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Respiratory System > Gas Exchange in the lungs > Flashcards

Gas Exchange in the lungs Flashcards

1
Q

What is the percentage of O2 present in air?

A

21%

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2
Q

What is the percentge of CO2 and NO2 in air?

A
  1. 4%

0. 5%

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3
Q

What is the partial pressure of oxygen and carbon dioxide in alveolar gas?

A
  1. 3 Kpa - O2

5. 3 Kpa CO2

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4
Q

What is alveolar pO2 determined by?

A

A balance between the rate of removal of O2 by the blood and the rate of replenishment of O2 by alveolar ventilation

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5
Q

What is alveolar pCO2 determined by

A

The rate at which CO2 enters the alveoli from the blood and the rate at which it is removed from alveolar gas by ventilation

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6
Q

What 3 factors is the rate of GE determined by?

A
  1. Area available for GE
  2. resistance to diffusion
  3. Gradient of partial pressure
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7
Q

What are the partial pressures of O2 and CO2 in the pulmonary capillary entering the alveoli?

A

6Kpa

6Kpa

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8
Q

What is the normal area of GE in the lung?

A

alveolar surface 70m2

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9
Q

What 5 things must the O2 must diffuse through to reach the RBC?

A
  1. The alveolar epithelial cell
  2. interstitial fluid
  3. Capillary endothelial cell
  4. Plasma
  5. RBC membrane
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10
Q

What is the overall distance the O2 has to diffuse across?

A

0.6um

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11
Q

What factors affect diffusion of gas in a fluid? (6)

A
  1. Pressure change
  2. Solubility of gas in solution
  3. Cross sectional area of fluid
  4. Distance the molecules must diffuse across
  5. MW of gas
  6. Temp of fluid
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12
Q

Why does carbon diffuse faster than oxygen?

A

CO2 is more soluble in water than oxygen (21X)

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13
Q

What is the pp of O2 and CO2 in arterial blood?

A

In a normal subject the pp of O2 and CO2 should be the same in arterial blood as in alveolar gas (13.3 Kpa and 5.3Kpa)

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14
Q

What affect does interstitial lung disease have on diffusion and why? (fibrotic lung disease)

A

It increases the diffusion distance as there is excessive collagen deposition in the interstitial space, with thickening of alveolar walls, therefore pO2 in blood is low (pCO2 is normal).

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15
Q

what will the pO2 be in interstitial lung disease and why?

A

Increased in the diffusion distance as there is excessive collagen deposition in the interstitial space, with thickening of alveolar walls, therefore pO2 in blood is low (pCO2 is normal).

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16
Q

What does diffusion resistance depend on?

A

The nature of the barrier

The nature of the gas

17
Q

What is the equation to work out permeability of a gas across a barrier?

A

The diffusion coefficient of molecules in the membrane X their solubility in the lipid bi-layer/ thickness of the membrane.

18
Q

What is the H2O pressure in tracheal air?`

A

6.28Kpa

19
Q

What does SVP (saturated vapour pressure) depend on?

A

Temperature independent of total pressure

20
Q

Wha is the SVP of H2O at 37 degrees?

A

6.28 Kpa

21
Q

How is CO2 carried in the blood?

A

8% is dissolved in the plasma
12% is carried as carboxy Hb on proteins
80% is HCO3- in plasma

22
Q

Whats the pressure of O2 and CO2 in ambient air?

A 
O2 = 20.8 Kpa 
CO2= 0.04 Kpa
23
Q

What are the difference in pressures for O2 and CO2 between the alveolar gas and the venous blood?

A

The pO2 is < pO2 in alveolar gas, so O2 diffuses into the blood
The pCO2 is > the pCO2 of alveolar gas, so CO2 diffuses into the alveoli and is expelled

24
Q

What happens during in exercise to the pCO2?

A

The pCO2 in the pulmonary capillary increases, there pressure gradient is steeper and CO2 is diffused across twice as fast.
Normally blood spends 3X as long in PC as needed so in exercise exchange is not limited

25
Q

Why is the pressure difference required for CO2 less than O2

A

Because CO2 is more soluble (20X faster)

26
Q

How long does it take for GE of O2?

A

within 0.5s of RBC arriving (RBC spend around 1s in capillary)

27
Q

What affect does pulmonary oedma have on diffusion resistance?

A

It increases the length of the diffusion pathway as fluid in the interstitial space and alveolus increases

28
Q

How does Emphysema affect the diffusion resistance?

A

Emphysema causes destruction of the alveolar walls resulting in large air spaces and reduction in total surface area available for GE (pO2 is low)

29
Q

How is diffusion resistance measured?

A

Carbon monoxide transfer factor
Measure the CO uptake following a single maximal breath of a gas mixture containing air 14% helium and 0.1% CO.
Inhaled CO is used because of its high affinity for Hb
Amount of CO transferred from alveoli to the blood is an estimate of the diffusion resistance

30
Q

What is meant by anatomical dead space?

A

The conducting portion of the respiratory tract up till the terminal bronchioles

31
Q

What is the normal volume for the anatomical (or serial) dead space?

A

150 ml

32
Q

How would you measure the volume of anatomical dead space?

A

Nitrogen washout test

33
Q

What is alveolar dead space or distributive dead space? Why might it occur?

A

The volume of air in the alveoli not taking part in GE
This could be due to insufficent blood suppy, damage by accident or disease - so even air that does reach there will be a proportion that is not exchanged.

34
Q

What is physiological dead space?

A

The sum of anatomical dead space + alveolar dead space

35
Q

How can the physiological dead space be determined?

A

Measure the pCO2 (or pO2) of expired and alveolar air. Alveolar air is diluted by dead space air to form the expired air and the degree of dilution is a measurement of the physiological dead space.

36
Q

What is the pulmonary ventilation rate composed of?

A

The dead space ventilation and the alveolar ventilation

37
Q

What is the ventilation perfusion ratio?

A

The imblance between alvolar ventilation and alveolar blood flow
VA/Q (BF)

Respiratory System (6 decks)

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