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Adaptations of the Circulatory System

In this worksheet, students will explain the adaptations of the organs 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.

The systems in the body all work together. The gaseous exchange system, the digestive system and excretory system all interact with the circulatory system in order to keep us alive. For example, during digestion, food is broken down by the stomach and small intestine. Water and dissolved food molecules are absorbed into the blood in capillaries. The glucose from the food is used for respiration, as well as oxygen from the gaseous exchange system. Waste products are expelled from the body via the excretory system. 

 

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 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 by the contraction (squeezing) of the ventricles. 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. 

The lumen is the hollow corridor that blood flows through. Arteries have a small lumen, keeping the blood under high pressure.

 

Capillaries 

Arteries divide into smaller blood vessels 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 it 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

 

Image of vein with valves

 

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, so veins don't need to have thick, strong, elastic walls. Instead, 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. Veins have larger lumens than arteries because they are under less pressure.

The bicuspid and tricuspid valves are really important -  they make sure blood travels the correct way. The blood flowing into the ventricles is prevented from flowing back into the atrium. 

The semilunar valves are found between the aorta and the left ventricle, and between the pulmonary artery and the right ventricle. The valves stop blood from flowing back into the ventricles.

 

 

Gas Exchange

The lungs are well 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 in the pulmonary vein and then pumped around your body through 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 in the pulmonary artery, to be exhaled.

This goes to show how the circulatory system and gaseous exchange system work together!

 

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, allowing 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 explain the adaptations of the organs of the circulatory system.

What are the names of some of the systems that interact with the circulatory system?

Digestive system

Gaseous exchange system

Skeletal system

Excretory system

Look at the image of the heart.

 

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 largest artery in the body is the aorta.

 

Describe the features of the aorta by filling in the blanks below.

 

Image of the aorta labelled on heart

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

What is the relationship between the digestive system and circulatory system? 

The digestive system breaks down food, releasing glucose and other nutrients into the blood which is part of the circulatory system

There is no relationship between the two

The digestive system delivers oxygen to the blood

 

Explain the role of semilunar valves.

They allow blood in the heart to move in any direction

They allow blood to flow into the ventricles

They stop blood from flowing back into the ventricles

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? 

 

Image of vein with valves

Veins contain valves which prevent the back flow of blood

Veins have thick muscular walls

Veins are only one cell thick

The body contains three different types of blood vessels:  veins, arteries and capillaries.

 

Decide on the features of these blood vessels by labelling X, Y and Z.

 

Features X  Y  Z 
 Valves      ✔
 Elastic fibres in blood vessel walls   ✔     
 Large lumen        ✔
 Walls are one cell thick      ✔  
 VeinCapillaryArtery
X
Y
Z

The body contains three different types of blood vessels: veins, arteries and capillaries.

 

Explain some of their adaptations.

Column A

Column B

Valves
Allows a larger passage for blood to travel under ...
Elastic fibres in blood vessel walls
Stop blood from flowing backwards
Large lumen
Allowing gas exchange to occur efficiently
Walls are one cell thick
Allow the wall to stretch and rebound back to orig...

Using the image below to help you, complete the steps describing how blood flows through the heart. The first one has been done for you.

 

Number 1 - Deoxygenated blood enters the right atrium from the vena cava. 

 

Image of the circulatory system

 

The image shows a section through the heart.   

C is the left atrium.

 

What are A and B, and what are their functions? 

 

Image of the heart

 

 

A - Pulmonary vein - Transports deoxygenated blood to the lungs

A - Aorta - Transports oxygenated blood to the body

B - Aorta - Transports deoxygenated blood to the body

B - Pulmonary vein - Transports oxygenated blood to the heart from the lungs

  • Question 1

What are the names of some of the systems that interact with the circulatory system?

CORRECT ANSWER
Digestive system
Gaseous exchange system
Excretory system
EDDIE SAYS
Our bodies are extraordinary organisms that are kept alive by the continuous activity of many different processes! There were three different systems listed above that need the circulatory system to transport essential substances around the body. These substances are needed for different processes such as respiration.
  • Question 2

Look at the image of the heart.

 

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
Did you get this one? The thicker walls of the ventricles allow for a greater 'push,' forcing the blood out of the heart with greater pressure, so allowing it to reach all areas of the body.
  • Question 3

The largest artery in the body is the aorta.

 

Describe the features of the aorta by filling in the blanks below.

 

Image of the aorta labelled on heart

CORRECT ANSWER
EDDIE SAYS
Here's a useful tip to help you to remember about the aorta: Arteries carry blood Away from the heart. The Aorta is one of the main Arteries. They all begin with the letter A! Because the aorta carries blood out of the heart, it needs to have very strong and muscular walls to withstand the high pressure that the blood is under.
  • Question 4

What is the relationship between the digestive system and circulatory system? 

CORRECT ANSWER
The digestive system breaks down food, releasing glucose and other nutrients into the blood which is part of the circulatory system
EDDIE SAYS
The digestive system relies on the blood (part of the circulatory system) to transport nutrients around the body. Without these nutrients, processes such as respiration couldn't occur!
  • Question 5

 

Explain the role of semilunar valves.

CORRECT ANSWER
They stop blood from flowing back into the ventricles
EDDIE SAYS
Valves are really important in keeping blood moving in the right direction. Without these valves, many health issues can arise. These valves are found between the aorta and the left ventricle and also between the pulmonary artery and the right ventricle. Their job is to stop blood flowing back into the ventricles.
  • Question 6

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? 

 

Image of vein with valves

CORRECT ANSWER
Veins contain valves which prevent the back flow of blood
EDDIE SAYS
Did you spot that option two was referring to arteries and option three applies to capillaries? It was option one that we needed here. Try to remember that veins contain valves! Veins carry blood towards the heart, which means that the blood is under less pressure than in arteries. This means that they need valves to stop the back flow of blood as it travels back to the heart.
  • Question 7

The body contains three different types of blood vessels:  veins, arteries and capillaries.

 

Decide on the features of these blood vessels by labelling X, Y and Z.

 

Features X  Y  Z 
 Valves      ✔
 Elastic fibres in blood vessel walls   ✔     
 Large lumen        ✔
 Walls are one cell thick      ✔  
CORRECT ANSWER
 VeinCapillaryArtery
X
Y
Z
EDDIE SAYS
Did you match them all correctly? Remember that veins have valves to prevent back flow. Capillaries are very thin (one cell thick), allowing quick gas exchange. Arteries have strong walls - necessary because of the pressure of the blood travelling through them.
  • Question 8

The body contains three different types of blood vessels: veins, arteries and capillaries.

 

Explain some of their adaptations.

CORRECT ANSWER

Column A

Column B

Valves
Stop blood from flowing backwards
Elastic fibres in blood vessel w...
Allow the wall to stretch and reb...
Large lumen
Allows a larger passage for blood...
Walls are one cell thick
Allowing gas exchange to occur ef...
EDDIE SAYS
This question refers back to the previous one but gives more detail. How did you get on with it? Veins are the blood vessels that contain valves. This is because the blood flowing in veins is under a much lower pressure than the blood in arteries. There is a risk of blood flowing backwards because of this and so the valves are there to prevent this from happening. Veins also contain a large lumen. This gives the blood more space to flow and makes it easier for the blood to move through the vessels, despite being under low pressure. Capillaries are very thin (one cell thick) allowing gas exchange to occur quickly and easily. Finally, arteries have strong walls filled with elastic fibres that can stretch to allow the movement of blood under high pressure.
  • Question 9

Using the image below to help you, complete the steps describing how blood flows through the heart. The first one has been done for you.

 

Number 1 - Deoxygenated blood enters the right atrium from the vena cava. 

 

Image of the circulatory system

 

CORRECT ANSWER
EDDIE SAYS
Well done if you got this one in the correct order! It should go like this: Deoxygenated blood enters the right atrium from the vena cava. Blood is pumped out of the atrium. Blood fills the right ventricle. Blood is pumped through the pulmonary artery. Remember that blood enters the atrium before entering the ventricle.
  • Question 10

The image shows a section through the heart.   

C is the left atrium.

 

What are A and B, and what are their functions? 

 

Image of the heart

 

 

CORRECT ANSWER
A - Aorta - Transports oxygenated blood to the body
B - Pulmonary vein - Transports oxygenated blood to the heart from the lungs
EDDIE SAYS
These are vital blood vessels to get your head around! The pulmonary vein carries oxygenated blood from the lungs to the heart, ready to be pumped to the body by the heart via the aorta. The aorta is an artery and carries oxygenated blood to the rest of the body. Another activity completed - great effort!
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