Blood viscosity effects on peripheral resistance?

• A. Increases peripheral resistance
• B. Decreases peripheral resistance
• C. No effect
• D. Only affects flow at capillaries

Answer: (A)

Blood viscosity is a measure of how thick or sticky the blood is. When viscosity increases, the layers of blood rub against each other and against vessel walls more, creating more internal friction. Peripheral resistance is the opposition the systemic vessels pose to blood flow; with higher friction, the heart must generate more pressure to maintain the same flow. That makes viscosity a direct contributor to resistance throughout the circulation, not just in one part of the vascular system. So thicker blood means higher resistance. If the blood were thinner, friction would lessen and resistance would drop. Viscosity affects flow in vessels of all sizes, not only capillaries.