CVS - Cardiac Cycle Flashcards
How do heart muscle cells generate a synchronised contraction?
The action potential passes from cell to cell via the cell membranes. One electrical event triggers the action potential excitation from cell to cell.
What type of cells are cardiac muscle?
Branched usually singly nucleated cells.
Discrete cells that are connected electrically.
What are pacemakers?
These are cells that generate one action potential at regular intervals. This spreads all over the heart. They are connected to contractile cells via gap junctions. The primary pacemaker in the heart is SAN.
What is the spread of excitation in the heart?
SAN sends action potential over the atria causing atrial systole to reach the AVN. Once it reaches the AVN it is delayed for 120ms. From the AV node the AP spreads down the septum between the ventricles. Then spreads through the ventricular myocardium from inner (endocardial) to outer (epicardium)
How do the ventricles contract?
From apex up
How long does systole last?
280ms
How long does diastole last?
700ms
What are the name of the AV valves?
Right - tricuspid
Left - mitral
When do the av valves open?
When atrial pressure is higher than intraventricular pressure
When do the av valves close?
When the intraventricular pressure rises above the atrial pressure. Some blood regurgitates back into the atria - this causes the valves to close.
What are the outflow valves?
Right - pulmonary valve
Left - aortic valve
What causes the lup sound?
The av valve closing at the start of ventricle systole.
What causes the dup sounds
The closing of the aortic valve at the end of systole.
When is ventricular pressure highest?
At the ejection of blood. 120mmHg
What causes a murmur?
The turbulent flow of blood.
