 Hello everyone welcome back to another session in dentistry and more so today we have a very interesting topic that is cardiac cycle in physiology so the first session of this video will be dealing about the heart its chambers the veins arteries which carry impure and pure blood respectively and the valves within the heart chambers and opening of the pulmonary artery and aorta and the process of purification of blood that is how the impure blood is purified and get distributed to various parts of the body. The second session will be about the process in detail that is the systole and diastole how the atrial contraction ventricular relaxation and iso volumetric contraction and relaxation and the heart sounds S1 and S2 all this will be dealt in the next part so let's start cardiac cycle. Human heart has four chambers the two upper chambers and two lower chambers the upper chambers are known as atria and the lower chambers are ventricles so this is right atrium left atrium right ventricle left ventricle so this is the right half of the heart this is the left half of the heart so right half carries impure blood and left half carries pure blood that is right atria atrium and right ventricle carries impure blood left atrium and left ventricle carries pure blood usually it never get mixed up this ventricle or atrium sometimes in the birth defect we heard about the atrial septal defect and the ventricular septal defect where the impure blood is mixed with pure blood that is a different condition that will be study later okay now we are focusing only on the parts and the structure of heart so next we have the veins and arteries attached to heart so this is superior vena cava inferior vena cava this is pulmonary veins so superior and inferior vena cava on the right atrium and pulmonary veins on the left atrium and we have pulmonary artery which is starting from right ventricle and aorta which is the largest artery is starting from left ventricle usually in our body the pure blood or oxygenated blood is carried by artery and impure blood or deoxygenated blood carries by vein but there is an exception that is pulmonary artery which is carrying impure blood from heart to length and pulmonary vein which carries pure blood or oxygenated blood from length to heart so that is the only exception in our body pulmonary artery and pulmonary vein usually artery carries pure blood that is why i am putting red color and vein carries impure blood but pulmonary artery and pulmonary vein do the opposite now let's see the valves of heart so we have two types of valves that is the valves which is separating atrium and ventricles and valves which is present at the pulmonary artery and aorta so the valves which is separating atrium and ventricle is known as tricuspid valve and bicuspid valve because it has three cusp that is why it is tri and this has two cusp okay so this separating atrium and ventricle and it has a significant role in heart sound these are involved in the heart sound first heart sound okay so the next valves are the semiluna valves okay the semiluna valves which is present between right ventricle and pulmonary artery and left ventricle and aorta which has this particular shape semiluna shape okay so these valves has significant role in the second heart sound that all we will be seeing the next session so the bicuspid valve which is present between left atrium and left ventricle is also known as mid-shell valve so this is atrio atrio ventricular valve is another name of tricuspid and bicuspid valves so that is about the valves and the veins and artery now let's see the process of blood exchange and its purification so the superior vena cava and inferior vena cava they are veins which carries impure or deoxygenated blood from the body superior vena cava which carries upper half impure blood and the inferior vena cava the lower half it carries impure blood to the right atrium okay from right atrium through the tricuspid valve it goes right ventricle so this part consists only impure blood right so from right ventricle this goes to lengths for purification by pulmonary artery so in lengths it gets purified that is oxygen carbon dioxide exchange happens and after purification the blood comes back to left atrium via pulmonary vein that is what I'm saying pulmonary vein carries pure blood okay usually vein carries impure blood but the exception is pulmonary vein which carries pure blood from lengths pulmonary artery carries impure blood from heart to lung so it reaches left atrium so this part contains only pure blood from left atrium it goes to left ventricle via bicuspid or mitral valve so from left ventricle it goes to the different parts of the body via aorta okay so this is how blood impure blood comes to heart it goes to lengths gets purified comes back to heart and gets distributed to various parts of the body so the process is like this the green arrows indicates the movement of blood some superior vein upper upper half of the body lower half of the body impure impure blood in right atrium right ventricle lengths left atrium left ventricle body so only exception is pulmonary artery and pulmonary vein which carries impure and pure blood okay so this is how impure blood is getting purified and distributed to various parts of the body so I explained you step by step okay one step this opens and this goes and this opens the semiluna valves opens it goes to the lengths it comes back the bicuspid valve opens it reaches left ventricle this aortic valve open it goes to body parts but it doesn't happen step by step so all the things all the things are mostly happening at the simultaneous time or within less than a second because our heart beats at a rate of 72 per minute okay so all the process were happening within a second that is 0.8 second so we have 72 beats per minute and 60 seconds so 60 by 72 we get 0.8 second so one cardiac cycle is 0.8 second duration so next session is about the contraction and relaxation of heart chambers and the production of heart sounds and the stages that is atrial contraction the ventricular relaxation iso volumetric relaxation and iso volumetric contraction the rapid ejection phase so all phases will be dealt in next session cardiac cycle is nothing but the sequence of events happening by every heartbeat that is all these sequences happening by every heartbeat it is basically divided into two scenario that is systole and diastole systole is contraction and diastole is relaxation so we have six phases that is the systole and diastole is again subdivided into six phases the six phases so the first fifth and sixth phases are the diastole and the second third and fourth phases are systole so it starts with atrial repolarization then iso volumetric contraction rapid ejection reduced rejection iso volumetric relaxation and ventricular filling so the cardiac cycle is initiated at the SA node okay so when the electric impulse is triggered from SA node there will be atrial depolarization that is the atrial chambers will be depolarized by the SA node activation okay that phases coincide with p wave in the ECG okay the ventricular volume this red line is ventricular volume this violet is ECG this black line is ventricular pressure and the blue line is atrial pressure and this pink line is aortic pressure and this one two three four five six are the six phases okay and this two three four are the systolic events and one five six are the diastolic events okay so the SA node activates there will be the first change that is atrial depolarization so during atrial repolarization what happens the passive flow of blood from atrium to ventricle happens that is a passive flow because the atrium is not very much contracted but it is started contracting so there will be passively blood flows from atrium to ventricle so that is this one okay there is not much change but the change is just started increasing in ventricular volume okay so the atrial pressure is also not increased it is just started by the SA node activation that is atrial depolarization after that the atrial contraction happens that is the spike so we can see this is going upward that is the ventricular volume is increased how it is increased there is active movement of blood from atrium to ventricle because there is opening of these valves happen before that it is not very much opened so this opening of valve is happened and there is pressure increases in atrium and the blood actively moves to ventricle so that is why this line is increased that is ventricular volume is increased this atrial pressure is increased okay so that is a P wave so after that we have the second phase iso volumetric contraction okay so before that what happens is the pressure increased the blood flows and the blood fills up the ventricles so after a period of time the atrial pressure slowly reduced okay because the blood is completely filled here the pressure will be built up here so automatically the pressure of atrial valve reduced that is what the downward inclination of this peak the pressure is reduced but the volume is constant when the pressure is reduced what happens is as I mentioned earlier when the pressure is reduced this valve closes okay so this tricuspid and bicuspid valve closes so that is why this is showing a parallel line okay that is the ventricular volume is parallel line that is all the four valves are closed right now okay but it is in a contracting motion that is it is not going the blood is not going anywhere but the contraction happens so this phase is known as iso volumetric contraction contraction is happening but blood is not going anywhere all the four valves are closed at this phase but the contraction happens that is why this black line is going up okay that is a ventricular pressure ventricular pressure is going up and what happens when this aortic pressure this line is aortic pressure when it is more than aortic pressure what happens is this valves that is semiluna valves opens because this black line is above the pink line okay so this is aortic pressure so when it is greater than aortic pressure the aortic and pulmonary valves open and blood goes into these two arteries that is a rapid ejection phase okay so before that we need to understand when this valve closes that is the tricuspid and bicuspid valve closes during this iso volumetric contraction phase the s1 sound heard okay this is the s1 sound when this tricuspid valve and bicuspid valve closes s1 sound heard and the systolic phase starts okay systolic phase starts by ventricular contraction when there is ventricular contraction happens the systole because systole is basically contraction so when ventricular starts contracting the systolic phase happens and it is going above the aortic pressure so this valves open and blood goes into pulmonary artery and aorta which is known as rapid ejection so after that what happens after that the volume of blood goes into this a these two arteries and the pressure started decreasing so pressure when the pressure started decreasing that is this line okay the fourth phase is a reduced ejection the volume ventricular pressure is started slowly decreasing and the blood flow is also started decreasing blood flow is also started decreasing because the bloods blood in the ventricle is going to pulmonary artery and aorta and during this phase we get the second heart sound s2 okay second heart sound is the closure of these semiluna valves okay so that is happening when there is the pressure that is a aortic and pulmonary artery pressure is lesser than the ventricular pressure okay so we can say this the pink line is going like this when the pressure drops lesser than the ventricular pressure so this closes and that happens after the reduced ejection okay just before the iso volumetric relaxation so iso volumetric relaxation is that phase when the all four valves are closed okay so this phase between this phase the closure of the semiluna valves happens and that sound is s2 so the first heart sound s1 is a closure of tricuspid and bicuspid or the atrio ventricular valves and the second heart sound is the closure of semiluna valves when the pressure of aortic and pulmonary falls and if when it is less than the ventricular pressure this closes and that happens at the end of phase four or reduced ejection so we have qrs complex and t wave in ecg so p wave we discussed already it is effort atrial depolarization whereas a qrs complex is a ventricular depolarization it happens just before the iso volumetric contraction okay so when there is ventricular depolarization the pressure of ventricles is keep on increasing so when the depolarization starts there will be a qrs complex okay whereas the t wave which is referred as a ventricular repolarization okay when the pressure of ventricles started decreasing so that moment is referred as t wave in ecg so this is ventricular depolarization where the pressure is keep on increasing and t wave is ventricular repolarization when the pressure started decreasing and the p wave is atrial depolarization and the pressure started decreasing here because the contractile pressure the ventricular pressure started decreasing here so automatically these two valves closes so that particular phase okay the momentary phase when all the four valves are closed is known as iso volumetric relaxation okay so iso volumetric relaxation is the fifth phase after iso volumetric relaxation what happens is again the pressure is low and low so the passive feeling will be happening from the right and left atrium to the right and left ventricle because the pressure is low here the semilunar valves closed but the passive feeling from the atrium to ventricle happens that is ventricular feeling okay so this is how the cycle which is little complicated but you need to understand the pressure changes in the chambers first the assay node activates then the depolarization happens that is associated with the p wave then contraction so pressure increases the valve opens blood fills in ventricles then there will be a phase these will be closed that time we hear the s1 sound and a momentary phase until this open is known as iso volum that until this semilunar valves open the phase is known as iso volumetric contraction because the contraction is happening but the blood is remaining same because it is not going anywhere that is associated with qrs complex in ecg after that the volumetric when ventricular pressure is keep on increasing so when the pressure increases the semilunar valves open and rapid ejection happens so after period of time the pressure decreases so that time the slow ejection or reduced ejection it is associated with t wave so after a period of time when the pressure decreased these valves will be closed so at that moment all the four valves will be closed and it is known as iso volumetric relaxation so since pressure is low here there will be passive flow of blood from the atrium to ventricle and the cycle repeats okay so passive flow happens and there will be again the activation of sa note so there will be actually depolarization blood will be moving from atrium to ventricle and there will be contraction pressure will be built up this will be open up and the entire cycle will be repeated so this is a cardiac cycle so we have a small section in cardiac cycle which is known as cardiac output so cardiac output is defined as the amount of blood pumped out of each ventricle per minute so cardiac output is commonly expressed in two forms that is stroke volume and minute volume stroke volume is 70 ml per beat whereas minute volume or cardiac output is multiplying the heart rate with stroke volume we get around 5 liters or 4900 ml per minute so it is the most commonly accepted measure that is a cardiac output so there are factors which affects heart rate and stroke volume the factors affecting heart rate are autonomic innovations various hormones the fitness level age and factors affecting stroke volume are heart size gender the contractility preload and afterload so that was about the cardiac output stroke volume and heart rate so that's all about cardiac cycle so we have learned the heart its chambers the valves arteries veins the heart sounds and the tricuspid bicuspid valves semilunar valves and the process of blood purification how the blood is collected to heart then from length the purified blood comes back and it distributed to various parts of the body by iota and we have learned the ecg wave the ventricular volume ventricular pressure atrial pressure aortic pressure and the cardiac cycle the six phases the systole and diastole the atrial depolarization iso volumetric contraction rapid and reduced ejection iso volumetric relaxation and ventricular feeling and also the heart sounds the p qrs and t waves and regarding the pressure change when the valves open when the pressure increases the valve opens when the pressure decreases the valve closes similarly with pulmonary and iota pulmonary artery and iota and also the cardiac output that is stroke volume and heart rate so it is a very important concept the process of blood purification actually the blood purification happens in lengths but the process of transfer of blood from heart to lengths and its return and its distribution to various parts of the body so understanding the mechanism of the blood transfer from heart to lung is very much vital in understanding the process of blood purification and this chapter the cardiac cycle and the cardiac output is very important so the essay questions and short notes are repeatedly asked for the university exam so hope you understood this concept so i have not gone into detail so i wanted you to understand the basic idea of the blood transfer and the purification of blood and the waves the ecg and other things and the phases of cardiac cycle so i'll come up with another topic in physiology thank you