iron metabolism

Question 1

the total body iron range between ………

Answer 1

3-5 gm

Question 2

list total body iron distribution

Answer 2

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)

Question 3

list the daily requirements of iron

Answer 3

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)

Question 4

list sources of iron

Answer 4

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

Question 5

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

Answer 5

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

Question 6

list factor inc iron absorption

Answer 6

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

Question 7

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

Answer 7

duodenum
heme carrier protein 1 (HCP1)

Question 8

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

Answer 8

heme oxygenase enzyme

Question 9

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

Answer 9

diet
Fe+3

Question 10

it’s reduced ti Fe+2 by …………

Answer 10

ferrireductase enzyme

Question 11

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

Answer 11

HCl
vit C ( ascorbic acid )

Question 12

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

Answer 12

HCl
vit C ( ascorbic acid )

Question 13

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

Answer 13

divalent metal transporter (DMT1)

Question 14

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

Answer 14

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 )

Question 15

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

Answer 15

ferroprotein protein

Question 16

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

Answer 16

hepatic peptide hepcidin
internalization
lysosomal degradation

Question 17

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

Answer 17

hepcidin

Question 18

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

Answer 18

inhibits
inhibiting the ferroprotein transporter

Question 19

a deficiency of hepcidin causes ……..

Answer 19

tissue iron overload

Question 20

hepcidin transcription is suppressed when …..

Answer 20

iron is deficient

Question 21

what’s the meaning of mucosal block ?

Answer 21

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

Question 22

iron transport = …….

Answer 22

transferrin (TF)

Question 23

how is the transferrin formed ?

Answer 23

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

Question 24

where TF is synthesized ?

Answer 24

TF is a glycoprotein , synthesized in the liver

Question 25

what's the function of TF ?

Answer 25

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

Question 26

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

Answer 26

erythroblasts endocytosis mitochondria

Question 27

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

Answer 27

total iron binding capacity (TIBC)

Question 28

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

Answer 28

free transferrin

Question 29

normally, the protein is ...........

Answer 29

only one third (35%) saturated with iron

Question 30

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

Answer 30

high

Question 31

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

Answer 31

low

Question 32

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

Answer 32

transferrin receptor receptor mediated endocytosis

Question 33

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.

Answer 33

acid PH 5 dissociate from protein ( apotransferrin) plasma

Question 34

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

Answer 34

iron regulatory proteins depend on iron level in the cell

Question 35

iron storage through 2 intracellular forms, illustrate .

Answer 35

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.

Question 36

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

Answer 36

1.elevated 2. decrease

Question 37

how does the iron excrete?

Answer 37

- there's no physiological excretory mechanism . - adult male loss about 1-2 mg/ day which is replaced by absorption

Question 38

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

Answer 38

- epidermis - hair - menstrual blood in female - gastrointestinal mucosal cells in stools

Question 39

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

Answer 39

accidental ingestion of iron tablets

Question 40

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

Answer 40

200-300 mg/kg body weight 100g

Question 41

list gastrointestinal symptoms of high dose of Fe supplements

Answer 41

constipation nausea vomiting ( diarrhea may occur)

Question 42

iron overload is treated by an ........

Answer 42

iron chelator.

Question 43

hereditary hemochromatosis caused by ..........

Answer 43

mutations to the high iron gene (HFE)

Question 44

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

Answer 44

- liver , pancreas , heart and skin - hyperpigmentation & hyperglycemia (bronze diabetes )

Question 45

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

Answer 45

elevated

Question 46

hereditary hemochromatosis treatment is .................

Answer 46

by phlebotomy or use of Fe chelators