Today’s question will test your understanding of a foundational concept in GI medicine.
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A 29-year-old female presents to her primary care physician with complaints of fatigue, pallor, and shortness of breath on exertion. She has a history of menorrhagia and follows a vegetarian diet. Her vital signs are all within normal limits. Laboratory studies show:
Hemoglobin: 9.7 g/dL
Serum ferritin: 6 ng/mL
Total iron-binding capacity: 550 ug/dL
The physician prescribes an oral iron supplement to treat her iron deficiency anemia. Which of the following structures will most greatly absorb the prescribed supplement?
A. Stomach
B. Duodenum
C. Jejunum
D. Ileum
E. Ascending colon
Detailed Breakdown of Answers + Correct Answer Below ⏬
ANSWER + QUESTION BREAKDOWN
The mental model used to answer this question comes from our detailed test-taking skills masterclass. Here’s how to think through this question:
Step 1. Read the last line to determine the actual question: “Which of the following structures will most greatly absorb the prescribed supplement?”
Step 2: Is this a first-, second-, or third-order question?
Answer: 1st order. The given supplement (iron) leaves you with the sole task of identifying where most of it gets absorbed.
Step 3: Ask yourself: “Where does the majority of iron get absorbed?”
Step 4. Look at the answer choices and select the option most closely resembling your final thought from “Step 3” above.
GENERAL ANALYSIS
The question involves identifying the part of the gastrointestinal tract where the majority of dietary iron is absorbed, particularly in the context of treating iron deficiency anemia with oral iron supplements.
ANSWER CHOICES:
CHOICE A: Stomach
Explanation: The stomach plays a role in solubilizing iron and converting it to a more absorbable form, but it is not the primary site of absorption.
CHOICE B: Duodenum
Explanation: The duodenum is the primary site for iron absorption. Iron is absorbed here in both heme and non-heme forms.
CHOICE C: Jejunum
Explanation: While the jejunum plays some role in nutrient absorption, it is not the main site for iron absorption.
CHOICE D: Ileum
Explanation: The ileum absorbs vitamin B12 and bile salts but not significant amounts of iron.
CHOICE E: Ascending colon
Explanation: The colon is involved in water and electrolyte absorption but does not absorb iron.
FINAL VERDICT…
The duodenum is the primary site for dietary iron absorption. This process involves several mechanisms, including reducing ferric (Fe³⁺) to ferrous (Fe²⁺) iron and transport across enterocytes. The presence of reducing agents like vitamin C enhances this absorption. Given its role in nutrient uptake, especially for conditions like iron deficiency anemia, understanding that the duodenum is where most iron absorption occurs is crucial for effective treatment with oral iron supplements.
CORRECT ANSWER: B) Duodenum
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