Lecture 24: Pulmonary Gas Exchange Flashcards

1
Q

At sea level the partial pressure of a specific gas in air can be determined by:

A

multiplying the percent of the gas in the air mixture by 760 mmHg

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2
Q

Henry’s law states that the amount of a given gas that dissolves in a given type and volume of liquid is:

A

directly proportional to the partial pressure of that gas at equilibrium.

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3
Q

Dalton’s law states that the total pressure exerted by the mixture of non-reactive gasses is:

A

equal to the sum of the partial pressures of the individual gasses.

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4
Q

Boyle’s law states that for a fixed amount of an ideal gas kept at a fixed temperature:

A

Pressure and volume are inversely proportional

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5
Q

The addition of water vapor to the mixture of air in the alveoli

A

decreases the partial pressures of all other gasses in the mixture.

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6
Q

What is the alveolar pressure at the end of a normal quiet inspiration cycle:

A

0 mmHG

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7
Q

Va/Q= 0.8

A

Normally Va/Q is 0.8 (pulmonary= 5L/min; Ventilation =4 L/min).

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8
Q

Va/Q=0

A

when Va=0, but there is still perfusion; this is due to airway obstruction (mucus plug). The blood gas composition remains unchanged.

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9
Q

Va/Q= Infinity

A

When Q= 0, but there is still ventilation (no gas exchange) this is due to vascular obstruction (PE). Alveolar gas composition remains unchanged because there is no blood contact. This creates a physiologic shunt.

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10
Q

Major components of air and relative concentrations:

A

Nitrogen 78%
Oxygen 21%
Argon 1%
CO2 0.03%

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11
Q

Pressure of gas

A

Directly proportional to the concentration of the gas molecules.

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12
Q

Rate of diffusion is

A

directly proportional to the pressure caused by that gas alone.

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13
Q

A gas dissolved in a fluid

A

also exerts its own partial pressure against a cell membrane.

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14
Q

5 Factors that affect rate of gas diffusion in a fluid:

A
  1. Solubility of gas in the fluid
  2. Cross-sectional area of the fluid
  3. Distance through which the gas must diffuse
  4. molecular weight of gas
  5. Temperature of fluid (remains reasonably constant)
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15
Q

What are the factors that control oxygen concentration in alveoli?

A

Rate of absorption of oxygen into the blood.

Rate of new oxygen entry into the lungs (Alveolar ventilation)

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16
Q

Explain why alveolar ventilation cannot increase partial pressure of O2 above 149 mmHg under normal conditions.

A

Maximum partial pressure in the atmosphere

17
Q

What are the factors that control carbon dioxide concentration in the alveoli?

A

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.

18
Q

Why alveolar ventilation cannot increase PO2 above 149 mm Hg under normal conditions.

A

Maximum partial pressure in atmosphere.

19
Q

List factors that will determine how rapidly a gas will pass through the respiratory membrane.

A
  1. Membrane Thickness
  2. Membrane Surface Area
  3. Diffusion coefficient of gas in the substance of the membrane
  4. Partial Pressure difference of gas between the two sides of the membrane.
20
Q

Va/Q Ratio represents:

A

Ventilation-perfusion ratio: Alveolar ventilation/ blood flow

21
Q

Where is gas exchange complete? for normal ventilation?

A

Gas exchange is complete in the initial 1/3 of the capillary

22
Q

Which of the following changes occurs during strenuous exercise?

A. Ventilation rate and O2 consumption increase to the same extent
B. Systemic arterial PO2 decreases to about 70 mmHG
C. Systemic arterial PCO2 increases to about 60 mmHg
D. Systemic venous PCO2 increases to about 60 mmHG
Pulmonary blood Flow decreases at the expense of systemic blood flow

A

A. Ventilation rate and O2 consumption increase to the same extent

23
Q
If an area of the lung is not ventilated because of bronchial obstruction, the pulmonary capillary blood serving that area will have a PO2 that is:
A. Equal to atmospheric PO2
B. Equal to mixed venous PO2
C. Equal to normal systemic arterial PO2
D. Higher than inspired PO2
E. Lower than mixed venous PO2
A

B. Equal to mixed venous PO2

If an area of lung is not ventilated, there can be no gas exchange in that region. The pulmonary capillary blood serving that region will not equilibrate with alveolar PO2 but will have a PO2 equal to that of mixed venous blood.