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AS biology-exchange systems

I am currently studying AS level biology and i am getting confused between distole, ventricular systole and atrial systole. I would appreciate it if someone could explain these processes to me in detail:smile:
Original post by Schoolishardwork
I am currently studying AS level biology and i am getting confused between distole, ventricular systole and atrial systole. I would appreciate it if someone could explain these processes to me in detail:smile:


So, as you might know, the heart is composed of 4 chambers, 2 atria at the top and 2 ventricles at the bottom. Atria collect blood from VEINS (ie venae cavae and pulmonary veins) and pump it into the ventricles, both ventricles then contract at the same time and pump blood to the lungs or the rest of the body via ARTERIES. Now, if you feel your chest, you'll feel your heart beat twice quickly and then stop, and then the process will repeat about 60-100 times per minute. The first "beat" is atrial systole, just think of systole as contraction, it is contraction of the 2 atria that forces blood into the ventricles. There is then a very brief pause to allow the ventricles to fill with blood, and then there will be the second "beat", this is ventricular systole, and is the blood being pumped into the arteries. Then there is the period of rest where there are no beats at all, this is diastole, and it is the time where blood refills the atria from the veins. This was a very large simplification, the process is a bit more complicated (because we haven't mentioned valves or the electrical activity of the heart), but hopefully it helps you to get your head around it!
If that was too simple and you want me to go into more detail I can, just let me know
Thankyou so much! This really helps!! :smile:
Original post by Schoolishardwork
I am currently studying AS level biology and i am getting confused between distole, ventricular systole and atrial systole. I would appreciate it if someone could explain these processes to me in detail:smile:


AortaStudyMore explained it well, i'll explain the cardiac cycle in terms of valves and pressure. it really is simple and makes sense once you get the hang of it. :smile:

Before i start, you should know that valves OPEN is there's higher pressure BEHIND them, and close when there's higher pressure in front of them (say it out loud a couple times, you'll remember it lol)

Imagine that there are 3 steps to the cardiac cycle

1-Ventricular diastole (relaxation), atrial systole (contraction): so here the ventricles are relaxed and the atria contract, reducing the volume of the atria and increasing the pressure, this pushes the blood to the ventricles (where the contents are at lower pressure). blood is pushed through the AV (atrioventricular valves) as pressure behind them (the atria) is higher than in front (the ventricles). (get it now? dont worry i have another example)

2-Ventricular systole, atrial diastole: The atria relax, ventricles contract, pressure increases and the volume decreases, the pressure is higher in front of the AV valves now than behind them, so they are forced shut, preventing backflow to the atria.
Brace yourself more valve talk lol
The semi lunar valves open, as pressure behind them (ventricles) is higher than in front of them) blood is forced into the arteries.

3-Cardiac diastole: Both ventricles and atria are relaxed, blood begins filling up the atria passively again.

See? it's all about pressure, you can explain blood flow and valves opening and closing by changes in pressure. Good luck!

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