13 Feb, 2012 Human Physiology II
The Cardiac Cycle
Know the diagram very well
Blue=vol in ventricle
Green = atrial pressure
Red=left ven pressure
Purple= aortic pressure
Line on top= ECG
3 phases of ECG
P-wave=atrial depolarization (contraction)
QRS complex= ventricular depolarization (contraction); when muscle contract the
pressure in ventricle rises at point #9 (RED) and gets above pressure in atrium and
closes the AV valve,
(ii)Diastole (relaxation; generally longer)
Two volvumes are important
Endystolic vol= vol after the heart has been filled with blood (EDV)
Ensystolic vol= blood left in the ventricle after it contract (still 60-75ml of blood in the
ventricle); they are never empty. (ESV)
-EDV- ESV = stroke volume (SV)
--All in the left ventricle.
REMEMBER TO READ THE FIGURE FROM THE BOOK.
-The diff btw left and right ventricles are “Pressure”
-Pressure are much lower in Right
-Pressure in aorta and ventricle go from 80 to 120 -Right ventricle goes to 0 in the ventricle and slightly above in pulmonary artery
-Blood drops of its pressure when it goes tissues
-How does blood come from our feet to our heart at low press? What drives it?
-Right side of heart pressures are almost 0, which provides no resistance for
blood to come back to the heart, this allows blood to come back to the heart, since there
is no pressure stopping it.
-Right atrium and ventricle have pressure of 0.
When ventricles contract they increase the pressure, and the pressure in the right
ventricle gets higher than pulmonary artery, and this is when pulmonary valve opens up
and blood flows out of the right ventricle to the lung. Then T-wave, ventricles relax
pressure goes down the pulmonary artery and pulmonary valve closes and does not
allow any more blood in.
-Pressure is very low, which is good for blood to move and spend time
-Pressure on the right side of the body in venous system & pulmonary artery, much
lower than the left side
Right vs. Left Ventricle
-Left ventricle takes up bulk of the heart ( lot of muscle) since it has to pump blood
so far, and against very high pressure .
Aorta pressure ranges is from 80 to 120mm Hg that means we have to generate
pressure higher than that to drive from left ventricle to aorta.
-Pulmonary artery needs 10-25 mmHg ; Afterload ( the work load)
The higher the pressure is in the arteries the more work they have to do, therefore
right ventricle is smaller, since it doesn’t have to fight against much pressure and
does not have to pump blood as far,
Left ventricle due to higher muscle mass it has:
(i) more cardiac cells
(ii) bigger (iii) generate more action potential (therefore we have higher greater QRS complex
amplitude vs. the P-wave)
-Ventricles are not the same,
-ECG is the Sum of all the action potential of each one of these muscle cells, way more
cells in the left ventricles than in the right ventricles.
-P-wave is smaller since there is so much muscle in the left ventricle.
-Left ventricle will have a greater QRS complex than the right ventricle
Cardiovascular system: to pump blood and get it to the system
Cardiac output=is the amount of the blood that flows through the heart per minute. (ml/
2 things that determine cardiac output
- (i) Heart rate
-(ii) Stroke vol
EDV(endysolitc vol) : fills the ventricles after its filled
ESV(ensystolic vol): the vol in the ventricle after the muscle is contracted
EDV- ESV =The difference between those two is the amount of blood that gets
squeezed out into the body (Stroke vol)
Stroke vol: 70ml/ beat
Q(cardiac output): 72 beats /min
= 5000 (5L)/min
You need 5L of blood flowing through system to survive.
Heart rate can go to 200beats and 150 stroke vol
=30L of blood flowing through the body during intense excerse
What controls HR & SV?
Regulation of HR -top figure shows action pot and SA node
-one of the main part of the action potential graph is the line that goes from -60 to -40
(pacemaker potential) This determines the firing rate of SA node.
--SA node then determines the heart rate.
--pink line shows Parasympathetic stimulation shows increased acetylcholine since
it’s the main neuro transmitter of the parasympatic nervous system.
-Parasympathetic activity slows heart rate, why is that?
(i) instead of ending it around -60, membrane potential drops much lower with
acetylcholine which means it has to go further distance to hit that threshold. Taking
more time, the heart beats will be further apart.
(ii) Slope of pink line is less than the black dotted line, therefore you have to go further
Acetylcholine of Na to go in, Na carries positive charge and is the main thing that
causes rise in pace maker potential. If we slow Na, the rise will be lower.
Acetylcholine causes increase in Potassium (K) to move out, and we take those positive
charges are moved out of the cell and they drops mem pot. Take these together and
they slow the rate at which we can get action potential firing.
The actual shape of action potential after threshold is about the same.
-Decreasing parasympathetic activity will have opposite effect
-Shows response to sympathetic activity
--Epinephrine(circulates in blood) and norephine phrine does same thing
-It increases the rate at which mem potential or pacemaker potential h