Ch 39 Physical principles of gas exchange

Question 1

What determines the vapor pressure of water?

Answer 1

The temperature of the water. Hotter = more kinetic energy of molecules and greater likelihood they will escape from the water surface.

Question 2

What five factors determine the rate of gas diffusion in a fluid?

Answer 2

1. Solubility of the gas in the fluid
2. Distance the gas particles must travel
3. Cross-sectional area of the fluid
   (4. Temperature of the fluid )…usually constant
4. Molecular weight of the gas

Question 3

How does the slow replacement of alveolar air maintain homeostasis?

Answer 3

*Takes about 7 breaths to fully replace the alveolar air in a human

Prevents sudden changes in gas concentrations in the blood and prevents excessive increases/decreases in tissue oxygenation, tissue [CO2], and tissue pH when respiration is INTERRUPTED

Question 4

What two factors determine the composition of expired air?

Answer 4

1. Amount of expired air that is dead space air
2. The amount that is alveolar air

Question 5

What layers comprise the alveolar membrane, following the path alveolar air takes to travel to capillary blood?

Answer 5

1. Fluid lining the alveolus
2. Alveolar epithelium
3. Epithelial basement membrane
4. Thin interstitial space
5. Capillary basement membrane
6. Capillary endothelial membrane

Question 6

What 4 factors determine how quickly a gas will diffuse through a membrane?
What pathological conditions can alter these?

Answer 6

1. Membrane thickness: altered by fibrosis and edema (if it doubles/triples, interferes)
2. Membrane surface area
   -Altered by emphysema, lung loss.
   -See functional alteration when it decreases to 1/4 of normal
3. The gas’s diffusion coefficient
4. Partial pressure difference of the gas between the two sides of the membrane
   -Not really altered, but the difference between tells the net tendency of the gas to move through a membrane

Question 7

How do the lungs increase oxygen diffusing capacity during exercise?

Answer 7

1. Opening up more pulmonary capillaries, dilating open ones (incr surface area)
2. V/Q becomes better matched

Question 8

What is the rate-limiting factor of oxygen usage in cells?

Answer 8

ADP. When PO2 > 1 mmHg, rate of O2 usage becomes constant for any given [ADP] in a cell

Question 9

What are the two factors that determine the total oxygen available to tissues each minute?

Answer 9

1. Rate of blood flow
2. Quantity of O2 that can be transported to the tissue in each 100ml of blood