Cardiac Cycle Flashcards
What are the typical pressure values for the left side of the heart?
Atrium 7-10mmHg,
Ventricle 120-10mmHg.
What are the typical pressure values for the right side of the heart?
0-4mmHg Atria, ventricles 25-4.
State the difference in pressure between the aorta and the pulmonary artery.
Pressure in the pulmonary circulation is significantly lower. Pulmonary 25/10, systemic 120/80
What is systole?
This is the contraction and ejection of blood from the ventricles. It begins when the ventricles begin to contract and finishes when they relax after the aortic/pulmonary valves have closed.
What happens during diastole?
Relaxation of the heart and filling of the ventricles
What is stroke volume?
This is the amount of blood pumped out of the heart with each beat
Describe cardiac myocytes contraction.
Heart muscle cells are specialised and connected electrically. In response to an AP, there is an increase in intracellular calcium which causes contraction.
How long is the cardiac action potential?
Approximately 280ms.
What determines if a valve is open or closed?
The pressure differences in either side of them.
What structures strengthen the heart valves?
Chordate tendineae which are attached to papillary muscles in the base of the ventricles to prevent valve inversion on ventricular contraction.
Where does the AP initiate from in the heart?
Pacemaker cells in the SAN. This depolarisation spreads over the atria and pauses at the AVN for approx 120ms. It then passes down the bundle of his and into the purkinje fibres and contraction occurs from outside to inside.
What is isovolumetric contraction/relaxation?
This is two stages in the cardiac cycle during which all valves are closed and so there is no change in volume of blood in the ventricles but the pressure is decreasing/increasing.
What valves are open/closed during atrial contraction?
The mitral and tricuspid valves are open and the aortic and pulmonary valves are closed.
When in the cardiac cycle is the first heart sound heard? What is observed on an ECG at this point?
It is heard after atrial contraction at the beginning of isovolumetric contraction when the M/T valves close. At this point depolarisation is spreading over the ventricles and so the QRS complex is seen.
What is diastasis?
This is where there is reduced filling of the ventricle because it is already at its inherent relaxed volume.
