Question

........ is a potent vasodilator.

• A. Histamine
• B. Serotonin
• C. Codeine
• D. Cimetidine

Hint:

Histamine plays a dual role in allergic reactions and regulating stomach acid.

Answer 1

The Correct Option is A

Step 1: Understanding Vasodilators 
Vasodilators are substances that widen blood vessels, reducing blood pressure. 
Histamine plays a key role in immune response and vasodilation.
Step 2: Classification of Given Options 
Histamine causes vasodilation and regulates stomach acid secretion. 
Serotonin affects mood and blood clotting but is not a vasodilator. 
Codeine is an opioid pain reliever.
Cimetidine is a histamine receptor 
blocker. 
Final Answer: Since histamine is the primary vasodilator, the correct answer is (A).

Answer 2

Histamine is a potent vasodilator primarily because it acts on the blood vessels by binding to histamine receptors (mainly H1 receptors) on the endothelial cells lining the blood vessels. This binding triggers the release of nitric oxide (NO) and other relaxing factors, which cause the smooth muscles in the vessel walls to relax and dilate. Vasodilation increases the diameter of the blood vessels, allowing more blood to flow through them easily. This process results in a decrease in vascular resistance and an increase in blood flow to specific tissues, which is crucial during immune responses such as inflammation and allergic reactions. By dilating blood vessels, histamine helps deliver immune cells and molecules to sites of injury or infection more rapidly. However, excessive vasodilation can also lead to symptoms like redness, swelling, and a drop in blood pressure. In summary, histamine’s role as a potent vasodilator makes it essential for immune system functioning and the body’s ability to respond to harmful stimuli effectively.