iron

Question 1

Where is iron primarily absorbed?

Answer 1

Iron is absorbed primarily in the duodenum and upper jejunum.

Question 2

How is non-heme iron absorbed?

Answer 2

1. Found in plant-based foods and supplements as Fe³⁺.
2. Reduced to Fe²⁺ by duodenal cytochrome B (DcytB) on the brush border of enterocytes.
3. Fe²⁺ is transported into enterocytes via the divalent metal transporter 1 (DMT1).

Question 3

How is heme iron absorbed?

Answer 3

1. Found in animal-based foods (e.g., hemoglobin, myoglobin).
2. Absorbed intact via the heme carrier protein 1 (HCP1) on enterocytes.
3. Inside the enterocyte, heme is broken down by heme oxygenase to release Fe²⁺.

Question 4

What happens to iron inside enterocytes?

Answer 4

1. Fe²⁺ can be stored as ferritin or exported into the bloodstream via ferroportin.
2. Export requires oxidation to Fe³⁺ by hephaestin or ceruloplasmin.
3. Fe³⁺ binds to transferrin in the blood for transport to tissues.

Question 5

How is iron absorption regulated?

Answer 5

• Hepcidin: A liver-derived hormone that inhibits ferroportin, reducing iron absorption when body iron stores are high.