The Cardiac Cycle Flashcards
How many stages does the cardiac cycle have?
2
What are the names of the two stages of the cardiac cycle?
Systole
Diastole
What is systole?
Contraction
What is diastole?
Relaxation
Where does contraction take place?
It occurs separately in the ventricles and the atria and is therefore described in two stages.
Where does relaxation take place?
Simultaneously in all chambers of the heart and is therefore treated as a single phase.
What are the two stages of contraction?
Atrial systole and ventricular systole.
Where does the blood that returns to the atria come from?
The pulmonary vein and vena cava.
What causes the atrioventricular valves to open?
When the pressure exceeds that in the ventricles.
What does the opening of the atrioventricular valves enable?
It allows blood to pass into the ventricles.
What is the passage of blood aided by?
Gravity
What does the relaxation of the ventricle walls cause?
It causes them to recoil.
What does the recoil of the ventricles walls do?
It reduces the pressure within the ventricles.
What is the pressure in the ventricles lower than in diastole?
It is lower than that in the aorta and the pulmonary artery.
When do the semi-lunar valves in the aorta and pulmonary artery close?
When the pressure of the ventricles is lower than in the aorta and the pulmonary artery.
What force the remaining blood into the ventricles?
The contraction of the atrial walls and the recoil of the relaxed ventricle walls.
Are the ventricle walls relaxed or contracted throughout arterial systole?
They are relaxed.
What does the short delay in ventricular systole allow?
It allows the ventricles to fill with blood.
In what stage of the cardiac cycle do the ventricle walls contact simultaneously?
Ventricular systole.
What increases the blood pressure within the ventricles?
The simultaneous contraction of the ventricle walls.
What happens to the atrioventricular valves in ventricular systole?
They shut.
What prevents the back flow of blood into the atria?
The atrioventricular valves.
What causes the pressure in the ventricles to rise further?
The closing of the atrioventricular valves.
What forces blood into the aorta and pulmonary artery?
The pressure in the ventricles is higher than that in the pulmonary artery.
What are the ventricle walls like?
They are thick.
How does the thickness of the ventricle walls affect the force of contraction?
They contract forcefully.
What does the forceful contraction cause?
It creates the high pressure that is necessary to pump the blood round the body.
Why is the muscle thicker in the left ventricle?
It has to pump blood to all of the body.
Why is the right ventricular wall thinner?
It just pumps blood to the lungs.
Why does the blood flow in one direction?
This is because of the pressure created by the heart muscle.
In which way does blood move?
From a region of high pressure to that of low pressure.
When are valves used?
They are used when the flow of blood from a high pressure to a low pressure is undesirable.
How are the valves in the cardiovascular system designed to be?
They are designed so that they open whenever the the difference in blood pressure either side of them favours the blood movement in the required direction.
When do the cardiovascular valves close?
When the pressure differences are reversed (when the blood would flow in the wrong direction).
What are the three types of cardiovascular valves?
Atrioventricular
Semi-lunar
Pocket
Where are the atrioventricular valves located?
Between the left atrium and the left ventricle and between the right atrium and the right ventricle.
What do the atrioventricular valves prevent?
The backflow of blood when the ventricles contract, as the pressure in the ventricles is greater than the pressure in the atria.
What does the closure of the atrioventricular valves ensure?
When the ventricles contract the blood moves into the aorta and pulmonary artery.
Where are the semi-lunar valves located?
In the aorta ad pulmonary artery.
What do the semi-lunar valves prevent?
They prevent the movement of blood back into the ventricles when the air pressure exceeds in the vessels exceeds that in the ventricles.
Why does the pressure in the aorta and pulmonary artery become greater than that in the ventricles?
The walls of the vessels recoil whilst the ventricle walls relax.
Where are pocket valves located?
In the veins.
What do pocket valves ensure?
That the blood flows back towards the heart when the veins are squeezed.
What are the valves made of?
Tough, but flexible, fibrous tissue.
What shape are the valves?
Cusp shaped.
What happens to the valves when the pressure is greater on the convex side?
They move apart to let blood pass between the cusps.
What happens to the blood when the pressure is on the concave side of the cusps?
The blood collects in the “bowls” which pushes the cusps together so that the valves close.
What allows the pressure in the circulatory system of mammals to be maintained and regulated?
The closed system- blood is confined to vessels.
What is the cardiac output?
This is the volume of blood pumped by one ventricle of the heart in one minute.
What are the units of cardiac output?
dm^3min^-1
What two factors does the cardiac output depend upon?
The heart rate;
Stroke volume
What is meant by heart rate?
The rate at which the heart beats.
What is the stroke volume?
This is the volume of blood pumped out at each beat.
How do you find the cardiac output?
Heart rate X Stroke volume
