**Question:** Red velvety appearance of stomach mucosa is seen in the poisoning of:

* A. Carbon monoxide
* B. Hydrogen cyanide
* C. Nitrous oxide
* D. Tetracycline

**Core Concept:**

The red velvety appearance of the stomach mucosa is an important clinical sign in recognizing certain poisonings, which can help guide diagnosis and prompt appropriate treatment. The stomach mucosa is richly supplied with blood vessels, making it highly sensitive to changes in blood flow, pH, and toxin exposure.

**Why the Correct Answer is Right:**

The correct answer, **D. Tetracycline**, refers to the toxic effects of this antibiotic on the stomach mucosa. Tetracycline is a broad-spectrum antibiotic that inhibits bacterial protein synthesis and is commonly used to treat various infections. However, its use can lead to a red, velvety appearance of the stomach mucosa due to a decrease in blood flow and mucosal damage. This is a result of the drug's interaction with the gastric mucosa and its binding to the collagen in the gastric mucosa, causing damage and reduced blood flow.

**Why Each Wrong Option is Incorrect:**

A. **Carbon monoxide (A)** causes carbon monoxide poisoning, which results in methemoglobinemia and vasoconstriction, leading to a bluish discoloration of the mucosa rather than the red velvety appearance described.

B. **Hydrogen cyanide (B)** causes cyanide poisoning, leading to lactic acidosis, respiratory distress, and altered consciousness, but does not typically result in the red velvety appearance of the stomach mucosa.

C. **Nitrous oxide (C)**, also known as laughing gas, does not cause the red velvety appearance of the stomach mucosa. Its primary effects include euphoria, amnesia, and increased respiratory rate, but not mucosal damage.

**Clinical Pearls:**

The red velvety appearance of the stomach mucosa should raise suspicion for tetracycline poisoning, particularly in cases of suspected antibiotic abuse or misuse. This clinical sign can aid in prompting a thorough evaluation for potential tetracycline toxicity and guiding further diagnostic and therapeutic steps. Inducing awareness of this clinical sign is important in recognizing the adverse effects of tetracycline use and preventing misuse of this antibiotic.

In conclusion, understanding the clinical signs and symptoms of various poisonings and their associated mucosal changes is crucial for accurate diagnosis and appropriate management of patients presenting with gastrointestinal symptoms.