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### Course: MCAT>Unit 7

Lesson 11: Respiratory system

# Oxygen movement from alveoli to capillaries

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 provide medical advice and are for informational purposes only. The videos are not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of a qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read or seen in any Khan Academy video. Created by Rishi Desai.

## Want to join the conversation?

• Rishi mentioned a number of reasons why the rate of O2 exchange might slow down. How much can it slow before the body starts to notice? In other words, does more oxygen diffuse through than can be absorbed by the blood, and if so, what fraction of normal does the rate have to get down to before the body is using O2 faster than the alveoli can deliver it?
• An average healthy adult absorbs over 1000ml/min of O2 into their blood stream, at rest - yet only consume about 250ml/min of O2 while at rest. So, there's a healthy "buffer" and the amount of O2 diffusing into your blood can drop quite a ways before you start to feel short of breath ("dyspnea") - particularly if the decrease is gradual, allowing time for the body to compensate.

The rate of absorption and consumption are both dependent on a variety of things - such as the percent of O2 you're breathing (about 21% on room air), the amount of hemoglobin in your blood, the solubility of O2 in your blood (which changes), etc.

There are mathematical equations you can use to compute O2 absorption and consumption also, that we use in medicine. A complicated, but fascinating topic!
• Could you link the video on the "alveolus" equation you mentioned?
• the wall of capillaries are composed of unicellular layer of endothelial cells, surrounding these cells is a basement membrane. BUT, i was taught that there is no connective tissue or smooth, muscle, because the capillary itself is large enough for a red blood cell or oxygen molecules to squeeze through. Could you double check on that part, please? thanks
• You are right, BUT you have to take into account the fact that capillarys are generally - with a few exceptions - embedded into some sort of connective tissue, e.g. the depicted layers of connective tissue that make up the lungs.
So while the capillary itself is made up of endothelium and little else, it will in most cases be surrounded by connective tissue making up the neighbouring structures/organs/tissues.
(1 vote)
• I had asked many knowledgeable people this question, such as my science teacher, none of which could answer this question. I'm aware that you could have Oxygen in a liquid form, so could you drink and breathe/respirate a form of liquid Oxygen?
• What would increase the uptake of oxygen and make the exchange faster in the alveoili
• So just applying this further, if a patient were to significantly increase the fat in their diet thus reducing the RQ, for example a ketogenic diet, the oxygen requirements for that patient go down, Right?
• I think you're right! People following a ketogenic diet have been shown to have a decreased CO2:O2 ratio (RQ). When CO2 levels go down, the O2 requirements also go down. This is probably why many people on keto have said that their diet helped with sleep apnea, which is partially caused by high CO2 levels (or a skewed RQ). Still, I'm not sure how significant the change is for medical practice (would you lower the %O2 for their mask/tank, for example).
(1 vote)
• 1)what determine in which direction carbon dioxide and oxygen will diffuse in the alveoli and blood?

how and where carbon dioxide and oxygen diffusion occur?
• concentration gradient, theyll flow from high concentration to low concentration, so when your blood co2 level is high, co2 will diffuse into your alveoli
• at rishi says all of those things are liquid. in epithelial cells does it mean the liquid in the cell
(1 vote)
• Yes, he means the cytosol. Cytosol is also known as intracellular fluid (ICF), which literally means "fluid inside of cells".