Module 2 - The Cardiac Cycle Flashcards
Cells, Chemical for Life, Transport and Gas Exchange
Brief Summary: Cardiac Cycle
Atrial systole - contraction of the atria.
Ventricular systole - contraction of the ventricles.
Diastole - all 4 chambers are relaxed. The heart fills with blood.
Atrial Systole: Summary
- Ventricles relax.
- Atrial wall contracts which increases pressure on the blood in the atria.
- Blood volume decreases in atria as blood is forced into the ventricle through the AV valve.
- Slight increase in ventricular volume and pressure as ventricles fill with blood.
Atrial Systole Breakdown: Muscle state and blood movement…
- Atrial walls contract.
- Passive flow of blood into the ventricles changes by atrial contraction forcing blood into the ventricles. Atria emptied of blood.
Atrial Systole Breakdown: State of valves and pressure changes…
- AV valves pushed fully open by the blood flowing through.
- Pressure rises in atria as they contract with a slight rise in ventricles as blood enters them.
Ventricular Systole Phase 1: Summary
- Atria relax (pressure falls).
- Ventricle walls contract causing increase in pressure (rises for 0.1s).
- Pressure in ventricle is greater than pressure in atria so AV valves are forced shut.
Ventricular Systole Phase 2: Summary
- As ventricular pressure rises and exceeds pressure in the arteries, the semi lunar valves open.
- Blood is forced into the aorta or pulmonary artery.
- Pressure and volume of blood in ventricle decreases.
Ventricular Systole Breakdown: Muscle state and blood movement…
- Ventricle walls contract.
- Blood is forced into the main arteries. (Right ventricle into pulmonary artery and left ventricle into aorta).
Ventricular Systole Breakdown: State of valves and pressure changes…
-AV valves pushed shut as pressure in the ventricles rises above pressure in the atria, backflow prevented. Heart tendons hold valves in place to prevent the valves inverting. Semi-lunar valves pushed fully open as blood enters the arteries.
Diastole: Summary
- Muscular walls of both atria and ventricles relax.
- Higher pressure in the pulmonary artery and aorta cause the semi-lunar valves to close and so preventing backflow of blood into the ventricle.
- Atria fill with blood so pressure in atria increases due to higher pressure in vena cava and pulmonary vein.
- Ventricles continue to relax so pressure in ventricles becomes less than in atria.
- Higher pressure in atria cause AV valves to open and blood flows passively into the ventricle.
Diastole Breakdown: Muscle state and blood movement…
- Muscle walls relaxed.
- The atria fill with blood, opening the AV valves. Blood slowly and passively enters the ventricles.
Diastole Breakdown: State of valves and pressure changes…
- Semi-lunar valves close since pressure in artery is higher than in the ventricle. AV valves open.
- Pressure in atria rises as they fill but then falls as AV valve opens. Pressure in ventricles falls but rises slightly again as they become full. Pressure in arteries falls but remains higher than in ventricles.
Valves and Pressures: AV valve…
AV valve opens:
-pressure is higher in the left atrium than in the left ventricle.
AV valve closes:
-pressure is lower in the left atrium than in the left ventricle.
Valves and Pressures: Aortic valve…
Aortic valve opens:
-pressure is lower in the aorta than the left ventricle.
Aortic valve closes:
-Pressure is higher in the aorta than the left ventricle.
“Lub” and “Dub”
“Lub”
=AV valve closing as ventricle contracts.
“Dub”
=semi-lunar valves closing from backflow of blood from aorta and pulmonary artery.
Why is the maximum pressure in the left ventricle far higher than in the atrium?
- The left ventricle has a thicker muscular wall than the left atrium. This means the left ventricle contractions are much stronger than those of the left atrium.
- Thus the left ventricle can produce a greater force than the left atrium. Therefore the left ventricle can exert a greater maximum pressure on the blood.
