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(LUSUMA) Respiratory System > S3) Properties of Gases > Flashcards

S3) Properties of Gases Flashcards

1
Q

What is Boyle’s Law?

A

Boyles Law: pressure (P) of a gas is inversely proportional to its volume (V) if temperature (T) and number of gas molecules remains constant in a closed system

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2
Q

Provide an example of Boyle’s Law in our bodies

A

Mechanism of inspiration & expiration

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3
Q

Define partial pressure

A

Partial pressure is the pressure exerted by a dissolved gas in a liquid

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4
Q

Explain the concept of partial pressure

A

In a mixture of gases, each gas has a partial pressure which is the pressure of that gas if it alone occupied the entire volume of the original mixture at the same temperature.

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5
Q

What is atmospheric pressure?

A

Atmospheric pressure is the pressure exerted by the weight of the air above the earth in the atmosphere

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6
Q

State the value of atmospheric pressure at sea level

A

101 kilopascals (kPa) = 1 atmosphere = 760 mmHg

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7
Q

Describe the composition of air

A
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8
Q

How can one calculate the partial pressure of a gas at sea level?

A

Partial pressure = atmospheric pressure x %gas

E.g. Partial pressure of O2 = 101 x 20.9% = 21.1 kPa

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9
Q

What effect do partial pressures have on gases in the body?

A
  • Gases dissolve and diffuse according to their partial pressure
  • Gases diffuse down their partial pressure gradient (high to low partial pressure)
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10
Q

What happens when inspired gases come in contact with body fluids?

A
  • Gas molecules dissolve to enter liquid
  • Water molecules evaporate to enter gas
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11
Q

How does saturation occur in the body?

A
  • Water molecules entering the air exert vapour pressure
  • When water molecules leave & enter water at same rate, the air is saturated with vapour
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12
Q

Provide an example of where saturation occurs in the body

A

Inhaled air in upper respiratory tract

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13
Q

State the value of Saturated Vapour Pressure (SVP) in the body

A

SVP = 6.28kPa at body temperature

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14
Q

How does the water vapour affect the partial pressure of the other gases?

A
  • Pressure of the rest of the gases = 101 – 6.28 = 94.7 kPa
  • Same ratios as in dry air
  • Eg. pO2 = (101 - 6.28) x 20.9% = 19.8 kPa*
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15
Q

For gases dissolved in a liquid, when is equilibrium reached?

A

When the rate of gas molecules entering water = rate of gas molecules leaving water

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16
Q

For gases dissolved in a liquid, what happens to partial pressures when equilibrium is reached?

A

Partial pressure of the gas in the liquid = partial pressure of the gas in the air above it

17
Q

Identify another term for the pressure of gas in a liquid

A

Tension

18
Q

Use 2 equations to show how partial pressure is different from the amount of a dissolved gas

A

Partial pressure = atmospheric pressure x %gas

Amount of gas dissolved = partial pressure x solubility coefficient of gas

19
Q

State the value of the solubility coefficient of O2 in plasma

A

0.01 /mmol.L-1 /kPa at 37°C

20
Q

In three steps, explain happens when O2 enters the alveoli

A

⇒ O2 enters plasma & dissolves

⇒ Dissolved O2 enters RBC to bind to Hb

⇒ Process continues till Hb fully saturated

21
Q

What happens after haemoglobin has been saturated?

A
  • O2 continues to dissolve till equilibrium is reached
  • At equilibrium, pO2 of plasma = pO2 of alveolar air
22
Q

What kind of oxygen is found in blood?

A

Blood contains both dissolved and Hb bound oxygen

23
Q

What does pO2 measure in the body?

A

pO2 is a measure of dissolved O2 in the blood

24
Q

What is the role of dissolved oxygen in the body?

A
  • Dissolved O2 is available to diffuse into tissues
  • As dissolved O2 leaves the blood, it is replaced by O2 bound to Hb
25
Q

What is the alveolar air composition?

A
  • Alveolar pO2 = 13.3 kPa
  • Alveolar pCO2 = 5.3 kPa
26
Q

What is the composition of air in the blood?

A

The blood equilibrates with alveolar air:

  • Arterial pO2 = 13.3 kPa
  • Arterial pCO2= 5.3 kPa
27
Q

Why is pO2 lower at high altitudes?

A
  • Atmospheric pressure is lower
  • Air is thinner and molecules are dispersed
  • Hence, less air molecules available when breathing
28
Q

The air inspired from a scuba tank is at higher pressure than on dry land.

Why?

A

Pressure below sea level = atmospheric pressure + weight of water

(LUSUMA) Respiratory System (19 decks)

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