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Flashcards in Diffusion and Gas Transport Deck (20):
1

Fick's law of diffusion

Vg = A/t x D x deltaP

D is proportional to solubility/sqrt(molecular weight)

A = surface area available for diffusion

D = diffusion coefficient

t = thickness of diffusion barrier

deltaP = pressure gradient driving diffusion

2

What does a molecule of O2 have to go through in order to get to the pulmonary capillaries?

gas space within alveolus

"alveolar-capillary membrane"

plasma

erythrocyte membrane and intraerythrocyte fluid

3

What is the most important factor that limites the transfer of O2 from alveolar gas to blood?

the reaction rate of O2 and hemoglobin

4

diffusion limited gas transfer

the diffusion pathway provides a barrier that limits gas transfer - perfusion has no impact on the transfer rate

ex. the effective solubiligy of blood for CO is very high because it binds very tightly to hemoglobin

as CO diffuses into the blood and its concentration rises, the partial pressure of CO int he blood only increases slowly

5

perfusion limitation

equilibration of gas partial pressures in the alveoli and capillary is achieved before the end of the capillary

rate of diffusion exceeds capacitance of blood

transport of gas from alveoli to tissue could be increased if cardiac output is increased

ex. NO2

6

Is oxygen diffusion or perfusion limited?

diffusion limited until about 0.25 sec, then turns into perfusion limited

7

What additional resistances to diffusion are there after a gas travels inside red blood cells?

diffusion through a blood-gas barrier (alveolar membrane)

chemical reactions (binding of O2 to Hb)

8

diffusion capacity (DL)

the rate of gas transfer divided by the pressure gradient across the alveolar/capillary membrane

9

What is the partial pressure of CO2 in the alveoli?

45 mmHg

10

What is the partial pressure of CO2 in the venous return?

40 mmHg

11

What is the minute ventilation for purely dissolved oxygen?

250 mL/min

12

What chemical reactions of CO2 can limit CO2 exchange? What are the implications of this?

formation of bicarbonate

the formation of carbamino compounds with blood proteins, mostly hemoglobin

the result is that the equilibration rate for CO2 is not much faster that that for O2

13

How much hemoglobin (gm%) is in a normal individual?

~15 gm%

*binds 1.34 mL O2

O2 capacity in the blood is 20.1 vol%

14

P50

the pressure of oxygen at which hemoglobin is half saturated

this value does not change with varying hemoglobin concentration

15

factors that increase P50

increased temperature

Bohr effect - decreased pH or increased PCO2

increased 2,3-diphosphoglycerate

16

relationship between saturation and capacity

% saturation = content/capacity

17

What effect does pH have on the hemoglobin saturation curve?

as the pH goes down, the curve shifts to the right

18

What effect does CO2 pressure have on the hemoglobin saturation curve?

as the partial pressure of CO2 increases, the saturation curve shifts right

19

Bohr effect

deoxyhemoglobin is a weaker acid than oxyhemoglobin, and it more readily accepts H+

higher levels of H+ in the tissue lowers the affinity of Hb for O2 in the tissue

20

Haldane effect

oxyhemoglobin is a stronger acid than deoxyhemoglobin

oxy-Hb therefore has a lower affinity for H+

addition of O2 in the lungs causes H+ to be released from Hb