Mass Transport in Animals - The Cardiac Cycle Flashcards
What are the two phases to a heart beat?
Systole and Diastole
What is systole?
Contraction (of muscles)
What is diastole?
Relaxation (of the heart)
What are the stage of the cardiac cycle?
- Diastole
- Atrial systole
- Ventricular systole
What happens during diastole?
- Blood returns to the atria of the heart through the pulmonary vein from the lungs and the vena cava from the body .
- Pressure rises as the atria fills up.
- When the pressure in the atria exceeds that in the ventricles, the atrioventricular valves open which allows blood to flow into the ventricles, with the aid of gravity.
- The muscular walls of both the atria and ventricles are relaxed at this stage.
- The relaxation of the ventricle walls causes them to recoil and reduces the pressure within the ventricle.
- This causes the pressure to be lower than in the aorta and the pulmonary artery so the semi-lunar valves in the aorta and pulmonary artery close.
What is atrial systole?
Contraction of the atria
What happens during atrial systole?
- Remaining blood is forced into the ventricles from the atria.
- This happens due to the contraction of the atrial walls alongside the recoil of the relaxed ventricle walls. (Ventricle walls stay relaxed throughout this stage).
What is ventricular systole?
Contraction of the ventricles
What happens during ventricular systole?
- Walls contract simultaneously after a short delay to allow the ventricles to fill with blood.
- This increases blood pressure within the ventricles which closes the atrioventricular valves, preventing backflow of blood into the atria.
- The atrioventricular valves closing increases pressure in the ventricles further.
- When this pressure exceeds the pressure in the aorta and the pulmonary artery, blood is forced from the ventricles into these vessels.
- Blood is pumped around the body due to the high pressure caused by the thick muscular walls.
- The left ventricle pumps blood to the extremities and the right ventricle pumps blood to the lungs.
What are the features of the atrioventricular valves?
- Found between the left atrium and left ventricle and right atrium and right ventricle.
- Prevent the backflow of blood when contraction of the ventricles means that ventricular pressure exceeds atrial pressure.
- Closure of these valves ensures that when the ventricles contract, blood within them moves to the aorta and pulmonary artery rather than back to the atria.
Where are the atrioventricular valves found?
Between the left atrium and left ventricle and between the right atrium and right ventricle.
What are the features of the semi-lunar valves?
- Found in the aorta and pulmonary artery.
- Prevent the backflow of blood into the ventricles when the pressure in these vessels exceeds that in the ventricles.
- This arises when the elastic walls of the vessels recoil which increases the pressure within them and when the ventricle walls relax, reducing the pressure within the ventricles.
Where are the semi-lunar valves found?
In the aorta and pulmonary artery.
What are the features of the pocket valves?
- Found in veins.
- Ensure that when veins are squeezed (e.g when skeletal muscles contract) blood flows back towards the heart rather than away.
Where are pocket valves found?
In the veins.
