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Flashcards in Iron Deck (39)
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1

Non-heme Iron

Transported by DMT1 (reduced). Vit C enhances absorption.

Found only in plants.

Primarily bound to phytates, making it unavailable for absorption.

Need to eat twice as much non-heme iron to compensate for lack of bioavailability.

2

Heme Iron Digestion

Gastric and intestinal proteases hydrolyze heme iron from the globin portion of hemoglobin and myoglobin.

hcp1(heme carrier protein) accepts heme into enterocyte

3

Gastric and Intestinal Proteases

Hydrolyze heme iron from the globin portion of hemoglobin and myoglobin.

Heme is carried across brush border of the enterocyte via hcp1 (heme carrier protein 1).

4

hcp1

Heme carrier protein 1.

Located in small intestine, it carries heme to an enterocyte.

5

Non-heme Iron Digestion

Hydrolyzed by HCl and proteases.

Stomach acid reduces Fe3+ (ferric ion).

Ferric iron passes from stomach to alkaline small intestine which creates insoluble ferric hydroxide.
Fe(OH)3

Or vitamin C can reduce ferric to ferrous iron which can be transported via DMT1.

6

DMT1

Transports ferrous iron.

Inversely regulated by iron status.

7

Integrin

Questionable ferric iron transporter.

8

Chelators and Ligands

Compounds that bind to form a complex.

Influences iron absorption both ways:
Loose, soluble complex = + absorption
Strong, insoluble complex = - absorption

9

Enhancers of Nonheme Iron Absorption

Sugars (fructose, sorbitol)
Acids (ascorbic, citrate, lactic, tartaric)
Meats and their digestive products

Mucin (vitamin A)

10

Inhibitors of Nonheme Iron Absorption

Polyphenols (tannins in tea and coffee)
Oxalis acid
Phytates

Ca, Zn, Mn, Ca, Zn, Cu

11

Entering Enterocyte (Chaperones)

First step in absorption. Binds to iron.

Ferric Iron: AA (cysteine and histidine), Mobilferrin

Ferrous Iron: Ferritin, Hemosiderin

12

Ferritin (storage)

Most iron is stored in ferritin, mainly in the liver.
Ferritin production is regulated by iron status.

Must be in oxidized (+3) form; 4,500 atoms stored.

Serum ferritin used to evaluate iron status.

13

Transferrin (transfer)
Glycoprotein synthesized in liver, found in blood

Transfers iron within blood stream.

Only carries 2 oxidized iron (ferric) atoms.

Contains 33% of body's iron.

Iron ^ = less transferrin

14

Siderophores

Bacteria binding protein.

Compete with transferrin for iron.

Infection.

15

Hepcidin (regulator)

Released from liver when iron stores are high.
Regulation based on transferrin.

Decreases ferroportin.

Liver detects iron status by binding of diferric transferrin to TfR1.
HFe is released, and binds to TfR2.

HFe-TfR2 complex senses iron status. Stimulates hepcidin synthesis.

Hepcidin targets enterocytes and macrophages. Degrades ferroportin which prevents iron from being exported into blood.

16

Hemochromatosis

Mutation that interferes with hepcidin release, thus causing excess iron storage.

Adult men and postmenopausal women who are not iron deficienct should not supplement.

17

RDA and UL

8mg men 18mg women

45 mg constipation, nausea, vomiting.
Increase risk for stomach cancer and CVD

18

Inhibitors

Calcium and zinc
Deficiency of copper or vitamin A

Polyphenols, phytates, oxalic acid, fiber, tannins

High pH

19

Enhancers

vitamin C, riboflavin, niacin, mucin (vit A), sugars, protein

Low pH

20

Heme Iron

Porphyrin ring. Derived from hemoglobin and myoglobin.

20% absorption

21

TfR

Transferrin receptors.
Endocytosis takes up transferrin, iron atoms then released.

22

Toxicity 45 mg

Inhibits zinc absorption.
Increases risk for stomach cancer and CVD.

Constipation, nausea, vomiting.

Death @ 200 mg.

23

Hemochromatosis

Genetic disorder.
Down regulates iron absorption, excess iron is stored. Organ damage.

24

How is iron excreted?

Can only be taken out via blood giving.

Mucosal cell sloughing. No purposeful excretion.

25

Why is it important for iron to be bound to something?

Ability to oxidize creates free radicals.
DNA damage (cancer).

Iron can be used by bacteria to proliferate, especially if protein deficient.

26

Copper

Oxidizes iron to bind to transferrin to be transported through the blood stream.

27

Ceruloplasmin and Hephaestin

Cu dependent enzyme that oxidizes iron to ferric (+3) form.

28

What vitamins can reduce iron?

Vitamin C, niacin, and riboflavin.

Take iron off ferritin.

29

Assessment

Serum ferritin

30

Hemosiderin

Found in many cells (primarily liver). Aggregates of ferritin.