Nutrition Iron Quiz

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Questions and Answers

What percentage of the body's iron is typically found in hemoglobin?

65-70% (correct)

20-25%

10%

40-50%

What form of iron is most readily absorbed by the body?

Heme iron (correct)

Ferrous iron

Non-heme iron

Ferric iron

What is the daily requirement of iron for postmenopausal women?

3-4 mg

1 mg

4 mg

2 mg (correct)

Which dietary source contributes more than 10% of total absorbed iron?

Meat and seafood Signup and view all the answers

How much iron is typically lost daily through normal physiological processes?

1 mg Signup and view all the answers

Which enzyme is responsible for converting ferric iron to ferrous iron in the intestine?

Ferric reductase Signup and view all the answers

What is the approximate absorption rate of dietary iron in a healthy diet?

5-10% Signup and view all the answers

During pregnancy, how much additional iron is needed daily?

3-4 mg Signup and view all the answers

What primarily controls the absorption and tissue distribution of iron in the body?

Ferroportin and its interaction with hepcidin Signup and view all the answers

Which of the following conditions is a stimulus for increased iron absorption?

Iron deficiency Signup and view all the answers

In patients with fully developed iron deficiency anemia, which of the following lab tests would most likely show decreased values?

Hemoglobin concentration Signup and view all the answers

What does the TIBC test indirectly measure?

Transferrin availability Signup and view all the answers

Which population is at the greatest risk for iron deficiency?

Women Signup and view all the answers

In patients with hereditary hemochromatosis, which of the following would most likely be observed?

High serum iron levels Signup and view all the answers

What is the expected laboratory finding in a patient with iron deficiency anemia regarding serum ferritin levels?

Decreased levels Signup and view all the answers

Which statement is true about TIBC in the context of iron deficiency?

It is usually high Signup and view all the answers

How is transferrin saturation calculated?

Serum iron divided by TIBC Signup and view all the answers

Which of the following is NOT a characteristic finding of iron deficiency anemia in a peripheral blood smear?

Hyperchromic red blood cells Signup and view all the answers

Which of the following conditions can lead to acquired hemochromatosis?

Ineffective erythropoiesis Signup and view all the answers

Which of the following components accounts for the largest pool of body iron?

Hemoglobin Signup and view all the answers

How does the body primarily control iron balance?

By changing the rate of iron absorption Signup and view all the answers

Which statement is true regarding the effects of medicinal iron supplements?

They do not cause hemochromatosis. Signup and view all the answers

What tool is used in clinical laboratories to measure iron metabolism?

Complete Blood Count (CBC) Signup and view all the answers

How does liver disease affect TIBC values?

TIBC values may decrease Signup and view all the answers

What role does transferrin play in iron transport?

Transferrin carries iron to cells with specific receptors. Signup and view all the answers

Which factor significantly decreases iron absorption?

Presence of phytates and oxalates Signup and view all the answers

How is iron released from transferrin after entering a cell?

In an acidic medium causing the release of iron Signup and view all the answers

What is the main source of iron for heme synthesis?

Iron from destroyed erythrocytes Signup and view all the answers

Which form of iron storage is readily mobilizable?

Ferritin Signup and view all the answers

What percentage of transferrin's binding sites for Fe3+ are typically saturated?

20% to 50% Signup and view all the answers

Where is most of the body's iron reserve located?

One-third in the liver and bone marrow Signup and view all the answers

What is a characteristic of hemosiderin compared to ferritin?

Hemosiderin releases iron more slowly than ferritin. Signup and view all the answers

Study Notes

Iron & Porphyrin Metabolism

Iron is the most abundant element on Earth but only trace amounts are found in living cells.
Most iron in the human body is in the porphyrin ring of heme, incorporated into proteins like hemoglobin, myoglobin, catalase, peroxidases, and cytochromes.
An average adult male/female has 4-5 grams of iron in their body.
65-70% of iron is in hemoglobin, 10% in myoglobin and other enzymes, and 20-25% is in storage form.
Daily iron requirement depends on age, gender, and physiological status.
Approximately 1 mg of iron is lost daily through shedding cells lining the gastrointestinal and urinary tracts.
A small number of erythrocytes are lost in urine and feces.
Men and postmenopausal women require approximately 1 mg of iron absorption per day.
Women of childbearing age need 2 mg per day to compensate for menstrual blood loss.
Pregnant and lactating women have increased iron demands (3-4 mg).
The growing fetus, blood loss during delivery, and feeding an infant increase the daily iron demand in pregnant women.

Types of Iron

Two types of absorbable dietary iron exist: heme and non-heme.
Heme iron, derived from hemoglobin and myoglobin in animal products (meat, seafood, poultry), is the most easily absorbed (15-35%) and contributes significantly to total iron absorption (10% or more).
Non-heme iron is derived from plants and fortified foods and is less readily absorbed.
A healthy diet contains 10-20 mg of iron per day.
Only 5-10% of this amount is absorbed, primarily in the duodenum and upper small intestine.
Most dietary iron is ferric (Fe³⁺) and must be converted to ferrous (Fe²⁺) to enter epithelial cells.
The brush border enzyme, ferric reductase, converts ferric iron to ferrous iron.

Iron Absorption & Transport

Ferrous iron is transported into cells by a divalent metal transporter (DMT1).
Substances like phosphates (eggs, cheese, milk), oxalates, phytates (vegetables), and tannates (tea) form insoluble complexes with iron, reducing absorption.
Heme iron is absorbed separately, directly by cells.
In epithelial cells, iron is incorporated into ferritin for storage or transferred to the blood.
Iron is toxic in free form, so it is bound to transferrin.
Each transferrin has two binding sites, typically 20-50% saturated with iron.
Transferrin carries iron to cells via specific surface receptors.
The holo-transferrin-receptor complex is internalized by endocytosis.
The acidic environment in the endocytic vesicle releases iron from transferrin.
Released iron is used for heme synthesis or stored as ferritin.
Iron stores in tissues are primarily ferritin (readily mobilized) and hemosiderin (insoluble, a derived form from ferritin, not as readily mobilized).
One-third of body iron reserves are in the liver, one-third in the bone marrow, and the remainder in the spleen and other tissues.

Iron Balance Control

Iron loss is continuous and largely not controllable; iron absorption is controlled by changes in absorption.
Major factors affecting iron absorption are body iron stores and red blood cell production rate.
Iron absorption and tissue distribution of iron is mainly controlled by the hepatic hormone hepcidin's interaction with ferroportin.
Ferroportin is expressed in iron-storing and transport tissues; it's also the sole cellular exporter of elemental iron in multicellular organisms.

Pathological Conditions: Iron Deficiency

Iron deficiency is the most common nutritional disorder and cause of anemia in humans.
It is more frequent in women, individuals with low socioeconomic status, those with gastrointestinal surgery, and patients with chronic diarrhea.
Iron deficiency develops in stages when iron reserves become exhausted; biochemical tests of iron metabolism become abnormal even if anemia isn't yet apparent.
Next steps in development are a decrease in hemoglobin concentration and paler red blood cells (hypochromic).
In full iron-deficiency anemia, MCV, MCH, and MCHC are also decreased.
Examination of peripheral blood smears shows hypochromic, microcytic, and anisocytosis (abnormal size and shape of erythrocytes).
Laboratory tests to diagnose differentiate iron deficiency from other types of hypochromic, microcytic anemia include serum iron (low), total iron-binding capacity (TIBC) (high), transferrin saturation (low), serum ferritin (low), and free erythrocyte protoporphyrin (FEP). (high).

Pathological Conditions: Iron Overload

Hereditary hemochromatosis is a genetic disease characterized by progressive iron store increase, leading to organ impairment.
Patients with hereditary hemochromatosis may absorb 4 mg or more of iron per day, even on a typical diet.
Excessive iron deposits in the liver, pancreas, heart, skin, and other organs are a hallmark.
Iron overload can also be acquired from ineffective erythropoiesis (e.g., beta-thalassemia major), blood transfusions, or medicinal iron supplements.

Lab Tools for Iron Metabolism

Clinically, three iron compartments account for 90% of total iron: hemoglobin (largest pool, measured via CBC), serum iron/transferrin, and serum ferritin.
The combination of these tests helps identify iron metabolism disorders.

Complete Blood Count (CBC)

A complete blood count provides the number of erythrocytes, hemoglobin concentration, and red blood cell indices.
The World Health Organization (WHO) defines anemia as hemoglobin concentrations less than 13 g/dL in men, <12 g/dL in women, and <11 g/dL in pregnant women.
Iron deficiency causes hypochromic, microcytic anemia, reducing values of MCV, MCH, and MCHC.
Hypochromic, microcytic anemias are often characteristic of thalassemia trait, sideroblastic anemia, and anemia of chronic disease.
RBC parameters indicate the presence of anemia but not necessarily the cause.

Serum Iron, TIBC, and Transferrin Saturation

Serum iron concentration fluctuates significantly, even among healthy individuals and across the day.
Diurnal variations limit the diagnostic usefulness of individual serum iron values.
Iron values should always be evaluated with TIBC (measures the max amount of iron serum proteins can bind).
Transferrin saturation is calculated by dividing serum iron by TIBC and provides an estimate of occupied transferrin binding sites.

Serum Ferritin

A small amount of ferritin circulates in plasma as iron-free apoferritin.
Serum ferritin levels accurately reflect the amount of storage iron.
Low serum ferritin values typically indicate iron deficiency (before serum iron and transferrin saturation show a significant change).
Elevated serum ferritin levels are a sign of iron overload.

Heme Synthesis and Porphyrias

Porphyrias

Porphyrias are genetically determined disorders affecting heme synthesis.
Deficiencies in seven enzymes involved in heme synthesis have been recognized.
Most porphyrias are inherited as autosomal dominant traits.
Excess porphyrins and their precursors accumulate behind the deficient enzyme, and these excesses are excreted in bodily tissues and fluids.
This excretion is a basis for diagnosing porphyrias.

Neurological Porphyrias

Four porphyrias are linked to acute episodes of abdominal pain, neurological issues, and/or psychiatric disturbances.
These include acute intermittent porphyria, variegate porphyria, hereditary coproporphyria, and ALA dehydratase deficiency.
Attacks commonly involve elevated ALA and PBG excretion.

Cutaneous Porphyrias

Three porphyrias primarily affect the skin, involving excess porphyrins, photosensitivity, and skin lesions.
The most common cutaneous porphyria is porphyria cutanea tarda (PCT).
PCT results from partial deficiencies in uroporphyrinogen decarboxylase.
Other cutaneous porphyrias include protoporphyria and congenital erythropoietic porphyria.

Delta-Aminolevulinic Acid (ALA)

Urinary ALA values are elevated in all neurological porphyria cases.
ALA excretion also increases in lead poisoning.

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Description

Test your knowledge on iron's role in the human body with this quiz. Questions cover iron absorption, dietary sources, and physiological needs across different life stages. Perfect for anyone studying nutrition or health sciences.