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
what occurs during the reduced ejection phase of ventricular systole?
describe the dichroic notch and T wave.
most blood already ejected (from rapid ejection)
almost 0 blood in ventricles but ventricle is still contracted
aortic pressure begins to fall as blood leaves the aorta faster than it enters, closure of the aortic semilunar valve.
transient dip in pressure due to closure of valve = dichroic notch
active contraction ceases, muscle re-polarises = T WAVE
what marks the end of ventricular systole
the atrial V wave, build up of blood (from veins)
a term associated with ventricular systole is the ESV, what does this mean?
End systolic volume = volume of blood in the ventricle at the end of ventricular systole
a term associated with ventricular systole is the EDV, what does this mean?
End diastolic volume = volume of blood in the ventricle at the end of ventricular filling
a term associated with ventricular systole is the SV, what does this mean?
stroke volume = volume of blood ejected, EDV - ESV
a term associated with ventricular systole is the EJECTION FRACTION, what does this mean?
proportion of the EDV ejected
= SV/ EDV
what are the three phases of ventricular diastole?
- isovolumetric relaxation
- rapid ventricular filling
- reduced filling
what occurs during the isovolumetric phase of ventricular diastole?
following closure of outflow valves ventricle relax rapidly
but ventricle pressure still higher than atrial pressure so valves are closed
what occurs during the rapid ventricular filling phase of ventricular diastole?
ventricular pressure falls below atrial pressure, AV valve open
atrial pressure falls rapidly –> blood into ventricle
assisted by elastic recoil of ventricular walls = sucking blood in
what occurs during reduced filling?
ventricles relax completely and filling slows
name three ways to measure the cardiac cycle
- pressure changes against time
- pressure volume loops
- volume changes against time
what do pressure volume loops describe
changes occurring in disease states that affect filling or pumping –> used to measure cardiac function
the heart is a single electrical system so mechanical events occur simultaneously on both sides,
what is the major difference between the right and left heart?
magnitude of systolic pressures
lungs have a much lower resistance to flow, therefore a decreased arterial pressure is required.
what is associated with the first heart sound?
associated with closure of AV valve
what is associated with the second heart sound?
closure of the outlet valves
what is associated with the third heart sound?
vibrations of ventricle wall due to blood entering PASSIVELY
–> generally weak and hard to hear except in horses
what is associated with the fourth sound?
occurs with atrial contractions –> hearing blood enter ventricle actively.
stiff heart in small animal –> might hear better
what is a murmur caused by?
turbulent blood flow
what can murmurs reflect?
valve defects
what is stenosis?
narrowing of the office so that flow through the narrowed orifice is turbulent
what is valve incompetence?
valve leaking when they’re closed
resulting in regurgitation of blood
what is a galloping rhythm?
a splitting of the first or second heart sound
what are some measurements of the hearts performance?
stroke volume
heart rate
cardiac output
