Lecture 11 - Alveolar Gas Exchange

Question 1

what factors does alveolar gas exchange depend on

Answer 1

perfusion and ventilation

Question 2

what is perfusion

Answer 2

blood to lungs

Question 3

What is the average ventilation rate to the lungs

Answer 3

7L/min

Question 4

what determines air flow in the lungs

Answer 4

ohms law; pressure gradient/resistance = airflow

Question 5

which parameter of air flow into lungs is most effective and most changed by the body

Answer 5

resistance for which radius is the main determinant

Question 6

What is the partial pressure of oxygen in air

Answer 6

160 mm Hg; oxygen is 21%

Question 7

What is the partial pressure of O2, CO2, and H20 in alveolar gas

Answer 7

100; 40; 47

Question 8

the amount of gas that can dissolve in a liquid is determined by

Answer 8

henry’s law

Question 9

what is the PO2 and C02 in arterial blood and venous blood

Answer 9

Art

• O2 = 95
• PCO2 = 40

Ven

• PO2 = 40
• PCO2 = 46

Question 10

What controls the O2 concentration in the alveoli

Answer 10

rate of new air in lungs

rate of absorption into blood (250 ml/min)

Question 11

Why is alveolar gas exchange slow

Answer 11

only about 1/7 of the volume of air that is in the lungs is “new” air

Question 12

What is 95% of the surface area in the lungs

Answer 12

type 1 pneumocytes where gas exchange occurs

Question 13

what do type 2 pneumocytes do

Answer 13

secrete surfactant; reabsorb water and Na

Question 14

What is the rate of gas exchange inversely proportional to

Answer 14

thickness

Question 15

how does CO2 diffuse compared to O2

Answer 15

20x faster

Question 16

how much gas is exchanged each minute

Answer 16

250ml O2 and 200ml of CO2

Question 17

the diffusion of gases

Answer 17

doesn’t not depend on other gases

Question 18

what are the limitations on diffusion

Answer 18

surface area available, thickness, solubility of gas, pressure gradient

Question 19

what determines available surface area for gas exchange

Answer 19

number of alveoli available

Question 20

what can negatively affect surface area in the lungs

Answer 20

damaged or ruptured alveoli such as that in emphysema

Question 21

what determines the thickness in the lungs

Answer 21

fluid layer, alveolar epithelium, intersitial space, blood vessel wall

Question 22

which area of the lung is susceptible to thickness changing

Answer 22

collagen deposition in interstitial space

Question 23

what element of diffusion changes most with exercise?

Answer 23

pressure gradient of gases

Question 24

in about what time does blood become sat with o2 in lungs

Answer 24

.25 sec

Question 25

what is a common limiter of perfusion? diffusion

Answer 25

perfusion-N2O; rapidly increases for Pc=PA

diffusion-CO; Pc=/=PA diffusion is limited

Question 26

how is diffusion capacity of lung measured

Answer 26

inhaling CO; hold for 10 sec; used as a correction factor in DLO2=1.23 x correction factor

Question 27

Surface tension affects which alveolus primarily

Answer 27

in large alv, radius is large so pressure is low
in small alv, radius is small so pressure is high

air flows into larger alveolus (pressure gradient higher) causing the small one to want to collapse

Question 28

what is the content of surfactant

Answer 28

80% phospholipids; 10 neutral lipids (cholesterol); 10% surfactant apoproteins

Question 29

where is surfactant stored in cells

Answer 29

immature lamellar bodies

Question 30

where is surfactant secreted from in cells

Answer 30

mature lamellar bodies

Question 31

where is used surfactant recollected in cells

Answer 31

MVB