Cardiac Cycle || Systole, Diastole, Blood flow in heart, Movement of Valves

Summary

This video explains the cardiac cycle, detailing the key phases and movements of the heart during each heartbeat. It covers the four phases of the cycle: inflow, isovolumetric contraction, outflow, and isovolumetric relaxation, and the events within them. The video also discusses the roles of the atria and ventricles, and the function of valves in maintaining proper blood flow. It highlights the time duration of each phase and provides a clear explanation of the mechanics from both the ventricles' and atria's perspectives. The entire process is outlined in a concise manner, making complex medical concepts accessible.

Takeaways

• 😀 The heart consists of four chambers: two atria and two ventricles, with specific functions in blood circulation.
• 😀 The right atrium receives blood from the body, while the left atrium receives blood from the lungs.
• 😀 Blood flows from the atria into the ventricles, with the right ventricle pumping to the pulmonary artery and the left ventricle to the aorta.
• 😀 Valves in the heart ensure blood flows in one direction, including the atrioventricular and semilunar valves.
• 😀 The cardiac cycle consists of four main phases: inflow, isovolumetric contraction, outflow, and isovolumetric relaxation.
• 😀 Systole refers to the contraction of the ventricles, and diastole refers to their relaxation during the cardiac cycle.
• 😀 Inflow phase involves the rapid filling of ventricles, with about 70% of blood entering during this phase.
• 😀 Isovolumetric contraction occurs when the ventricles contract, but all valves are closed, leading to no blood flow.
• 😀 The outflow phase is marked by the opening of the semilunar valves and the ejection of blood from the ventricles into the arteries.
• 😀 The isovolumetric relaxation phase occurs when the ventricles relax but all valves remain closed, leading to no blood flow.
• 😀 The total duration of one cardiac cycle is about 0.8 seconds, with 0.5 seconds spent in diastole and 0.3 seconds in systole.

Q & A

What are the main anatomical components of the heart involved in the cardiac cycle?

The heart consists of four chambers: two atria and two ventricles. The right atrium receives blood from the systemic circulation, while the left atrium receives blood from the pulmonary circulation. The blood flows from the atria to the ventricles, and the ventricles pump blood into the pulmonary artery (right ventricle) and the aorta (left ventricle). Valves between the chambers and arteries help direct the blood flow.

What is the difference between systole and diastole in the cardiac cycle?

Systole refers to the contraction of the ventricles, while diastole refers to the relaxation phase of the ventricles. These phases are important in regulating the heart's pumping action and blood flow.

How are the phases of the cardiac cycle classified?

The cardiac cycle is divided into four phases: Phase 1 - inflow, Phase 2 - isovolumetric contraction, Phase 3 - outflow, and Phase 4 - isovolumetric relaxation. These phases describe the movements of the heart chambers and the opening and closing of valves.

What occurs during Phase 1 (inflow) of the cardiac cycle?

During Phase 1, blood flows from the atria into the ventricles. This phase includes rapid ventricular filling (70% of ventricular filling), followed by diastasis (20%) and atrial systole (10%), where the atria contract to complete the filling of the ventricles.

Why is Phase 2 called isovolumetric contraction?

Phase 2 is called isovolumetric contraction because, during this phase, all the heart valves are closed, and the ventricles contract without any blood flow. The volume of blood in the ventricles remains constant, but the pressure rises.

What is the significance of the semilunar valves in the cardiac cycle?

The semilunar valves are located between the ventricles and the major arteries (pulmonary artery and aorta). These valves open during ventricular contraction to allow blood to be ejected into the arteries and close to prevent the backflow of blood during ventricular relaxation.

What happens during the outflow phase (Phase 3)?

Phase 3, or outflow, consists of two stages: rapid ejection and slow ejection. During these stages, the ventricles eject blood into the major arteries (pulmonary artery and aorta). Initially, blood is ejected rapidly, followed by slower ejection as the ventricles continue to contract.

What occurs during Phase 4 (isovolumetric relaxation) of the cardiac cycle?

In Phase 4, the ventricles relax without blood flow since all valves are closed. The pressure in the ventricles decreases, but the volume of blood remains constant because the valves are still closed, leading to no flow of blood.

How long does the entire cardiac cycle last, and what is the breakdown of its phases?

The total duration of one cardiac cycle is about 0.8 seconds at a heart rate of 75 beats per minute. Diastole lasts 0.5 seconds, which includes isovolumetric relaxation and ventricular filling. Systole lasts 0.3 seconds and includes isovolumetric contraction and the ejection phase.

How does the activity of the atria differ from the ventricles during the cardiac cycle?

While the ventricles are primarily responsible for pumping blood into circulation, the atria assist by filling the ventricles. Atrial systole occurs at the end of ventricular diastole and lasts 0.1 seconds, while the atria remain in diastole during the rest of the cycle, collecting blood from the systemic and pulmonary circulation.