Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Respiratory > Properties of gases and diffusion > Flashcards

Properties of gases and diffusion Flashcards

1
Q

What is the kinetic theory of gases?

A
  • Gases are a collection of molecules moving randomly around a space
  • Pressure is generated by collisions of molecules with a surface
  • More frequent and harder collisions = higher pressure
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is Boyle’s Law?

A
  • Pressure of a gas is inversely proportional to its volume
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is Dalton’s Law?

A
  • In a mixture of gases, total pressure = sum of partial pressures of individual gases
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is atmospheric pressure?

A
  • 101kPa at sea level
  • At high altitude atmospheric pressure is lower
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is partial pressure of O2 at sea level?

A
  • 21.1 kPa
  • pO2 = fraction of O2 in air (0.209) x atmospheric pressure (101kPa)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is partial pressure of O2 at sea level?

A
  • 21.1 kPa
  • pO2 = fraction of O2 in air (0.209) x atmospheric pressure (101kPa)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What happens when air enters the upper respiratory tract?

A
  • It is humidified
  • Water molecules exert air vapour pressure - this is affected by temperature
  • At body temperature, saturated vapour pressure = 6.28 kPa
  • Water vapour displaces 6.28 kPa of atmospheric gas pressure
  • 101 kPa - 6.28 = 94.72 kPa (total gas pressure in upper respiratory tract)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

How do gases diffuse in the body?

A
  • From an area of high partial pressure to an area of low partial pressure
  • Not affected by concentrations of gases in gas mixtures or liquids
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the difference between PAO2 and PaO2?

A
  • PAO2 and PACO2 refer to pressures of these gases in alveoli
  • PaO2 and PaCO2 refer to pressures of gases in arterial blood
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is the pO2 and pCO2 in alveolar air?

A
  • pO2 = 13.3. kPa (lower than inhaled air)
  • pCO2 = 5.3 kPa (higher than inhaled air)

Because:
- Inhaled air mixes with residual air
- Gas exchange is always happening
- Blood equilibrates to these levels

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Why is alveolar pO2 different from upper respiratory tract pO2?

A
  • When we breathe, we do not replace all air in the lungs
  • We inhale 350ml of fresh air every time we breathe in
  • This represents ~ 10% of all the air in the lungs
  • Fresh air is diluted by old air in lungs
  • Older air has O2 being continually extracted, and CO2 constantly being added
  • Therefore, PAO2 is lower than pO2 in URT
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Outline how tidal volume affects how much air reaches the respiratory portion of the lungs?

A
  • Typically we inhale/exhale ~500ml air at rest (tidal volume)
  • In healthy lungs ~30% (150ml) of normal tidal volume fills anatomical dead space
  • 350ml of air reaches respiratory portion of lung - this is alveolar ventilation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Outline the behaviour of a gas as it dissolves in a liquid?

A
  • Equilibrium is reached when rate of gas entering water = rate of gas leaving water
  • At equilibrium partial pressure of the gas in the liquid = partial pressure of the gas in the air above it
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is KH?

A
  • Henry’s constant
  • The solubility of a gas in a liquid at a defined temperature
  • In the human body KH is the solubility of a gas at body temp in plasma
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the equation that gives us the amount of a dissolved gas?

A
  • Amount dissolved = partial pressure x solubility coefficient of that gas
  • E.g. for O2 = 0.01 x 13.3 = 0.13 mmol O2 dissolved
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

How does O2 binding to haemoglobin affect its equilibrium?

A
  • The reaction of Hb and O2 must be completed before equilibrium can be reached and partial pressure established
  • Initially O2 dissolves in plasma and binds to Hb in RBCs
  • Once Hb is fully saturated, O2 continues to dissolve in plasma until equilibrium is recahed
16
Q

What kinds of O2 does blood plasma contain?

A
  • Both dissolved and Hb bound O2
  • PO2 is a measure of dissolved O2 in blood
17
Q

How is O2 moved into tissues?

A
  • Dissolved O2 is available to diffuse into tissues down its partial pressure gradient
  • As dissolved O2 leaves the blood, it is replaced by O2 bound to Hb
18
Q

What allows gas exchange to occur at the lungs?

A
  • Low oxygen partial pressure and high CO2 partial pressure in venous blood allows oxygen to diffuse from lungs into blood and CO2 to diffuse from blood into lungs
19
Q

Why is alveolar gas composition steady?

A
  • Amount of O2 brought in by ventilation = amount of O2 diffusing into blood
  • Amount of CO2 removed by ventilation = amount of CO2 diffusing from blood into alveolus
20
Q

What are the values for PO2 and PCO2 in venous blood?

A
  • pO2 = ~6.0 kPa
  • pCO2 = ~ 6.1 kPa
  • pO2 is lower in mixed venous blood than in alveoli
  • pCO2 is higher in mixed venous blood than in alveoli
21
Q

What are the components of the diffusion barrier?

A
  • Fluid film lining alveolus
  • Epithelial cell of alveolus
  • Interstitial space
  • Endothelial cell of capillary
  • Plasma
  • Red blood cell membrane
22
Q

Which factors affect the rate of diffusion?

A
  • Partial pressure difference across membrane
  • Surface area available for diffusion
  • Thickness
  • Diffusion coefficient of the individual gas
23
Q

Diffusion also depends on the properties of the individual gas. Which properties are relevant?

A
  • The solubility of the gas in the liquid - greater solubility = faster rate of diffusion
  • Molecular weight of gas - greater molecular weight = slower rate diffusion
24
Q

Compare the diffusion of O2 with the diffusion of CO2

A
  • CO2 has a greater molecular weight than O2 but is much more soluble
  • CO2 diffuses 20x faster than O2
  • Larger difference in partial pressures compensates for slower diffusion of O2
  • In a diseased lung, O2 gas exchange is more impaired than CO2 gas exchange
25
Q

Outline the factors affecting gas exchange in the lungs

A
  • Surface area of alveolar capillary membrane is about 100m^2
  • Barrier <0.4 micrometers thick
  • Oxygen exchange complete in 1/3 of the time blood spends in the capillary
  • Have plenty of reserve for exercise
26
Q

How is the thickness of the membrane in the lungs affected by disease?

A
  • Increases as a result of oedema fluid in the interstitial space and in alveoli
  • Lung fibrosis increases thickness of alveolar capillary membrane
27
Q

How is the surface area of the membrane in the lungs affected by disease?

A
  • Decreased by removal of an entire lung
  • Emphysema decreases surface area
28
Q

When is gas exchange optimal?

A
  • V/Q ratio of individual alveolar units is approximately 1
29
Q

What do we mean when we say that ventilation and perfusion should be matched throughout the lung?

A
  • There are many alveoli that all may have widely differing amounts of ventilation and perfusion in different alveolar units
  • Alveoli with increased ventilation should have increased perfusion and vice versa
30
Q

What happens when PAO2 is low?

A
  • Hypoxic vasoconstriction of pulmonary arterioles occurs
  • This diverts blood to better ventilated alveoli
31
Q

What can cause V/Q mismatch with V/Q greater than 1?

A
  • Asthma
  • COPD early stages
  • Pneumonia
  • RDS in new-born (some alveoli not expanded)
  • Pulmonary oedema (fluid in alveoli)
32
Q

What is the pulmonary shunt?

A
  • Triggered by a smooth muscle reflex as a consequence of low O2 concentration
  • Minimised by normal reflex pulmonary hypoxic vasoconstriction
  • diverts blood away from poorly ventilated areas
33
Q

Why is there no use in prescribing 100% inspired oxygen to a patient with pulmonary shunting?

A
  • 100% inspired oxygen is unable to overcome the hypoxia caused by shunting
  • The alveoli being oxygenated with 100% O2 have no perfusion due to the shunt, so O2 will not pass into the capillaries
34
Q

What are the consequences of inadequate ventilation of an alveolar unit?

A
  • PACO2 increases
  • PAO2 falls
  • A new steady state is established
  • Diffusion continues at this new level
  • Blood equilibrates at the new alveolar PAO2 and PACO2
  • In mixed blood pO2 is low and pCO2 is high
35
Q

Outline VQ mismatch where perfusion is affected but ventilation is ok

A
  • A decrease in perfusion relative to ventilation is an example of increased dead space
  • E.g. pulmonary embolus blocking a capillary
  • Can be corrected by supplying 100% inspired oxygen - blood will redistribute between other capillaries that are exchanging gases without issue.

Respiratory (21 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions