Lecture 9 Flashcards
Describe gaseous diffusion?
Takes place in a number of locations in the body. It is driven by a difference in partial pressure of gas. The pressure required to prevent gas from diffusion out of a solution (partial pressure).
What is the partial pressure of a dissolved gas?
The pressure required to prevent a gas from diffusing out of a solution.
Describe Dalton’s Law?
Where barometric pressure is comprised of the many pressures of the gases in the atmosphere - the sum of the pressure of the gases.
“The partial pressure of a gas in solution has the same magnitude as the partial pressure of the gas in the air which it is in equilibrium.”
Describe gas solubility/Henry’s Law?
The amount of gas dissolved per unit of volume per unit of partial pressure. If you increase the partial pressure of the gas in solution you will get more of the gas into solution and if highly soluble more content dissolved.
Describe the difference between the solubility of Oxygen and Carbon Dioxide?
Oxygen = 3mL L-1 (100mmHg) is soluble.
Carbon Dioxide = 60mL L-1 (100mmHg). Carbon Dioxide is 20x more soluble in blood than oxygen.
Describe the diffusion of oxygen across the alveolar membrane?
There is no active transport, it is entirely passive driven by difference in partial pressure.
What is the rate of oxygen transport dependent on?
Directly proportional:
- The ability to diffuse across a membrane.
- The area of a membrane available for exchange.
- The solubility of the gas.
Inversely proportional:
1. Thickness.
What is the diffusing capacity of the lung?
The four unknowns that we cannot measure in diffusion of oxygen across the alveolar membrane. Also known as the Diffusive Conductance of the lung.
Describe the fact of diffusion distance on diffusion time?
When the distance is great, the gradient will be low so it will take longer for oxygen to diffuse. If you decreased the distance you have a steeper gradient and diffusion time is quicker. When you introduce circulation network (capillaries) you increase the gradient and decrease diffusion time.
How do you measure the diffusing capacity of the lung?
Don’t measure by use of oxygen but by carbon monoxide (use at low partial pressure).
Why do we use carbon monoxide?
It has the same solubility as oxygen, also CO has a better avidity to Hb. And it stays there until RBC is recycled after a period of months. Thus the partial pressure of CO in the capillaries remains zero as CO does not re-circulate back into the alveoli.
Describe the diffusion limitation vs percussion limitation?
At the start of capillary the partial pressure of oxygen is 40mmHg (due to mixed blood). When you have poor diffusion, the capillary won’t be fully saturated with oxygen. The RBC gets fully saturated with Nitrous Oxide very quickly, whereas CO has very low partial pressure.
Describe steady-state gas exchange?
Advection 1: The rate of oxygen consumption is the difference between the rate of oxygen inspired and expired.
Diffusion 1: The rate of which oxygen crosses the membrane is given by the diffusion capacity of the lung.
Advection 2: The amount of oxygen disappearing out of the blood is given by Cardiac Output times the difference in concentration of oxygen of systemic arterial and venous blood. Maintain ability to lower venous value during exercise.
Diffusion 2: Same amount of oxygen per unit time entering the cells as oxygen entering the mouth.
