Respiratory membrane physiology - Diffusion of gases | Respiratory system mbbs 1st year

Physiology lecture on respiratory membrane physiology details Diffusion across respiratory membrane
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For the gases to cross the alveoli and enter into the blood and vice versa, the gases should cross the respiratory membrane.
The factors which affect rate of diffusion of gases across any membrane is given by Fick’s law which states that rate of diffusion across respiratory membrane is directly proportional to the area of the membrane, partial pressure gradient and inversely proportional to membrane thickness. Then it is also directly proportional to their solubility in the medium and inversely related to the square root of their molecular weight.
In Fick’s law the two factors of the gas i.e its the molecular weight of oxygen and solubility together form the diffusion coefficient of the gas. The molecular weight of oxygen is less but its blood solubility is much lesser than carbondioxide.. because of this carbondioxide diffuses 20 times faster than oxygen.
So for this respsiratory membrane, the rate at which different gases will cross is expressed by diffusion capacity of the lungs for a given gas. Normally diffusion capacity of lungs for oxygen is 25 ml/min/mm Hg. That means 25 ml of oxygen will cross this membrane in 1 min for every each mmHg partial pressure difference. Obviously diffusion capacity will be much larger for carbondioxide.
Now consider a situation in which respiratory membrane thickens, As Fick’s law states that rate of diffusion is inversely proportional to the thickness of the membrane, so obviously the rate of diffusion of gases will be affected. With increase in the thickness, diffusion time for oxygen will increase say upto 0.5 or even 0.6 sec. This time is adequate for rest, since till 0.8 sec a column of blood is available. But during activity, when the heart rate becomes faster and duration of cardiac cycle decreases, then there will not be adequate time for oxygen to equilibrate and hence it will cause hypoxia. So in this case, perfusion is not the limitation, rather the rate of diffusion becomes the limiting factor. This is known as diffusion-limited.
Since the rate of diffusion carbon dioxide is faster, its diffusion will not be limited. So even with increased respiratory membrane thickness, carbon dioxide could be expelled from the body. That is the reason that even in severe cases of thickening of respiratory membrane like in pulmonary fibrosis hypoxia occurs but carbondioxide retention does not occur.
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Chapters:
00:00 Introduction
00:54 Respiratory membrane layers
01:36 Factors affecting rate of diffusion of gases across respiratory membrane
04:14 Diffusion capacity of respiratory membrane
05:37 Application of diffusion of gases across respiratory membrane
06:05 Diffusion vs perfusion limited
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[@m.shahan8865]

Too good video mam Very informational in short time

[@PhysiologyOpen]

Glad you liked it

[@Yasdadgb.]

Maam i watched all of your physiology videos. Videos are so helpful , i have no words to say you Thanks 🙏 🙏

[@PhysiologyOpen]

Thanks Prabhat. I am so greatful. Believe me I needed this motivation. Do share the channel and videos. I really need that❤️

[@sagarawachar]

You have made physiology so easy madam..

[@PhysiologyOpen]

So happy 😃

[@krishsavani3082]

Mam very very beautiful explanation 👌 you are great teacher...thank you very much

[@PhysiologyOpen]

Thanks a lot. Really happy

[@harshasinha3966]

You've made my life so much easiest. Thankyouuuuu ma'am. Thankyou so much!

[@PhysiologyOpen]

My pleasure 😊

[@aadityasinha6961]

In a very simple and easy you have explained it ma'am , thank you !! 😊

[@PhysiologyOpen]

My pleasure as always

[@arshithgowda8728]

Better explanation 🙏🤗

[@PhysiologyOpen]

😊

[@kuldeepmaurya1410]

Great knowladge in less time 🙏🙏

[@PhysiologyOpen]

😊👍

[@joynobjumu7241]

thank you so much for this video. ❤❤

[@PhysiologyOpen]

You are welcome

[@shraddhap9899]

Nice one maam. More of these videos, plz.

[@PhysiologyOpen]

Coming soon

[@dr.swadeshmohanty1925]

Amazing lecture mam.....

[@PhysiologyOpen]

Thank you so much

[@mohammadmahdikazemi7769]

thanks for video. excuse me could you please answer to this question. why difference of o2 pressure is 11mm hg instead of 64 mm hg in formula

[@PhysiologyOpen]

Which formula...can you point to the time in video

[@modiudit8627]

That means if we add b-1blocker which reduces heart rate could be effective during exercise 🧐

[@PhysiologyOpen]

Then person will not be able to exercise...

[@saicreations8060]

Mam why is there 8 times difference between O2 and CO2? I did not understand that.

[@PhysiologyOpen]

Ok first a task ..if you don't mind..solubility of Co2 is 20 times that of O2...if you figure out the molecular weights of oxygen and carbon dioxide and place the values in diffusion coefficient (solubility / square root of molecular weight ), you will get the diffusion of CO2 is 8 times that of oxygen (hint : molecular weight is more than oxygen )

[@shreeyakc2927]

Why is time taken 0.3 sec 😥

[@PhysiologyOpen]

Well that depends on the characteristics of the membrane , ofthe gas and on partial pressure gradient. Some time will be taken...thats nature