© boardworks ltd 2004 1 of 49 ks4 biology the heart and circulatory system

© Boardworks Ltd 20041 of 49

KS4 Biology

The Heart and Circulatory System


How the heart pumps blood


The circulatory system

Structure of the heart

Valves in the heart

Summary quiz

Contents


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


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.


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


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.


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.


The two sides of the heart


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?



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


The oxygen-poor blood needs to lose the carbon dioxide and pick up more oxygen. How does it do this?


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


lungslungs

Where does this oxygen-rich blood then travel to?


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


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?


body’scells

body’scells

lungslungs


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


Which way does blood flow?






Valves in the heart

Summary quiz

Contents


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?


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


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


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


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


Inside the heart – labels


Inside the heart – labelling activity


Chambers of the heart – activity






Valves in the heart

Summary quiz

Contents


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?


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


Naming the heart valves


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


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


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.


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.






Valves in the heart

Summary quiz

Contents


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.


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.


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?



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?



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?



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?



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?



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?


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…


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?


…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


The sequence of a heartbeat


Journey of blood around the body






Valves in the heart

Summary quiz

Contents


Multiple-choice quiz

© boardworks ltd 2004 1 of 49 ks4 biology the heart and circulatory system

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