Component 3.2 - The Cardiac Cycle Flashcards
What is cardiac output?
The volume of blood expelled by the heart in one minute
How do you calculate cardiac output?
Stroke volume x number of heart beats per minute
What is the atrial systole?
The atrium walls contract and the blood pressure in the atria increases. This pushes the blood through the tricuspid/bicuspid valves, down into the ventricles which are relaxed.
What is ventricular systole?
The ventricle walls contract and increased blood pressure in the ventricles. This forces blood up through the semi-lunar calves, out of the heart into the pulmonary artery and aorta
Why do the bicuspid and tricuspid valves close? And what does this prevent?
They close when pressure in ventricles exceeds pressure in atria which prevents the back flow of blood
What is diastole? And why does this causes the semi-lunar valves to close?
The ventricles relax, the volume in the ventricles increases and so pressure in the ventricles falls.
This risks the blood in the pulmonary artery and sorts flowing backwards, this tendency causes the semi-lunar valves to shut.
Describe the flow of blood through the left side of the heart
1) The left atrium relaxes and receives oxygenated blood from the pulmonary vein
2) When full, the pressure forces open the bicuspid valves (between atrium and ventricle)
3) Relaxation of the ventricle draws blood from the left atrium
4) The left atrium contracts, pushing the remaining blood into the left ventricle
5) With The left atrium relaxed and with the bicuspid valve closed, the left ventricle contracts.
6) The high pressure from the ventricle pushes blood up out the heart, through semi-lunar valves into the aorta and closes the bicuspid valves.
Why do atria walls have little muscle compared to ventricle walls?
Because in the atria the blood only has to go to the ventricles, whereas ventricle walls need to generate more pressure, as they have to send the blood to the lungs or the rest of the body.
Why does the left ventricle have thicker, muscular wall than the right ventricle?
Because it has to pump blood all round the body, whereas the right ventricle has to pump the blood a shorter distance to the lungs.
What does the SAN do?
It causes a wave of electrical simulation to arise which spreads over both atria causing them to contract together. Acts as pacemaker
Where is the SAN found?
In the wall of the right atrium
What does the AVN do?
The AVN introduces a delay in the transmission of the electrical impulse. This ensures that the ventricles do not contract before the atria have finish contracting (are empty).
What does the P-wave on an electrocardiogram show?
The depolarisation of the atria during atrial systole
What does the PR interval on an electrocardiogram show?
It is the time taken for the excitation to spread from the atria to the ventricles, through the atria-ventricular node.
What is does the QRS complex on an electrocardiogram show?
It shows the spread of depolarisation through the ventricles, resulting in ventricular systole
