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© Boardworks Ltd 20041 of 49
KS4 Biology
The Heart and Circulatory System
© Boardworks Ltd 20042 of 49
How the heart pumps blood
The Heart and Circulatory System
The circulatory system
Structure of the heart
Valves in the heart
Summary quiz
Contents
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Which organs are involved in this system?
How do substances move around the body?
The body has its own transport system that carries substances around the body.
The body’s transport system is called the circulatory system.Why is it given this name?
heart
blood vessels
blood
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What is carried by the circulatory system?
carbondioxide
oxygen
Which gases are transported to and from the body’s cells by the blood flowing in the circulatory system?
Oxygen is the gas needed for respiration and is transported to the body’s cells.
Carbon dioxide is the waste gas produced by respiration that must be carried away from the body’s cells.
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The arrangement of the circulatory system means that these two types of blood do not mix. Why is this important?
Two types of blood
The circulatory system carries two types of blood:
oxygen-rich blood
c
oxygen-poor blood
blood travelling to the body cells
high oxygen content
low carbon dioxide content
blood travelling away from the body cells
low oxygen content
high carbon dioxide content
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How are the two types of blood (oxygen-rich and oxygen-poor) kept apart inside the heart?
At the heart of the circulatory system
The heart is the organ at the centre of the circulatory system. It pumps blood around the body.
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Inside the heart
The inside of the heart is divided into two sections so that the two types of blood (oxygen-rich and oxygen-poor) are kept apart.
oxygen-poor blood
right sideof the heart
oxygen-rich blood
left sideof the heart
Remember that the heart is always labelled as if it is in a body facing you, so the right side of the heart is on the left of the diagram.
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The two sides of the heart
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How does blood circulate around the body?
Blood is pumped around the body by the heart.
It takes about 30 seconds for blood to go once around the body.
Starting with the left side of the heart, what route does the blood follow to complete one circuit of the body?
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How does blood circulate around the body?
The left side of the heart pumps oxygen-rich blood to the rest of the body.
This blood supplies the body’s cells with oxygen.
What gas does the blood then pick up from the body’s cells and where does the blood go next? body’s
cellsbody’scells
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The oxygen-poor blood needs to lose the carbon dioxide and pick up more oxygen. How does it do this?
How does blood circulate around the body?
Blood picks up carbon dioxide from the body’s cells.
This oxygen-poor blood then travels back to the right side of the heart.
body’scells
body’scells
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lungslungs
Where does this oxygen-rich blood then travel to?
How does blood circulate around the body?
Next, the right side of the heart pumps oxygen-poor blood to the lungs.
In the lungs the blood gets rid of the waste carbon dioxide and collects more oxygen.
body’scells
body’scells
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The oxygen-rich blood then returns to the left side of the heart.
This completes the blood’s journey around the body.
Why is the journey of blood through the circulatory system called a double circulation?
How does blood circulate around the body?
body’scells
body’scells
lungslungs
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During one complete circuit of the body, blood passes through the heart twice.
The heart has two jobs to do and so the circulatory system involves a double circulation.
What are the two jobs that the heart carries out during this double circulation?
A double circulatory system
body’scells
body’scells
lungslungs
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Which way does blood flow?
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The Heart and Circulatory System
The circulatory system
Structure of the heart
How the heart pumps blood
Valves in the heart
Summary quiz
Contents
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The structure of the heart – exterior
The heart pumps blood around the circulatory system. What is the heart made of?
The heart is made of muscle and keeps pumping blood around your body, even when you are asleep!
muscletissue
What do the blood vessels on the outside of the heart do?
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The heart needs blood too!
The heart is full of blood but also needs its own blood supply so that the muscle can keep pumping.
blood vessels supply blood
to muscle tissue
The blood vessels on the outside of the heart carry oxygen-rich blood to the heart muscle cells. Oxygen-poor blood is then carried away from these cells by outer blood vessels and back into the heart.
muscletissue
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The structure of the heart – interior
The inside of the heart is divided into two sections to keep oxygen-rich and oxygen-poor blood separate.
Each side of the heart is also divided into two sections.
Each section of the heart is called a chamber.How many chambers are there?
right sideof the heart
left sideof the heart
4
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The chambers of the heart
The four chambers of the heart have special names:
A lower chamber is called a ventricle.
An upper chamber is called an atrium (plural atria).
rightventricle
rightatrium
leftventricle
leftatrium
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What do atria and ventricles do?
The chambers of the heart have different functions.
The atria collect blood that enters the heart.
The ventricles pump blood out of the heart.
blood tothe body
blood from the body
blood to the lungs
blood from the lungs
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Inside the heart – labels
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Inside the heart – labelling activity
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Chambers of the heart – activity
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The Heart and Circulatory System
The circulatory system
Structure of the heart
How the heart pumps blood
Valves in the heart
Summary quiz
Contents
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Preventing backflow
Blood always flows in the same direction as it moves through the heart during each circulation of the body.
Why is it important that blood does not flow backwards?
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The chambers of the heart are separated by valves which prevent blood from flowing in the wrong direction.
Heart valves
There are valves between the atria and the ventricles……and there are valves leading out of the ventricles.
valve between right atrium and right ventricle
valve between left atrium and left ventricle
valve leading out of
right ventricle
valve leading out of
left ventricle
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Naming the heart valves
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How are valves held in place?
The valves between the atria and ventricles are connected to the inner walls of the heart by tough tendons.
valve open
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How are valves held in place?
The tendons allow the valves to close and hold the valve flaps in place. They prevent the valves from flipping up and turning inside out. Why is this important?
valve open valve closed
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How do valves work?
A valve acts like a door that only opens in one direction.
If the door is held by someone at a fixed point, only the arm moves as the door opens and closes.
When the door is closed the arm is fully extended, so the door can only be opened in one direction.
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How do valves work?
A valve acts like a door that only opens in one direction.
In the heart, the tendons holding the valve are like the arm holding the door.
One end of each tendon is fixed to the wall of the heart and so the valve can only open in one direction.
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The Heart and Circulatory System
The circulatory system
Structure of the heart
How the heart pumps blood
Valves in the heart
Summary quiz
Contents
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How does the heart pump blood?
Imagine the force needed to squeeze a tennis ball.
That’s how much force the heart uses to pump blood around the body!
How does the heart produce enough force to keep doing this 24 hours a day?
The heart can pump blood because it is made of muscle. Muscle tissue works by contracting (squeezing) and relaxing.
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How does the heart pump blood?
All the parts of the heart on either side, work togetherin a repeated sequence.
The two atria contract and relax; then the two ventricles contract and relax.
This is how blood moves through the heart and is pumped to the lungs and the body.
One complete sequence of contraction and relaxation is called a heartbeat.
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Heartbeat animation
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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?
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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?
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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?
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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 outof the heart.
What happens to the open valves when the ventricles are empty?
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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?
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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?
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What does a doctor hear when they listen to a patients’ heart?
Listening to a beating heart: lub-dub
The “lub” is caused bythe closing of the valves leading to the ventricles.
The “dub” is caused by the closing of the valvesleading out of the heart.
lub-dub,
The sound of a heartbeat is the sound of the heart valves.
lub-dub, lub-dub, lub-dub, lub-dub, lub-dub…
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Measuring a beating heart
You can measure how fast your heart is beating by taking your pulse.
Each pulse that you feel is due to the pressure of blood leaving the heart asthe left ventricle contracts.
Place the fingertips of one hand on the opposite wrist, where an artery passes near the surface of the skin.
What is your heart rate, in beats per minute, right now?
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…in one hour?
…in one day?
…in one year?
…in 70 years?
How many heartbeats?
If your heart beats at an average rate of 70 times per minute, how many heartbeats are there…
70 x 60 =
4, 200 x 24 =
100, 800 x 365 =
36, 792, 000 x 70 =
100, 800100, 800
36, 792, 00036, 792, 000
2, 575, 440, 0002, 575, 440, 000
4, 2004, 200
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The sequence of a heartbeat
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Journey of blood around the body
© Boardworks Ltd 200448 of 49
The Heart and Circulatory System
The circulatory system
Structure of the heart
How the heart pumps blood
Valves in the heart
Summary quiz
Contents
© Boardworks Ltd 200449 of 49
Multiple-choice quiz