What is blood pressure?

• A. The speed of blood flow
• B. The amount of oxygen carried by blood
• C. The blood's temperature
• D. The pressure exerted by the blood against the walls of blood vessels

Answer: (D)

Blood pressure is the force that circulating blood pushes against the walls of arteries as the heart works to pump blood through the body. It reflects how hard the heart is pushing and how much resistance the vessels offer. The reading has two numbers: one when the heart contracts (systolic) and one when the heart relaxes between beats (diastolic), measured in millimeters of mercury (mmHg). This measurement is essential because enough pressure is needed to deliver blood to all tissues, but not so high that it damages vessels. Too low can mean organs aren’t getting enough blood; too high raises the risk of heart disease and stroke.

The other options describe different aspects of blood or its flow, not the force on vessel walls. The speed of blood flow refers to how fast blood moves, which can change with demand and vessel size but isn’t the pressure on the walls. The amount of oxygen carried by blood describes oxygen content, not pressure. Temperature is a separate property and doesn’t define the force blood exerts against vessel walls.