What is the term for the force exerted by blood against a unit area of the blood vessel walls?

Blood pressure is defined as the force that blood exerts against the walls of blood vessels. This measurement reflects how much pressure the blood is applying to the vascular system during both the contraction of the heart (systolic pressure) and the relaxation phase (diastolic pressure).

Understanding the other terms provides clarity on why blood pressure is the correct answer. Blood volume refers to the total amount of blood circulating within the body, which influences pressure but is not a direct measurement of force against vessel walls. Cardiac output is the amount of blood that the heart pumps in a minute, reflecting heart function but not the pressure within the blood vessels. Osmotic pressure relates to the pressure required to prevent the flow of water across a semipermeable membrane due to solute concentration, which does not pertain to the pressure exerted by blood in veins or arteries.

In summary, blood pressure specifically quantifies the force that blood applies to the vessel walls, making it the most accurate term in this context.