6. According to the Department of Health, blood pressure is: The pressure exerted by circulating blood upon the walls of blood vessels The pressure when blood cells move towards and away from the heart The pressure when the heart relaxes The pressure when the heart contracts

The correct definition of blood pressure is: **The pressure exerted by circulating blood upon the walls of blood vessels.** This definition encompasses the overall concept of blood pressure, which is a measure of the force that blood exerts on the walls of blood vessels as it circulates throughout the body. The other options provided do not accurately describe blood pressure: - The pressure when blood cells move towards and away from the heart is not a standard definition of blood pressure. - The pressure when the heart relaxes refers to diastolic pressure, which is a component of blood pressure but not the definition itself. - The pressure when the heart contracts refers to systolic pressure, which is also a component of blood pressure. In summary, blood pressure is best defined as the pressure exerted by circulating blood upon the walls of blood vessels.