Lecture 17 - The Cardiac Cycle Flashcards
What causes a valve to open
When the pressure behind it is greater than the pressure in front of it
What do the valves prevent
Backflow of blood
What are the 5 phases of the cardiac cycle
Phase one - passive filling
Phase two - atrial contraction
Phase three - isovolumetric ventricular contraction
Phase four - ejection
Phase five - isovolumetric ventricular relaxation
What are the heart sounds generated by
The closing of the valves
What is used to detect the heart sounds
A phonocardiogram
What does the first heart sound coincide with
The beginning of systole
What produces the first heart sound
Closure of the AV valve
What does the second heart sound coincide with
The onset of diastole
What is the second heart sound produced by
Closure of the aortic and pulmonary valves
Abnormal heart sounds in pathological conditions are known as
Murmurs
What happens to the pressure of the atria and ventricles during phase 1
The ventricular pressure falls below the atrial pressure
What happens when the ventricular pressure falls below the atrial pressure
The AV valves open
What happens during phase one
Blood which entered the atria during ventricular systole is released into the ventricles
When blood starts to move into the ventricles what happens to the pressure within the heart chambers
The atria and ventricular pressure fall rapidly
What % of the final filled volume do the ventricles contain at the end of phase one
80%
Are the aortic and pulmonary valves open or closed during phase one
Closed
Phase one is equivalent to what on the ECG
TP interval
During mid-diastole what blood is flowing into the atria
Blood from the venous system
What occurs during phase two
The SA node produces an AP so the atrial muscle cells are stimulated to depolarise
What is late diastole represented by on the ECG
The P wave
What happens towards the end of the P wave
The atrial contract, increasing atrial pressure
What happens when the atria contract
Most of the blood is propelled into the ventricle and ventricular pressure increases slightly
Volume in each ventricle at the end of diastole is
Roughy 130ml for standing and 160ml for lying down
Are the AV valves open or closed at the end of phase two
Open
What marks the end of diastole
The beginning of ventricular contraction
What happens to the AP after atrial contraction
It is conducted to the ventricular muscle
What is formed on the ECG when ventricular muscle is stimulated
The QRS complex
What happens to the ventricular pressure during phase 3
There is a rapid increase in ventricular pressure
What does the rapid increase in ventricular pressure cause
The AV valves to snap shut
Are the aortic and pulmonary valves open during phase 3
No
Why is phase three known as the isovolumetric stage
As all the valves are shut so no blood can flow in or out of the ventricles
When will the aortic valves open
Only when the pressure of the ventricles exceeds the pressure in the aorta
What happens during phase four
The ventricular pressure exceeds the aortic pressure and the aortic and pulmonary valves open
What is the diastolic pressure of the aorta
80mmHg
What is the systolic pressure of the aorta
120mmHg
What is the diastolic pressure of the pulmonary artery
8 mmHg
What is the systolic pressure of the pulmonary artery
25 mmHg
What is phase 5 represented by on the ECG
The T wave
What does the T wave show
Ventricular repolarisation
What occurs during phase 5
The end of ventricular systole. The ventricular muscle is starting to relax
What occurs to ventricular pressure during phase 5
It starts to fall below atrial pressure
What does the diacritic notch show
The ventricular pressure falling below atrial pressure
What valves are shut during phase 5
AV, aortic and pulmonary valves
