the cardiac cycle Flashcards
what is the cardiac cycle
the sequence of events in one full heart beat
how long is one heart beat
about 0.8 seconds in a human adult
what is the role of the heart
to create pressure that pushes blood around the blood vessels.
why must the muscular walls of the chamber contract in a coordinated sequence
to allow the heart to fill with blood before it can pump it away
what happens in diastole
the heart relaxes, and the atria and the ventricles fill with blood
what happens to blood pressure and volume as the heart fills
the blood pressure of the blood in the heart builds but the pressure of the arteries is at a minimum
what happens in systole
the atria contract (atrial systole) and then the ventricles (ventricular systole)
what happens to the blood pressure in ssytole
it increases dramatically inside the heart and forces blood out
where is blood pumped in the right side
from the heart to lungs
where is blood pumped in the left side
from the heart to the rest of the body
what happens to the volume and pressure of the blood at the end of systole
its low in the blood and at a maximum in the arteries
what are the 3 stages of the cardiac cycle
atrial systole, ventricular systole, diastole
what happens at atrial systole
the atria filled with blood from the vena cavae and pulmonary veins contract and this forces blood through the atrioventricular valves into the ventricles. the ventricles are now filled with blood
what happens at ventricular systole
the ventricles contract forcing blood up through the semilunar valves and into the aorta and pulmonary artery. the force of contraction closes the AV valves preventing blood from flowing back into the atria
what happens at cardiac diastole
as the ventricles relax, the drop in blood pressure causes the semilunar valves to close. the atria start to fill with blood and as the pressure increases, blood starts trickling down into the ventricles again
what happens to the chambers in atrial systole
atria contract
ventricles relax
what happens to the chambers at ventricular systole
ventricles contract
atria relax
what happens to the chambers at cardiac diastole
ventricles and atria relax
where does blood flow in atrial systole
into the ventricles
where does blood flow in ventricular systole
into the aorta and pulmonary artery
where does blood flow in diastole
into the atria and ventricles
what happens to the valves at atrial systole
AV valves open
SL valves close
what happens to the valves at ventricular systole
SL valves close
AV valves open
what is the role of the valves
to ensure blood flows in the right direction.
how are the valves opened and closed
by changes in blood pressure in various chambers of the heart
what happens to the ventricular walls after systole
they relax and recoil. the pressure in the ventricles rapidly drops below the pressure in the atria
what does blood do to the AV valves
pushes them open
what happens to the pressure of the atria and ventricles as blood flows through them
it rises slowly and fills with blood
when do the valves close
they remain open while the atria contract and close when the atria relax
what causes the closure of the valves
the swirling action in the blood around the valves when the ventricle is full
what happens to the blood pressure in the ventricles as they contract
rises
when does the blood move upward from the ventricle
when the pressure in the ventricles rises above that in the atria
what keeps the AV valves closed
the movement of the blood from the ventricles back into the atria
what are the role of the tendinous cords attached to the valves
prevent the valves from turning inside out which stops blood flowing back into the atria
what happens before ventricular contraction
the pressure in the major arteries is higher than the pressure in the ventricles causing the semilunar valves to close
what does ventricular systole do the pressure of the ventricles
it raises the blood pressure very quickly
what causes the semilunar valves to push open
once the pressure in the ventricles rise above the pressure in the major arteries the SL valves are pushed open. the blood is under pressure so is forced out of the ventricles
what happens when the ventricle walls have finished contracting
the heart muscle starts to relax (diastole)
what does the elastic tissue in the walls of the ventricles do
it recoils and stretches the muscle out again and returns the ventricle to its original size.
what does the stretching of the muscle do
causes the pressure in the ventricles to drop quickly
what happens when the pressure in the ventricles drop below the pressure in the major arteries
the blood starts to flow back towards the ventricles.
how do the semilunar valves close
semilunar valves are pushed closed by the blood collecting in the pockets of the valves. this prevents blood returning back to the ventricles
what is the pulse
the pressure wave created when the left semilunar valve closes. its easily felt at the neck or wrist
what is cardiac output
the amount of blood pumped around the body
what does cardiac output depend on
stroke volume and heart rate
what is stroke volume
the volume of blood pumped by the left ventricle in each heartbeat
what is the stroke volume of an adult at rest
75ml
what is heart rate
number of times the heart beats per minute
what is the heart rate of an adult at rest
70bpm
how to work out cardiac output
stroke volume x heart rate
what is the typical resting cardiac output
4-6 litres per minute
when can cardiac output rise
up to 40 litres per minute in highly trained endurance athletes
where do electrical impulses initiate
an electrical impulse travels from the sinoatrial node to the walls of the atria causing them to contract
where does the impulse go after the SAN
it reaches the atrioventricular node which delays the impulse by 0.1 seconds
what carries the impulse from the AVN to the apex
bundle branches
how do the ventricle walls contract
the singal spreads through the ventricle walls causing them to contract
how can the sounds of the heartbeat be heard
through a stethoscope
how is the heartbeat created
made by blood pressure closing the heart valves
what does the heart sound like
lub dub
what is the “lub” sound
blood is forced against the atrioventricular valves as the ventricles contract
what is the “dub” sound
backflow of blood closes the semilunar valves in the aorta and pulmonary artery as the ventricles relax
what causes the valves to open and close
pressure changes in the heart chambers
what helps create a more even flow of blood
the structure of the artery walls
describe how the structure of the artery walls create a more even flow of blood
- the artery walls close to the heart have a lot of elastic tissue
- when blood leaves the heart the walls stretch
- as blood moves in and out the aorta, the pressure in the aorta starts to drop
- the elastic recoil of the walls help maintain the blood pressure in the aorta
- the further the blood flows along the arteries the further the pressure drops and the fluctuations are less obvious
why is it important to maintain the pressure gradient between the aorta and the arterioles
this is what keeps the blood flowing towards the tissue
when does aortic pressure rise and fall
when ventricles contract as blood is forced into the aorta. it then gradually falls but never below around 12kPa because of the elasticity of its wall which creates a recoil of action
why is a recoil of the walls important
so blood is constantly delivered to the tissues. it produces a temporary rise in pressure at the start of the relaxation phase.
why is atrial pressure always relatively low
the thin walls of the atrium cannot create much force.
when is atrial pressure at its highest
when they are contracting
when does atrial pressure drop
when the left atrioventricular valve closes and its walls relax.
what happens when the atrial walls relax
the atria then fill with blood which leads to a gradual buildup of pressure until a slight drop when the left atrioventricular valve opens and some blood moves into the ventricles
when does ventricular pressure increase
its low at first but increases as the ventricles fill with blood as the atria contracts
when does pressure rise in the ventricles
the left atrioventricular valve closes and pressure rises dramatically as the thick muscular walls of the ventricle contract
how is blood forced through the aorta from the ventricles
as the pressure rises above that of the aorta blood is forced into the aorta past the semilunar valves pressure falls as the ventricles empty and the walls relax.
what happens to ventricular volume as the atria contract
it rises. the ventricles fill with blood
