KEY STAGE 4
THE HEART AND
CIRCULATORY SYSTEM
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The next organ system we will be considering can be known by two names…..
How are substances transported around the body?
Blood system Circulatory system
The circulatory system is made of two parts:
1. The heart
2. The blood vessels
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.
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 Deoxygenated
Oxygenated
This section of the system including
the right side of right the heart, deals
with the deoxygenated deoxygenated
blood.
This section of the system including the left side of the left
heart, deals with the oxygenated oxygenated
blood.
Lungs
At all times these two types of blood cannot mix. Why do you think this is?
Because of this our circulatory system is in two parts. It is in fact called a double circulatory system.
The Human Circulatory System
In this unit we are going to focus on 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.
The Heart
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.
The Heart
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
These valves are rather like doors that only open in one direction.
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
valve
tendon
wall of ventricle
These tendons can be compared to an arm holding onto the handle of
a door.
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.
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.
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.
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.
Valve
Ventricle Artery
The blood ‘slaps’ against the valve and then passes along the artery.
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.
The following diagram shows the position and
name of the main valves in the heart.
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.
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.
The staged cycle then repeats itself.
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.
Just before we finish our study, let’s take a last look at the heart…..
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.
This journey is enormous. The left ventricle has to pump blood all over the body!
This journey is far less
demanding. The right ventricle
only has to pump blood from the heart to the adjacent lungs.
Therefore, the left ventricle needs a thicker wall to generate a stronger ‘squeeze’ on the blood.
Body cells Lungs
Drag the labels to the correct numbered boxes on the diagram of the blood system
Multiple choice questions
What is the alternative name for the blood system?
A the heart system
B the circulatory system C the transporting system D the pumping system
Which of the following organs are found in the blood system?
A heart, lungs, brain and bladder B arteries, heart and stomach C arteries, veins and heart D heart, veins and pancreas
The function of the circulatory system is to...
A transport substances, such as oxygen and dissolved nutrients, around the body.
B support the movement of the body.
C digest large molecules of food.
D carry chemical messages between the brain and the nerves.
What is the wall of the heart mainly made from?
A. fat tissue B. skin tissue C. nerve tissue D. muscle tissue
The blood system is often known as the “double circulation” system. Why is this?
A The blood carries two vital materials.
B There are actually two parts to the heart.
C The system is divided into two separate circuits.
D The blood flows in two directions.
How many chambers are there in the human heart?
A four
B it varies from human to human C two
D none of the above
Look at the diagram below.
Name the chamber that is labelled W (be careful!).
A the right ventricle B the left ventricle C the right atrium D the left ventricle
W X
Z Y
If blood entered the chamber X, where would it then go?
A It would leave the heart.
B It would pass into chamber Z.
C It would pass across into chamber W.
D It would flow into all the other chambers.
W X
Z Y
Which chamber is the left ventricle?
A W B X C Y D Z
W X
Z Y
Which side of the heart has the thickest wall?
A the left B the right
C both sides are the same thickness D middle is thicker
W X
Z Y
Into which chambers does blood enter the heart?
A the right and left atrium B the right and left ventricle
C the right atrium and the left ventricle D the right ventricle and the left atrium
Through which two chambers does blood leave the heart?
A
the right and left atrium B the right and left ventricle
C the right atrium and the left ventricle D the right ventricle and the left atrium
Which of these combinations lists the two circuits that blood makes through the body?
A Heart - Lungs - Body - Lungs
B Heart - Body - Heart - Body - Lungs C Body - Lungs - Heart - Body - Heart D Heart - Lungs - Heart - Body
Look at the diagram below.
P
S
Q R
U T
What is part T?
A an atrium B a ventricle C a capillary D a chamber
P
S
Q R
U T
Part Q shows...
A a heart valve.
B the atrium.
C a chamber.
D a heart door.
P
S
Q R
U T
Arrow R pumps blood to the...
A the ventricles.
B the body.
C the liver.
D the lungs.
P
S
Q R
U T
Arrow P shows the blood coming from the...
A the stomach.
B the head.
C the body.
D the lungs.
P
S
Q R
U T
