This document discusses gas exchange in the lungs, specifically the diffusion of gases. It covers three main factors that gas exchange depends on: the alveolar-capillary membrane, the partial pressure gradient, and pulmonary capillary blood flow. Several factors can affect the diffusion of gases across the alveolar-capillary membrane including differences in partial pressures, surface area, thickness, and solubility of the gas. The partial pressure gradient provides the driving force for diffusion. Various laws like Henry's Law and Fick's Law govern the diffusion process. Capillary blood flow and its measurement also influence gas exchange rates in the lungs.

2. Diffusion of Gas Exchange in Lungs
Dr. K. Ambareesha PhD,.
Assistant Professor Physiology, GMC, Sec,bad

3. Learning Objectives
1. Introduction
2. Factors on which gas exchange depends
3. Alveolo capillary membrane
a. Factors affectng diffusion of gses
b. Clincal significance
4. Partial pressure gradient
5. Laws governing diffusion
a. Henrs law
b. Ficks law
6. Difusion coefficient
7. Capillary blood flow , its measuremt and factors affecting it

4. Diffusion of gases manly depends on:
1. Alvelo capillary membrane
2. Partial pressure gradient
3. Pulmonary capillary blood flow

5. Introduction

6. I. Alveo - capillary membrane

7. Factors affecting Diffusion
1. Difference in partial pressure
2. Diffusing capacity
3. Surface area
4. Solubility of gas
5. Thickness
6. Molecular weight

8. DαPG
DαS
DαA
Dα1/MW
Dα1/D
DαGas solubility/√MV
Pressure Gradient
Solubility of a gas in fluid
Medium
Total surface area
Molecular weight of gas
Thickness of membrane
Diffusion coefficient
FACTORS AFFECTING DIFFUSION

9. Clinical significance
Alveo capillary obstruction syndrome
Types:
1. Thickening of membrane Ex: interstitial fibrosis
2. Increased distance between alveo - capillary membrane Ex:
interstitial edema in heart failure

10. Fibrosis of the lung

11. SURFACE AREA OF MEMBRANE IS ALTERD

12. SURFACE AREA OF MEMBRANE IS ALSO
ALTERD

13. II. Partial pressure gradient
Diffusion Gradient:
Diffusion of a gas depends upon the difference of partial pressure
of individual gas across the alveolo - capillary membrane of that
particular gas.

14. Laws Governing Diffusion
Amount of the gas
dissolved in a liquid at
a given temperature
PP and solubility of
the gas
Henr’s Law:
α

15. Fick’s Law
Volume of the gas
diffusing/min across
the membrane
α
Membrane surface area
Diffusion coefficient
PP difference of a gas
Thickness (T)

16. DIFFUSION OF OXYGEN

17. DIFFUSION OF OXYGEN AT CELLULAR
LEVEL

18. DIFFUSION OF CO2 AT CELLULAR
LEVEL

19. DIFFUSION OF CO2 AT ALVEOLI

20. Partial pressure of different gases

21. Diffusion coeffiient
DC α its solubility
√ Its MW

22. Capillary blood flow
1.Transient time of 0.75 sec
2.Different for different gases

23. Diffusing capacity
Is a measure of rate of gas transfer into
the lungs per partial pressure gradient

24. Measurement
1.CO is used to determine
2.Its uptake limited by diffusion
3.Ability of CO for Hb is 210 times greater than oxygen
4.Most common techniqu is simple breath test

25. Factors affecting DC
1.Hb and capillary blood volume affects it
2.It is not only depends on diffusion across the membrane and
also on hematocrit
3.A decrease in either hematocrit or capillary blood volume
decreases the DC

26. THNK YOU