Lecture 9 Heart Physiology Flashcards
Electrical cells of heart
1%
Pale striated appearance
Low actin and Myosin
Contractile cells of heart
99%
Striated appearance
High actin and Myosin
Action potentials spread (propagate) along the..
Surface membrane of electrical and contractile cells.
Where does depolarization start?
sinoatrial node (SAN). This signal spreads to neighbouring cells.
In a contractile cell:
increased cytosolic Ca2+ level, X-bridge attachment and contraction
What connects cardiac cells together?
Intercalated disks and gap junctions.
Intercalated discs connect
most cells of the heart.
Gap Junctions consists of
Pores with low resistance to ionic current.
Allows current flow between adjacent cells.
Connect electrical cells
Connect contraction cells
Connect electrical cells and contraction cells
why don/t Contractile cells communicate the signal quickly?
High actin and myosin
Functional syncytium
Individual cells work as a unit.
communicate using gap junctions
SA node (sinoatrial)
where signal begins to tell the heart to beat (contract)
sits above right atrium
where does the SA node signal go?
3 directions
right atrium
left atrium
AV node
Right atrium receives signal from SA node to..
contract
Left atrium receives signal from SA node to..
contract
Why and How does the SA node signal get to the left atrium?
Both atriums have to contract simultaneously
Goes across the interatrial bundle
How does the SA node get to the AV node?
through internodal bundles
Internodal bundles
Connects the SA (sinoatrial) node and AV (atrioventricular) node
AV node (atrioventricular) (what it does, where does the signal go)
Between right atrium and right ventricle
Collects signal from SA node and holds signal (pause)
Paused signal is passed to the AV bundle
Why does the AV node have to hold the signal from SA node?
both the atria need to contract first before the ventricles contract.
No pause will result in contraction of atrium and ventricles at same time and blood will be pushed all around the place in the heart.
AV bundle (what it does, where does the signal go?)
Runs through the centre wall of heart ( septum)
Branches into 2 different directions to the left and right side of heart.
Purkinje fibres
Purkinje fibres
Brings signal back up through the ventricular wall
Signal is sent to contractile cells along the wall which causes ventricles to contract.
Why do the purkinje fibres bring the signal back up through the ventricular wall?
Get the maximum amount of blood from the ventricle.
Excitation and conduction pathway
Quiescence
P wave (1st phase)
P - R interval
QRS complex (3rd phase)
R - T interval
T wave (5th phase)
Straight period after T wave (6th phase)
Quiescence
straight line no electrical signal
heart is filling with blood
Ready to contract
P wave (1st phase)
SA node fires
Left and right atria is depolarizing
P - R interval
Straight period in between P wave and QRS complex (2nd phase)
Atria fully depolarized (and contracting)
Signal finished
AV node is holding the signal not allowing anything else to depolarize
QRS complex (3rd phase)
signal from AV node released
Repolarization of Atria
Depolarization of ventricles
R - T interval
Straight period between QRS complex and T wave (4th phase)
Ventricles fully depolarized
Atria fully repolarized
T wave (5th phase)
Repolarization of ventricles
Straight period after T wave (6th phase)
Ventricles fully repolarized
Ready to go back to quiescence
2 heart sound
lubb (1st)
Dupp (2nd)
associated with snapping shut valves
ECG
electrocardiogram.
pressure in atria, ventricles, aorta.
Initiate contraction
SA node fires Sends an electrical signal
Depolarizion of right and left atrium (contraction)
P wave
Atrial Systole (contraction) phase
P wave
Both atria contract
AV valves open
Semilunar valves close (aortic and pulmonary)
AV node holds signal
Increase atrial pressure
Increase ventricular volume
Isovolumetric ventricular contraction phase
QRS complex
AV valves close
Semilunar valves close (aortic and pulmonary)
Blood volume of ventricles remain same
Increase Ventricular pressure
Atria repolarizes
Ventricles depolarize
Ejection phase
Between QRS complex and T wave
Semilunar valves burst open (aortic and pulmonary)
Pressure pushes blood from ventricles into the Aorta and Pulmonary artery
Pressure in ventricles still continue to increase
Aorta pressure increases
Isovolumetric ventricular relaxation phase
T wave
AV valves close
Semilunar valves close
ventricles repolarize
Pressure in ventricles decrease (steep)
Blood volume in ventricles constant
Quiescence phase
Period after T wave
AV valves open
Passively refill ventricles with blood
Blood volume in ventricles increase
Pressure in ventricles low
Ready for next heart beat
