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BIOC33/BIOC34 Lec 4

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University of Toronto Scarborough
Biological Sciences
Stephen Reid

BIOC34 Lec 4 - Jan. 15  Assignments o First one due = lab 6 o Go through exercises in simulation - have to present data and answer some questions o Not formal reports - just need to present data and answer questions  Cont. with regulation of cardiac function o Important points to note: changes in pressure related to atria, aorta because these pressure changes determine ifAV and semilunar valves will be opened or closed - look at these in perspective to left ventricle of heart o Look at numbers and variables associated with blood pressure  Cardiac cycle o Follow progression from mid-late diastole o Then 2 stages of systole/contraction  When heart is contracting (Isovolumetric contraction), volume of blood in the heart is not changing because the pressure differences are such that all the heart valves are closed  Ejection phase (ventricular ejection) • Blood is pumped from left ventricle to aorta and gets distributed to the systemic circuit and lungs o Early diastole  Isovolumetric relaxation stage - heart muscles relax but there is no change in blood volume because pressure relationship  Early diastole - valves are open, ventricles begin to fill again o Important variables on chart - volume of ventricle (very bottom)  Late stage of diastole where it is finishing filling process, systole - dramatic drop, then starts to fill again  Latter stages of diastole are the beginning of the cycle o Important points to keep in mind - when ventricular pressure goes above or below atrial pressure and aortic pressure o Cardiac cycle is in diastole 2/3 of the time - important to allow the heart to have sufficient time to fill with blood. Important in regulating stroke volume  Late diastole (1) o Have passive filling of blood on the left hand side from pulmonary arteries, through the left atria and into left ventricle - get an increase in passive filling o See that atrial pressure is slightly higher than ventricular pressure and aortic pressure is much higher than the two of them o Have passive filling phase where blood is going from lungs into atria into ventricle and have a little bump when the atria actually contracts  When it contracts, there is a slight increase in atrial and ventricular pressure and it forces the extra little bit of blood into the ventricles. This helps to slightly boost the pressure in the ventricle  During this stage, the ventricular pressure is lower than atrial pressure, so that means theAV valves remain open.As long as the pressure in ventricle is lower than pressure in atria,AV valves stay open.  The pressure in aorta is significantly greater, so semilunar/aortic valve stays closed  Cardiac cycle o Heart is filled now both passively and slightly through atrial contraction o Ready to go through systole  Systole (2) Isovolumetric contraction o Contraction of cardiac muscle - causes increase in pressure in ventricle - ventricular pressure goes above atrial pressure and keeps going up but remains below aortic pressure o Heart is contracting but no blood is leaving the heart because all the valves are closed o AV valves separating atria and ventricle are closed because ventricular pressure is above atrial pressure, when this happens the valves close and it happens on both sides of the heart o During this phase, ventricular pressure stays below aortic pressure - as long as pressure in aorta is greater than ventricle, aortic/ semilunar valve stays closed  No blood is leaving the heart at this point o Isovolumetric change - there is a small decrease in volume - not due to blood leaving the heart, due to blood contracting and squeezing in on chambers o Ventricular pressure is as high and it is ready to exceed aortic pressure to the point where we see blood being ejected  Ventricular ejection (systole [3]) o Pressure in ventricle exceeds pressure in aorta o Ventricular pressure keeps going up as it contracts o Aortic pressure also goes up and it mirrors the increase and decrease of ventricular pressure  Aortic pressure is always slightly less o During this phase, have ventricular pressure going above aortic pressure - triggers opening of aortic valve. Pressure in the ventricle is still higher than in the atria so AV valves remain closed o Since blood is being ejected, see a large decrease in ventricle volume - due to blood leaving ventricles and entering aorta o Blood has been ejected and now ready for heart to go into relaxation phase  Early diastole (4) - Isovolumetric phase o This phase (4) begins when the pressure in the ventricle falls below pressure in the aorta - it is still higher than atrial pressure at this point o No change in ventricular volume o Ventricular pressure causes aortic semilunar valves to close. The fact that ventricular pressure stays higher than atrial pressure keeps theAV valves closed o Notice a blip in aortic pressure (dicrotic notch)  Late diastole (1) o At end of the isovolumetric phase, pressure in ventricle falls below pressure in atria allowing AV valves to open and blood to move through atria into ventricle  Mid to late early diastole (1) o Start with passive filling; blood flowing through lungs and pulmonary veins into atria and into ventricle - get an increase in ventricular volume o Atria contracts to cause a further increase in volume o Throughout this stage, pressure in atria is higher than pressure in ventricle soAV valve is open but semilunar valves are closed o Isovolumetric contraction (2) - ventricle pressure is higher than atrial pressure so AV valves close but pressure in ventricle is less than pressure in aorta - aortic valves are closed o Enter ventricular ejection phase (3) - semilunar valves open so blood can be ejected; volume of ventricle decreases; large increase in ventricular pressure which is mirrored by an increase in aortic pressure  Pressure in ventricle is higher than atrial pressure soAV valves are closed o This series of pressure-volume changes occurs in every cycle of the heartbeat o Diastole = 2/3 of this cycle, systole = 1/3 o 3 things happening in aortic pressure  Decrease in aortic pressure during diastolic phase  Increase during ventricular ejection (systole)  Slight blip when semilunar valve closes during isovolumetric relaxation • Known as dicrotic notch  Aortic pressure (1a) o During phase 1 + 2, aortic valve is closed but there is still flow of blood out of the aorta into systemic circulation o Decrease in aortic pressure during diastole - makes sense because blood is flowing from aorta into systemic circulation. Pressure in aorta drops during this time o Blood flow to systemic circulation or pulmonary circulation is NOT pulsatile; blood flow is continuous and smooth during both diastole and systole  Aortic pressure (1b) o Aorta acts as a “windkessel vessel” on the LHS - pulmonary artery on RHS does the same to the blood going to lungs o Awindkessel vessel can expand and build up pressure and relax and release pressure to assist in smooth flow of blood from aorta into downstream arteries o When heart is in systole, blood flows from left ventricle into aorta, cause aorta to swell when blood is in them.As the heart relaxes and the semilunar valve closes, there is no longer any contractile force from the ventricle driving blood into the aorta and further down into systemic circulation o Once in diastole, smooth flow of blood continues because aorta (which was swollen) begins to relax and move into good shape and forces the blood from upper regions into lower regions so it expands and then relaxes, forcing the blood down and so on o Get the expansion of aorta when it relaxes, serving as the driving force to push blood into the arterial system. No stop in blood flow when heart goes into diastolic phase  Aortic pressure (2) o Sharp increase in aortic pressure is due to ventricle contracting - it forces blood into aorta.At this stage, blood flow into aorta is greater than blood flow out of the aorta, so pressure in aorta increases  Pressure increase is important because as it builds up, it will be able to dissipate and relax back into shape when heart enters diastolic phase  Aortic pressure (3) o Dicrotic notch: closure of the semilunar (aortic) valve o Now in the ventricular ejection phase.Aortic pressure has gone up because ventricular pressure has also gone up. Ventricles are contracting - ventricular pressure is going into aorta. Ventricular pressure goes downward and continues smoothly and consistently downward.Aortic pressure abruptly increases o Small, sharp increase and then decreases in a much slower manner o Reason for this upswing is because of the closure of the aortic valve. The semilunar valve has the flaps of tissue protruding into aorta when it is open and snapping back downwards when it closes. When the pressure in the ventricle falls below the pressure in the aorta, the driving force to keep this valve open is removed and the valve snaps back down and closes. When this happens, cut off the open system between ventricle and aorta and this helps give a boost in the aorta. There is a reverberating pressure wave that causes this slight increase in pressure. Therefore, it is caused by the abrupt and quick closing of the semilunar valve  Systo
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