7.5 - The Cardiac Cycle Flashcards
What are the two phases of the cardiac cycle?
Systole (contraction) and diastole (relaxation)
What are the two stages on systole
- Atrial systole
- Ventricular systole
What happens in the relaxation of the heart (diastole)
- Blood enters atria and ventricles from pulmonary veins and vena cava
- atria are relaxed and fill with blood
- ventricles are also relaxed
What happens in atrial systole?
- atria contract pushing blood into the ventricles
- ventricles remain relaxed
What happens in ventricular systole?
- blood pumped into pulmonary arteries and the aorta
- atria relax
- ventricles contract pushing blood away from the heart through pulmonary arteries and the aorta
What are the three main valves?
- Atrioventricular valves
- Semi - lunar valves
- Pocket valves
What is the role of Atrioventricular valves?
They prevent the back flow 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.
What is the role of the semi - lunar valves?
Prevent the back flow of blood into the ventricles when the pressure in these vessels exceed that is the ventricles. This arises when the elastic walls of the vessels recoil increasing the pressure within them and when the ventricle walls relax reducing the pressure within the ventricles.
Where are pocket valves?
In veins
What is the role of pocket valves?
Ensure that when the veins are squeezed, e.g when the skeletal muscles contract, blood flows back towards the heart rather than away from it.
Do mammles have a open or closed circulatory system?
Closed
What does a closed circulatory system mean?
Blood is confined to vessels, and this allows the pressure within them to be maintained and regulated
What is the cardiac output?
The volume of blood pumped by one ventricle of the heart in one minute
What are the two factors the cardiac output dcepends on?
- The heart rate (the rate at which the heart beats)
- The stroke volume (volume of blood pumped out at each beat)
Cardiac output =
Heart rate x stroke volume
In the cardiac output graph describe the curve of ventricular pressure.
- low at first
- grad increases as ventricles fill with blood as the atria contract
- left atrovntricular valves close
- pressure rises dramatically as the thick muscular walls of the ventricle contract
- as pressure rises above that of the aorta, blood is forced into the aorta past the semi - lunar valves
- pressure falls as the ventricles empty and the walls relax
In the cardiac output graph describe the atrial pressure
- always relatively low bc the thin walls of the atrium cant create much force
- it is highest when they are contracting
- drops when the L atrioventricular valves closes and its walls relax
- atria then fill with blood - leads to a grad build up of pressure
- slight drop when L atrioventricular valve opens and some blood moves into the ventricle
In the cardiac output graph describe Aortic pressure.
- rises when ventricles contract as blood is forced into the aorta
- grad falls but never below 12 kPa bc of the elasticity of its wall (creates a recoil action)
- the recoil produces a temporary rise in pressure at the start of the relaxation phases
In the cariac output graph describe the ventricular volume.
- rises as the atria contract and the ventricles fill with blood
- drops suddenly as blood is forced out into the aorta when the semi - lunar valve opens
- volume increases again as the ventricles fill with blood.
