3.2A. Gas exchange in the respiratory system. Flashcards
I. What are the 6 layers of respiratory membrane?
6 layered (only 1,0 μm thick):
1) surfactant layer
2) alveolar epithelium
3) epithelial basement membrane
4) interstitial space
5) capillary basement membrane
6) capillary endothelium
II. Gas exchange in the respiratory membrane
1. What is gas exchange in the respiratory membrane?
Movement of gas (O2, CO2) across the alveolar blood-gas barrier occurs by simple diffusion (V)
II. Gas exchange in the respiratory membrane
2. What is the formula for gas exchange in the respiratory membrane?
- V = transport of gas
- A = surface
- D = diffusion coefficient
- (P1-P2) = partial pressure between 2 sides
- T = thickness of barrier
II. Gas exchange in the respiratory membrane
3. What is the short version of the formula for Gas exchange in the respiratory membrane? Why?
II. Gas exchange in the respiratory membrane
4. What are the pO2 & pCO2 values for alveolus?
II. Gas exchange in the respiratory membrane
5. What are the pO2 & pCO2 values for Capillary (venous blood)?
II. Gas exchange in the respiratory membrane
6. What are the pO2 & pCO2 values for Pressure gradient (Δ)?
II. Gas exchange in the respiratory membrane
7. The pressure gradient is 10 times larger for O2 than CO2, but the amount of them transported is almost the same. .
-> WHY?
DL (diffusion capacity) is different for O2 and CO2
=> Diffusion capacity for CO2 is 20x time larger than that for O2
II. Gas exchange in the respiratory membrane
8. What are the characteristics of DL (diffusion capacity) (1) between CO2 & O2; (2) between resting exercise?
1/ DL for O2 is much smaller than for CO2
- CO2 is about 20x more soluble than O2 in water
=> DL is 20x larger for CO2 than O2
2/ There is also a difference in diffusion capacity during exercise and rest
=> DL will be larger during exercise due to increasing (1) CO and (2) Area (a factor in DL)
II. Gas exchange in the respiratory membrane
9. There is also a difference in diffusion capacity during exercise and rest
-> How?
- DL is much larger during exercise
1. Factor which changes is the surface area (A)
2. CO 3-4x larger during exercise
-> pulmonary circulation↑
-> blood flow will ↑ and extend the lungs
-> number of open capillaries ↑
-> surface area ↑
III. Transit time of blood in capillaries
1. Characteristics of Transit time of blood in capillaries?
Transit time of blood in pulmonary capillaries is around 0,75 seconds – available for gas exchange. Actually, only 1/3 (0,25 sec) of the transit time is enough for the blood to get oxygenated
- At 0,25 seconds = pO2 already 100mmHg in capillaries
- Other 2/3 of the time is there as a backup if needed (i.e. O2 is abnormal)
III. Transit time of blood in capillaries
2. What causes abnormal O2?
- If for some reason A, D, T (= DL) is not appropriate
- Example: pulmonary edema
+) Fluid occurs in interstitial space, presence of fluid increases the thickness (T) of layer
-> ↓ DL causes slower than normal O2-exchange
III. Transit time of blood in capillaries
3. Characteristics of Diffusion-limited gas exchange
- Partial pressure of soluble gas (ex: CO) in the blood does not equilibrate with alveolar pressure before exiting the capillary
- Its transport in the blood is limited by its ability to diffuse (CO can bind to Hb)
- In tissues, the distance between the capillary and a cell is easily > 1,0μm
- Thickness will be larger, and therefore the transport of gas for O2 and CO2 will take longer time
=> In tissues: O2 and CO2 are diffusion-limited
IV. Gas tensions
1A. What is the Henry’s law?
Henry’s law explains that the concentration of O2 dissolved in water is proportional to PO2 in gas phase (the amount is linear with pressure – by Dr. Hunyady).
- Eg., if alveolar air has PO2 of 100 mmHg, then the capillary blood that equilibrates with alveolar air also will have PO2 of 100 mmHg.
IV. Gas tensions
1B. What is the formula for Henry’s law?
- Solubility factor for O2 is α = 0,03 O2/L H2O/mmHg, α for CO2 is 20x more
- P = partial pressure of a gas
IV. Gas tensions
2. Why is the partial pressure in solution important?
1) The dissolved gas amount is linearly proportional with the partial pressure of the gas
2) Partial pressure of a gas (Pgas) determines the direction of the gas flow
IV. Gas tensions
3. How does the partial pressure of a gas (Pgas) determine the direction of the gas flow?
- Gas always flows from higher pressure to lower pressure until they become equal
=> Direction of gas flow is determined by the Pgas, until higher pressure decreases and lower pressure increases, and the common pressure will be equal
=> equilibrium
V. Partial pressure of gases in the respiratory system and the circulation
1. What are the values for Partial pressure of O2 and CO2 in arterial blood?
V. Partial pressure of gases in the respiratory system and the circulation
2. Why is pO2 not 100mmHg in the left heart (outflow)? (95mmHg)
The difference is due to 2 reasons:
1) Mixing with blood of the bronchial system, which is a bit venous blood (pO2↓)
2) Ventilation-perfusion mismatching is due to the graviton
=> Why equilibrium is not complete
