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1.8 Know the cardiac cycle (atrial systole, ventricular systole and cardiac diastole) and relate the structure and operation of the mammalian heart, including the major blood vessels, to its function
The mammalian heart
👇 You may wish to revise the heart anatomy for IAL Edexcel Biology 👇
- Heart is a muscular organ
- Double pump/ double circulation, i.e. blood passes through the heart twice in one cardiac cycle
- Left and right side of the heart separated by a septum to prevent mixing of oxygenated and deoxygenated blood
- Left side receives oxygenated blood from the lungs and pumps it to the body
- Right side receives deoxygenated blood from the body and pumps it to the lungs for gaseous exchange
The cardiac cycle
- Consist of rhythmic contraction (systole) and relaxation (diastole) of the atria and ventricles to keep blood circulating continuously around the body
- Each heartbeat consists of two sounds, “lub” and “dub”, which are made when the atrio-ventricular (A-V) valves and semilunar valves are forced shut respectively
- There are 3 stages in each cardiac cycle
Cardiac diastole
- Entire heart relaxes
- Blood enters the left and right atria through the pulmonary vein and vena cava respectively
- Atria pressure > ventricular pressure
- A-V valves are forced open and blood begins to fill up the ventricles
Atrial systole
- Atria contract and all the blood is emptied into the ventricles
- Ventricular pressure > atria pressure
- A-V valves are forced shut
Ventricular systole
- Ventricles contract from the apex of the heart upwards
- Ventricular pressure > pressure in pulmonary arteries and aorta
- Semilunar valves are forced open and blood flows out of the ventricles
Important point to note for IAL Biology
Valves open and close as a result of pressure differences (pressure gradients), but NOT because of muscles in the valves contracting.
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And now you know why our heart goes "lub-dub" when we get nervous ;)
References:
1. Edexcel AS Biology Revision Guide. Edexcel.