In hemodynamics, turbulence occurs when Reynolds number exceeds?

• A. Below 1000
• B. Equal to 2000
• C. Exceeding 2000
• D. Only in large arteries

Answer: (D)

Turbulence in blood flow is driven by the Reynolds number, which compares inertial forces to viscous damping. When this ratio gets large, the flow can break into chaotic swirls rather than remaining smooth. In vessels, laminar flow is common at normal conditions, but once the Reynolds number passes a certain threshold, turbulence can emerge. A commonly cited range for transition in straight tubes is around 2000 or so, though pulsatile flow, vessel compliance, bends, and disturbances from stenosis or jets can shift this threshold.

Importantly, turbulence is not limited to large arteries. It can occur in any vessel when flow conditions produce a high Reynolds number or significant disturbances. So the idea that turbulence happens only in large arteries isn’t correct; what matters is the balance of inertial to viscous forces, rather than the vessel size alone.