14. Principles of Gas Transport | Lung Diffusion Capacity| Partial pressure of gases in blood
Channel: Cool Concepts in Physiology, Anatomy (& Life)
Date: 07/07/2021

Following questions have been delved in detail: 
LO-1: Enumerate the various components of the Respiratory Membrane 
Respiratory Unit (also called “respiratory lobule”) 
Composed of:
Respiratory bronchiole 
Alveolar ducts 
Atria
Alveoli

LO-2: Describe factors affecting gas diffusion across respiratory membrane
Lung Diffusion Capacity (DL)
DL is another expression of Fick’s Law
Combines:
  Diffusion coefficient
  Surface area 
  Membrane thickness 
  Time required for gas to combine with proteins in pulmonary capillary blood 
Measured using CO
In various diseases, Dl changes in a predictable way. 
- In emphysema, for example, Dl decreases because destruction of alveoli results in a decreased surface area for gas exchange. 
- In fibrosis/pulmonary edema/pneumonia (inflammatory fluid accumulation within or around the alveoli) - Dl decreases because the diffusion distance (membrane thickness or interstitial volume) increases. 
- In anemia, Dl decreases because the amount of hemoglobin in red blood cells is reduced (recall that Dl includes the protein-binding component of O2 exchange). 
- During exercise, Dl increases because additional capillaries are perfused with blood, which increases the surface area for gas exchange. 

LO-3: Discuss the various forms of gas-solution interplay and concept of ‘partial pressure’.
Gases are carried in additional forms:
Dissolved in liquid*
Bound to proteins**
Chemically modified***
Hence total gas concentration in solution= dissolved gas + bound gas + chemically modified gas
Partial pressure of gas in a solution is exerted only by dissolved form!!

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COMPLETE 1st YEAR  MBBS Practicals: https://bit.ly/3jZaW01
COMPLETE 2nd YEAR  MBBS Practicals: https://bit.ly/3yMoX7q

2nd YEAR MBBS Lectures: https://bit.ly/2VNGI8b
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USMLE/PLAB/FCPS Guidance - EMBRACE Series Complete playlist: https://bit.ly/3jWsNED
TTS-BTS- To the Students - By the Students: https://bit.ly/3CPpAzr
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