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biochemistry > iron metabolism > Flashcards

iron metabolism Flashcards

1
Q

the total body iron range between ………

A

3-5 gm

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2
Q

list total body iron distribution

A
  1. Hb iron : 75% of total body iron
  2. fixed tissue iron :
    e.g. myoglobin , cytochrome C ( in respiratory chain ) , catalase & peroxidase enzyme
  3. labile tissue iron: ( changeable) stored iron in the form of ferritin and small amount of hemosedrin
  4. plasma iron : transport form of iron (transferrin)
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3
Q

list the daily requirements of iron

A

15-20 mg/ day
only 3-6% of iron intake is absorbed into the blood which equal to iron lost by the sloughing of cells (0.6 mg / day)

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4
Q

list sources of iron

A
  1. heme iron: meat, fish, easily absorbed ( absorbed intact by endocytosis )
  2. non-heme iron: vegetables “ spinach” ,fruits, grains, eggs & milk ( poorly absorbed)
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5
Q

list factor dec iron absorption ( form insoluble complexes with iron )

A
  1. oxalic acid (spinach)
  2. phosphates (milk , dairy product , egg )
  3. phytates in beans
  4. tannic acid in tea and coffee
    - to drink tea , coffee or milk it’s better to leave at least an hour before and after a meal containing iron
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6
Q

list factor inc iron absorption

A
  1. requirements of body :
    inc rate of erythropoiesis (e.g. after hemorrhage ) , pregnancy and lactation
  2. vit C :
    help in reduction of ferric to ferrous and form soluble complex
  3. gastric HCl :
    helps absorption , so absorption dec in achlorhydria and partial gastrectomy
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7
Q

heme is absorbed by intestinal cells in the ……..by ……

A

duodenum
heme carrier protein 1 (HCP1)

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8
Q

in enterocytes , Fe +2 is released from heme by …….

A

heme oxygenase enzyme

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9
Q

non heme iron is present in the ……. in the ……. state .
cooking of food facilitates release iron

A

diet
Fe+3

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10
Q

it’s reduced ti Fe+2 by …………

A

ferrireductase enzyme

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11
Q

the reduction is facilitated by ………..in the stomach and …….

A

HCl
vit C ( ascorbic acid )

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12
Q

the reduction is facilitated by ………..in the stomach and …….

A

HCl
vit C ( ascorbic acid )

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13
Q

iron is transported into the enterocyte with a protein via …….

A

divalent metal transporter (DMT1)

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14
Q

what’s the fate of absorbed Fe+2 from heme or non heme sources ?

A
  1. oxidized again inside intestinal cells to Fe+3 by ferroxidase.
    then combine with apoferritin (mucosal cell protein) to form ferritin for temporary storage
  2. transport out of the enterocytes by basolateral membrane protein (ferroprotein), oxidized by Cu - containing membrane protein (hephaestin) and taken up by the plasma transport protein transferrin (2Fe+3/ transferrin molecule )
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15
Q

……….. the only known exporter of iron from cells to the blood

A

ferroprotein protein

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16
Q

ferroprotein protein regulated by ……..
that induces …….. and …….of ferroprotein

A

hepatic peptide hepcidin
internalization
lysosomal degradation

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17
Q

…….. hormone released from the liver whan iron levels in the body becomes too high

A

hepcidin

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18
Q

hepcidin …… iron passage from the small intestine epithelial cell into the blood by attaching and …………

A

inhibits
inhibiting the ferroprotein transporter

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19
Q

a deficiency of hepcidin causes ……..

A

tissue iron overload

20
Q

hepcidin transcription is suppressed when …..

A

iron is deficient

21
Q

what’s the meaning of mucosal block ?

A

-“ control at level of absorption “
- the intestinal content of ferritin is limited so once saturated with iron , the absorption of iron is inhibited

22
Q

iron transport = …….

A

transferrin (TF)

23
Q

how is the transferrin formed ?

A

in the plasma , Fe+2 is changed to Fe+3 and bound to apotransferrin forming transferrin

24
Q

where TF is synthesized ?

A

TF is a glycoprotein , synthesized in the liver

25
Q

what’s the function of TF ?

A

transport iron ( 2Fe +3 / TF) in the circulation to sites where iron is required

26
Q

TF bind to receptor in cell membrane of ……… ingested by …….and iron delivered to ….. where heme is synthesized.

A

erythroblasts
endocytosis
mitochondria

27
Q

…….. represents the capacity of transferrin to bind iron

A

total iron binding capacity (TIBC)

28
Q

TIBC measure the ………that is ready to carry iron

A

free transferrin

29
Q

normally, the protein is ………..

A

only one third (35%) saturated with iron

30
Q

Low TIBC levels usually indicate …..levels of iron in the blood

A

high

31
Q

High TIBC levels typically indicate ……levels of iron in the blood

A

low

32
Q

there are ………..on the surfaces of many cells for transferrin . binding of transferrin on its receptor is internalized by ……

A

transferrin receptor
receptor mediated endocytosis

33
Q

the……….inside lysosome cause the iron to ………, that is not degraded within the lysosome. instead, it re-enter the …….to pick up more iron to cell is need.

A

acid PH 5
dissociate from protein ( apotransferrin)
plasma

34
Q

the translation of the mRNA of transferrin receptors and ferritin is regulated by …………

A

iron regulatory proteins depend on iron level in the cell

35
Q

iron storage through 2 intracellular forms, illustrate .

A
  1. ferritin:
    - predominant storage form
    - in all cells, especially intestinal mucosa, liver, spleen, BM
    - apoferritin can take 4000-4500 ferric ions / molecule to form ferritin
    - ferritin is 1ry intracellular iron storage globular protein. it keeps iron in a soluble and non-toxic form.
  2. hemosiderin:
    when iron is excess, the storage capacity of the apoferritin is exceeded. this leads to iron deposition adjacent to ferritin spheres in the form of brown aggregated deposits.
36
Q

1.excess iron (hemochromatosis) = ………ferritin
2. iron deficiency anemia = …….ferritin

A

1.elevated
2. decrease

37
Q

how does the iron excrete?

A
  • there’s no physiological excretory mechanism .
  • adult male loss about 1-2 mg/ day which is replaced by absorption
38
Q

loss of iron occurs ONLY through the normal shedding of tissues like :

A
  • epidermis
  • hair
  • menstrual blood in female
  • gastrointestinal mucosal cells in stools
39
Q

acute Fe poisoning can occur due to …….
it’s one of the most common causes of poisoning death in children under 6

A

accidental ingestion of iron tablets

40
Q

the lethal dose of iron tablet in children is ……. and adult …….

A

200-300 mg/kg body weight
100g

41
Q

list gastrointestinal symptoms of high dose of Fe supplements

A

constipation
nausea
vomiting
( diarrhea may occur)

42
Q

iron overload is treated by an ……..

A

iron chelator.

43
Q

hereditary hemochromatosis caused by ……….

A

mutations to the high iron gene (HFE)

44
Q

excess iron deposited in ……………. damaging their cells and inducing ……..&………..

A
  • liver , pancreas , heart and skin
  • hyperpigmentation & hyperglycemia (bronze diabetes )
45
Q

in hereditary hemochromatosis , serum iron and transferrin saturation are ……

A

elevated

46
Q

hereditary hemochromatosis treatment is ……………..

A

by phlebotomy or use of Fe chelators

biochemistry (9 decks)

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