The heart as a pump Flashcards
where is the heart located?
within a fluid filled membrane sac called the pericardium
what is the inner lining of the pericardium
epicardium
what is the walls of the heart that are composed of muscle cells called?
myocardium (composed of myocytes)
what is the in surface of walls that is in contact with blood?
the endocardium
what prevents back flow from the ventricles back to the atrium?
atrio-ventricular valves
what is the right and left AV valve called?
Right - tricuspid
Left - mitral
what prevents backflow from the pulmonary trunk into the right ventricle?
pulmonary valve
what prevents the backflow from the aorta into left ventricle?
aortic valve
what are the two phases following a single heart beat?
contractile (systole)
relaxation filling phase (diastole)
what is cardiac ejection fraction?
the amount of blood ejected per min
stroke volume (left ventricle contraction)
how can you calculate stroke volume?
end diastolic volume - end systolic volume
what does ejection fraction depend on?
volume, heart chamber dimensions, ventricular heart rate, valve function, preload and afterload
what is preload?
the pressure of the blood on the ventricles at the end of diastole
what is afterload?
the pressure in the wall of the left ventricle during ejection
where does the depolarisation stimulus for the normal heartbeat originate?
sinoatrial node (SA)
- collection of pacemaker cells
- fire spontaneously
- exhibit automaticity
where do nerve cells terminate in the heart?
the SA node
what is the control of heart rhythm?
- pacemaker generates wave of signals to contract (SA node)
- signals delayed at AV node
- Signals pass to heart apex
- signal spread through ventricles
What are the different stages of a ECG wave?
first bump = atrial events (P wave)
QRS - ventricular events
T waves - repolarisation
what is the normal sinus rhythm?
60-100bpm
what is the frequency of the heartbeat and hr regulated by?
input from the autonomic nervous system
what is the intrinsic rate of the SA node in the absence of any input?
90-100 bpm
How can cardiac myocytes be described?
electrically excitable
what is the resting intracellular voltage of myocardial cells?
-90mV
how does an action potential occur?
when Na enters the cell and sets up a depolarisation current
