Respiratory Physiology Lecture 4 Part 19/ 20: Gas Exchange Flashcards
Why do gases have pressure?
Gas molecules are constantly in motion and this motion exerts a pressure
What does gas pressure increase to?
Pressure increases in response to anything that increases movement
- Temperature
- Concentration of gas molecules
Dalton’s Law:
in a mixture of gases (eg. Air), each gas operates independently
- Thus,total pressure is the sum of individual pressures (Partial pressures)
Partial pressures of air
What happens to air as it is breathed in?
becomes more H2O because it is humdified
Patm at sea level
760 mmHg
Partial pressure of atmosphere gas components?
How does gas get across the blood-gas barrier
diffusion via ficks law
Fick’s Law
The rate of transfer of a gas through a sheet of tissue/unit time (V; L/min) is proportional to the tissue area and the difference in gas partial pressure between the two sides, a diffusion constant, and inversely proportional to the tissue thickness.
Ficks Law equation
What is the diffusion constant (D)?
The amount of gas transferred between the alveoli and the blood/unit time
What is diffusion proportional to?
Diffusion is also proportional to the gas solubility (Sol) in fluids or in tissue
What influences the diffusion process?
The solubility of the gas in a fluid influences the diffusion process
Solubility of CO2 vs O2
CO2 solubility is much higher than O2
- The bond between carbon and oxygen is not as polar as the bond between hydrogen and oxygen, but it is polar enough that carbon dioxide can dissolve in water. This is why, carbon dioxide is highly soluble in water rather than carbon monoxide and oxygen.
- CO2 and O2 similar molecular weight therefore CO2 diffuses 20 times more rapidly than O2
Henry’s Law:
the amount of gas dissolved in a liquid is directly proportional to the partial pressure of gas in which the liquid is in equilibrium
Partial pressures are the same in __________
gas and liquid
- Henrys law
Partial pressures are the same in __________
gas and liquid
- Henrys law
AMOUNT OF GAS IN LIQUID is also determined by
its solubility
- Concentration of a GAS (In liquid) = P x solubility
- Thus, if two gases are at the same partial pressure but differ in solubility, their content within solution will differ
How does gas contribute to partial pressure?
Only gas that is dissolved in solution contributes to partial pressure
- (ie. If O2 bound to Hb, no longer dissolved in solution - important later for gas transport in blood)
How is gas coming in humidified?
comes in contact with wet mucous membrane
Partial pressure of gases
-
Air
- PO2 = 160 mmHg
- PCO2 = 0.3 mmHg
-
Alveoli
- PO2 = 105 mmHg
- PCO2 = 40 mmHg
-
pulmonary veins
- PO2 = 100 mmHg
- PCO2 = 40 mmHg
-
pulmonary arteries
- PO2 = 40 mmHg
- PCO2 = 46 mmHg
Why is PO2 in AIR > PO2 in ALVEOLI?
- Warming ↑ and humidification of air in respiratory tract:↓ PO2
- Loss of O2 to blood diffusion: ↓ PO2
- Mixing of inspired air with functional residual volume: ↓ PO2
Determinants of alveolar PO2
- PO2 in the atmosphere
- Alveolar ventilation (VA
- VA = (VT – VD) x respiratory frequency
- Metabolic rate
- Perfusion
Determinants of alveolar PCO2:
- PCO2 in the atmosphere (Essentially zero)
- Alveolar ventilation (VA)
- Decrease VA there will be less exhalation from the alveoli to the atmosphere PCO2 will be increased at level of alveoli
- Metabolic rate
- Perfusion
How does metabolic rate effect alveolar PO2 and PCO2?
Exercise muscles use more oxygen so PO2 going back is smaller than even the 40 and will increase the pressure differential so PO2 at the level of alveoli will be decreased and more CO2 being produced so PCO2 will be greater
Increasing ALVEOLAR VENTILATION will …?
Increasing ALVEOLAR VENTILATION will increase alveolar PO2 and decrease alveolar PCO2
Increasing METABOLIC RATE will…?
Increasing METABOLIC RATE (O2 consumption and CO2 production) will decrease alveolar PO2 and increase PCO2
