Pulmonary Gas Exchange

Question 1

What is Dalton’s Law?

Answer 1

Ptotal of non-reactive gases = sum of partial pressures of individual gases.

Question 2

What is Boyle’s Law?

Answer 2

P = 1/V

For a fixed amount of an ideal gas kept at a fixed temperature.

Question 3

What is Henry’s Law?

Answer 3

At a constant temperature, the amount of a gas that dissovles in a type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.

Question 4

What is the ideal gas law?

Answer 4

P = nRT/V

Question 5

What is the partial pressure of oxygen at the alveolar membrane?

Answer 5

150 mm Hg

Question 6

What is the partial pressure of gas determined by?

Answer 6

concentration and solubility coefficient of the gas.

Partial pressure = [dissolved gas]/solubility coefficient

Question 7

What are the major components of the air?

Answer 7

Nitrogen (78%)

Oxygen (21%)

Argon (0.93%)

Carbon dioxide (0.03%)

Question 8

Pressure is ___ proportional to the concentration of gas molecules.

Answer 8

directly

Question 9

What is the vapor pressure of water?

Answer 9

The partial pressure exerted to escape from the liquid to the gase phase.

At normal body temperature, vapor pressure = 47 mm Hg

Question 10

What is vapor pressure dependent upon?

Answer 10

temperature of the water

Question 11

What factors affect rate of gas diffusion in a fluid?

Answer 11

solubility of gas in the fluid

cross-sectional area of the fluid

distance through which the gas must diffuse

molecular weight of the gas

temperature of fluid

Question 12

HOw do the solubility coefficients of oxygen and carbon dioxide compare?

Answer 12

Solubility of oygen = 0.024

Solubility of carbon dioxide = 0.57

Because carbon dioxide is more soluble in water than oxygen, it will exert a partial pressure that is less than 1/20th that of oxygen.

Question 13

What are the factors that control oxygen concentration in the alveoli?

Answer 13

Rate of absorption of oxygen into the blood

Rate of new oxygen entry into the lungs.

Question 14

Why can alveolar ventilation not increase pO2 above 149 mm Hg under normal conditions?

Answer 14

Too high of a level of alveolar ventilation is needed.

Question 15

What are the facotrs that control carbon dioxide concentration in the alveoli?

Answer 15

Rate of carbon dioxide excretion (pressure increases in direct proportion to excretion)

alveolar ventilation (alveolar PCO2 decreases in inverse proportion to alveolar ventilation).

Question 16

What are the components of the alveolar respiratory membrane?

Answer 16

capillary endothelium

capillary basement membrane

interstitial space

epithelial basement membrane

alveolar epithelium

Question 17

The respiratory membrane allows for the diffusion of what gases?

Answer 17

oxygen and carbon dioxide

Question 18

What factors determine how rapidly a gas will pass through the respiratory membrane?

Answer 18

membrane thickness

membrane surface area

Diffusion coefficient of gas

partial pressure difference of gas between two sides of the membrane.

Question 19

What does the Va/Q ratio refer to?

Answer 19

It is a ratio of ventilation-perfusion

Question 20

When is the Va/Q ratio normal?

Answer 20

When both factors are normal for a given alveolus.

Question 21

What is the normal Va/Q ratio?

Answer 21

0.8

This indicates gas exchange is complete in initial third of capillary.

Question 22

What occurs when Va/Q = 0?

Answer 22

There is still perfusion, but there is an airway opstruction.

Blood gas composition remains unchanged.

Question 23

What occurs when Va/Q = infinity?

Answer 23

There is still ventilation, but no gas exchange.

This is due to a vascular obstruction (i.e. pulmonary embolism).

Alveolar gas composition remains unchanged because there is no blood contact. This creates a physiologic shunt.

Question 24

What is shunted blood?

Answer 24

venous blood passing through pulmonary capillaries that does not become oxygenated.

It ocurs whenever Va/Q is below normal.

Question 25

The greater the physiologic shunt, the ___ the amount of blood that fails to be oxygenated.

Answer 25

Greater

Question 26

What occurs when ventilation of some of the alveoli is great but alveolar blood flow is low?

Answer 26

There is far more available oxygen in the alveoli than can be transported away from the alveoli by the flowing blood. The ventilation of these alveoli is wasted.

Question 27

What is the physiologic dead space?

Answer 27

The sum of oxygen transported (When there is an exess of oxygen) + anatomic dead space