Lecture 6: The Cardiac Cycle Flashcards
What is the Cardiac Cycle?
sequence of co-ordianted electrical and mechanical events that ensures effective cardiac pump function
what occurs during systole?
contraction
what occurs during diastole?
relaxation
what are the two atrioventricular heart valves? where are they located?
b/w the atria and ventricles
L side = mitral (Bicuspid)
R side = tricuspid
what are the outlet valves and where are they located?
b/w the ventricles and the major arteries
right heart = pulmonary semilunar
left heart = aortic semi lunar
are there valves between the atria and the great veins?
NO
describe the moment of valves ie/ when does a valve open/shut?
valve movement = passive
opens when pressure in the proximal chamber exceeds pressure in the distal chamber
what is the role of papillary muscles in reference to valves?
do not help close valvular orifice
prevent excessive bulging of valves into atrial chambers during ventricular contraction
what initiates contraction and the first step of the cardiac cycle?
SA node
p wave of atrial depolarisation
what is the second stage of the cardiac cycle?
atrial systole - contraction of the atria completes ventricle filling
what is the a wave of an ecg and why does it occur during stage one of the cardiac cycle?
there are no valves between the atria and the great veins therefore some regurgitation occurs
a wave of venous pressure reflects atrial systole
how much blood does atrial contraction provide the ventricles at rest.
only about 20% active contraction
up to 80% of ventricular filling occurs due to venous pressure not the active contraction –> ventricle suck blood in
as heart rate increases, atrial contribution increases as there is less time for the heart to be in diastole and fill
what are the three phases of ventricular sysotle
- isovolumetric contaction
- rapid ejection
- reduced ejection fraction
describe what occus during isovolumetric contraction (ventricular systole)
describe the C wave during isovolumetric contraction
valve closed, pressure increases, no volume change.
the onset of ventricular systole causes increase in ventricular pressure.
depol associated with QRS
rise in pressure causes AV valve to close, pressure in ventricle still higher than in aorta so semilunar valves budge into the atria = C WAVE
what occurs during rapid ejection during ventricular systole
ventricular pressure increases above diastolic arterial pressure
semilunar valves OPEN –> blood up into arteries
initially very rapid about 50% of the blood