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Physiology Part 2 > Lec 35 Gas Diffusion > Flashcards

Lec 35 Gas Diffusion Flashcards

1
Q

What is general gas law?

A 
PV = nRT in BTPS
P = pressure in mmHg
V = volume in L
n = number of moles
R = gas constant
T = temperature
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2
Q

What is BTPS?

A

Body Temp: 37 C or 310 K
Ambient P
Saturated with water vapor

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3
Q

What is water vapor pressure at T = 37 C?

A

47 mmHg

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4
Q

When do you use BTPS?

A

gas phase

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5
Q

When do you use STPD?

A

liquid phase [gas dissolved in blood]

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6
Q

What is STPD?

A

Standard Temp = 0 C, 273 K
Standard P = 760 mmHg
Dry gas

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7
Q

What is standard temp

A

0 C, 273 K

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8
Q

What is standard pressure

A

760 mmHg

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9
Q

What is boyle’s law?

A
  • special case of general gas law

- at constant temp: P1V1 = P2V2

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10
Q

Example of boyle’s law in inspiration?

A

inspiration –> diaphragm contracts –> get increase lung volume –> get decreased gas pressure to keep PV constant –> decreased P is driving for for airflow into lung

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11
Q

What is partial pressure for dry gas x?

A 
Px = Pb * F
Pb = barometric pressure
F = fractional concentration
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12
Q

What is partial pressure for humidified gas x?

A 
Px = (Pb - Ph2o) * F
Pb = barometric pressure
F = fractional concentration
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13
Q

What is definition of partial pressure of gas x?

A

the pressure gas x would exert if it occupied total volume of mixture

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14
Q

What is daltons law?

A

total pressure of mixture of gases = sum of partial pressures of all gases in the mixture

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15
Q

What is barometric pressure equation?

A

Pb = Po2 + Pco2 + Pn2 + Ph2o

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16
Q

What is percent of O2/N2/CO2 gases in dry air at barometric pressure 760 mmHg?

A

O2: 21%
N2: 79%
CO2: 0%

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17
Q

What is Ph2o in humidified tracheal air at 37 C?

A

47 mmHg

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18
Q

What happens to dalton’s law at high altitude?

A

have reduced barometric pressure –> decreased PO2 of inspired air –> lower alveolar PO2

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19
Q

What is henry’s law? when does it apply?

A
  • applies for concentration of dissolved gas free in solution [not bound to plasma proteins or Hb]
  • Cx = Px * S
    Cx = concentration of dissolved gas ml/100 mL blood
    Px = partial P gas
    S = solubility gas in blood mL/100 mL/mmHg
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20
Q

At equilibrium what is relationship partial P gas in liquid and gas phases?

A

partial P gas in liquid = partial P gas in gas phase

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21
Q

At equilibrium what is alveolar air PO2? pulm capilllary blood PO2?

A

both are 100 mmHg

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22
Q

What dissolved gas does not apply in henry’s law concentration? what dissolved gas is included?

A

dissolved gas that is bound to plasma proteins or Hb not included
only dissolved gas that is free is included

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23
Q

How do you calculate concentration of dissolved O2?

A

concentration dissolved O2 = PO2 * solubility

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24
Q

What is solubility of O2?

A

0.003 mL O2/ 100 mL blood/ mmHg

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25
Q

What is the concentration of dissolved O2 in arterial blood?

A

0.3 mL/ 100 mL

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26
Q

How are gases transferred across cell membranes / capillaries?

A

simple diffusion

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27
Q

What 4 factors affect rate of diffusion of gases?

A
  1. driving force [partial pressure difference]
  2. diffusion coefficient
  3. surface area available
  4. thickness of barrier
28
Q

What is Fick’s law?

A 
Vx = DAΔP / ΔX
Vx = rate of transfer of gas by diffusion [Vx = vol of gas trasnferred per unit time]
D = diffusion coefficient
A = surface area
ΔP = partial pressure difference [ driving force]
ΔX = thickness of membrane barrier
29
Q

In fick’s law what 3 things are directly proportional to Vx? What 1 thing is inversely proportional to Vx?

A 
directly
- ΔP: driving force, partial pressure difference of gases
- D: diffusion coefficient
- A: surface area
indirectly
- ΔX: thickness of membrane barrier
30
Q

What is the driving force for diffusion of a gas? What is the value in normal alveoli diffusion

A

partial pressure difference of gas across the membrane ΔP

PO2 alveolar - PO2 mixed venous blood = 100 - 40 = 60 mmHg

31
Q

What 2 things does diffusion coefficient D of a gas depend on?

A
  • molecular weight

- solubility

32
Q

Does CO2 or O2 have higher D?

A

CO2 had 20 x higher D than O2

33
Q

Does CO2 or O2 diffuse faster?

A

CO2 diffuses 20x faster than O2 at any given partial pressure

34
Q

What is total gas content in soln [blood] sum of [3 things]?

A

dissolved gas + gas bound to protein + chemically modified gas

35
Q

Is the amount of gas dissolved in solution directly or indirectly proportional to pressure of gas in solution?

A

directly proportional

36
Q

At given partial pressure, higher solubility does what to concentration?

A

higher solubility –> high concentration

37
Q

Which gas is exclusively carried in dissolved form?

38
Q

What forms of bound O2 in solution?

A
  • O2 bound to Hb inside RBCs
39
Q

What forms of bound CO2 in solution?

A
  • CO2 bound to both Hb inside RBCs and to plasma proteins
40
Q

What percent of CO2 chemically modified? how is it modified?

A
  • 90% of CO2 converted to H2CO3 by carbonic anhydrase in RBC

- H2CO3 –> H+ + HCO3-

41
Q

What percent of CO2 dissolved in plasma as CO2?

42
Q

What percent of CO2 bound to Hb in RBC?

43
Q

What is PO2 and PCO2 in dry inspired air?

A 
PO2 = 160
PCO2 = 0
44
Q

What is PO2 and PCO2 in humidified tracheal air?

A 
PO2 = 150
PCO2 = 0
45
Q

What is PO2 and PCO2 in alveoli?

A 
PO2 = 100
PCO2 = 40
46
Q

What is PO2 and PCO2 in mixed venous blood?

A 
PO2 = 40
PCO2 = 46
47
Q

What is PO2 and PCO2 in systemic arterial blood?

A 
PO2 = 100
PCO2 = 40
48
Q

What is cause of discrepancy between alveolar air PO2 and systemic arterial blood PO2?

A

2% of cardiac output bypasses alveoli via physiologic shunts –> bronchial blood flow and coronary venous return

49
Q

What is PO2 and PCO2 in peripheral tissues?

A 
PO2 = 40 mmHg
PCO2 = 46 mmHg
50
Q

What is diffusion-limited gas exchange across alveolar-capillary barrier?

A
  • total amount gas transported across alveolar-capillary barrier is limited by diffusion process
  • as long as partial P gradient maintained, diffusion will continue along length of capillary
51
Q

What 3 things can bind Hb inside RBCs

52
Q

What are 4 examples of diffusion limited gas exchange?

A
  1. transport of CO: because CO binds Hb as it enters blood so doesn’t create partial pressure in blood so never equilibrates
  2. transport O2 in emphysema: destruction of alveoli wall so smaller surface area so decreased diffusion
  3. transport O2 in pulm fibrosis: increased thickness so much slower diffusion
  4. transport O2 in exercise: increased blood flow so diffusion becomes limit
53
Q

What is limited in diffusion of CO?

A

diffusion limited

54
Q

What is limited in diffusion of O2 in emphysema?

A

diffusion limited

55
Q

What is limited in diffusion of O2 in pulmonary fibrosis?

A

diffusion limited

56
Q

What is limited in diffusion of O2 in exercise?

A

diffusion limited

57
Q

What is perfusion limited gas exchange?

A
  • total amount of gas transported across alveolar/capillary barrier is limited by blood flow [perfusion]
  • partial pressure gradient is not maintained, only way to increase amount of gas transported is by increasing blood flow
58
Q

In what kind of limited gas exchange is partial pressure maintained? not maintained?

A
  • maintained in diffusion limited gas exchange

- not maintained in perfusion limited gas exchange

59
Q

What are 3 examples of perfusion limited gas exchange?

A
  • O2 under normal conditions
  • CO2
  • N2O [since highly dissolved and not bound]
60
Q

Where does pressure gradient become equal in perfusion limited gas exchange in capillary?

A

in the first 1/3 of capillary

61
Q

What is limited in diffusion of O2 in normal conditions?

A
  • perfusion limited
  • gradient for diffusion maintained in beginning b/c O2 binds Hb first so not
  • as dissolved O2 increases, so does blood PO2
62
Q

What is limited in diffusion of CO2 in normal conditions?

A

perfusion limited

63
Q

What is limited in diffusion of N2O in normal conditions?

A

perfusion limited

64
Q

What is significance of O2 doing all its diffusion in first 1/3 of capillary?

A

its now perfusion limited so theres lots of room to increase diffusion by increasing blood flow in exercise

65
Q

What is used to measure DL [diffusion capacity of lung]? Why?

A
  • CO is used
  • because its transfer is exclusively limited by diffusion process since it binds Hb as soon as it enters blood it basically has no dissolved partial pressure

Physiology Part 2 (19 decks)

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