Which two factors determine the amount of friction in blood flow?

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Multiple Choice

Which two factors determine the amount of friction in blood flow?

Explanation:
Friction (resistance) to blood flow is set by factors that govern how hard blood has to push along and past the vessel walls. According to Poiseuille’s law, resistance increases with the length of the vessel and decreases with the radius (diameter) of the vessel, with the radius having a very strong effect because resistance is proportional to 1/r^4. So a longer vessel provides more contact along the path, raising friction, while a smaller diameter markedly increases friction due to the steep r^4 relationship. Blood viscosity also affects friction, but when asked for the two primary determinants, vessel length and internal diameter are the ones that directly set the amount of friction. Cardiac output and mean arterial pressure influence overall flow but do not set friction in the same direct way.

Friction (resistance) to blood flow is set by factors that govern how hard blood has to push along and past the vessel walls. According to Poiseuille’s law, resistance increases with the length of the vessel and decreases with the radius (diameter) of the vessel, with the radius having a very strong effect because resistance is proportional to 1/r^4. So a longer vessel provides more contact along the path, raising friction, while a smaller diameter markedly increases friction due to the steep r^4 relationship. Blood viscosity also affects friction, but when asked for the two primary determinants, vessel length and internal diameter are the ones that directly set the amount of friction. Cardiac output and mean arterial pressure influence overall flow but do not set friction in the same direct way.

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