Lecture 9 Flashcards
What does the P wave indicate on the ECG?
Atria depolarising
What phase begins during the P wave?
Atrial systole
describe the action isovolumetric contraction phase?
Atria will repolarise and ventricles depolarise
The isovolumetric contraction phase is associated with which ECG phase?
QRS wave
Which valves shut during the QRS wave?
AV valves
What causes the Lubb sound?
The shutting of the AV valves?
What causes the large QRS spike in the ECG?
Atrial repolarisation and venturicular depolarisation
What causes blood to flow out of the ventricle?
The semilunar valves open when the pressure in the ventricles is greater than the pressure in the aorta
Ventricular ejection phase pressure rises because?
The blood volume drops but the pressure rises because the ventricles are squeezing blood
What causes the semilunar valves to close?
Pressure in ventricles fall
What causes the second heart sound?
The semilunar valves close, Dupp
What phase of the cardiac cycle causes the T wave?
Isovolumetric ventricular relaxation
Where does depolarisation start?
Sinoatrial node (SAN)
What is the sinoatrial node?
A couple thousand very small cells. The SAN acts as a pacemaker and tells the heart when to beat
How does the signal spread to neighbouring conduction cells?
Gap junctions
How does the impulse spread between both types of cardiac cells?
Intercalated disks and gap junctions
What do intercalated disks connect?
Most cells of the heart
What are gap junctions?
Pores with low resistance to ionic current. Allowing current flow between adjacent cells
Gap junctions can spread the impulse to?
Along the conduction pathway
between electrical and contractile cells
between contractile cells
For the heart to beat millions of cardiac cells have to behave as?
One function synctium
The conduction pathway begins at?
The sinoatrial node
From the sinoatrial node the conduction pathway splits into?
The left and right atrium causing depolarisation of the atrium
and the internal bundle to the Atrioventricular node
The atrioventricular node sends an impulse through the AV bundle which branches into?
The right and left ventricle causing contraction using purkinje fibres in the lateral walls
Why is the SAN known as the pace maker?
because it tells the heart when to beat
What is the function of the atrioventricular node?
To collect the electrical signal from the internodal bundle and put a pause on it before sending it along.
Why does the atrioventricular node put a pause on the signal ?
The delay is essential as it means the atria have enough time to contract and fill the ventricles
What is quiescence?
When the heart is fully relaxed and not depolarising or depolarising
What is the first part of the excitation and conduction pathway?
Excitation spreads from the SA node
What is the order of the conduction pathway?
excitation from the SA node Atria full depolarise and contract Atria repolarise and AV node sends excitation to ventricles Ventricles depolarise and contract Ventricles repolarise and relax
What is the P wave?
atrial repolarisation
What is the QRS wave?
Ventricular depolarisation and atrial repolarisation
What is the T wave?
ventricular repolarisation
What does depolarisation cause?
Contraction
What does repolarisation cause
Relaxation
A large spike in pressure indicates which phase of the cardiac cycle?
Isovolumetric contraction phase
