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KS4 Biology
The Heart and
Circulatory System
1 of 49
© Boardworks Ltd 2004
Heartbeat animation
Stages of a heartbeat
Stage 1:
A heartbeat begins
with the heart muscle relaxed
and valves
closed.
Blood flows into the two atria
and both sides fill up with
blood.
This blood has to be pushed
through the valves to get into
the ventricles. How does this
happen?
Stages of a heartbeat
Stage 2:
The atria contract and the
blood is squeezed which
causes the valves leading to
the ventricles to open.
Blood then flows from the atria
into the ventricles.
What happens to the open
valves when the atria are
empty?
Stages of a heartbeat
Stage 2 (continued):
The valves between the atria
and the ventricles close.
This prevents any backflow.
What happens next
to the blood in the ventricles?
Stages of a heartbeat
Stage 3:
Almost immediately, the
ventricles contract and the
blood is squeezed again.
The pressure of the blood
forces open the valves
leading out of the heart.
Blood is pumped out
of the heart.
What happens to the open
valves when the ventricles are
empty?
Stages of a heartbeat
Stage 3 (continued):
When the ventricles are
empty, the valves leading out
of the
heart close and the heart
muscle relaxes.
This completes the sequence
of contraction and relaxation in
one heartbeat.
What will happen next?
Stages of a heartbeat
Stage 1 (again):
The atria fill up with blood as
the heartbeat sequence
begins again.
Why are the walls
of the atria thinner than the
walls of
the ventricles?
Why is the wall of the left
ventricle thicker than the right
ventricle?
---Blood vessels on the outside of the heart- coronary arteries
---Muscles of the heart are thick-so nutrients and oxygen in the blood
inside is not able to diffuse to all the muscle quickly
----so heart muscle needs constant supply of nutrients and oxygen –
to keep on working- coronary arteries does it
--- If a coronary artery gets blocked the cardiac muscle run short of
oxygen
--- can not respire, so it does not have the energy to contract-heart stops
beating
--- HEART ATTACK or CARDIAC ARREST
Pacemaker
--The rate at which the heart beats is controlled by a patch of muscle in the
right atrium called PACEMAKER
-- It sends electrical signals through the walls of the heart at regular intervals,
according to the need of the body
-- If it stops working-an artificial pacemaker is placed to do the job
Systole
Cardiac muscle contracts-heart becomes smaller-squeezing blood out
Diastole
Cardiac muscle relaxes –heart becomes larger-allowing the blood to flow into
atria and ventricles
Blood flow through valves
--there is a valve each between left and right atrium and ventricle-atrioventricular
valves
-- valve on the left side of the heart –made up of 2 parts-bicuspid /mitral valve
-- valve on the right side of the heart –made up of 3 parts-tricuspid valve
Function
-- to stop blood flowing back from ventricles to atria. It is important as when
ventricles contract, the blood is pushed up into the arteries, not back into atria
--tendons attached to the valves stop them from going to far
Questions:
1. What kind of muscle is found in the heart?
2. Which part of the heart receive blood from the a) the lungs b) the body?
3. Which part of the heart pump blood into a) pulmonary artery b) aorta
4. Why do ventricles have thicker walls than atria?
5. Why does the left ventricle have a thicker wall than the right ventricle?
6. What is the function of the coronary arteries?
7. What is a) systole b) diastole
8. Where are the atrioventricular valves? What is their function?
9. Why are these valves supported by tendons?
10. What is pacemaker?
Listening to a beating heart: lub-dub
What does a doctor hear when they listen to a patients’ heart?
lub-dub,
lub-dub,
lub-dub,
lub-dub,
lub-dub,
lub-dub…
The sound of a heartbeat is the sound of the heart valves.
The “lub” is caused by
the closing of the valves leading to
the ventricles.
The “dub” is caused by
the closing of the valves
leading out of the heart.