Exam #3: Gas Exchange Flashcards
What is effective respiration?
Enough oxygenation to meet tissue demand
What is the main driver of gas exchange?
- The gradient in partial pressure of gases
- Gases diffuse “downhill” along the gradient of decreasing partial pressure
What is Dalton’s Law of Partial Gas Pressures?
Pressure of a gas is directly proportional to the concentration of its molecules
Ptotal= P1 + P2 +P3 Pb= PN2 + PO2 + PCO2 + Pothers
Pb= 760 mmHg
Px=Fx (PB-PH20)
How is the the total dry gas pressure obtained?
Subtract water vapor pressure from the total barometric pressure
Px= Fx (PB- PH20)
What is Henry’s Law?
When gas is DISSOLVED in fluid & encounters a surface, it exerts its own partial pressure
Partial pressure= Concentration of dissolved gas/ solubility coefficient
How does the solubility of CO2 compare to O2?
CO2»>O2
- This means CO2 dissolves easily.
- At EQUAL concentrations, oxygen exerts a higher partial pressure than CO2
What is the ideal gas law?
PV=nRT
What is the functional implication of the ideal gas law?
If P1>P2 or vice versa, then gas exchange will take place until:
P1V1= P2V2
E.g. in anesthesiology, when gas is administered, gas exchange will occur until Palveoli = Pblood
How do gases diffuse in fluids & tissues?
Gas molecules diffuse proportionally to gas partial pressure difference
What is Fick’s law of diffusion?
The amount of gas that moves across a tissue sheet is:
- Proportional to area
- Inversely proportional to thickness
Write the equation for net rate of diffusion.
Diffusion is proportional to:
- Pressure
- Area
- Solubility
And inversely proportional to:
- distance through which the gas must diffuse
- square root of molecular weight of gas
Describe gas exchange at the respiratory membrane.
Oxygen
- 100 P02 in alveoli
- 40 PO2 in venous circ.
Net into circulation
What two things are required for adequate respiration?
Diffusion
Perfusion
What is the difference between PAO2 & PaO2?
A= alveoli a= arterial
What is the respiratory unit?
Location of gas exchange
- Bronchioles
- Alveolar ducts
- Atria
- Alveoli
How is diffusion effected in atelectasis?
Collapse of lung tissue
- Decreased dP
- Increased distance
- Decreased SA
How is diffusion effected in pneumonia?
Markedly increased distance = decreased diffusion
How is diffusion effected in pulmonary edema?
Increased capillary hydrostatic pressure
- Increased distance
- Diffusion effectively blocked
Hydrostatic pressure increases & can cause pink frothy sputum (capillary blood)
How is diffusion effected in pulmonary fibrosis?
Increased distance due to increase collagen & elastin deposition
Describe oxygen diffusion between the alveoli & pulmonary capillary.
Arterial end= pulmonary arterial end
- Low PO2 (40 mmHg)
- Alveoli= 100mmHg
Oxygen in
Equilibration occurs by the time the blood reaches the venous end i.e. to go into the left side of circulation
During exercise & tachycardia how does equilibration of oxygen change?
Takes longer
What happens to the diffusion of oxygen in the tissues?
Arterial PO2» Venous & capillary= net diffusion of oxygen into the tissues
- Opposite occurs with CO2
Draw the change in PO2 as blood travels through the circulation.
N/A
What causes the drop in PO2 from pulmonary capillaries to systemic arterial blood?
Pulmonary shunting occurs i.e. deoxygenated blood from bronchioles returns straight to the left side of the circulation
