What We Know
About Gas Exchange in Lungs
Oxygen & Carbon Dioxide
The body requires oxygen in order to produce energy for
our cells to do work. Therefore, it is essential that we have an efficient
system of obtaining oxygen from the air. Our bodies also produce a toxic
gas called carbon dioxide
that must be efficiently removed from the body to prevent cell damage.
When we inhale, we pick up oxygen from air. When we exhale, we flush
out carbon dioxide.
Each breath lasts only a few seconds (even less if we
are running.) Isn't it amazing that gas exchange occurs so
quickly? What is it about gases that lets them exchange so quickly?
Structures of the Respiratory System
Here is a list of structures to become familiar with:
Mouth and Nose- these are the openings
where respiratory gases enter and leave the body.
- Trachea (windpipe)- this passage way connects the
mouth and nose to the lungs.
- Lungs- these are the balloon-like structures that
temporarily hold air in the body.
- Bronchial tube- the trachea breaks up into these smaller
tubes to enter the right and left lungs.
- Bronchioles- within the lungs the bronchi split into
these even smaller tubes which attach to the alveoli.
- Alveoli- these are the small sac-like structures
where gas exchange occurs with the blood.
(Note: The above structures are listed in the order they
are used during inspiration and in reverse order for expiration.)
Here is a detailed picture of the respiratory system: (The structures we will discuss are highlighted. Click
here for a larger version)
Do you see how air moves into the lungs?
Why do you think the bronchi become so
Why do you think there are veins and
arteries at the alveoli?
What keeps food from going into the lungs?
Here are a few things that will help answer
some of your questions:
- Air enters your body through your mouth and
nose. The nasal passage connects to the oral passage at the back
of the mouth where a tube called the trachea connects the mouth
and nose to the lungs. Dirt from the air is filtered before it ever reaches
the lungs by the hairs and mucus in the nose. This hair and mucus trap
some of the dirt and germs found in the air to protect the lungs from
Why do we have nose hairs?
- The trachea, or windpipe, is a tube that connects
the nose and mouth to the lungs. You can see and feel your trachea on
the front of your neck. The tube has C-shaped cartilaginous
around it to prevent the tube from collapsing and blocking the air flow
to and from the lungs. Air is the only substance designed to go down the
Why do you think the trachea is only meant for
air? What happens if something blocks the trachea?
- A little flap covers the trachea each time you swallow to direct
food and drinks to go down the esophagus, a tube that leads to the stomach.
When food and drinks find their way into the trachea, you’ll know it immediately!
You’ll begin coughing in order to push the food back out of the
trachea to allow air to pass through uninhibited.
What happens when a person laughs so hard, that milk can
come out of their nose?
the trachea approaches the lungs, it branches into two tubes. One tube
leads to the right lobe of the lungs, and the other tube leads to the
left lobe of the lungs. These tubes are known as the bronchial tubes.
The bronchial tubes enter the lungs and begin branching into smaller and
- These smaller tubes are called bronchioles. The
walls of the bronchioles contain smooth muscle that is used to dilate
or constrict the lungs depending upon the body’s need for oxygen. The
bronchioles continue the branching process until they reach small, thin
sacs called alveoli. The function of the lungs depends primarily on these
Does this branching allow the tubes to fill the lungs
Asthma is a disease in which dust, pollen, or other
things to which you are allergic change the diameter of the bronchioles.
What does this do? Why?
What is the benefit of having such a large amount of
surface for gas exchange to take place?
How about a look at a pair of lungs?
These are sheep lungs with a cut trachea at the top. Left: lateral view
as seen from animal's right side. Right: ventral view, with heart
removed. Look closely at the end of the trachea in the picture on
the right to see how it branches into the bronchi. Click
here to see a larger version
Next we're going to discuss the alveoli in detail
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