Cardiac cycle COPY Flashcards
What are the exchange vessels?
Capillaries
What are the capacitance vessels?
Veins
What is the function of capacitance vessels?
Act as stores of blood
enable changes in amount of blood pumped around the body as demand changes
What are the resistance vessels?
Arterioles, precapillary sphincters
What is the function of resistance vessels?
Restrict blood flow in tissues which are easy to perfuse
to drive blood flow to tissues that are more difficult to perfuse
How does the cardiac output of the right side of the heart compare to the left side of the heart?
They’re equal
What is systole?
Contraction and ejection of blood from ventricles
What is diastole?
Relaxation and filling of ventricles
What is the pressure in the left atrium?
8-10mmHg
What is the pressure in the LV?
120/10mmHg
What is the pressure in the aorta?
120/80mmHg
What is the pressure in the right atrium?
0-4mmHg
What is the pressure in the RV?
25/4mmHg
What is the pressure in the pulmonary artery?
25/10mmHg
How do the pressures of the systemic and pulmonary circulations compare to each other?
Systemic circulation at high pressure
Pulmonary circulation at low pressure
What is stroke volume?
Amount of blood ejected from the LV per heart beat
What is the average stroke volume?
70ml
At a heart rate of 70bpm, what is the cardiac output? What is the signifiance of this?
5L/min
Equivalent to blood volume in body
What is the arrangement of heart muscle?
Like the figure 8
Which valves are tricuspid - have three cusps?
Aortic valve
Pulmonary valve
Tricuspid valve
Which valve is bicuspid - has two cusps?
Mitral valve
What do the cusps of the mitral and tricuspid valves attach to? Via what?
Attach to papillary muscles
via chordae tendinae
What is the function of the papillary muscles and chordae tendinae?
Prevent inversion of valves during systole
What are the phases of the cardiac cycle?
Atrial contraction Isovolumetric contraction Rapid ejection Reduced ejection Isovolumetric relaxation Rapid filling Reduced filling
Which phases form diastole?
Isovolumetric relaxation
Rapid filling
Reduced filling
Atrial contraction
Which phases form systole?
Isovolumetric contraction
Rapid ejection
Reduced ejection
If the cardiac cycle is 0.9s long, how long is systole? How long is diastole?
Systole = 0.35s
Diastole = 0.55s
What is heart rate?
Number of cardiac cycles per minute
A change in heart rate is accommodated by change in duration of systole or diastole?
Diastole
What is a Wiggers diagram?
Shows changes in pressure, volume, electrical activity, sound
during the cardiac cycle
How does a Wiggers diagram of the right side of th eheart compare to that of the left side of the heart?
Very similar
except right side is at lower pressures
What happens in atrial contraction?
P wave on ECG - atrial depolarisation
A wave - increase in atrial pressure
Ventricular volume increases to EDV
Atrial contraction accounts for what percentage of ventricular filling?
10%
What is EDV?
End diastolic volume
Volume in left ventricle at end of diastole
What is the average EDV?
120ml
What happens in isovolumetric contraction?
Ventricular pressure increases - ventricle contracting
C wave - atrial pressure increases due to closure of mitral valve
QRS complex in ECG - ventricular depolarisation
S1 sound - closure of mitral valve (tricuspid valve too)
Why is it called isovolumetric?
Both valves are closed
no change in volume of blood in left ventricle
What happens in rapid ejection?
Ventricular pressure increases - ventricle contracting
Aortic valve opens - ventricular pressure exceeds aortic pressure
Aortic pressure increases - filling with blood from ventricle
X descent - atrial pressure decreases as base pulled down
Ventricular volume decreases - ventricle ejecting blood into aorta
What happens in reduced ejection?
Ventricular pressure decreases - repolarisation of ventricle
Aortic pressure decreases - less filling with blood from ventricle
V wave - atrial pressure increases as it fills with blood
ESV - end systolic volume, volume of blood in ventricles at end of systole
T wave on ECG - ventricular repolarisation
What hapens in isovolumetric relaxation?
Ventricular pressure decreases - ventricles relax
Aortic valve closes - aortic pressure exceeds ventricular pressure, backflow of blood, valve closes
Dicrotic notch - increase in aortic pressure, walls of aorta pulled inwards as valve closes
S2 sound - aortic valve closure (pulmonary valve too)
What is the average ESV?
40ml
How is stroke volume calculated?
SV = EDV - ESV
What happens in rapid filling?
Mitral valve opens - atrial pressure exceeds ventricular pressure
Y descent - atrial pressure decreases as it empties of blood
Ventricular volume - increases as ventricle fills with blood from atria
S3 sound - ventricular filling
How does blood fill the ventricles from the atria?
Passively
When is the S3 sound normal? When is it a sign of pathology?
Normal in children
Sign of pathology in adults
What happens in reduced filling?
Diastasis - ventricules reach their max. relaxed volume, 90% of EDV
How do the walls of the right and left ventricles compare to each other? Why?
Left ventricle has thicker wall than right ventricle
because it needs to withstand higher pressures
