Iron

Question 1

Main role of iron in the body

Answer 1

Oxygen transport

Question 2

What structure is the iron enclosed in in the haemoglobin molecule?

Answer 2

A porphyrin (heme) which is a heterocyclic organic ring structure.

Question 3

Describe the process of haemoglobin formation.

Answer 3

• Occurs in the bone marrow
• Heme synthesised from glycine and iron
• Heme joined with globin molecule

Question 4

What happens to iron in RBC senescence?

Answer 4

• Cells in the reticuloendothelial system engulf the RBC
• Iron released from the porphyrin and taken up by transferrin
• Iron returns to the bone marrow for recycling or to the liver or spleen for storage (ferritin).

Question 5

Name the transport and storage proteins for iron

Answer 5

Transferrin and ferritin

Question 6

Name the two forms of dietary iron

Answer 6

Heme and non heme

Question 7

Sources of heme iron

Answer 7

Red meat, poultry and fish

Question 8

Sources of non-heme iron

Answer 8

Fortified cereals, pulses, vegetables

Question 9

Dietary intake and absorption of heme vs non heme iron

Answer 9

Heme iron represents only 5-10% of our dietary intake of iron but we absorb up to 25% of that which is ingested compared with around 5% of non-heme nested iron.

Question 10

Mechanisms of loss of iron

Answer 10

Women through menstruation.
Other way through bleeding.
Men? GI cancer?

Question 11

How much iron is consumed and lost daily?

Answer 11

Around 2-3g. If not need by the body it stays in the enterocytes which are then lost when sloughed off (these cells have a high turnover)

Question 12

Mechanisms of iron absorption. general

Answer 12

Iron enters the enterocyte. Then attached to ferritin and enters labile iron pool in enterocyte. If the body requires iron it then is passed to transferrin protein where it can enter the blood stream and be recirculated. If the iron is not required it remains in the enterocyte and is sloughed of when the cell dies (2-3 days).

Question 13

Absorption of heme iron

Answer 13

• heme iron enters the enterocyte freely attached to haemoglobin.
• Heme oxygenase removes the iron from the haemoglobin
• Fe enters the labile iron pool
• If required by the body exits the enterocyte via an iron regulatory protein (ferroportin)

Question 14

Non-heme

Answer 14

• Requires reduction from 3+ to 2+ state before entering the enterocyte.
• Reduction occurs in the stomach as a result of acidity levels
• Also through dietary reducing agents such as meat factor protein, Vitamin C, lactic acid (fermented milk products)
• cytochrome enzymes on the enterocyte also help in reduction
• Then transported into the enterocyte via a divalent methyl transport protein
• Join heme iron in labile iron pool where it follows the same pathway as heme iron

Question 15

Describe TfR1

Answer 15

Transferrin receptor protein. Allow the uptake of iron into the cells.

Question 16

What signals to the enterocyte to release iron from the labile iron pool?

Answer 16

Hepcidin, a hormone produced by the liver which controls the release of iron from the enterocytes labile iron pool

Question 17

Name and describe a condition associated with excessive iron

Answer 17

• Haemochromotosis.
• Where there is inadequate regulation by hepcidin.
• Liver ends up storing excessive iron and cirrhosis can occur
• Only treatment is bleeding

Question 18

Iron inhibitors (bind with non-heme iron and render them insoluble)

Answer 18

Tannins
Phytates (bran and seeds)
Dietary fibres
Oxylates (spinach)
Calcium (milk)
Polyphenols