2.6- structure and function of the heart Flashcards
what are the 4 chambers of the heart?
two atria
two ventricles
describe the flow of blood to and from the heart
body sends deoxygenated blood through the vena cava and to the right atrium
right atrium flows deoxygenated blood into the right ventricle
right ventricle sends deoxygenated blood through the pulmonary artery to the lungs
lungs send oxygenated blood through the pulmonary veins and to the left atrium
left atrium flows oxygenated blood into the left ventricle
left ventricle sends oxygenated blood through the aorta and into the body
where do the 2 branches in the pulmonary artery lead?
lungs
what is the largest vein in the body?
vena cava
what is the largest artery in the body?
aorta
what are the 2 different valves in the heart called?
atrioventricular valves
semi-lunar valves
where are the atrioventricular valves located and what is their purpose?
between the atria and ventricles
allow blood to flow from atria to ventricles and prevent backflow from ventricles to atria
where are the semi-lunar valves located and what is their purpose?
situated at the origins of the pulmonary artery and aorta
open during ventricular contraction allowing blood to flow into the arteries
when do semi-lunar valves close and why?
when arterial pressure exceeds ventricular pressure
close to prevent backflow
what is heart rate?
the number of heartbeats that occur per minute
what is stroke volume and what can make it greater?
the volume of blood expelled by each ventricle on contraction
the stronger the contraction
what is cardiac output?
the volume of blood pumped out of a ventricle per minute
how is cardiac output calculated?
cardiac output= heart rate X stroke volume
what is the cardiac cycle and what is its average length?
pattern of contraction and relaxation in the heart during one complete heartbeat
0.8 seconds
4 steps of the cardiac cycle stage 1
DIASTOLE
return of blood via the venae cavae and pulmonary veins to the atria
this causes the volume of blood in the atria to increase
eventually atrial pressure exceeds that in the ventricles
this pushed the AV valves open and blood starts to enter the ventricles
4 steps of the cardiac cycle stage 2
ATRIAL SYSTOLE
two atria contract simultaneously
they send the remainer of the blood down into the ventricles through open AV valves
ventricles are still in the relaxed state of ventricular diastole
they fill up with blood and the SL valves remain closed
4 steps of the cardiac cycle stage 3
VENTRICULAR SYSTOLE
ventricles contract and AV valves close
as the cardiac muscle contract, the pressure exerted on the blood in the ventricles soon exceeds the blood pressure in the arteries
SL valves pushed open and blood pumped out heart and into aorta and pulmonary arteries
DIASTOLE
higher pressure of blood in the arteries closes SL valves again and next cardiac cycle starts
what sounds can be heard with the help of a stethoscope from the heart?
closing of the AV and SL valves during each cardiac cycle
what is a pacemaker also known as?
sino-atrial node (SAN)
where is the sino-atrial node located and what does it do?
in the wall of the right atrium
sets the rate at which the heart contracts
what does the sino-atrial node do and what does this mean?
it exhibits spontaneous excitation
pacemaker initiates electrical impulses making cardiac muscles contract at a certain rate
how does the sino-atrial node work and what can it function without?
works automatically
function without nerve connections from the rest of the body
what is spread that originates from the SAN and what does this do?
a wave of excitation through the muscle cells in the wall of the 2 atria
makes 2 atria contract simultaneously (atrial systole)
what picks up this wave of excitation and where is it passed to?
atrio-ventricular node located centrally near the base of the atria
bundle of conducting fibres which divides into left and right continuous branches
