Cardiovascular Physiology Flashcards
When the SA node fires, where does it travel?
The signal spreads to both atria, then the AV node.
How does cardiac muscle function as a single unit in response to electrical stimulation?
Gap junctions within intercalated discs
How many times does each fire per minute?
- SA node
- AV node
- Inter-ventricular fibers
- 90-100x
- 40-50x
- 20-40x
Timing of excitation from SA node to AV node to the ventricles
SA node is the starting point. ~50 msec excitation spreads to both atria and down AV node.
~200msec delay at the AV node. This allows for atria to fully contract.
~50msec excitation spreads to both ventricles. Allows ventricles to fill with blood before ejection.
~300m sec total from SA node to ventricles
Explain what happens when a cardiac muscle cell receives an action potential
- Resting potential is at -90mv. Rapid depolarization due to the opening of voltage-gated Na+ channels. Na+ floods into the cell.
- Once the cell reaches peak depolarization, it will begin to repolarize due to the slow leak of K+ out of cells, making the cell more negative due to the loss of positive ions.
- Before the cell can re-polarize too much, Ca2+ channels open and allow Ca2+ into the cell. This balances the loss of K+ ions, keeping the membrane potential stable at a plateau. The plateau/refractory period is long to allow blood to fill in chambers before contraction.
- Ca2+ enters the cell and can bind to troponin and cause contraction.
- Then the cell repolarizes due to opening of K+ channels and closing of Ca2+ channels. Ca2+ is removed by active transport.
How do Ca2+ ions enter the cell
Can either be supplied by the SR or by diffusion across the cell membrane during the action potential.
What is the difference in the depolarization graphs between the SA nodal cell, Atrial cell, purkinje cell, and ventricular cell?
SA nodal cell depolarization is less abrupt than the other three. SA nodal cell does not have a plateau phase and has very fast firing. The height of depolarization only reaches 0mv.
Atrial cells, purkinje cells, and ventricular cells have abrupt depolarizations that reach +25mv and plateau phases,.
What do each represent on an EKG?
- P wave
- P-Q interval
- QRS complex
- T wave
- Q-T interval
- Atrial depolarization.
- Time from atrial to ventricular excitation. About 200ms.
- Ventricular depolarization. Masked is atria repolarization/ Atria is in diastole.
- Ventricular repolarization.
- Time from start of ventricular depolarization to repolarization.
Average heart rate
75 beats per minute
EDV- End diastolic volume
Blood volume in ventricles prior to ventricular contraction. Usually 130mL.
ESV- End systolic volume
Blood left behind after ventricular contraction.
ESV usually around 60mL.
Stroke volume
SV: EDV-ESV- 75mL
Volume of blood ejected from the heart in one beat.
Regulated by increasing or decreasing the force of contraction.
CO- cardiac output
CO= heart rate x stroke volume in L
Four stages of the cardiac cycle
- Isovolumetric ventricular contraction
- Ventricular ejection
- Isovolumetric ventricular relaxation
- Rapid ventricular filling
What occurs during stage 1 of the cardiac cycle- isovolumetric ventricular contraction?
Beginning of ventricular systole. Peak of R wave in the QRS complex. AV valves close (first heart sound) as pressure in the ventricles increase higher than the atria. Then the semilunar valves open.
