**Core Concept**
Omeprazole is a proton pump inhibitor (PPI) that irreversibly inhibits the H+/K+ ATPase enzyme system at the secretory surface of gastric parietal cells. This enzyme is responsible for secreting gastric acid.

**Why the Correct Answer is Right**
Omeprazole's mechanism of action involves covalently binding to the sulfhydryl group of cysteine residues on the H+/K+ ATPase enzyme, resulting in irreversible inhibition. This inhibition lasts for the lifespan of the parietal cell, which is approximately 48-72 hours. The duration of action of omeprazole is therefore longer than that of H2 receptor antagonists, which have a duration of action of around 8-12 hours.

**Why Each Wrong Option is Incorrect**
* **Option A:** This is incorrect because omeprazole's duration of action is not limited to the time it takes for the drug to be eliminated from the body.
* **Option B:** This is incorrect because the duration of action of omeprazole is not primarily determined by its plasma half-life.
* **Option C:** This is incorrect because the duration of action of omeprazole is not limited to the time it takes for the drug to be absorbed from the gastrointestinal tract.

**Clinical Pearl / High-Yield Fact**
It's essential to note that the duration of action of omeprazole can be affected by factors such as liver function, kidney function, and the presence of other medications that may interact with omeprazole.

**Correct Answer:** C. 72 hours