Bodily Defenses Image Map

Gas Exchange in the lungs

Exterior view of Alveoli. This is where gas exchange takes place in the lungs.

Alveoli are tiny balloon-like sacs, in the lungs, where gas exchange takes place and they serve as the barrier between the external environment (the air) and the internal environment (the blood).

Because gas must exchange in a second or two between blood vessels and the air inside of our lungs, how do you suppose the process is made efficient?

  •  These small sacs have very thin walls that are full of blood vessels called capillaries. The walls are so thin that the oxygen, brought in during inhalation, can diffuse through them to enter your blood. 
  • Likewise, carbon dioxide is carried by your blood to the blood vessels in the alveoli where it diffuses through the thin walls and into the air in your lungs. That "used" air is now ready for exhalation. Each lung has millions of alveoli, and your body needs all of them to get enough oxygen into your blood! 

Why are there so many capillaries at the alveoli?  Why are they shown in blue and red?

What is the problem with the buildup of tar and other hazardous materials from smoking in the lungs?  

Why are dust masks so important for some jobs?

Blue Blood

Okay, it is not really blue. Blue blood is more of a dark red color, close to maroon.  However, during surgery and dissections, the veins that carry this blood appear blue.  This change in color is due to the lack of oxygenation in the hemoglobin of the blood cells.

What color is oxygenated blood? (Hint: The answer is bright ____.)

  • Deoxygenated (blue) blood travels into the capillaries surrounding the alveoli. The blood drops off its carbon dioxide molecules and picks up oxygen. Once the blood cells pick up oxygen, it becomes oxygenated (red) blood. The blood now exits the pulmonary capillaries and carries oxygen to all the tissues in the body.
  • Deoxygenated blood does contain oxygen, but it is present at a smaller concentration than oxygenated blood.  The term deoxygenated is used for convenience.

Does anybody really have blue blood?  Why do bruises appear blue at first (they change to a yellowish color later, as the blood is chemically broken down)?

Muscles involved in Gas Exchange

  • Breathing requires the help of a muscle known as the diaphragm
  • The diaphragm is a large, sheet-like muscle at the bottom of your chest cavity. It helps you exhale and inhale by moving up and down, respectively. 
  • When your diaphragm contracts (moves up), you inhale air. 
  • When your diaphragm relaxes (moves down), you exhale air. 
  • Without your diaphragm, you lungs couldn’t fill up with fresh air or push old air out.

Why do you think the diaphragm is located at the bottom of your chest cavity?





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