Pulmonary Gas Exchange

Question 1

Components of air and their relative concentrations

Answer 1

Atmospheric pressure:

• 78.09% nitrogen
• 20.95% O2
• 0.93% Argon
• 0.03% CO2

Question 2

Components of air at alveoli saturated with 6.18% water vapor

Answer 2

• 73.26% Nitrogen
• 19.65% O2
• 0.87% argon
• 0.03% CO2

Question 3

What are the three gas laws

Answer 3

• Dalton’s law
• Boyle’s law
• Henry’s law

Question 4

What is Dalton’s law

Answer 4

The total pressure exerted by the mixture of non-reactive gases is equal to the sum of the partial pressure of individual gases

Question 5

What is Boyle’s Law

Answer 5

For a fixed amount of an ideal gas kept at a fixed temperature, P (pressure) and V (volume) are inversely proportional

Question 6

What is Henry’s Law

Answer 6

At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid directly proportional to the partial pressure of that gas in equilibrium with that liquid

Question 7

Ideal gas law

Answer 7

P= nRT/V

Question 8

Pressure is directly proportional to the

Answer 8

concentration of the gas molecules

Question 9

The rate of diffusion is directly proportional to

Answer 9

pressure caused by that gas alone

Question 10

A gas dissolved in a fluid also exerts its own ______ against a cell membrane

Answer 10

partial pressure

Question 11

What is the partial pressure of CO2 at alveolar membrane

Answer 11

0.21 mm Hg

Question 12

What is the partial pressure of O2 at alveolar membrane

Answer 12

=760x0.197

= 150mmHg

Question 13

The partial pressure of a gas in solution is determined not only by its concentration but also by the __________ of the gas. This is _____ law

Answer 13

Solubility coefficient, Henry’s

Question 14

equation for Henry’s law

Answer 14

partial pressure= dissolved gas / solubility coefficient

Question 15

What is the solubility of oxygen

Answer 15

0.024

Question 16

What is the solubility of carbon dioxide

Answer 16

0.57

Question 17

Because carbon dioxide is _____ soluble in water than oxygen, it will exert a partial pressure (for a given concentration) that is ____ than _____ that of oxygen

Answer 17

more, less, 1/20th

Question 18

______ of water is the partial pressure exerted to escape from the liquid phase to the gas phase

Answer 18

Vapor pressure

Question 19

What is the vapor pressure of water at normal body temperature (37 degrees C)

Answer 19

47mmHg

Question 20

Vapor pressure of water depends on the _____ of water. and decreases with

Answer 20

Temperature, decreases with a decrease in temperature

Question 21

What are the 5 factors that affect rate of gas diffusion in a fluid

Answer 21

• Solubility of gas in the fluid
• Cross-sectional area of the fluid
• Distance through which the gas must diffuse
• Molecular weight of gas
• Temperature of fluid (remains reasonably constant)

Question 22

What is the functional residual capacity of the lungs of the average man

Answer 22

2300mL

Question 23

only ____ mL of new air is brought into the alveoli with each normal inspiration, and this same amount of old alveolar air is expired. Therefore, the volume of alveolar air replaced by new atmospheric air with each breath is only ____ of the total (2300mL), so multiple breaths are required to exchange most of the alveolar air

Answer 23

350mL, 1/7th

Question 24

oxygen concentration in the alveoli, as well as its partial pressure, is controlled by

Answer 24

• Rate of absorption of oxygen into the blood

- Rate of new oxygen entry into the lungs (alveolar ventilation)

Question 25

to quadruple oxygen consumption, alveolar ventilation must

Answer 25

also be quadrupled

Question 26

Why can alveolar ventilation not increase PO2 above 149n, Hg under normal conditions

Answer 26

Because this is the maximum PO2 in humidified air at sea level pressure (if the person breathes gases that contain partial pressures of O2 higher than 149mmHg the alveolar PO2 can approach these higher pressures at high rates of ventilation.

Question 27

At moderate exercise the alveolar ventilation must increase _____ to maintain the normal alveolar PO2 of ____

Answer 27

4x, 104mmHg

Question 28

Carbon dioxide concentration in the alveoli, as well as its partial pressure, is controlled by

Answer 28

- Rate of carbon dioxide excretion - Alveolar PCO2 increase in direct proportion to rate of excretion - Alveolar ventilation - Alveolar PCO2 decreases in inverse proportion to alveolar ventilation

Question 29

As Alveolar ventilation increases PCO2

Answer 29

decreases

Question 30

As PCO2 excretion increases Alveolar PCO2

Answer 30

increases

Question 31

What is the respiratory membrane (pulmonary membrane)

Answer 31

all terminal portions of the lungs, not merely in the alveoli

Question 32

Layers of the respiratory membrane

Answer 32

1. ) A layer of fluid containing surfactant that lines the alveolus and reduces the surface tension of the alveolar fluid 2. ) The Alveolar epithelium, which is composed of thin epithelial cells 3. ) An epithelial basement membrane 4. ) A thin interstitial space between the alveolar epithelium and the capillary membrane 5. ) A capillary basement membrane that in many places fuses with the alveolar epithelial basement membrane 6. ) The capillary endothelial membrane

Question 33

Components of the Respiratory unit

Answer 33

- Respiratory Bronchiole - Alveolar ducts - Atria - Alveoli

Question 34

What is the overall thickness of the respiratory membrane

Answer 34

as little as 0.2 micrometers and averages 0.6 micrometers

Question 35

what is the total surface area of the respiratory membrane of a healthy adult male

Answer 35

about 70 square meters

Question 36

Factors that determine how rapidly a gas will pass through the respiratory membrane

Answer 36

- Membrane thickness - Membrane surface area - Diffusion coefficient of gas in the substance of the membrane - Partial pressure difference of gas between the two sides of the membrane

Question 37

any factor that increases membrane thickness (ex. Edema or fibrosis) to more than ____ or ____ normal can interfere with gas exchange

Answer 37

2x or 3x

Question 38

Ventilation-Perfusion ratio

Answer 38

Va/Q= alveolar ventilatio/blood flow

Question 39

What is normal ventilation-perfusion ratio

Answer 39

0.8 ventilation= 4L/min / (pulmonary blood flow=5L/min)

Question 40

Gas exchange is complete in _____ of capillary

Answer 40

initial third

Question 41

what is normal alveolar CO2

Answer 41

40

Question 42

What is normal alveolar O2

Answer 42

100

Question 43

VA/Q equals 0 when Va=____ but there is still perfusion

Answer 43

0

Question 44

what is the reason for Va/Q=0

Answer 44

-due to airway obstruction (i.e. mucus plug)

Question 45

What happens to blood gas when Va/Q=0

Answer 45

Blood gas composition remains unchanged. This means it is the same O2 and CO2 as it was when it entered the capillary as when it comes out

Question 46

When is Va/Q equal to infinity

Answer 46

when Q=0, thus meaning there is still no ventilation (no gas exchange) - due to vascular obstruction ()i.e. Pulmonary embolism)

Question 47

What happens to alveolar gas composition when Va/Q is equal to infinity

Answer 47

Alveolar gas composition remains unchanged(stays same as atm levels) because there is no blood contact. This creates a physiologic shunt

Question 48

Normal Alveolar perfusion PO2= and PCO2=

Answer 48

``` PO2= 104 mmHg PCO2= 40 mmHg ```

Question 49

The greater the physiological shunt, the _____ the amount of blood that fails to be oxygenated

Answer 49

greater

Question 50

Explain the physiologic shunt

Answer 50

Whenever Va/Q is below normal a certain fraction of the venous blood passing through the pulmonary capillaries does not become oxygenated. Also some blood is also shunted through bronchial vessels rather than through alveolar capillaries The greater the physiologic shunt, the greater the amount of blood that fails to be oxygenated

Question 51

Physiological dead space

Answer 51

- Sum of wasted alveolar ventialation (this is caused form great ventilation and poor blood flow leading to more oxygen available than can be transported by blood) plus anatomic dead space

Question 52

What is PO2 and PCO2 when Va/Q=0

Answer 52

PO2=40 | PCO2=45

Question 53

What is PO2 and PCO2 when Va/Q=infinity

Answer 53

PO2=149 | PCO2= 0