CH.4 The Diffusion of Pulmonary Gases

Question 1

Mechanics of Ventilation

Answer 1

–Moves bulk amount of air in and out of lungs
–Respiration: movement of gases across alveolar-capillary
–Process occurs by gas diffusion

Question 2

Dalton’s Law

Answer 2

–Law of partial pressures
–Total pressure exerted by mixture of gases is equal to sum of pressures exerted independently by each gas in mixture
–Pressure exerted by each gas (its partial pressure) is directly proportional to percentage of that gas in gas mixture

Question 3

Partial pressure of Atmospheric changes

Answer 3

–Earth’s atmospheric gases consist of nitrogen, oxygen, carbon dioxide, and other trace gases
–the percentage of oxygen in atmosphere is approximately 21 percent, and assuming normal Pb of 760 mmHg at sea level, partial pressure of oxygen is calculated
– Atmospheric PO2=0.21*760=159.6 mmHg

Question 4

Partial Pressure of Atmospheric gases

Answer 4

–the percentage of oxygen in atmosphere is approximately 21 percent, and assuming normal Pb of 760 mmHg at sea level, partial pressure of oxygen is calculated
– Atmospheric PO2=0.21*760=159.6 mmHg

Question 5

Partial Pressure of
Atmospheric Gases

Answer 5

– Partial pressure of each of atmospheric
gases (PN2, PO2, PCO2, and some trace
gases) collectively make total atmospheric
pressure of 760 mmHg
– Atmospheric pressure decreases with increase in altitude
– Due to density of different gases surrounding earth that decrease with increased altitude

Question 6

Partial Pressure

Answer 6

–Concentration of all atmospheric gases remains the same at both high and low elevations

Question 7

Pressure Gradient

Answer 7

– movement of gas from area of high pressure (high concentration) to area of low pressure (low concentration)
–Primary mechanism responsible for moving air in and out of lungs during ventilation

Question 8

Gas Diffusion

Answer 8

–movement of “individual gas molecules” from area of high pressure to area of low pressure

Question 9

Diffusion Gradients

Answer 9

– the partial pressure differences in an individual gas (nitrogen, oxygen, carbon dioxide) move independently from high-pressure areas to low-pressure areas.

Question 10

Alveolar Gas

Answer 10

–is assumed to have absolute humidity of 44 mg/L and water vapor of 47 torrential

Question 11

Alveolar gas Equation

Answer 11

–PAO2= [PB-PH2O] FIO2- PaCO2 (1.25)

–PAO: is the partial pressure of oxygen in the alveoli
–PB: is the barometric pressure. should be 760
–PH2O: partial pressure of water vapor in the alveoli (47 mm Hg)
–FIO2: fraction of inspired oxygen
–PaCO2: partial pressure of arterial carbon dioxide
– the number 1.25 is a factor that adjusts for alterations in oxygen tensions
– Respiratory Exchange Ratio: ratio for the amount of oxygen that moves into the pulmonary capillary blood and into the alveoli

Question 12

Diffusion of Pulmonary Gases: AC Membrane

Answer 12

– the liquid lining of the intra-alveolar membrane
–the alveolar epithelial cell
–basement membrane of the alveolar epithelial cell
loose connective tissue (interstitial space)
–basement membrane of the capillary endothelium
–capillary endothelium
–plasma in the capillary blood
–erythrocyte membrane
–intracellular fluid

Question 13

Diffusion across the AC membrane

Answer 13

–in the lungs, a gas molecule must diffuse through the alveolar-capillary
–normal gas pressure for O2 and CO2 as blood moves through AC-membrane

Question 14

Oxygen and Carbon
Dioxide Diffusion Across
the AC Membrane

Answer 14

–under normal resting conditions, blood moves through alveolar capillary membrane in approximately 0.75 seconds

Question 15

Fick’s Law

Answer 15

–states that the rate of gas transfer across a sheet of tissue is directly proportional to the surface area of the tissue
–to the diffusion constants, and to the difference in partial pressure of the gas between two sides of tissue

Question 16

Gas Diffusion

Answer 16

–the diffusion of gas place according to Fick’s law
–Fick’s Law: A= amount of gas that diffuses from one point to another (surface area)
D= diffusion constant P1-P2 (difference in partial pressure between two points)
T= the thickness of the

Question 17

Clinical Application of Fick’s Law: Area (A)

Answer 17

– decreased alveolar surface area: caused by alveolar collapse or alveolar fluid, which decreases ability of oxygen to enter pulmonary capillary blood vessels

Question 18

Clinical Application of Fick’s Law: P1-P2

Answer 18

–decreased alveolar oxygen pressure (PAO2 or P1): caused by high altitudes or alveolar hypoventilation, which reduces diffusion of oxygen into pulmonary capillary blood.

Question 19

Clinical Application of Fick’s Law: Thickness (T)

Answer 19

– increased alveolar tissue thickness caused by alveolar fibrosis or alveolar edema reduces movement of oxygen across alveolar-capillary membranes