Physiology L03
Slide#65:
-Diagrams on the right show the action potential form in each region that the
electrical activity passes through.
-different forms is due to that: different tissues in the heart have different ionic
channels present.
-This all happen at the cellular level, but in clinic practice, how do we measure
this?
Slide#66:
-by ECG (ElectroCardioGram) , electrical currents that happen in the heart, are
translated on the surface of our body.
-The physicians put electrodes on the two arms and 6 electrodes across the
chest and through that they measure the movement of action potential, then
take the different directions of action potentials they measured and group them
together to understand what happens in the heart while it is beating.
-By looking to that ECG, they can determine whether the person has any
blocked artery. They use it to identify any abnormality of the heart.
Slide#67:
-Atrial repolarization is hidden beneath QRS which is the depolarization of the
ventricles.
-Remember: AV node slows the action potential to make sure of filling the
ventricle and emptying the atrium.
-Contraction of the heart occurs in ST segment = plateau phase. ST phase is the
time between depolarization and repolarization.
Slide#68:
-At step 3 : the action potential reached the AV node and began to spread
through the ventricles.
-Repolarization of atria and depolarization of ventricles occur in the same time.
-At step 5 = T wave.
Slide#69:
-If there is a problem in AV node, the QRS will be delayed in ECG.
- T wave is large because the ventricles are thick tissues and thus take more
time to repolarize.
Slide#73:
-Remember: movement of blood in all parts of the heart is from higher to lower
pressure.
Slide#74: back to slide#14.
Slide#75:
-Passive ventricular filling: means by method we discussed in slide#20.
-Most of filling occurs because of the pressure differences, only 20% of the
filling occurs by contribution of systole.
Slide#77:
-atrial systole does not contribute a lot in the cardiac cycle.
-Isometric contraction of the skeletal muscle: change in tension without change
in length. Isovolumic contraction: change in pressure with no change in
volume. From the beginning of systole, the heart is generating a force (tension)
in the ventricle, but there is no change in the volume, no shortening of the
muscle.
-Because the pressure is high, the valve opens, and the blood comes out
quickly (rapid ejection period) then it slows down (slow ejection period)
because the pressure decreases.
-in Isovolumic , whether contraction or relaxation, period, there is no blood
comes in or out, because valves are closed, and thus there is no change in
volume.
Slide#78:
-Ventricular systole-first phase = isovolumic contraction, the heart here is not
changing size, and not contracting, it is only generating force, to increase the
pressure in ventricle to be enough to open the valves and cause the ventricular
systole-second phase.
Slide#79:
-When the pressure in the left ventricle increase, the aortic valve opens, and
blood moves to the aorta.
-When you measure the blood pressure, you measure the aortic pressure that
is done by the left ventricle.
-The diagram represents action potential in the left ventricle, and all followed
events occur in ventricle.
-For this ventricle, to eject blood, what phase do we need? QRS.
Slide#80:
-After contraction of atria, mitral valve should be closed: After atrial systole,
the pressure decreases in the atrium, the ventricle is full of blood, valve closes.
-Ventricular pressure increases until it exceeds 80 (minimum aortic pressure),
which cause the aortic valve to open, and the left ventricle pushes the blood
out. The pressure in the ventricle starts to decrease, (both ventricular and
aortic, see the overlap in the diagram), then the aortic valve closes, and the
heart begins to relax (Isovolumic relaxation).
-Dicrotic Notch: this happens when the aortic valve closes, when the aorta is
full of blood and starts to push the blood toward the closed valve. **(Dicrotic
Notch: is the sudden drop in pressure after systolic contraction)
Slide#82:
-In V-wave, the AV valves are closed.
Slide#83:
-The largest volume of the heart = End diastolic volume =120ml.
- The smallest volume of the heart = End systolic volume = 50ml.
- Volume of ejected blood through systole = 70ml = stroke volume.
Slide#85: will be explained in next slides.