Bodily Defenses Image Map

The System for Transporting Gases

Your heart beats with about the strength it takes to squeeze a tennis ball. Squeeze a tennis ball and see how hard that is.  Now think what it must be like for your heart to do this 70 times a minute, 60 minutes an hour, 24 hours a day - for a lifetime!

The Circulatory System

The  heart, the blood, and the blood vessels make up a system for the transport of gases, nutrients, and chemical wastes.  The primary functions of the circulatory system are the following:

  1. To transport nutrients and oxygen to the cells.
  2. To remove waste and carbon dioxide from the cells.
  3. To provide for efficient gas exchange.

Blood vessels allow oxygenated blood and nutrients to reach the tissues and wastes to be removed from the tissues.

The blood is the medium that carries oxygen and nutrients to the tissue and is also the medium by which waste is transported to the appropriate locations.

The Heart

The heart is made up of cardiac muscle and is divided into 4 different chambers. The top two compartments are called atria, while the bottom two compartments are called ventricles.

Interior anatomy of the human heart


Exterior view of the human heart

Blood Vessels

There are three basic types of blood vessels:

1. Arteries- these carry "oxygen rich" blood away from the heart, except in the case of the artery to the lungs.

2. Capillaries- these are the sites of gas exchange between the tissues.

3. Veins- these return "oxygen poor" blood to the heart, except for the vein that carries blood from the lungs.

On the right is a diagram showing how the three connect. Notice the artery and vein are much larger than the capillaries.  This junction is called a capillary bed.


  • The capillaries have very thin walls and there are many of them.

Why do you think this is?

Why are the capillaries shown with two different colors?

Why is the vein shown as blue?


Click here to watch an animation of the heart beating

The circulatory path of blood

Note: Arterial blood (oxygen rich blood)  is in red , and venous blood (contains less oxygen) is in blue.

Now, can you draw the parts of the circulatory system and show which parts contain oxygen-rich blood and which parts contain oxygen poor blood?

Lets take a look at Blood Pressure and how it relates to the system for transporting gases.      

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