10 Questions
What is the primary function of the alveoli in the lungs?
To facilitate the exchange of respiratory gases
What is the average diameter of an individual alveolus in the human lung?
0.2 mm
What is the thickness of the walls of the alveoli?
0.001 mm
What is the approximate number of alveoli in the human lungs?
300 million
Where does the exchange of respiratory gases (oxygen and carbon dioxide) occur?
In the capillary beds surrounding the alveoli
What is the role of the capillaries in the respiratory system?
To facilitate the exchange of oxygen and carbon dioxide
What happens to the deoxygenated blood as it passes through the capillary beds around the alveoli?
It absorbs oxygen and becomes oxygenated
What happens to the carbon dioxide in the deoxygenated blood as it passes through the capillary beds around the alveoli?
It is released into the air in the alveoli
What is the purpose of the extensive network of bronchioles in the lungs?
To deliver air to the millions of alveoli
What is the main purpose of the dense network of capillaries surrounding the alveoli?
To facilitate the exchange of respiratory gases between the alveoli and the bloodstream
Study Notes
Diffusion in Humans
- In the lungs, oxygen and carbon dioxide molecules diffuse down their own concentration gradients between the moisture on the inner lining of the alveoli and the blood.
- This diffusion occurs down a concentration gradient.
Air Sacs and Alveoli
- Alveoli are perfectly adapted for the process of diffusion, having thin and moist walls that help oxygen and carbon dioxide to diffuse.
- A single alveolus has a thin wall, one cell thick, and is surrounded by a dense network of capillaries.
- The capillaries also have very thin walls, which helps the diffusion of oxygen and carbon dioxide into and from the blood.
How the Alveoli and Capillaries Work
- Air containing oxygen enters the lungs and passes into each alveolus from outside.
- Deoxygenated blood containing carbon dioxide comes from the rest of the body.
- Oxygen diffuses into the blood from the alveoli, while carbon dioxide diffuses from the blood into the alveoli.
- The blood becomes oxygenated, and oxygenated blood leaves the lungs and returns to the heart.
Inhaled and Exhaled Air
- Inhaled air into the lungs: 20.95% oxygen, 79% nitrogen, 0.04% carbon dioxide, and 0.01% water vapor.
- Exhaled air out of the lungs: 16% oxygen, 79% nitrogen, 4.0% carbon dioxide, and 1% water vapor.
Breathing
- Breathing is the process of moving air in and out of the lungs.
- Breathing is achieved by making the chest cavity larger or smaller, which results in a change in pressure within the lungs.
- This change in pressure forces air either in (inhale) or out (exhale) of the lungs, known as ventilation of the lungs.
- Inspiration (breathing in) involves the contraction of rib muscles and diaphragm muscle, which increases the volume of the chest cavity.
Test your knowledge on diffusion in the human respiratory system. Explore topics such as concentration gradients of carbon dioxide and oxygen, the process of diffusion between alveoli and blood, and the differences between inhaled and exhaled air.
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