Lecture 9: The Excitable Heart

Question 1

Put it all together 🙃

Answer 1

1. the First event is the sinoatrial node fires the signal that depolarises the left and right atrium. Atrial depolarisation is assocaited with the P wave. Right after the P wave, atrial and ventricular pressure increases. Ventricular volume increases as well as it fill with blood. AV valves are open so the blood can flow. Aortic and pulmonary valves are closed.
2. Next is the isovolumetric ventricular contraction phase. AV valves have closed and this makes “lubb sound”. Depolarisation moves from AV node down into the ventricles. Depolarisation of the ventricles, as well as repolarisation of the atria, makes up the QRS complex. This causes an extremely rapid increased pressure in the ventricles as both valves are closed. Ventricular volume doesn’t change at this point.
3. Ventricular ejection phase. Eventually ventricular pressure increases and it reaches aortic pressure. Once the pressure exceeds aortic pressure, the aortic and pulmonary valves burst open and blood is pushed out of the ventricles and through the aortic and pulmonary arteries. This results in an increased aortic pressure and ventricular for as long as they can to get all the blood out. During this time ventricular volume decreases rapidly.
4. Now it goes back to where it started so is time for isovolumetric relaxation phase. Aortic and pulmonary valves close (dupp sound) and the blood left in the ventricles is trapped. The ventricle walls relax by repolarisaing which is the T wave. Now that there is a small amount of liquid with relaxation occuring, it causes the pressure in the ventricles to go so low it is lower than atrial pressure.
5. After this the AV valves open back up and passive filling phase occurs. The ventricles fill back with blood so it is ready for its next contraction.