Gas Exchange And Transport

Front 1

Diffusion of gases characteristics (2)

Back 1

1. Random (Brownian) movement of gas molecules due to kinetic energy
2. Collisions - intermolecular and with boundaries of system (gas cyclinder, capillary membrane, alveolar membrane)

Front 2

What is the definition of pressure?

Back 2

force/area

Front 3

What are the units of gas pressure?

Back 3

mmHg (torr), cm H20, psi, Pa, atm

Front 4

SI unit?

Back 4

Pa

Front 5

Total gas pressure is proportional to?

Back 5

the total concentration of gas molecules

Front 6

In a mixture of gases, each gas exerts a partial pressure; the partial pressure of the gas is proportional to?

Back 6

its fractional concentration in the mixture, ie, Pgas = F gas x Pt

Front 7

Dissolved gas molecules have (3)?

Back 7

kinetic energy, diffuse in solution, and exert pressure (tension)

Front 8

The pressure of a gas in a solution is proportional to its?

Back 8

concentration (Henry's Law)
Cgas = alpha x Pgas

Front 9

Net diffusion of a gas occurs in response?

Back 9

to a difference in gas partial pressure

Front 10

What law does this involve?

Back 10

Fick's Law

Front 11

What is the diffusivity of oxygen, co2, co, n2, helium?

Back 11

oxygen: 1.0
co2: 20.3
CO: 0.81
N2: 0.53
Helium: 0.95

Front 12

Composition of alveolar gas is _______ from that of atmospheric air.

Back 12

different

Front 13

What is are 4 reasons alveolar gas is different than atmospheric air?

Back 13

1. Alveolar gas is only partially replaced by atmospheric air with each breath
2. Oxygen is absorbed from alveolar gas
3. Carbon dioxide is added to alveolar gas
4. atmospheric air is humidified as it enters the resp. system

Front 14

FRC is 2300 mL, how much new air is delivered to the alveoli with each normal breath? This amount of alveolar gas is also removed.

Back 14

350 mL

Front 15

Thus, with each breath only _____ of the total alveolar gas is replaced by new air, this is important in?

Back 15

1/7, preventing sudden changes in blood gas concentrations

Front 16

What is absorbed from alveolar gas?

Back 16

Oxygen

Front 17

How is the alveolar partial pressure of oxygen (PA02) determined?

Back 17

by the balance between oxygen delivery (via alveolar ventilation) and oxygen absorption

Front 18

For a normal person breathing normal atmospheric air at sea level, PAO2 cannot exceed?

Back 18

150mmHg, even with a marked increase in alveolar ventilation

Front 19

Breathing gas with a higher PO2, however can increase?

Back 19

PA02

Front 20

What is ADDED to alveolar gas?

Back 20

carbon dioxide

Front 21

What is the CO2 production/excretion rate? Alveolar ventilation rate?

Back 21

200mL/min, 4.2L/min

Front 22

With those rates what is the alveolar PCO2?

Back 22

40mmHg

Front 23

PACO2 is inversely related to?

Back 23

alveolar ventilation

Front 24

Atmospheric air is _______ as it enters the respiratory system.

Back 24

humidified

Front 25

What is the SVP of water at body temp?

Back 25

47mmHg

Front 26

The partial pressure of H20 of alveolar gas is?

Back 26

47mmHg

Front 27

Humidification does what to the partial pressures of inspired oxygen and nitrogen?

Back 27

lowers

Front 28

Composition of expired gas, is a combo of?

Back 28

dead space gas and alveolar gas

Front 29

What changes progressively during the course of expiration?

Back 29

P02 and PC02

Front 30

The alveolar wall contains an extensive?

Back 30

network of interconnecting capillaries that form a "sheet" of blood around the alveolus itself

Front 31

The structures separating alveolar gas from blood in the alveolar capillaries are collectively called?

Back 31

the respiratory membrane (blood-gas barrier)

Front 32

What is the average total thickness of the respiratory membrane?

Back 32

0.6 micrometers

Front 33

The structures separating alveolar gas from blood in the alveolar capillaries include?

Back 33

1. Fluid lining of the alveolus, including surfactant
2. Very thin Type I epithelial cells
3. Epithelial basement membrane
4. Interstitial space
5. Capillary basement membrane
6. Capillary endothelium

Front 34

What is the total surface area of the respiratory membrane?

Back 34

is estimated to be 50-100 meters squared

Front 35

What is the total amount of blood in the pulmonary capillaries at any time?

Back 35

60-140 mL

Front 36

What factors affect the rate of gas diffusion across the respiratory membrane? (4)

Back 36

1. Thickness of the respiratory membrane (d)
2. Surface area of the respiratory membrane (A)
3. Diffusivity of the gas in the respiratory membrane (S/MW0.5)
4. Difference in gas partial pressure across the respiratory membrane (deltaPgas)

Front 37

Rate of diffusion is inversely related to?

Back 37

thickness

Front 38

What can increase the thickness of the respiratory membrane and impair gas exchange?

Back 38

pulmonary interstitial edema and fibrosis

Front 39

Rate of diffusion is directly related to?

Back 39

surface area

Front 40

What can reduce surface area?

Back 40

surgical removal of lung tissue and in certain pulmonary diseases (emphysema is associated with coalescence of alveoli)

Front 41

Diffusivity is directly related to? and inversely related to?

Back 41

gas solubility in the membrane and inversely related to molecular weight of the gas

Front 42

What diffuses 20 times faster through the membrane than oxygen?

Back 42

Carbon dioxide

Front 43

Carbon dioxide diffuses how many times faster than nitrogen?

Back 43

40

Front 44

What is the definition of diffusion capacity of the respiratory membrane?

Back 44

volume of gas that diffuses across the membrane per minute in response to a partial pressure difference of 1 mmHg

Front 45

What is oxygen's diffusion capacity at rest?

Back 45

20ml/min(mmHg)

Front 46

What is the maximum diffusion capacity of o2?

Back 46

65ml/min(mmHg)

Front 47

Why can there be an increase in diffusion capacity of oxygen? (2)

Back 47

1. Opening of "dormant" capillaries
2. Better ventilation-perfusion matching

Front 48

What is carbon dioxides diffusion capacity?

Back 48

technical difficulties preclude direct measurement

Front 49

What is the estimated carbon dioxide diffusion capacity?

Back 49

400-450ml/min(mmHg) at rest and maximum of 1200-1300mL/min (mmHg)

Front 50

At rest, the transit time of the RBC in the pulmonary capillary is about?

Back 50

0.75 seconds

Front 51

P02 of blood entering the capillary is? PAO2 is?

Back 51

40mmHg (mixed venous P02), 100mmHg

Front 52

Describe oxygen uptake

Back 52

Oxygen diffuses down its large partial pressure gradient; at rest, capillary P02 increases to that of alveolar gas (diffusion equilibrium occurs) by the time blood has moved about 1/3 the length of the capillary (0.25 sec)

Front 53

There is said to be a very large "_______ _______"

Back 53

diffusion reserve

Front 54

Even with strenuous exercise, where blood transit time may be as little as 0.25 sec, diffusion equilibrium.....?

Back 54

for oxygen occurs, and end-capillary PO2 is essentially the same as PA02

Front 55

Diffusion impairment (disequilibrium) is unusual, but may occur in what certain circumstances?

Back 55

1. Patient with thickened respiratory membrane
2. Exercise at high altitude, particularly in patient with thickened respiratory membrane

Front 56

PC02 of blood entering the pulmonary capillary is? PACO2 is?

Back 56

45 mmHg (mixed venous PCO2), 40 mmHg

Front 57

Describe carbon dioxide removal

Back 57

Co2 diffuses down its partial pressure gradient; diffusion equilibrium normally occurs by the time the blood has moved about 1/3 the length of the capillary (0.25)

Front 58

Diffusion impairment of C02 may create a?

Back 58

difference between end-capillary PCo2 and PACo2, particularly during exercise

Front 59

With Fick's Law, what factors is the rate of diffusion directly related to and inversely related to?

Back 59

Directly: partial pressure of gas, solubility, and surface area
Inversely: thickness and MW