If you're seeing this message, it means we're having trouble loading external resources for Khan Academy.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Respiratory system

9 videos
3B: If you place your hand on your ribs and take a deep breath, you’ll notice that your chest expands and your back straightens. As this occurs, air is rushing through your windpipe and branches off to either your left or right lung. After about 20-30 more branch points, oxygen in the air ends up in the alveoli where it diffuses into the surrounding liquid, slipping into the blood. This rapid microscopic gas exchange allows oxygen to be taken up during inhalation as carbon dioxide leaves during exhalation.

Meet the lungs

VIDEO 9:36 minutes
Every time you take a breath, oxygen makes it way into your lungs. Follow along on that journey! Rishi is a pediatric infectious disease physician and works at Khan Academy.

Inhaling and exhaling

VIDEO 12:59 minutes
Find out exactly why air goes in and out of the lungs. Rishi is a pediatric infectious disease physician and works at Khan Academy.

How does lung volume change?

VIDEO 8:10 minutes
Learn about how muscle contraction and lung recoil actually help the lungs change their volume with every breath! Rishi is a pediatric infectious disease physician and works at Khan Academy.

O2 and CO2 solubility

VIDEO 7:45 minutes
Get an intuition for why carbon dioxide is so much more soluble than oxygen when it goes into water. Rishi is a pediatric infectious disease physician and works at Khan Academy. These videos do not provide medical advice and are for ...

Henry's law

VIDEO 8:39 minutes
Explore the relationship between partial pressure of a gas and the concentration of the gas molecule within a liquid. Rishi is a pediatric infectious disease physician and works at Khan Academy. These videos do not provide medical advice ...

Fick's law of diffusion

VIDEO 12:22 minutes
Learn all of the different ways to maximize the amount of particles that diffuse over a short distance over time. Rishi is a pediatric infectious disease physician and works at Khan Academy. These videos do not provide medical advice and ...

Oxygen movement from alveoli to capillaries

VIDEO 11:46 minutes
Watch as a molecule of oxygen makes its way from the alveoli (gas layer) through various liquid layers in order to end up in the blood. Rishi is a pediatric infectious disease physician and works at Khan Academy. These videos do not ...

The respiratory center

VIDEO 9:23 minutes
Find out how the respiratory center collects information from all over the body and then helps regulate your breathing. Rishi is a pediatric infectious disease physician and works at Khan Academy. These videos do not provide medical ...