What is viscosity in relation to blood pressure?

• A. The thickness of blood; thicker blood increases pressure
• B. The amount of blood volume in arteries
• C. The speed of blood flow
• D. The elasticity of vessel walls

Answer: (A)

Viscosity is the thickness of a fluid and its internal friction as it flows. In blood, higher viscosity means the blood resists flow more, so the heart must generate more pressure to push it through the vessels. This is why thicker blood tends to raise blood pressure for a given amount of blood flow.

The other factors aren’t viscosity: blood volume in arteries is about how much blood is present (volume), the speed of blood flow is velocity (how fast it moves), and the elasticity of vessel walls relates to how stretchable or compliant the vessels are, not how thick the blood is.