Which of the following is the PRIMARY mechanism by which iron deficiency impairs hemoglobin synthesis?

Question

Accepted Answer

B. Reduced availability of iron as a substrate for heme synthesis. ## Mechanism of Anemia in Iron Deficiency

**Key Point:** Iron is an essential component of the heme moiety of hemoglobin. Without sufficient iron, the body cannot synthesize adequate heme, directly limiting hemoglobin production.

### Heme Synthesis Pathway

```mermaid
flowchart TD
  A[Glycine + Succinyl-CoA] --> B[ALA synthase]
  B --> C[ALA]
  C --> D[Porphobilinogen]
  D --> E[Protoporphyrin IX]
  E --> F["Iron (Fe²⁺) + Ferrochelatase"]
  F --> G[Heme]
  G --> H["Heme + Globin chains"]
  H --> I[Hemoglobin]
  style F fill:#ffcccc
  style I fill:#ccffcc
```

**High-Yield:** Iron is the final substrate in heme synthesis. Ferrochelatase catalyzes the insertion of Fe²⁺ into protoporphyrin IX to form heme. Without iron, this step cannot proceed, and hemoglobin synthesis is blocked at the heme level.

### Why Iron Deficiency Causes Microcytic Anemia

1. **Insufficient heme synthesis** → Reduced hemoglobin content per RBC
2. **Impaired hemoglobin accumulation** → RBCs mature with less hemoglobin
3. **Microcytic (small) RBCs** → Body attempts to produce more RBCs to compensate (↑ RBC count, but ↓ MCV and MCH)
4. **Hypochromic RBCs** → Low color intensity due to low hemoglobin concentration

**Clinical Pearl:** The hallmark of iron deficiency anemia is **microcytic hypochromic anemia with elevated RBC count**—the body tries to maintain oxygen delivery by producing more (smaller, paler) RBCs.

Answer

A. Impaired globin chain synthesis

Answer

C. Decreased erythropoietin production by the kidney

Answer

D. Increased hemoglobin glycation

Which of the following is the PRIMARY mechanism by which iron deficiency impairs hemoglobin synthesis?

Explanation

Mechanism of Anemia in Iron Deficiency

Heme Synthesis Pathway

Why Iron Deficiency Causes Microcytic Anemia

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