Learn: Cardiac Cycle, Cardiac Output and Blood Pressure

Welcome!You've already learnt about the heart and blood vessels, so now we’ll build on that by exploring how the heart pumps blood, how cardiac output is calculated, and how blood pressure is regulated. Let’s get started!

What is the Cardiac Cycle?The cardiac cycle describes the sequence of events in one heartbeat. It includes contraction (systole) and relaxation (diastole) of the heart chambers. This ensures oxygenated blood is delivered to the body and deoxygenated blood is sent to the lungs.

Phases of the Cardiac CycleThere are three main phases:Atrial systole: The atria contract to push blood into the ventricles.Ventricular systole: The ventricles contract, ejecting blood into the arteries.Diastole: The heart relaxes, and chambers refill with blood.

Cardiac OutputCardiac output is the volume of blood pumped by the heart per minute. It is calculated using the formula:Cardiac output (CO) = stroke volume (SV) × heart rate (HR)Stroke volume is the amount of blood ejected by the ventricles per beat, and heart rate is the number of beats per minute.

What is Blood Pressure?Blood pressure is the force exerted by blood against the walls of blood vessels. It is measured in millimetres of mercury (mmHg) and recorded as two numbers:Systolic pressure: Pressure during ventricular contraction.Diastolic pressure: Pressure during ventricular relaxation.

Regulation of Blood PressureBlood pressure is regulated by the nervous system and hormones. The sympathetic nervous system increases heart rate and vasoconstriction, raising pressure. The parasympathetic nervous system lowers heart rate, reducing pressure.

Review Time!Great work! You've learned about the cardiac cycle, cardiac output, and blood pressure. Let’s test your understanding with some final questions.

Lesson Complete!Well done! You've now mastered the cardiac cycle, cardiac output, and blood pressure. Keep practising to reinforce your understanding.