Gas Exchange And transport

Question 1

Percentages of different gases in air

Answer 1

. 78% Nitrogen
. 21% O2
. 1% argon
. Trace amounts CO2, H2O vapor, other gases, and pollutants

Question 2

Dalton’s law

Answer 2

. Partial pressure of a gas (x) in a gas mixture is the pressure that gas would exert if it occupied the total volume of the mixture in absence of the other components 
. Px = PB x Fx
. Px: partial pressure of gas x
. PB: total barometric dry gas pressure 
. Fx: fractional component of gas x

Question 3

T/F total barometric pressure will change with altitude, but the percentage of each gas in the total air mixture will stay the same

Answer 3

T

Question 4

Henry’s law

Answer 4

. States that the concentration of a gas dissolved in a liquid (Cx) is equal to the partial pressure of that gas (Px) times its solubility in that liquid (alpha)
Cx = alpha x Px

Question 5

Partial pressure gradient

Answer 5

. Gas diffuses down its partial pressure gradient
. Normally, O2 diffuses from the alveoli and dissolves in pulmonary capillary blood until blood PO2 becomes equal to th partial pressure of O2 int he alveolar gas (PAO2)
. CO2 normally diffuses from pulmonary capillary blood and evolves as CO2 gas in the alveoli (PACO2) until alveolar PCO2 is equal to blood PCO2

Question 6

composition of alveolar air

Answer 6

. Alveolar air has different composition than atmospheric air
. At body temp the partial pressure of H2O vapor is 47 mmHg

Question 7

Effect of humidification of inspired air on partial pressure of gases

Answer 7

. It dilutes the partial pressure of the other inspired gases by 47 mmHg because the sum of all individual gas partial pressures must equal total barometric pressure

Question 8

Alveolar gas equation

Answer 8

. PAO2 = PIO2 - (PACO2/RQ)
. PAO2: PO2 within alveoli
. PIO2: partial pressure of inspired O2
. PAO2 and PACO2 have an inverse linear relationship to one another

Question 9

Partial pressure of O2 w/in alveoli throughout respiratory cycle

Answer 9

. Remains fairly constant
. O2 w/in alveoli continually moves down its partial pressure gradient into the blood
. New O2 arriving in the lungs w/ each breath replaces that which has already diffused into the pulmonary capillaries
. Pulmonary blood PO2 equilibrates w/ the alveolar PO2, the PO2 w/in the arterial blood also remains fairly constant at around 100 mmHg

Question 10

Partial pressure of CO2 throughout respiratory cycle

Answer 10

. Body tissues continuously produce CO2
. CO2 added up in blood in the systemic capillary beds, and then is transported to the lungs
. When in lungs, CO2 diffuses down its partial pressure gradient, from the blood into the alveoli
. CO2 is removed from lungs during expiration
. Because CO2 arriving from the body tissues is constantly removed from the lungs, the PACO2 remains relatively constant throughout the cycle at 40 mmHg

Question 11

Gas transfer w/in the pulmonary capillaries

Answer 11

. Blood entering pulmonary capillaries is systemic venous blood w/ a PO2 of 40 mmHg, and PCO2 of 46 mmHg
. Blood flows through pulmonary capillaries, is exposed to a PAO2 of 100 mmHg and PACO2 of 40 mmHg
. O2 flows down gradient from alveolar air into blood
. After O2 equilibration, blood leaving pulmonary capillaries has PO2 of 100 mmHg
. CO2 flows down gradient from blood into alveolar air
. After CO2 equilibration, blood leaving pulmonary capillaries has PCO2 of 40 mmHg
. Blood now higher in O2 and lower in CO2 is returned to heart and pumped to body

Question 12

PO2 w/in the systemic capillaries

Answer 12

. Arterial blood reaches systemic capillaries is same blood that left lungs w/ PO2 of 100 mmHg and PCO2 is 40 mmHg
. Each cell consumes O2 and produces CO2
. Cellular PO2 is 40 mmHg and PCO2 is 46 mmHg
. Values change based on cellular metabolism
. O2 moves by diffusion down gradient from systemic capillary blood (PO2 100 mmHg) into adjacent cells (PO2 40 mmHg) until equilibrium
. PO2 of blood that leaves systemic capillaries is equal to tissues PO2 (40 mmHg)

Question 13

PCO2 w/in systemic capillaries

Answer 13

. CO2 diffuses out of tissues (PCO2 46 mmHg) into capillary blood (PCO2 40 mmHg) down gradient until blood PCO2 equilibrates w/ the tissues PCO2
. PCO2 of the blood that leaves the systemic capillaries is equal to the tissue PCO2 ($^ mmHg)

Question 14

Graham’s Law

Answer 14

. In the gas phase, the diffusion rate of molecules is inversely proportional to sq rt of molecular weights
. Diffusion rate = 1/ sq rt (MW)

Question 15

Fick’s Law

Answer 15

. Volume of a gas that diffuses across a tissue sheet per unit time (Vgas)
. Vgas = A sol (P1-P2)/ d sq rt MW
. A: area of sheet
.d= thickness of the sheet
. D: diffusion constant (permeability coefficient of tissue for that gas)
(P1-P2): partial pressure gradient across membrane
. Sol: solubility
. MW: molecular weight

Question 16

Blood flow in lungs during exercise

Answer 16

. During exercise when pulmonary blood pressure is raised as a result of inc. CO, many previously closed pulmonary capillaries are opened
. This inc. the SA available fo gas exchange

Question 17

Surface area of respiratory membrane in emphysema

Answer 17

. Many alveoli coalesce with dissolution of alveolar walls
. New alveoli are much larger than the original alveoli
. Total SA of respiratory membrane may dec. to 20% its original size

Question 18

Alveolar membrane thickness and affect on diffusion

Answer 18

. 0.5 um in thickness
. Rate of diffusion through the membrane is inversely proportional to thickness of the membrane
. Any factor that inc. the thickness can interfere w/ normal respiratory exchange of gases

Question 19

Pathological conditions that inc. thickness of respiratory membrane

Answer 19

. Pulmonary edema: excess accumulation of interstitial fluid btw alveoli and pulmonary capillaries
. Pulmonary fibrosis: involves replacement of delicate lung tissue w/ thick fibrous tissue in response to certain chronic irritants
. Pneumonia: characterized by inflammatory fluid accumulation w/in or around the alveoli

Question 20

Rate of gas transfer across the pulmonary membrane is proportional to ____

Answer 20

. Solubility of that gas
. Inversely proportional to its molecular weight
.

Question 21

CO2 and O2 solubility

Answer 21

. CO2 is more soluble in body tissues than is O2
. The rate of diffusion CO2 diffusion across respiratory membrane is 20 times more rapid than O2 for a given partial pressure gradient
. CO2 passes through alveolar membrane easier than O2

Question 22

Perfusion limited gas transfer

Answer 22

. Limit of time available for gas transfer
. N2O moves across respiratory membrane easily and dissolves in plasma
. N2O doesn’t combine w/ any substance in blood to its partial pressure in blood inc. rapidly
. Partial pressures on both sides of respiratory membrane equilibrate rapidly preventing further gas transfer
. Continued transfer of N2O can occur only if new blood is supplies to pulmonary capillary
. Amount of N2O taken up in blood depends on the rate of perfusion

Question 23

Diffusion limited gas transfer

Answer 23

. Gas tensions in the alveoli and the capillary blood fail to reach equilibrium during blood transit time through the capillary

Question 24

carbon monoxide gas transfer

Answer 24

. CO diffuses across respiratory membrane into the capillary blood down its partial pressure gradient
. Hb has high CO affinity so a large amount of CO is taken up by RBCs
. Partial pressure of CO in plasma remains low and CO gas continues to cross respiratory membrane down its partial pressure
. CO equilibrium btw alveoli and plasma is never achieved and the partial pressure gradient for CO will be high the entire time the blood spends in the pulmonary capillary
. CO limited only be diffusivity of alveolar membrane

Question 25

O2 uptake along pulmonary capillary

Answer 25

. Perfusion limited
. O2 diffuses across membrane and some O2 will bind to RBC but some stays dissolved in plasma
. Rise in PO2 in plasma will eventually cause equilibration

Question 26

Under resting conditions, the capillary PO2 is nearly the same as alveolar PO2 by the time ____

Answer 26

RBC is 1/3 along the way of the capillary

Question 27

O2 uptake along the pulmonary capillary during exercise

Answer 27

. CO inc. and the time th eRBC spends in capillary may be reduced
. PO2 of blood will equilibrate w/ alveolar PO2 before the blood completely passes though the capillary
. W/ disease, there may not be enough time for equilibration and PO2 will inc. More slowly in capillary blood showing diffusion impairment

Question 28

Diffusing capacity

Answer 28

. DL = Vgas/PAgas
. Vgas: amount of gas transferred
. PAgas: partial pressure of gas in alveoli

Question 29

How DLCO is measured

Answer 29

. Single breath of CO
. Single inspiration of dilute mixture is made and the rate fo disappearance of CO for alveolar gas calculated
. Done by measuring inspired and expired concentrations of CO w/ infrared analyzer
. Normal value 25 ml/min/mmHg
. Can inc. 2-3x during exercise

Question 30

Examples of conditions have thicken the barrier

Answer 30

. Interstitial/alveolar edema

. Interstitial/alveolar fibrosis

Question 31

Conditions that cause dec. surface area

Answer 31

. Emphysema
. Low CO
. Low pulmonary capillary blood volume

Question 32

Conditions that cause Dec. uptake by erythrocytes

Answer 32

. Anemia

. Low pulmonary capillary blood volume