The cardiac cycle Flashcards
What is the cardiac cycle?
The performance of the human heart from the beginning of one heartbeat to the beginning of the next
What are the 3 stages of the cardiac cycle?
- Cardiac diastole - Relaxation of the heart
- Atrial systole - Contraction of the atria
- Ventricular systole - Contraction of the ventricles
Where does diastole take place?
Diastole takes simultaneously in all of the chambers in the heart.
What happens during diastole?
All 4 chambers are relaxed and are re-filled with blood.
Both the atria and ventricles are relaxed and the blood enters at low pressure through the veins, the pulmonary vein and the vena cava into the atria.
As the blood flows in the atria the blood pressure begins to increase causing the AV valves to become opened allowing for the blood to enter the ventricles.
What happens during atrial systole?
Contraction of atrial walls & recoil of relaxed ventricle walls forces blood into ventricles from atria.
Or,
The atria contracts when it is 50% empty. This ensures all the blood is emptied from the atria and enters the ventricles.
This causes the pressure within the ventricles to slightly increase shutting the AV valves, to prevent the backflow of blood back to the atria.
What happens during ventricular systole?
The ventricle chambers contract and force the blood up and out of the heart and into the arteries.
Blood always moves from a … to … pressure
Blood always moves from a high to low pressure.
How are valves in the cardioventricular system designed?
They are designed so that they open whenever the difference in blood pressure either side of them favours the movement of blood in the required direction.
When do valves close?
Valves close when blood flows in the opposite direction to which is desirable.
What are the 3 types of valves that control blood flow?
- atrioventricular valves (tricuspid and bicuspid valves)
- semi-lunar valves (pulmonary valve and aortic valve)
- pocket valves.
Where are the AV valves?
Between the right atrium and the right ventricle - tricuspid valve
Between the left atrium and left ventricle - bicuspid valve
What do the AV valves do?
They prevent the backflow of blood when contraction of ventricles means that ventricular pressure exceeds atrial pressure.
Where are the SL valves located?
In the aorta and pulmonary artery.
What do the SL valves do?
They prevent the backflow of blood into ventricles when the pressure in these valves exceeds the pressure that’s in the ventricles.
Where are pocket valves located?
In veins that occur throughout the venous system.
What do the pocket valves do?
They ensure that when veins are squeezed, blood flows back towards the heart rather than away from it.
What is the design of valves like?
Are they different or the same to each other?
What are the valves made up of?
The design of valves is basically the same for all valves.
Valves are made of a number of flaps of tough, flexible, fibrous tissue.
Valves are cusp-shaped.
How do valves work in preventing the backflow of blood?
When pressure is greater on the convex side of these cusps, they move apart to allow the blood to pass through.
When pressure is greater on the concave side, blood collects within the ‘bowl’ of the cusps. This pushes them together to form a tight fit that prevents the passage of blood.
What is cardiac output?
The volume of blood pumped by 1 ventricle of the heart in 1 minute.
What is the equation for cardiac output?
heart rate X stroke volume.
(stroke volume = vol of blood pumped out at each beat.
