7.5- THE CARDIAC CYCLE Flashcards
How many times does the human heart undergo a sequence of events each minute when at rest?
sequence of events that’s repeated around 70 times each minutes when at rest
What is the sequence of events that the heart undergoes called?
cardiac cycle
What are the two phases to the beating of the heart?
contraction (systole)
relaxation (diastole)
How does contraction occur separately?
occurs separately in ventricles + atria
As contractions occurs separately in ventricles + atria, how many stages is it described in?
in two stages
For some of the time, how does relaxation take place?
relaxation takes place simultaneously in all chambers of heart
Through where does blood return to the atria of the heart? (2) (diastole)
through pulmonary vein (from lungs) vena cava (from body)
What rises as the atria fill? (diastole)
as atria fill, pressure in them rises
What happens when the pressure in the atria exceeds that in the ventricles? (diastole)
atrioventricular valves open allowing blood to pass into ventricles
What is the passage of blood from atria to ventricles aided by? (diastole)
aided by gravity
When blood passes from the atria to ventricles, how are the muscular walls of the atria + ventricles? (diastole)
muscular walls of atria + ventricles relaxed at this stage
What does the relaxation of the ventricle walls cause? (diastole)
causes them to recoil + reduces pressure within the ventricles
When the ventricle walls relax + reduces pressure within the ventricles, what is the pressure in the ventricles like in comparison to that in the aorta + pulmonary artery? (diastole)
pressure lower than in the aorta + pulmonary artery
As the pressure in the aorta + pulmonary artery is higher when the muscular walls of ventricles relax, what happens? (diastole)
semi-lunar valves in aorta + pulmonary artery closes, accompanied by characteristic ‘dub’ sound of heart beat
What forces the remaining blood into the ventricles from the atria, after diastole? (atria systole)
contraction of atrial walls, along with recoil of relaxed ventricle walls
How are the muscle of the ventricle walls throughout this stage? (atria systole)
throughout this stage muscle of ventricle walls remains relaxed
Why is there a short delay after atrial systole? (ventricular systole)
to allow ventricles to fill with blood
What happens after the short delay to allow ventricles to fill with blood? (ventricular systole)
ventricle walls contract simultaneously
What happens when the ventricle walls contract simultaneously? (ventricular systole)
increases blood pressure within them, forcing them to shut atrioventricular valves + preventing backflow of blood into atria
What is the ‘lub’ characteristic of the heart beat? (ventricular systole)
valves closing
What happens with the atrioventricular valves closed? (ventricular systole)
pressure in ventricles rises further
What happens once the pressure in the ventricles exceed that in the aorta + pulmonary artery? (ventricular systole)
blood forced from ventricles into vessels
What sort of walls do the ventricles have? (ventricular systole)
thick muscular walls
What does it mean as the ventricles have thick muscular walls? (ventricular systole)
means they can contract forcefully
As the ventricles have thick muscular walls that can contract forcefully, what does this mean? (ventricular systole)
creates high pressure necessary to pump blood around body
Where does the thick wall of the left ventricles have to pump blood? (ventricular systole)
has to pump blood to extremities of body
Where does the relatively thinner wall of the right ventricle have to pump blood to? (ventricular systole)
has to pump blood to lungs
How is blood kept flowing in one direction through the heart + around the body?
by pressure created by heart muscle
From what region will blood to?
blood will always move from region of higher pressure to one of lower pressure
What is used in circumstances where pressure differences would result in blood flowing in opposite direction from that which is desirable?
valves used to prevent any unwanted backflow of blood
What are valves in the cardiovascular system designed to do?
open whenever difference in blood pressure either side of them favours movement of blood in required direction
When are valves in the cardiovascular system designed to close?
when pressure differences reversed, that is, when blood would tend to flow in opposite direction to that which is desirable
Examples of valves in the cardiovascular system? (3)
atrioventricular valves
semi-lunar valves
pocket valves
Where are the atrioventricular valves?
between left atrium + ventricle and right atrium + ventricle
What do the atrioventricular valves do?
prevent backflow of blood when contraction of ventricles means ventricular pressure exceeds atrial pressure
What does the closer of the atrioventricular valves ensure?
ensures that when ventricles contract, blood within them moves to aorta + pulmonary artery rather than back to atria
Where are the semi-lunar valves?
in aorta + pulmonary artery
What do the semi-lunar valves do?
prevent backflow of blood into ventricles when pressure in aorta + pulmonary artery exceed that in ventricles
When does the pressure in aorta + pulmonary artery exceed that in the ventricles? (semi-lunar valves)
when elastic walls of aorta + pulmonary artery recoil, increasing pressure within them
and when ventricle walls relax reducing pressure within ventricles
Where are the pocket valves?
in veins that occur throughout the venous system
What do the pocket valves ensure?
ensure that when veins squeezed, e.g. when skeletal muscles contract, blood flows back towards heart rather than away from it
What are the valves made up of?
number of flaps of tough, but flexible, fibrous tissue, which are cusp-shaped
What happens when the pressure is greater on the convex side of the cusps rather than the concave side? (valves)
they move apart to let blood pass between cusps
What happens when pressure on concave side than on convex side? (valves)
blood collects within ‘bowl’ of cusps
this pushes them together to form tight fit that prevents passage of blood
What sort of circulatory system do mammals have?
closed circulatory system
What does it mean to have a closed circulatory system?
blood confined to vessels
What does blood being confined to vessels in a closed system allow?
pressure within them to be maintained + regulated
What is cardiac output?
volume of blood pumped by one ventricle of heart in one minute
What unit is cardiac output usually measured in?
dm3min-1
What two factors does cardiac output depend on?
heart rate (rate at which heart beats) stroke volume (volume of blood pumped out at each beat)
What is the equation for cardiac output?
heart rate * stroke volume
