What governs the amount of blood that enters the arterial system?

The correct answer is cardiac output, as it directly impacts the volume of blood being pumped into the arterial system from the heart. Cardiac output is defined as the amount of blood the heart pumps in a minute and is determined by the heart rate and stroke volume. When cardiac output increases, more blood is delivered to the arterial system, leading to a corresponding increase in blood volume in the arteries.

High cardiac output typically occurs during physical exertion or moments of stress, while lower cardiac output may be seen at rest or during sleep. Therefore, understanding cardiac output is crucial for evaluating how much blood enters the arterial system and influences overall circulation and blood flow dynamics.

Blood pressure is certainly related to the volume of blood in the system but is more a result of cardiac output and peripheral resistance. Peripheral resistance deals with the opposition that blood encounters as it flows through the vessels, affecting blood flow but not governing the amount of blood entering the system. Heart rate alone does not capture the entirety of blood flow dynamics, as it must be considered alongside stroke volume to accurately assess cardiac output.