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Recall the Main Structures and Functions of the Circulatory System

Worksheet Overview

QUESTION 1 of 10

Did you know that your heart beats about 100,000 times a day?! And that it sends about 2,000 gallons of blood around your body?! That’s around the same amount as 16,000 pints of milk!

The cells in our body need a good supply of oxygen and nutrients.  They also need to get rid of waste substances. Our blood carries out both of these functions. The circulatory system consists of blood vessels such as arteries, veins and capillaries, and a pump called the heart.
 

Image of the circulatory system

 

Blood passes through the heart twice on every full circuit of the body. This is called a double circulatory system. A double circulatory system separates the blood with oxygen from the blood without oxygen. Blood with oxygen is called oxygenated blood. Blood without oxygen is called deoxygenated blood.

Each organ of the body is supplied with blood from its own artery.  This blood is oxygenated. Deoxygenated blood is taken away from organs by veins. 

When blood has been pumped out of the left ventricle of the heart, it begins to make its journey around the body in an artery called the aorta.  The blood is rich in oxygen. Oxygen is carried by red blood cells. The oxygen leaves the red blood cells as they pass through the capillaries.  Capillaries are the network of blood vessels which pass in between the cells in the body. As blood leaves the capillaries, it enters veins. Veins return blood to the heart.

 

 

Arteries

When blood flows out of the heart, it enters the arteries. The blood is at very high pressure because it has been forced out of the heart as the ventricles have contracted (squeezed).  Arteries have very strong walls to be able to cope with the high pressure of the blood flowing through them.  The blood moves through the arteries with every heartbeat.  The thick muscular walls stretch and then bounce back into place because of the elastic fibres in the walls of arteries.


 

Capillaries

Arteries divide into smaller blood vessels.  The smallest blood vessels are called capillaries. The function of a capillary is to take nutrients and oxygen to cells and take waste products away. The structure of a capillary helps them to do this. Capillaries have very thin walls - they are only one cell thick. This means that the substances can diffuse in and out very quickly.


 

Veins

Capillaries eventually join up again and form veins.  By the time the blood gets to the veins, it is at a much lower pressure than it was in the arteries.  Veins don't have thick, strong, elastic walls. Veins have valves to stop the blood from flowing backwards. Arteries do not have valves because the force of the heartbeat keeps the blood moving.


 

Gas Exchange

The lungs are adapted for gas exchange. Breathing involves exchanging gases in the lungs. 

 

Image of the human lungs

 

When you breathe in, oxygen in the inhaled air travels down your trachea, which branches off into bronchi (one branch is called the bronchus). This further divides into bronchioles and eventually, the oxygen diffuses through the tiny alveoli (air sacs) in your lungs into your bloodstream. The oxygen is transported to the heart via the pulmonary vein and then pumped around your body via the aorta from the heart. Carbon dioxide is the waste gas produced by respiration. Carbon dioxide diffuses from cells into the bloodstream and is pumped to the lungs via the pulmonary artery to be exhaled. 

 

Image of alveolus and gas exchange

 

 

 

The alveoli have a few adaptations that make gas exchange very efficient. They are only one cell thick, making them very thin, which allows gases to pass through easily and quickly. They also have a large surface area, allowing large amounts of gases to be exchanged with each breath.

 

In the following activity, you will recall the main structures and functions of the circulatory system.

Which side of the heart pumps oxygenated blood? 

 

Image of the human heart

Left-hand side

Right-hand side

Both sides

The image shows a section through the heart.

 

Name the structures labelled A, B and C on the image below.  

 

Image of the heart

 ABC
Aorta
Pulmonary vein
Left atrium

Why do the ventricles of the heart have thicker walls than the atria? 

 

Image of the hearts atria and ventricles

Atria pump blood out of the heart so have thicker walls

Ventricles receive blood from the atria

Atria collect blood coming into the heart

Ventricles have to pump blood out of the heart so have thicker walls

The body contains three different types of blood vessels.

 

What are the names of these blood vessels?

Arteries

Neurones

Veins

Capillaries

Insulin

The largest artery in the body is the aorta.

 

Describe the features of the aorta.

 

Image of the aorta labelled on heart

Arteries

Neurones

Veins

Capillaries

Insulin

Capillaries have some special features that help them to do their job.

 

How are capillaries suited to their function?

 

They have a thick, muscular wall

They are only one cell thick

They contain valves

The vena cava is the largest vein in the body. It carries deoxygenated blood back to the heart.

 

How are veins like the vena cava suited to their function? 

Veins contain valves which prevent the back flow of blood

Veins have thick, muscular walls

Veins are only one cell thick

 
 

The lungs can be seen in the image below. 

 

Match up the parts a, b, c, and d with their correct structure.

 

Image of the lungs

Column A

Column B

a
Alveoli
b
Trachea
c
Bronchus
d
Bronchiole

Breathing involves the exchange of gases in the lungs - a process that occurs by diffusion.

 

What happens when you breathe in? 

Column A

Column B

Oxygen in inhaled air diffuses through...
... throughout the body
The oxygen is then transported...
...into the bloodstream and is exhaled via the lun...
Carbon dioxide is the waste gas...
...produced by respiration
Carbon dioxide diffuses from body tissues ...
...the alveoli in the lungs and into the bloodstre...

Alveoli have several adaptations that help to make gas exchange very efficient.

 

Select the adaptations that are true about the alveoli.

 

Image of gas exchange in alveolus

 

  • Question 1

Which side of the heart pumps oxygenated blood? 

 

Image of the human heart

CORRECT ANSWER
Left-hand side
EDDIE SAYS
Try not to get confused - you have to imagine the image of the heart as if it's inside your body. So, right side on paper is actually left-hand side in real life! Oxygenated blood is kept separate from deoxygenated blood in the double circulatory system. The oxygenated blood is pumped from the left-hand side of the heart.
  • Question 2

The image shows a section through the heart.

 

Name the structures labelled A, B and C on the image below.  

 

Image of the heart

CORRECT ANSWER
 ABC
Aorta
Pulmonary vein
Left atrium
EDDIE SAYS
This was quite a tricky diagram to work through, wasn't it? With only three options to choose from, it was possibly easiest to work through this using a process of elimination. The aorta was maybe the easiest to spot because it is such a large blood vessel. It is a massive artery that carries oxygenated blood from the heart to the rest of the body. This is A. Veins carry blood into the heart. They nearly always carry deoxygenated blood, but the the pulmonary vein is the exception to this. It carries oxygenated blood from the lungs to the heart. This is labelled B. Finally, the remaining option, C, was the left atrium. This is where the oxygenated blood enters from the lungs and you can see from the image that it is a chamber, rather than a blood vessel. Well done for working through this one.
  • Question 3

Why do the ventricles of the heart have thicker walls than the atria? 

 

Image of the hearts atria and ventricles

CORRECT ANSWER
Ventricles receive blood from the atria
Ventricles have to pump blood out of the heart so have thicker walls
EDDIE SAYS
Understanding how the double circulatory system works is the key to this question. Blood enters the heart through the atria, which means that the pressure is not very high. Blood is pumped out of the heart through the ventricles. The ventricles have thicker walls to allow for a greater 'push,' forcing the blood out of the heart with huge pressure, allowing it to reach all areas of the body.
  • Question 4

The body contains three different types of blood vessels.

 

What are the names of these blood vessels?

CORRECT ANSWER
Arteries
Veins
Capillaries
EDDIE SAYS
This was a pretty straightforward question but do you know what the other options are? A neurone is another name for a nerve cell and insulin is a hormone involved in blood sugar regulation!
  • Question 5

The largest artery in the body is the aorta.

 

Describe the features of the aorta.

 

Image of the aorta labelled on heart

CORRECT ANSWER
EDDIE SAYS
Remember: Arteries carry blood Away from the heart. The Aorta is one of the main Arteries. They all begin with the letter A!
  • Question 6

Capillaries have some special features that help them to do their job.

 

How are capillaries suited to their function?

 

CORRECT ANSWER
They are only one cell thick
EDDIE SAYS
How did you find this question? Capillaries are extremely thin - they're only one cell thick! This means that gases and nutrients can diffuse really quickly from the blood into cells. If the capillaries were thicker, it would take longer for gases and nutrients to be exchanged and the blood wouldn't be able to meet the demands of the body.
  • Question 7

The vena cava is the largest vein in the body. It carries deoxygenated blood back to the heart.

 

How are veins like the vena cava suited to their function? 

CORRECT ANSWER
Veins contain valves which prevent the back flow of blood
EDDIE SAYS
Veins always carry blood into the heart - the word vein includes the word in! This means that they won't have much pressure behind the blood, so they don't need thick muscular walls, unlike the arteries. However, there is the danger of blood flowing backwards as it tries to reach the heart with very little pressure behind it. This is why veins need valves. Try to remember: Veins contain Valves!
  • Question 8
 
 

The lungs can be seen in the image below. 

 

Match up the parts a, b, c, and d with their correct structure.

 

Image of the lungs
CORRECT ANSWER

Column A

Column B

a
Trachea
b
Alveoli
c
Bronchiole
d
Bronchus
EDDIE SAYS
If you weren't too sure about this diagram, it might be a good idea to study the image in the Introduction to try to get it sorted in your head before moving on. The lungs have different structures that help them to do their job, which is gas exchange. The bronchi and bronchioles allow for the quick movement of gas throughout the lungs. The alveoli help to exchange gases very quickly into the blood.
  • Question 9

Breathing involves the exchange of gases in the lungs - a process that occurs by diffusion.

 

What happens when you breathe in? 

CORRECT ANSWER

Column A

Column B

Oxygen in inhaled air diffuses th...
...the alveoli in the lungs and i...
The oxygen is then transported...
... throughout the body
Carbon dioxide is the waste gas.....
...produced by respiration
Carbon dioxide diffuses from body...
...into the bloodstream and is ex...
EDDIE SAYS
Did you match them all correctly? Hopefully, you didn't get muddled between oxygen and carbon dioxide. Both oxygen and carbon dioxide diffuse between the lungs and the bloodstream - oxygen goes into the bloodstream and carbon dioxide goes out! Oxygen and carbon dioxide have the opposite pathways, so if you take the time to remember the pathway of one gas, the other gas should be easier to remember!
  • Question 10

Alveoli have several adaptations that help to make gas exchange very efficient.

 

Select the adaptations that are true about the alveoli.

 

Image of gas exchange in alveolus

 

CORRECT ANSWER
EDDIE SAYS
Did you get them all? The alveoli are extremely well adapted for their vital role. They are very thin - only one cell thick - so that gases can easily diffuse in and out. They are also moist, which encourages gas molecules to easily dissolve, allowing gas exchange to happen quickly. They're also covered by a network of capillaries, enabling gases to pass almost directly between the lungs and bloodstream. Finally, although very small, there are a large number of them, so they have a large combined surface area. Well done for completing this activity.
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