Cardiac cycle, stages, physiology, Diastole and systole in the cardiac cycle.

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Chapters

0:00 Introduction
0:28 Phases of Cardiac Cycle
2:46 The Systole

The cardiac cycle is the performance of the human heart from the ending of one heartbeat to the beginning of the next. It consists of two periods: one during which the heart muscle relaxes and refills with blood, called diastole, following a period of robust contraction and pumping of blood, dubbed systole. After emptying, the heart immediately relaxes and expands to receive another influx of blood returning from the lungs and other systems of the body, before again contracting to pump blood to the lungs and those systems. A normally performing heart must be fully expanded before it can efficiently pump again. Assuming a healthy heart and a typical rate of 70 to 75 beats per minute, each cardiac cycle, or heartbeat, takes about 0.8 seconds to complete the cycle.[2] There are two atrial and two ventricle chambers of the heart; they are paired as the left heart and the right heart—that is, the left atrium with the left ventricle, the right atrium with the right ventricle—and they work in concert to repeat the cardiac cycle continuously, (see cycle diagram at right margin). At the start of the cycle, during ventricular diastole–early, the heart relaxes and expands while receiving blood into both ventricles through both atria; then, near the end of ventricular diastole–late, the two atria begin to contract (atrial systole), and each atrium pumps blood into the ventricle below it.[3] During ventricular systole the ventricles are contracting and vigorously pulsing (or ejecting) two separated blood supplies from the heart—one to the lungs and one to all other body organs and systems—while the two atria are relaxed (atrial diastole). This precise coordination ensures that blood is efficiently collected and circulated throughout the body.[4]

[GeorgeDee_]

This 4 minute video explains it better than the 1 hour explanation by the lecture

[Tstar]

There is a mistake with this video at 1:43. It states "oxygen-starved blood returning from the circulatory system passes through the pulmonary veins and fill the left atrium". It should state "oxygen-rich blood returning from the pulmonary circulation via the pulmonary veins and fills the left atrium".

[KuldevSeecoomarie]

More schools need more teachers like you. One of the best biology teachers. Keep it up. I watch many of your videos for clarity and compare what I was taught to your lessons.

[zfjegzq]

THANK YOU FOR THIS VIDEO!! I’ve sat for hours through lecture and it only took your video to finally understand this concept.

[trinadymanke]

This is the BEST video I've found on YouTube!! THANK YOU!

[annecolindres]

This explains it so easily!!! All these other videos are like 20 mins long!! I was getting so confused! Thank you for this easy video!!

[ppdack]

At 1:47 you say the blood returning from the lungs through the pulmonary veins into the Left atrium is oxygen starved when I think you meant to say oxygen rich.

[afifakhan]

Cardiac Cycle

How does the heart function? Let us take a look. To begin with, all the four chambers of heart are in a relaxed state, 1.e., they are in joint diastole. As the tricuspid and bicuspid valves are open, blood from the pulmonary veins and vena cava flows into the left and the right ventricle through the left and right atria. The semilunar valves are closed at this stage. The SAN now generates an action potential which stimulates both the atria to undergo a simultaneous contraction-the atrial systole. This increases the flow of blood into the ventricles by about 30 per cent. The action potential is conducted to the ventricular side by the AVN and AV bundle from where the bundle of His transmits it through the entire ventricular musculature. This causes the ventricular muscles to contract. (ventricular systole), the atria undergoes relaxation (diastole), coinciding with the ventricular systole. Ventricular systole Increases the ventricular pressure causing the closure of tricuspid and
bicuspid valves due to attempted backflow of blood into the atria. As the ventricular pressure Increases further, the semihinar valves guarding the pulmonary artery (right side) and the aorta (left sidel are forced open. the circulatory pathways. The ventricies now relax (ventricular diastole) and the ventricular pressure falls causing the closure of semilunar valves which prevents the backflow of blood into the ventricles. As the ventricular pressure declines further, the tricuspid and bicuspid valves are pushed open by the pressure in the atria exerted by the blood which was being emptied into them by the veins. The blood now once again moves freely to the ventricles. The ventricles and atria are now again in arelaxed (joint diastole) state, as earlier. Soon the SAN generates a new action potential and the events described above are repeated in that sequence and the process continues.

This sequential event in the heart which is cyclically repeated is called the cardiac cycle and it consists of systole and diastole of both the atria and ventricles. As mentioned earlier, the heart beats 72 times per minute, Les that many cardiac cycles are performed per minute. From this it could be deduced that the duration of a cardiac cycle is 0.8 seconds During a cardiac cycle, each ventricle pumps out approximately 70 ml. of blood which is called the stroke volume. The stroke volume multiplied by the heart rate (no. of beats per min.) gives the cardiac output. Therefore, the cardiac output can be defined as the volume of blood pumped out by each ventricle per minute and averages 5000 ml.or 5 litres in a healthy individual The body has the ability to alter the stroke volume as well as the heart rate and thereby the cardiac output. For example, the cardiac output of an athlete will be much higher than that of an ordinary man.

During each cardiac cycle two prominent sounds are produced which can be easily heard through a stethoscope. The first heart sound (lub) is associated with the closure of the tricuspid and bicuspid valves whereas the second heart sound (dub) is associated with the closure of the semilunar valves. These sounds are of clinical diagnostic significance.

[Abdullahabbas]

3D animation is a reason for that online is much better than offline coching centres...

Explained better in short duration 🤗🤗

[mashahudmunna]

Thank you sir. It always helps me to understand the systole and diastole. Love from Bangladesh ❤️❤️❤️

[fly_]

thank god i found this channel! thankx alot .. seriously it just took few minutes to learn this otherwise i could have spent whole day learning from book

[lana-fyfr]

Love the animation, makes it sooo much easier to conceptualise and grasp. Thank you!

[jananirajasri_]

You explained the best and I needed this lecture for Indian cbse board class 11 th cardiac cycle ❤

[sweetbutterfly]

isn't it meant to be oxygen rich blood from pulmonary circulation into the left atrium?

[PrinceJohnson-ukpg]

So brief and concise
Just what I've always wanted
Thank you sirr

[emmanuelmomoh]

The blood entering the right atrium from the IVC and SVC are oxygen depleted while that entering from the pulmonary veins are oxygen-rich. Please correct the error. thank you

[amenodorime]

Such easy concept but no book explains it easily

[bee]

you did mention that diastole involves “oxygen-starved blood to fill the left atrium from the pulmonary arteries.” Should have said oxygen rich if I understand correctly… otherwise I am extremely confused.

[shivanijadhav]

Love from India Your explanation was superb.🔥🔥🔥

[bilalhassan]

This was one of the best video i came through Thankyou so much♥️