Summary GCSE Biology (AQA) revision notes for the heart and circulatory system

Describe the passage of blood through the heart




heart valves

Job: to ensure that the blood only flows in one direction through the heart

When are they used: as the atria contract, valves close as the ventricles open and
blood is forced into the ventricles. theses valves close as the ventricles contact so
there is no backflow

How: tendons prevent them from inverting




Blood Vessels

, Arteries

 small lumen so the blood is under high
pressure
 walls made from elastic tissue so it can stretch
 muscle layer can contract to control flow and
push blood along
 blood flows through fast so there is no risk of backflow and
therefore no valves





Veins

 thinner wall because they don't have to withstand
high blood pressure
 lots of energy has been lost and the wide lumen
both result in slow flowing blood
 this means there's a risk of backflow so veins
have valves
 located next to muscles so as the muscle contracts it presses on the vein walls,
pushing blood through





Capillaries

 found all over the body
 walls are only one cell thick
 substances move in and out of the
blood, through the walls, to the
surrounding tissues
 they are microscopic and the lumen is
so small that only one red blood cell can
pass through at a time



Composition of Blood