AS Biology - Cardiac cycle (OCR A Chapter 8.5)

Summary

This video explains the cardiac cycle, breaking it down into three main stages: atrial systole, ventricular systole, and diastole. It explores how blood flows through the heart, highlighting the role of different pressures in the atria, ventricles, and aorta, and the function of the heart valves (AV and semilunar valves) that prevent backflow. With an in-depth look at the graph representing these pressures, the video also clarifies the heart's rhythmic sounds and their connection to valve closure. The cycle lasts about 0.7 to 0.8 seconds and repeats with each heartbeat, ensuring the heart effectively pumps blood throughout the body.

Takeaways

• 😀 Diastole refers to the relaxation phase of the heart, allowing blood to fill the chambers.
• 😀 Systole refers to the contraction phase of the heart, where blood is pushed out of the chambers.
• 😀 The heart never undergoes systole simultaneously in all chambers, as that would prevent blood flow.
• 😀 The cardiac cycle consists of three major stages: atrial systole, ventricular systole, and diastole.
• 😀 Atrial pressure refers to the blood pressure in the atria, while ventricular pressure refers to the pressure in the ventricles.
• 😀 The aortic pressure is the pressure in the aorta, responsible for moving blood out of the heart to the body.
• 😀 During atrial systole, the atria contract to fill the ventricles with blood, while the ventricles are relaxed.
• 😀 In ventricular systole, the ventricles contract to push blood out of the heart, and the atria relax.
• 😀 Diastole is the relaxation phase of the entire heart, allowing blood to refill both the atria and ventricles.
• 😀 The heart's 'thump-thump' sound is caused by the closing of the atrioventricular and semilunar valves.
• 😀 The entire cardiac cycle lasts about 0.7 to 0.8 seconds, with each stage playing a critical role in maintaining efficient blood flow.

Q & A

What is diastole, and why is it important in the cardiac cycle?

Diastole refers to the relaxation phase of the heart, during which the heart chambers, both atria and ventricles, relax and fill with blood. This phase is crucial because it allows the heart to refill with blood before the next contraction, ensuring proper circulation.

What is systole, and how does it differ between atrial and ventricular phases?

Systole is the contraction phase of the heart. Atrial systole refers to the contraction of the atria to push blood into the ventricles, while ventricular systole refers to the contraction of the ventricles to expel blood into the aorta or pulmonary artery. These phases occur in different chambers but are part of the same overall cycle.

Why can’t the whole heart undergo systole at the same time?

If the entire heart were to undergo systole simultaneously, no blood would be able to flow anywhere. The atria and ventricles need to contract in a coordinated manner, with the atria contracting first to fill the ventricles, followed by the ventricles contracting to push blood out of the heart.

What are the three key pressures involved in the cardiac cycle, and what do they represent?

The three key pressures are atrial pressure, ventricular pressure, and aortic (or pulmonary artery) pressure. Atrial pressure is the blood pressure inside the atria, ventricular pressure is the pressure inside the ventricles, and aortic pressure is the pressure in the aorta (or pulmonary artery), representing the blood pressure as it exits the heart.

How does ventricular pressure compare to atrial pressure during ventricular systole?

During ventricular systole, the ventricular pressure increases significantly, becoming much higher than the atrial pressure. This causes the atrioventricular (AV) valves to close to prevent blood from flowing back into the atria.

What is the significance of the semilunar valves during ventricular systole?

The semilunar valves (aortic and pulmonary) open during ventricular systole as the ventricular pressure becomes higher than the aortic pressure. This allows blood to flow from the ventricles into the aorta or pulmonary artery, directing it to the body or lungs.

Why do the semilunar valves close during diastole?

The semilunar valves close during diastole to prevent blood from flowing back into the ventricles. Once the ventricular pressure drops below the aortic pressure, the semilunar valves close, ensuring that blood does not flow backward into the heart.

What happens during the phase of diastole in terms of heart chamber relaxation and valve actions?

During diastole, both the atria and ventricles relax, causing the ventricular pressure to drop. This leads to the closing of the semilunar valves and the opening of the atrioventricular valves, allowing blood to flow from the atria into the ventricles, refilling them in preparation for the next cycle.

What is the approximate duration of each phase of the cardiac cycle?

Atrial systole lasts about 0.1 seconds, ventricular systole lasts about 0.3 seconds, and diastole lasts around 0.4 seconds. The entire cycle typically takes about 0.7 to 0.8 seconds.

What causes the 'thump-thump' sound of the heart?

The 'thump-thump' sound of the heart is caused by the closing of the heart valves. The first sound (S1) is from the closure of the atrioventricular valves, while the second sound (S2) is from the closure of the semilunar valves.