7.5 The cardiac cycle Flashcards
What are the two phases of beating of the heart called
Systole (contraction)
Diastole (relaxation)
Where in the heart can systole occur
What about diastole
Systole occurs separately in the ventricles and the atria so is therefore described in two stages
Diastole occurs simultaneously in all 4 chambers of the heart, so can be treated as one stage
Describe the diastole (relaxation) phase of the heart
Blood returns to the atria of the heart through pulmonary vein (from the lungs), and through the vena cava (from the body)
As the atria fill up with blood, the pressure inside them rises, and when there is more pressure in them than in the ventricles , the atrioventricular valves open and allow the blood to pass into the ventricles.
Gravity also aids this passage of blood
The muscular walls of both the atria and ventricles are relaxed as this occurs.
The relaxation of the ventricle walls at this time cause them to recoil and reduce the pressure within the ventricle so it is lower than that in the aorta and pulmonary artery.
This makes the semi lunar valves in the atria and pulmonary artery shut, making the characteristic dub sound of heart
Describe the cardiac cycle
. Blood enters atria and ventricles from pulmonary veins and vena cava
Here, the atrioventricular valves are open so blood flows from the atria into the ventricles.
This is the diastole of the heart, as both the atria and ventricles are relaxed
. Then, the atria contract to push remaining blood into the ventricles (which are still relaxed) , so the atrioventricular valves are still open.
This is called atrial systole
. Then, blood is pumped from the ventricles away from the heart, into the arteries and aorta as the ventricles contract and semi lunar valves open.
The atria are relaxed here.
This is called ventricular systole
What is atrial systole
When the atria walls contract, and there is recoil of the relaxed ventricles at the same time.
This forces blood from atria into the ventricles through the atrioventricular valves
What is ventricular systole
. After a short delay to allow the ventricles to fill with blood, their walls contract simultaneously
. This increases blood pressure within the ventricles which makes the atrioventricular valves shut to prevent back flow of blood back into the atria.
The sound of these closing is the lub sound
With the atrioventricular valves closed, pressure in the ventricles increases, and once it exceeds that in the aorta and pulmonary artery, blood is forced into them through the semi-lunar valves that open.
When these valves shut after pressure is higher in the vessels than in the ventricles, there is a dub sound
How do valves control the flow of blood in the heart
. Blood is kept flowing in one direction in the heart and around the body by the pressure created by the heart muscle, as blood always moves from a region of higher pressure to lower pressure
. However, sometimes the pressure difference could make blood flow in the opposite direction, so in these circumstances the valves shut to prevent back flow of blood
Where are pocket valves found and what do they do
They are found in veins, that occur in the venous system, and they ensure that the veins are squeezed
What are semilunar valves
Found in the aorta and pulmonary artery, and prevent back flow of blood back into the ventricles when the pressure in these vessels exceeds that of the ventricles
. This arises when the elastic walls of the vessels recoil, increasing the pressure within them, and when the ventricles relax, reducing the pressure in them
What are valves made from
Flaps of tough and flexible, fibrous tissue which are cusp shaped, in other words like deep bowls.
Mammals have a double circulatory system, what does this mean for them
The pressure within them can be maintained and regulated
What is cardiac output, and what does it depend on
It is the volume of blood pumped by one ventricle of the heart, in one minute
Measured in dm3min-1 and depends on two factors:
The heart rate (rate at which the heart beats)
The stroke volume ( Volume of blood pumped out at each beat)
What is the equation to calculate cardiac output
Cardiac output=
heart rate X stroke volume
What is an electrocardiogram
The heart undergoes a series of electrical current changes, and these can be displayed on a cathode ray oscilloscope, creating a trace known as an electrocardiogram
