The cardiac cycle Flashcards
What are the two processes in LV contraction?
- Isovolumic contraction
- Maximal ejection
How does the left ventricle contract?
- Depolarisation causes Ca2+ to arrive at contractile proteins
- LV pressure rises above the LA pressure
- Mitral valve closes (first heart sound)
- LV pressure rises (Isovolumic contraction) > aortic pressure
- Aortic valve opening and ejection begins
How does the LV relax?
- LV pressure peaks and then rapidly decreases due to ejection
- Calcium in cytoplasm taken ip into sarcoplasmic reticulum
- Reducing ejection phase
- LV pressure < aortic pressure so aortic valve closes (second heart sound)
- Isovolumic relaxation and mitral valve opens
How does ventricular filling take place?
- LV pressure < Atrial pressure and MV opens
- Rapid filling (ventricular suction/active relaxation helps filling)
- filling temporarily stops when LV pressure = LArterial pressure
- filling renewed when arterial contraction booster rises LA pressure
What happens during the P wave (ECG)?
- Depolarisation of SAN
- This is not the contraction of the atrium.
- Ventricles relax and mitral valve open. After p wave you have atrial contraction, LA empties into LV and pressure of LA lowers. Although LV fills up with blood, it dilates so the pressure is still lower than LA and prevents blood from going back into LA.
What happens during the QRS complex?
- Depolarisation of ventricle 40msec
- Blood fills LV and mitral valve closes as LV gets full.
- Aortic valve closed.
- Isovolumic contraction begins- same volume but pressure increases as the volume is squeezed and creates pressure of 120mmHG.
- This contraction allows aortic valve to open and the pressure is lower than the LV pressure so blood is emptied into the aorta at high speed.
- The moment blood is ejected into the aorta is the end of isovolumic contraction because the volume is no longer the same. - Isovolumic contraction then ejection.
What happens during the T wave?
- Repolarisation of the ventricle
- Ventricles are still contracting, however the ejection starts to decrease and there is a fall in pressure
- ATP hydrolysis breaks bond of Ca++ TnC and muscles relax
- Pressure drops down to 80mmHG and aortic valve closes
- 25% of volume still left in LV and pressure continues to decrease
- This is known as isovolumic relaxation and goes down to 0mmHg
What happens after the T wave (filling)?
- During this time LA has been filling up with blood and as it becomes full, pressure is increased from 0-12mmHg and forces mitral valve to open.
- Blood rushes into LV- early filling phase (still in diastole) which is responsible for 85-95% of blood that fills the ventricle. We do not rely on atrial contraction for survival.
- Atrial pressure decreases and ventricular pressure starts to increase.
- There is a period of equal pressure between LA and LV and blood rushes to and from each side- called diastasis (stagnation).
- Ventricles are in relaxation phase but pressure increases as blood fills.
- P wave arrives and leads to SAN depolarisation, LA depolarisation and contraction which fills the ventricle with the remaining 5-15% of blood.
When is systole physiologically and clinically/cardiology?
Physiologically- systole is both isovolumic contraction and ejection
Clinically/cardiology - it is between 1st and 2nd HS M1-A2
When is diastole physiologically and clinically/cardiology?
Physiologically- Diastole starts before A2 then isovolumic relaxation. After you get the filling process.
In cardiology it is A2-M1.
What is the preload?
Preload: Load before ventricular contraction
What is the afterload?
Afterload: load after ventricle starts to contract
What causes the preload to increase?
Preload increases with a leaky mitral valve, blood can go back up the atrium, therefore on the next beat your preload would have normal filling plus what went back to atrium. Ventricle needs to raise pressure in order to overcome resistance (the volume that needs to be pumped), so ventricular wall thickens (hypertrophy).
What is Starling’s Law?
The larger the volume of the heart, the greater the energy of its contraction and amount of chemical change at each contraction
(Positive ionotropic effect)
What is the Force-Length interaction?
Decrease in length of sarcomere results in a lower maximal force produced. Cardiac sarcomere at 80% of its optimal length, it only has 10% of its maximal force.
