4 - Gas Exchange Transport Flashcards
What is the equation for diffusion? What do the variables stand for?
Vgas = D * (A/T) * ∆P
Vgas = amount of gas diffused D = diffusion coefficient = [solubility/(molecular weight ^ 1/2)] A = surface area T = thickness ∆P = P1 - P2 = difference in pressure across the barrier
What is the equation for how much of a gas is dissolved in water? (Henry’s Law)
Solubility * partial pressure
O2diss = 0.003mlO2/dl/mmHg * PO2
CO2diss = 0.06mlCO2/dl/mmHg * PCO2
Why do O2 and CO2 diffuse at roughly the same rate even though CO2 is much more soluble?
There is a much bigger oxygen pressure gradient across the capillary-alveolus border
CO uptake is [perfusion/diffusion] limited, so it is used to measure the [perfusion/diffusion] capacity of the lung.
N2O uptake is [perfusion/diffusion] limited, so it is used to measure the [perfusion/diffusion] capacity of the lung.
CO - diffusion limited –> measure diffusion capacity
N2O - perfusion limited –> measure perfusion capacity
In healthy people, O2 and CO2 are [perfusion/diffusion] limited. In people with capillary-alveolar thickening, Pc[CO2/O2] might not reach equilibrium with the alveolar concentration.
perfusion limited
PcO2
What does an abnormally high A-aDO2 indicate?
A pathological problem with compromised gas exchange (ex: emphysema, pneumonia, asthma)
In normal resting conditions, hemoglobin has [1/2/3/4] O2 bound in systemic venous blood and [1/2/3/4] O2 bound in systemic arterial blood.
Venous - 3 bound O2 (75% saturated)
Arterial - 4 bound O2 (100% saturated)
(the 3 extra O2 represent a reserve capacity)
Why is it important to have dissolved oxygen in blood even though it does not greatly contribute to oxygen content?
- maintains PO2 necessary to keep hemoglobin saturated
- only free O2 can diffuse across cell membranes (not hemoglobin-bound O2)
How do you calculate the amount of oxygen delivered to resting tissue?
It is the difference between arterial O2 content and venous O2 content
[Increased/decreased] hemoglobin-O2 affinity means that it is easier to release O2 to the tissues
Decreased
[Increased/decreased] temperature leads to decreased hemoglobin-oxygen affinity and thus [increased/decreased] O2 delivery to the tissues.
Increased temp –> decreased affinity –> increased delivery
[Increased/decreased] pH leads to decreased hemoglobin-oxygen affinity and thus [increased/decreased] O2 delivery to the tissues.
Decreased pH –> decreased affinity –> increased delivery
[Increased/decreased] PCO2 leads to decreased hemoglobin-oxygen affinity and thus [increased/decreased] O2 delivery to the tissues.
Increased PCO2 –> decreased affinity –> increased delivery
[Increased/decreased] 2,3-DPG (aka 2,3-BPG) leads to decreased hemoglobin-oxygen affinity and thus [increased/decreased] O2 delivery to the tissues.
Increased 2,3-DPG –> decreased affinity –> increased delivery
How do CO and NO affect oxygen delivery?
They both competitively inhibit hemoglobin-O2 binding and shift the dissociation curve to the left (effectively increasing affinity and reducing delivery)
