Contents. The Heart and Circulatory System. How are substances transported?. Structure of the heart. How valves work. How the heart works. Summary quiz. How are substances transported in our bodies?. The next organ system we will be considering can be known by two names….
The next organ system we will be considering can be known by two names…..
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 dioxidewaste gas must be taken away from the cells.
blood high in oxygen
blood low in oxygen
As these gases are carried by the blood, it means that in terms of the presence of gas, we have two types of blood.
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.
This section of the system including the left side of the heart, deals with the oxygenated blood.
This section of the system including the right side of the heart, deals with the deoxygenated blood.
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.
Each of these chambers has its own function.
Look at the diagram on the next slide to see what that is.
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.
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 close but not invert.
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.
However, the valves remain firmly shut.
The blood will naturally push against the valve.
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
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.
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.
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 lungs
blood from the body
1. The heart beat begins when the heart muscles relax and blood flows into the atria.
The staged cycle then repeats itself.
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 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!
Therefore, the left ventricle needs a thicker wall to generate a stronger ‘squeeze’ on the blood.
on the diagram of the blood system.