**Question:** If a patient with Raynaud's disease immerses his hand in cold water, the hand will:

**Core Concept:** Raynaud's disease is a condition characterized by episodic digital ischemia, which is caused by a sympathetic overreaction in response to cold exposure or emotional stress. This leads to vasoconstriction of the blood vessels in the affected areas.

**Why the Correct Answer is Right:** When a patient with Raynaud's disease immerses their hand in cold water, the sympathetic nervous system is activated, causing the hand's blood vessels to constrict. This is due to the overreaction of the sympathetic nervous system in response to cold stimuli, leading to a reduction in blood flow to the hand.

**Why Each Wrong Option is Incorrect:**

A. This option is incorrect because immersing the hand in cold water will cause vasoconstriction due to the increased sympathetic activity in Raynaud's disease.
B. This option is incorrect because vasodilation is the opposite of what occurs in Raynaud's disease. Cold water will exacerbate the condition by stimulating vasoconstriction.
C. This option is incorrect because vasoconstriction occurs in Raynaud's disease in response to cold exposure, as explained earlier.
D. This option is incorrect because vasodilation is the opposite of what occurs in Raynaud's disease. Cold water will exacerbate the condition by stimulating vasoconstriction.

**Clinical Pearl:** In Raynaud's disease, it is essential to avoid cold exposure and emotional stress to prevent episodes of digital ischemia. It is crucial to educate patients on the triggers and symptoms of their condition to manage it effectively.

**Correct Answer:** D. Vasoconstriction

Explanation: In Raynaud's disease, the sympathetic overreaction causes vasoconstriction of blood vessels in the affected areas. When the patient immerses the hand in cold water, the cold stimulus triggers increased sympathetic activity, leading to vasoconstriction and worsening of the condition.