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3 Respiratory Unit > 5 Properties of Gases and Gas exchange in the Lung > Flashcards

5 Properties of Gases and Gas exchange in the Lung Flashcards

1
Q

What is Dalton’s law?

A

In mixture of gases- each component exerts partial pressure

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2
Q

What unit do we use to measure pressure in medicine?

A

kPa

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3
Q

What % oxygen does air contain?

A

21%

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4
Q

If the partial pressure of oxygen in alveolar air is 13.3% and the air is allowed to equilibrate with the blood in the pulmonary capillaries, what will be the partial pressure of oxygen in the blood leaving the alveolus?

(Atmospheric pressure= 101.1 kPa)

A

Partial pressure of oxygen in the blood leaving the alveolus: 13kPa

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5
Q

Partial pressure of a gas and content of dissolved gas in a liquid are not the same. Henry’s law shows the relationship between them. What is Henry’s law?

A

Dissolved gas in liquid (mmol/L) = partial pressure of gas (kPa) x solubility coefficient of gas

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6
Q

What is the solubility coefficient?

A

Amount of gas that will dissolve in 1L of plasma at 37 degrees C, when exposed to given partial pressure

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7
Q

How does the solubility coefficent of CO2 differ from that of O2?

A

Solubility coefficent of CO2 > Solubility coefficent of O2

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8
Q

What is the standard vapour pressure of water vapour at body temperature (37 degrees C) ?

A

6.28 kPa

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9
Q

Where does inhaled air become saturated with water vapour?

A

Upper respiratory tract.

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10
Q

The normal value of partial pressue of oxygen in the alveolar gas is about 13.3 kPa. Since atmospheric partial pressure of oxygen is about 21 kPa, explain the difference.

A
  • Inhaled air saturated with water vapour- partial pressure of O2 = 19.8 kPa
  • In alveoli- O2 taken up by blood- so partial pressure lower
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11
Q

What is the normal value for the partial pressure of CO2 in the alveolar gas?

A

5.3kPa

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12
Q

What is meant by ‘mixed venous blood’?

A

Blood from superior vena cava, inferior vena cava and coronary sinus

(ie deoxgenated venous blood from body)

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13
Q

What are the partial pressures of oxygen and carbon dioxide in the mixed venous blood reaching the capillaries?

A

pO2= 6kPa

pCO2​= 6kPa

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14
Q

Name the 3 factors which determine the the rate of gas exchange in the alveoli.

A
  • Area available for exchange
  • Resistance to diffusion
  • Gradient of partial pressure
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15
Q

There are 5 key structures which the gas must diffuse through from entering the alveoli to entering a red blood cell. What are these structures?

What is the thickness of this barrier overall?

A
  1. Alveolar epithelia cell
  2. Interstitial fluid
  3. Capillary endothelilal cell
  4. Plasma
  5. Red cell membrane

Thickness: 0.6 micron

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16
Q

How much faster does carbon dioxide diffuse compared to oxygen?

A

21 x faster

17
Q

Diseases causing diffusion defects will affect oxygen concentration first and will only start to affect carbon dioxide concentration towards the end stages of the disease. Why is this?

A

CO2 diffuses 21 times faster than O2 for given gradient.

18
Q

Once the blood enters an alveolar capillary, how long does it take for the blood to become fully saturated with oxygen?

A

0.5 seconds

(1/3rd of way along)

19
Q

Identify some lung diseases which cause diffusion defects:

A
  1. Interstitial lung disease
  2. Pulmonary oedema (fluid in interstitium and alveolus)
  3. Emphysema- reduces total SA
20
Q

How is diffusion resistance calculated?

A

Measuring CO uptake

following single, maximal breath of gas mixture

containing 14% helium and 0.1% CO

(almost all CO entering blood binds to Hb)

(Difference between PaCO and PACO does not change for whole time blood in contact with alveoli)

amount transfered from alveoli to blood= estimate of diffusion distance

23
Q

Convert 101 kPa to mmHg and atms.

A

101 kPa = 760 mmHg = 1 atm

24
Q

What is oxygen tension?

A

Partial pressure of oxygen in liquid

(Tension= partial pressure of gas in liquid)

25
Q

The presence of haemoglobin in the blood increases the oxygen carrying capacity of the blood by how much?

30
Q

What is the solubility co efficient for CO2 and Oxygen? What are their partial pressures in the alveoli?

A

O2= 0.13 mmol/L

Partial pressure in alveoli is 13.3 kPa

CO2= 0.23 mmol/L

Partial pressure in alveoli is 5.3 kPa

31
Q

What 2 abnormalities with regards to pO2 and pCO2​ would likely be seen in a patient with long-term diffuse lung fibrosis?

A

Low pO2

Normal pCO2

32
Q

A 26yr old athlete has just finished a 200m sprint. What factor has the greatest effect in increasing oxygen delivery to his muscles out of:

  • Increased CO2 in tissues
  • Drop in pO2 in tissues
  • Increase in red cell 2,3 DPG concentration
  • Drop in blood pH
  • Increase in body temperature
A

= Large drop in pO2 in tissues

3 Respiratory Unit (25 decks)

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