 1% in soft tissue available for exchange
33
What is the adult body content of calcium?
M: 1200mg F: 1000mg
34
What is the form of calcium in the body?
Hydroxyapatite: Ca10(PO4)6(OH)2
35
What are the processes that require calcium?
- bone formation - blood clotting - muscle contraction - intercellular signalling - nervous system - endocrine system (exocytosis) - cardiovascular system
36
What are normal plasma calcium levels?
9mg/dL
37
What are the levels of calcium for hypercalaemia?
>15mg/dL
38
What happens in hypercalaemia?
- 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
39
What are the levels needed for hypocalaemia?
<6mg/dal
40
What happens in hypocalaemia?
- makes nerve and muscle hyperexcitable | - opposite mechanism to hypocalaemia
41
Intracellular Ca2+
- 1% in cells | - stored in mitochondria and ER
42
Extracellular Ca2+
- 0.1% | - 2.4mM = 9.4mg/del
43
What is the distribution of calcium in the plasma?
- 50% ionised - 41% protein bound - 9% calcium complexes to anions
44
What is the active form of calcium?
Ionised
45
What are the processes that maintain calcium levels?
1. Absorption 2. Reabsorption 3. Resorption
46
1. Calcium absorption
- intake of 1000mg - 350mg is absorbed - 250 is lost each day through secretions and sloughed cells
47
2. Calcium reabsorption
- 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
3. Calcium resorption
- 2 processes 1. Osteocytic osteoclasts (fast: mins to hours) 2. Slow phase
49
How does osteocytic osteolysis work?
- under control of parathyroid hormone | - increase in PTH causes secretion of Ca2+ in to extracellular fluid
50
How does the slow calcium resorption work?
- 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
What is calcium regulated by?
1. Parathyroid hormone 2. Vitamin D3 3. Calcitonin
52
Parathyroid cells
- chief cells: secrete PTH | - oxyphil hormones: unknown function
53
Parathyroid calcium signalling
- parathyroid glands have calcium sensing receptors (CaSR) - respond to increase in Ca2+ levels - leads to a decrease in production of PTH
54
PTH
- 88AAs | - half-life: 20-30mins
55
What does PTH do?
- increases calcium absorption in kidneys - activates Vit d - increases bone erosion
56
Vitamin D3 characteristics
- steroid hormone derived from cholesterol - generated in skin by Uv radiation - half-life: days-weeks - 2 different forms: active and inactive
57
What are the steps of the biosynthesis of Vit D3?
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
Vit D active form
OH group is added to position 1
59
Vit D inactive form
OH is added to position 24
60
What does Vit D do for calcium maintenance?
- increases calcium absorption - increases calcium reabsorption - calcification (small effect)
61
Calcitonin characteristics
- secretes by para follicular C cells in thyroid gland - small peptide, half-life=10mins - decreases plasma Ca
62
What is the action of calcitonin?
- main effect is the inhibition of calcium erosion and release in bone - increases Ca2+ secretion - not a main hormone though
63
What are the causes of hypoparathyroidism?
1. Autoimmune disease of parathyroid | 2. Loss of parathyroids due to surgery
64
What are the symptoms of hypoparathyroidism?
- muscle tetany - fatigue and headaches - tingling - seizures - bronchospasms - cardiac arrhythmia S
65
What is rickets?
Lack of Vit D deficiency
66
What causes a lack of Vit D?
1. Lack of solar exposure | 2. Dietary deficiency
67
What is rickets type 2?
Vit D receptor mutation
68
What is the effect of rickets?
Kids: reduced longitudinal bone growth and weak bones Adults: bone pain and fractures
69
What is primary hyperparathyroidism?
- tumour in parathyroid gland | - results in excess PTH secretion and excess demineralisation of bone
70
What are the symptoms of primary hyperthyroidism?
- depression of cns PNS - muscle weakness - constipation, kidney stones - coma
71
What is secondary hyperparathyroidism?
- high PTH in response to hypocalaemia | - can be caused by rickets
72
What does hyperparathyroidism cause?
- osteomalacia | - chronic renal disease
73
Calcium requirements ...... during pregnancy
Increase
74
What are dietary sources of calcium?
- dairy - meat - some seafood - spinach - beet greens - beans - peanuts
75
Calcium from food sources is absorbed ....... percent better than supplements
30
76
What are the diverse functions of vitamins?
- 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
What are the criteria for vitamins?
- essential for normal development and life | - required in diet (cannot be synthesised) - some exceptions
78
What are the lipid-soluble vitamins?
- A - D - E - K
79
What are the water-soluble vitamins?
- B vitamins (8) | - C
80
........... soluble vitamins are more likely to accumulate in the body
Lipid
81
What is the name given to vitamin C?
Ascorbic acid
82
What is the name given to vitamin B1?
Thiamin
83
What is the name given to vitamin B2?
Riboflavin
84
What is the name given to vitamin B3?
Niacin
85
What is the name given to vitamin B5?
Pantothenic acid
86
What is the name given to vitamin B6?
Pyridoxine and pyridoxamine
87
What is the name given to vitamin B7?
Biotin
88
What is the name given to vitamin B9?
Folic acid
89
What is the name given to vitamin B12?
Cobalamin
90
Which vitamins exhibit toxicity?
B6 E K
91
Which vitamins are enzyme cofactors?
All B vitamins
92
Which vitamins are antioxidants?
E (tacopherol) | C
93
Which vitamins are regulators and extras?
A (retinol/retinal/retinoic acid) D K (koagulation vitamin)
94
What does vitamin C do?
Primary water-soluble antioxidants and free radical scavenger
95
What is folic acid used for?
Essential in purine and pyrimidine synthesis (co-factor)
96
What does vitamin K do?
Specific K dependent proteins: blood coagulation factors

Nutritional Physiology (13 decks)

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