Contents
The Heart and Circulatory System
How are substances transported?
Structure of the heart
How valves work
How the heart works
Summary quiz
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How are substances transported in our bodies?
The next organ system we will be considering can be
known by two names…..
Blood system
Circulatory system
The circulatory system is made of two parts:
1. The heart
2. The blood vessels
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What we use in the air
One of the substances that the circulatory system
transports are respiratory gases.
For example, the oxygen that the body needs, must
be taken to the cells and the carbon dioxide waste
gas must be taken away from the cells.
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Dissolved gases in blood
As these gases are carried by the blood, it means that in
terms of the presence of gas, we have two types of blood.
blood high in oxygen
blood low in oxygen
oxygenated
deoxygenated
At all times these two types of blood cannot mix.
Why do you think this is?
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A double circulatory system
Because of this our circulatory system is in two parts.
It is in fact called a double circulatory system.
This section of the system
including the right side of
the heart, deals with the
deoxygenated blood.
Lungs
Body cells
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This section of the
system including the
left side of the heart,
deals with the
oxygenated blood.
The human circulatory system
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Contents
The Heart and Circulatory System
How are substances transported?
Structure of the heart
How valves work
How the heart works
Summary quiz
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The heart: structure and function
In this unit we are going to
focus on the heart..
The Heart
This is the pump at the centre of the circulatory system.
Not all living organisms have hearts.
Also, the shape of the heart can change, depending on
what species you look at.
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One big muscle
The heart is made almost entirely of muscle. It is unlike
any other muscle in your body because it never tires.
And even though it is full of blood it still needs it own
blood supply.
Oxygenated blood is carried to the heart by the
coronary arteries.
Each side of the heart has two chambers.
1. An top chamber or atrium and
2. A bottom chamber or ventricle
Each of these chambers has its own function.
Look at the diagram on the next slide to see what that is.
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Diagrammatical representation
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Contents
The Heart and Circulatory System
How are substances transported?
Structure of the heart
How valves work
How the heart works
Summary quiz
11 of 35
The valves: structure and function
Besides the chambers there is also another very important part
of the heart – the valves.
These valves are found between the top and bottom chambers
on both sides of the heart.
blood
valve
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These valves are
rather like doors
that only open in
one direction.
Valves in action
As the atrium fills
with blood, the
valves are closed.
When the atrium
contracts and squeeze
the blood, the valves
are pushed open.
These valves are connected to the side wall of the heart
by tough tendons.
These tendons allow the valves to close but not invert.
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Tendon holding a valve
valve
tendon
wall of
ventricle
These tendons can be compared to an arm holding
onto the handle of a door.
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Analogy of a valve
The arm
bends
as the
door is
opened.
When the
door is
closed
the arm is
fully
extended.
It would be impossible for the door to open in the
other direction without the person moving with it.
The tendon (represented by the arm) is held in a fixed
position and therefore the valve (door) can only open
in one direction.
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Preventing backflow
The blood will
naturally push
against the valve.
However, the
valves remain
firmly shut.
In this way, the blood can be moved from chamber to
chamber quite efficiently.
The valves prevent the blood from moving in the wrong
direction.
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More valves
we also find
valves here
...and here!
These extra valves stop the blood from re-entering the
heart when it is pumped from the ventricles.
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Lub - dub
When the blood knocks against the first heart valves, it
makes a ‘lub’ like sound.
When the blood knocks against the second set of
heart valves, it makes a ‘dub’ like sound.
artery
ventricle
The blood ‘slaps’ against
the valve and then passes
along the artery.
valve
These two sounds – lub and dub – are actually what we
hear as our heartbeat. So our heartbeat is in fact the
sound of the valves opening and closing.
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The heart’s main valves
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Contents
The Heart and Circulatory System
How are substances transported?
Structure of the heart
How valves work
How the heart works
Summary quiz
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The action in motion
Now that we can name all of the parts of the heart it is
time to see how they work to push blood around the body.
The heart pumps blood when its muscle contracts. As
the muscle contracts the chamber gets smaller and
squeeze the blood out.
The two sides of the heart work together. The atria
contract and relax at the same time, as do the ventricles.
The next two slides describe what occurs inside the heart
during one heart cycle.
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The action in motion
blood from the
body
blood from
the lungs
1. The heart beat begins
when the heart muscles
relax and blood flows into
the atria.
2. The atria then contract and
the valves open to allow
blood into the ventricles.
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The action in motion
3. The ventricles contract
forcing the blood to leave the
heart. At the same time, the
atria are relaxing and once
again filling with blood.
The staged cycle then repeats itself.
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Left and right ventricles
Do you notice anything
different about the two
sides of the heart?
Well, the left ventricle wall
is clearly thicker than the
right ventricle wall.
Why is this?
To answer this question, think about where the blood is
going when it leaves the right and left ventricles.
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Different destinations
lungs
This journey is
far less
demanding. The
right ventricle
only has to pump
blood from the
heart to the
adjacent lungs.
This journey is
enormous.
The left
ventricle has
to pump blood
all over the
body!
body cells
Therefore, the left ventricle needs a thicker wall to
generate a stronger ‘squeeze’ on the blood.
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Drag the labels to the correct numbered boxes
on the diagram of the blood system.
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Traffic control
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Label the heart
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Answer the questions
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Oxygenated or deoxygenated?
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Getting things in order
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Controlled circulation
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Contents
The Heart and Circulatory System
How are substances transported?
Structure of the heart
How valves work
How the heart works
Summary quiz
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Multiple-choice quiz
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