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Edexcel AS Biology SNAB
BY FAYE…read more

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The Heart
The heart is made up of four chambers:
Left atria
Right atria
Left ventricle
Right ventricle
The ventricles are thicker than the atrias
because they have to push blood out of the body
whereas the atria only pushes blood into the
The left ventricle is thicker than the right
ventricle because it has to contract more
forcefully so blood goes all around the body,
whereas the right ventricle just pushes blood to
the lungs
Atrioventricular valves stop blood going back
into the atrium when ventricles contract.
Semilunar valves stop blood flowing back into
the heart when ventricles contract. Links the
ventricles to the pulmonary artery and aorta.…read more

Slide 3

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Atrial systole
Atrial systole: Low pressure blood
flows into the left and right atria from the
pulmonary veins and vena cava. This
causes pressure against
atrioventricular valves, which causes
them to open and causes blood to leak
into the ventricles.
The atria contract forcing remaining
blood into the ventricles.
Semilunar valves are closed during
atrial systole.…read more

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Ventricular systole
Immediately after atrial systole,
ventricular systole begins.
The ventricles contract from the base
There is a higher pressure in the
ventricles than in the atrium which,
closes the AV valves.
There is a higher pressure in the
ventricles then in the pulmonary
artery and aorta which causes the
Semilunar valves to open.
This forces blood into the pulmonary
artery and aorta.…read more

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The atria and ventricles relax during
diastole and there pressure is lowered.
There is higher pressure in the
pulmonary artery and aorta then the
ventricles, which closes the Semilunar
There is high pressure in the pulmonary
veins and vena cava, so the atria fill up
with blood.
The ventricular pressure is below that of
the atria, so blood can flow passively
into the ventricles without contraction.
Then the atria contract, which starts the
whole process again.…read more

Slide 6

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Blood vessels in the heart
Pulmonary veins: Bring oxygenated blood to the
heart from the lungs.
Pulmonary artery: Takes deoxygenated blood from
the heart to the lungs.
Vena cava: Brings deoxygenated blood from the body
to the lungs.
Aorta: Takes oxygenated blood to the body.…read more

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