Revision Notes

9.2 Heart

Heart Structure: Basics

  • The heart is labelled as if it was in the chest so what is your left on a diagram is actually the right hand side and vice versa
  • The right side of the heart receives deoxygenated blood from the body and pumps it to the lungs
  • The left side of the heart receives oxygenated blood from the lungs and pumps it to the body
  • Blood is pumped towards the heart in veins and away from the heart in arteries
  • The two sides of the heart are separated by a muscle wall called the septum
  • The heart is made of muscle tissue which are supplied with blood by the coronary arteries


Structure of the heart, IGCSE & GCSE Biology revision notesStructure of the heart

Exam Tip

Remember A-A: Arteries carry blood Away from the heart

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Heart Structure

  • The ventricles have thicker muscle walls than the atria as they are pumping blood out of the heart and so need to generate a higher pressure
  • The left ventricle has a thicker muscle wall than the right ventricle as it has to pump blood at high pressure around the entire body, whereas the right ventricle is pumping blood at lower pressure to the lungs
  • The septum separates the two sides of the heart and so prevents mixing of oxygenated and deoxygenated blood


Structure of the heart showing the different valves, IGCSE & GCSE Biology revision notesStructure of the heart showing the different valves

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The Function of Valves

  • The basic function of all valves is to prevent blood flowing backwards
  • There are two sets of valves in the heart:
    • The atrioventricular valves separate the atria from the ventricles
    • The valve in the right side of the heart is called the TRICUSPID and the valve in the left side is called the BICUSPID
    • These valves are pushed open when the atria contract but when the ventricles contract they are pushed shut to prevent blood flowing back into the atria
    • The semilunar valves are found in the two blood arteries that come out of the top of the heart
    • They are unusual in that they are the only two arteries in the body that contain valves
    • These valves open when the ventricles contract so blood squeezes past them out of the heart, but then shut to avoid blood flowing back into the heart
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Pathway of Blood through the Heart

  • Deoxygenated blood coming from the body flows into the right atrium via the vena cava
  • Once the right atrium has filled with blood the heart gives a little beat and the blood is pushed through the tricuspid (atrioventricular) valve into the right ventricle
  • The walls of the ventricle contract and the blood is pushed into the pulmonary artery through the semilunar valve which prevents blood flowing backwards into the heart
  • The blood travels to the lungs and moves through the capillaries past the alveoli where gas exchange takes place (this is why there has to be low pressure on this side of the heart – blood is going directly to capillaries which would burst under higher pressure)
  • Oxygen-rich blood returns to the left atrium via the pulmonary vein
  • It passes through the bicuspid (atrioventricular) valve into the left ventricle
  • The thicker muscle walls of the ventricle contract strongly to push the blood forcefully into the aorta and all the way around the body
  • The semilunar valve in the aorta prevents the blood flowing back down into the heart

Author: Jenna

Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.

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