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Difficulty: MediumExplicit Details

Iron is an essential micronutrient for human health, but excess levels can lead to tissue damage. In 2001, researchers discovered that the liver secretes a peptide hormone called hepcidin, which serves as the primary regulator of systemic iron balance. Hepcidin acts by binding to ferroportin, the only known cellular iron exporter found on the surface of macrophages and enterocytes. Upon binding, hepcidin induces the internalization and degradation of ferroportin. This action directly halts the release of iron into the blood plasma, effectively lowering circulating iron levels. Consequently, when hepcidin levels are abnormally low, ferroportin remains active, leading to excessive iron absorption and accumulation in vital organs.

According to the text, how does hepcidin affect circulating iron levels?

  1. A
    It directly binds to circulating iron molecules in the plasma to prevent tissue damage.
  2. It induces the internalization and degradation of ferroportin, which halts the release of iron into the blood plasma.Answer
  3. C
    It serves as a cellular exporter that transports iron directly out of enterocytes.
  4. D
    It triggers the liver to synthesize more ferroportin when systemic iron levels drop.

Answer

Hepcidin lowers circulating iron levels by binding to ferroportin and causing it to be internalized and degraded, thereby preventing iron from being released into the blood plasma.
The correct option is directly supported by the passage, which explicitly describes how hepcidin binding to ferroportin induces its internalization and degradation, halting the release of iron into the blood plasma and lowering circulating levels.

Step-by-Step Solution

1
Identify where the text explains the mechanism by which hepcidin lowers iron levels.
The text states: 'Upon binding, hepcidin induces the internalization and degradation of ferroportin. This action directly halts the release of iron into the blood plasma, effectively lowering circulating iron levels.'
This locates the specific explicit details addressing the question stem.
2
Match the text's description with the choices provided.
The statement describing the internalization and degradation of ferroportin matches the text exactly.
Explicit detail questions require finding the option that restates text details without introducing external assumptions.

Key Concept

Identifying Explicit Details
Estimated Time:1m 30s
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Explicit Details

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