Chapter 5: Iron

How much total body iron do men have?

About 4 grams.

How much total body iron do women have?

About 2–3 grams.

What is iron in the body?

The most abundant trace element in humans.

Where is most body iron found?

In red blood cells as hemoglobin.

What percentage of iron is in hemoglobin?

About 65–70%.

What percentage of iron is in myoglobin?

About 3–5%.

What percentage of iron is in enzymes?

About 1%.

What percentage of iron is stored?

About 20–30%.

Where is iron stored?

Liver, spleen, and bone marrow.

What forms are used for iron storage?

Ferritin and hemosiderin.

Which enzymes contain iron?

Cytochromes, catalase, and peroxidase.

What is hemoglobin iron?

The main portion of body iron located in erythrocytes.

What is tissue iron?

Iron present in enzymes and tissues.

What is the labile iron pool?

A readily available exchangeable pool of iron.

What is transport iron?

Iron bound to transferrin in plasma.

How much of total body iron is transport iron?

About 0.1%.

Why is transport iron important despite being small?

It delivers iron safely to tissues.

Why does iron not circulate freely?

Free iron is toxic.

What is transferrin?

A plasma glycoprotein that transports iron.

What is apotransferrin?

Transferrin without iron.

What is transferrin after binding iron?

Apotransferrin bound to Fe3+.

How many Fe3+ ions can transferrin bind?

Two.

What does transferrin do?

Transports iron safely in blood and delivers it to cells.

Where is transferrin delivery especially important?

Bone marrow for hemoglobin synthesis.

What happens to iron inside cells?

It is used, stored as ferritin/hemosiderin, or exported.

How much iron is ingested daily?

About 10–20 mg/day.

What does stomach HCl do to iron?

It reduces Fe3+ to Fe2+.

Which iron form is absorbable?

Fe2+.

Where is iron mainly absorbed?

Duodenum.

How much dietary iron is absorbed?

About 10–15%.

What happens to unabsorbed iron?

It is excreted in feces.

How else is small iron loss possible?

Urine, skin, and intestinal mucosa.

What is apoferritin?

The protein shell that binds iron to form ferritin.

What is ferritin?

The main soluble iron storage protein.

How much iron is stored as ferritin according to the slide?

About 10–20%.

Which protein exports iron from enterocytes into plasma?

Ferroportin.

What is DMT1?

Divalent metal transporter 1, transporting Fe2+ into enterocytes.

Where does DMT1 act?

In the duodenum enterocytes.

What is hepcidin?

The main regulator of iron metabolism.

What does hepcidin inhibit?

Ferroportin.

What happens when iron levels are low?

Hepcidin is low and ferroportin stays active.

What is the result of low hepcidin?

More iron enters circulation.

What happens when iron levels are high?

Hepcidin is released by the liver.

What does hepcidin do to ferroportin?

It binds ferroportin and causes internalization and degradation.

What is the result of high hepcidin?

Iron absorption and release into blood decrease.

Simple rule for low iron regulation?

Low iron → low hepcidin → more absorption.

Simple rule for high iron regulation?

High iron → high hepcidin → less absorption.

What are the three possible fates of intracellular iron?

Immediate use, storage, or export.

What happens if iron is immediately needed?

It is transported to where it is required for metabolism.

What happens if iron is not immediately needed?

It is stored as ferritin.

How can cells release iron?

Through ferroportin.

What does ceruloplasmin do in iron export?

It oxidizes Fe2+ to Fe3+ so iron can bind transferrin.

Which cells export most iron?

Macrophages, hepatocytes, and enterocytes.

What do macrophages do in iron metabolism?

Recycle iron from old red blood cells.

What do hepatocytes do in iron metabolism?

Store iron and release it when needed.

What do enterocytes do in iron metabolism?

Absorb dietary iron and release it into blood.

Who is most at risk for iron deficiency?

Children, young women, and elderly people.

Which tests diagnose iron deficiency?

Bone marrow staining, serum iron, transferrin, TIBC, UIBC, transferrin saturation, ferritin, erythrocyte protoporphyrin, soluble transferrin receptor, and reticulocyte hemoglobin.

What staining can show bone marrow iron?

Prussian blue staining.

What does serum iron measure?

Circulating iron.

What does serum transferrin measure?

The main transport protein for iron.

What does TIBC measure?

Total capacity of transferrin to bind iron.

What does UIBC measure?

Reserve capacity of transferrin binding sites not occupied by iron.

What does transferrin saturation show?

The percentage of transferrin binding sites occupied by iron.

What does serum ferritin reflect?

Body iron stores.

What happens to ferritin in iron deficiency?

It decreases.

What happens to erythrocyte protoporphyrin in iron deficiency?

It increases.

What happens to soluble transferrin receptor in iron deficiency?

It increases.

What does reticulocyte hemoglobin show?

Recent iron supply to red blood cell precursors.

What is hemosiderosis?

Iron overload without tissue damage.

What causes hemosiderosis?

Excess iron intake, supplements, or multiple transfusions.

What is hemochromatosis?

Iron overload with tissue damage due to chronic accumulation.

Which organs are damaged in hemochromatosis?

Liver, pancreas, heart, skin, and endocrine glands.

What are classic symptoms of hemochromatosis?

Bronze skin, cirrhosis, and diabetes mellitus.

What are additional symptoms of hemochromatosis?

Cardiomyopathy, endocrine disorders, and joint disease.

What is primary hemochromatosis?

A genetic disorder causing increased intestinal iron absorption.

What is secondary hemochromatosis?

Iron overload due to external causes such as transfusions or excess iron therapy.

What is hemosiderin?

A golden-brown granular pigment and insoluble storage form of iron.

What causes hemosiderin formation?

Breakdown of red blood cells and excess iron storage.

Where is hemosiderin detected microscopically?

Inside cells, especially macrophages.

What is normal serum iron in adult men?

14.0–27.0 micromol/L.

What is normal serum iron in adult women?

12.5–25.0 micromol/L.

What is normal serum iron in newborns?

25.0–34.0 micromol/L.

What causes low serum iron?

Malnutrition, malabsorption, bleeding, infections, autoimmune diseases, and carcinomas.

Why can infection lower serum iron?

Iron is sequestered in macrophages.

Why can carcinoma lower serum iron?

Iron becomes trapped in the reticuloendothelial system and unavailable.

What causes increased serum iron?

Iron overload, decreased erythropoiesis, hepatitis, cirrhosis, and oral contraceptives.

How can lead poisoning increase serum iron?

It decreases erythropoiesis.

Which vitamin deficiencies can increase serum iron through decreased erythropoiesis?

Vitamin B12, B6, and folic acid deficiencies.

Why do hepatitis and cirrhosis increase serum iron?

Stored iron is released from damaged liver.

How is serum iron measured?

Colorimetric test after iron is released, reduced, and forms a colored complex.

What is the serum iron measurement principle?

Fe3+ is released from transferrin, reduced to Fe2+, reacts with chromogen, and is measured spectrophotometrically.

Which chromogen is used in serum iron measurement?

Ferrozine.

What color complex forms in serum iron measurement?

Purple or pink complex.

What does color intensity show in serum iron testing?

Serum iron concentration.

Why is serum iron alone unreliable?

It varies with diet, hemolysis, and daily rhythm.

When is serum iron usually higher?

In the morning.

Which factors affect serum iron levels?

Diet, iron supplements, acute infection, menstrual cycle, and circadian rhythm.

How much can iron fluctuate during the day?

Up to 70% between morning and night.

What happens to TIBC in iron deficiency anemia?

It increases.