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Resp > Lecture 3 -Properties Of Gases And Diffusion > Flashcards

Lecture 3 -Properties Of Gases And Diffusion Flashcards

1
Q

What is Dalton’s law?

A

States that each gas in a mix of gasses exerts its own pressure called a partial pressure

The total of all the partial pressures of gases in a mixture it the total pressure

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2
Q

What makes a gas move from one area to another?

A

A partial pressure gradient

A gas will move from an area where theres a higher partial pressure to a lower partial pressure

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3
Q

What affects the speed which gases diffuse from one area to another?

A

Steeper the gradient the faster the movement

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4
Q

What does pAO2 refer to?

A

Partial pressure of O2 in alveolar air

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5
Q

What does paO2 refer to?

A

Partial pressure of O2 in arterial blood

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6
Q

Why is the partial pressure of oxygen that gets inhaled different to the partial pressure of oxygen in the trachea?

A

The air gets humidified so some of the oxygen ends up as water vapour

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7
Q

What is the name given to the partial pressure exerted by water vapour at body temperature?

A

Saturated vapour pressure

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8
Q

When doing partial pressure calculations how do you need to consider saturated vapour pressure?

A

You need to subtract the saturated vapour pressure (6.28KPa) from the total/atmospheric pressure

You need to essentially work it from the humidified atmospheric pressure in the body

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9
Q

What is Henrys constant (KH)?

A

Describes how soluble a gas is in a liquid at a certain temperature

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10
Q

What is Henrys law?

A

The amount of gags dissolved in a liquid is proportional to the gases partial pressure above the liquid and its solubility in that liquid

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11
Q

What are the units for concentration of a gas in a liquid?

A

mmol/L

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12
Q

What is the normal partial pressure of oxygen in alveolar air?

A

13.3KPa

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13
Q

What happens to the partial pressure of oxygen in the pulmonary capilaries when the partial reassure of O2 in the alveolar air is 13.3KPa?

A

The partial pressures equilibrates causing the partial pressure of oxygen in the blood in the capillaries to also be 13.3KPa

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14
Q

How is partial pressure of a gas different from the amount of a gas dissolved?

A

Partial pressure is the force of the gas exerted

Amount of gas dissolved is the amount of molecules of a gas dissolved in a solvent

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15
Q

What is the equation for amount of a gas dissolved?

A

Amount dissolved = partial pressure x solubility coefficient of gas

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16
Q

What units measure partial pressures?

A

KPa

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17
Q

What 2 components need to be considered when determining he total gas content?

A

The amount of the gas dissolved in the plasma and the amount of gas bound to. Carrier like Haemoglobin

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18
Q

How does partial pressure of O2 and CO2 change as the air travels from the trachea into the alveoli?

A

pO2 gets lower
pCO2 gets higher

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19
Q

Why is the partial pressure of Oxygen of the alveolar air lower than inhaled air and pCO2 of alveolar air higher than inhaled air?

A

Inhaled air mixes with the old residual air (old air has lower pO2 higher pCO2)

O2 diffuses across alveolar wall

CO2 enters into alveoli from pulmonary capillaries

20
Q

What determines alveolar pO2?

A

Rate at which O2 is taken up by the blood from the alveoli (Q) and rate at which its replenished by alveolar ventilation (V)

21
Q

What is the V:Q ratio?

A

The ratio by which the alveoli is ventilated to the which the alveoli is perfused with blood

22
Q

What layers does oxygen have to diffuse across to reach a red blood cell?

A

Fluid film lining alveolus
Epithelial cell of alveolus
Interstitial space
Endothelial cell of capillary
Plasma
Red cell membrane

23
Q

What factors affect rate of diffusion across the alveolus into the blood?

A

Partial pressure gradient

SA available for diffusion/gas exchange

Thickness/distance molecules must diffuse

Diffusion coefficient for that gas

24
Q

How does Pulmonary fibrosis affect gas exchange?

A

Leads to lots of thick fibrotic tissue being deposited in the interstitium of the lungs

This increases they diffusion distance molecules must diffuse reducing gas exchange rate

25
Q

What are the 2 main properties of a gas affecting the rate of diffusion of the gas?

A

Solubility of the gas in the liquid

Molecular weight of the gas

26
Q

What diffuses faster, O2 or CO2 and why?

What has a greater affect on rate of diffusion, solubility or molecular weight?

A

CO2 since despite having a larger molecular weight than O2 it is much more soluble in plasma than oxygen

Solubility has a much greater affect on rate of diffusion than molecular weight

27
Q

Why is the partial pressure gradient of oxygen from the alveolar air compared to the capilaries very steep compared to the partial pressure gradient of CO2?

A

O2 diffuses much slower so needs more compensation since it’s solubility is much lower

28
Q

In diseased lungs, the exchange of which gas is affected more, oxygen or carbon dioxide and why?

A

Oxygen

Since CO2 diffuses much more easily since its way more soluble

29
Q

How does Emphysema impair difffusion/gas exchange?

A

Leads to destruction of alveoli so reduces surface area for gas exchange

30
Q

How does pulmonary oedema impair diffusion/gas exchange?

A

Fluid in the interstitial space increases the diffusion distance impairing gas exchange

31
Q

What is a a normal ventilation/perfusion ratio?

A

Normal V/Q = 0.8

32
Q

What is the V in V/Q ratio?

A

V = alveolar ventilation

33
Q

What is the Q in V/Q ratio?

A

Q = pulmonary blood flow (perfusion

34
Q

How does the Ventilation perfusion ratio differ in different parts of the lung?

A

Apex of lung the ventilation is good but the amount of blood its receiving (perfusion) is less due to gravity keeping the capillaries closed

At bottom of lung the Q is better but the Ventillation isn’t as good

35
Q

When an area of the lung is poorly ventilated how does the body react to try and maintain V/Q?

A

Vasoconstriction of blood vessels leading to the poorly ventilated area to keep blood away

(Hypoxic pulmonary vasoconstriction)

36
Q

During exercise what does the body due to get the ventilation/perfusion matching to reach 1?

A

Exercise increases cardiac output leading to vasodilation of the apical arteries in the lungs increasing its perfusion

37
Q

Will the value of V:Q (ventilation:perfusion) be lesser or greater than 1 if a poorly ventilated alveolus is perfused?

A

V decreases
Q stays the same
So V:Q would decrease so would be less than 1

38
Q

Will the value of V:Q (ventilation:perfusion) be lesser or greater than 1 if we ventilate a poorly perfused alveolus?

A

V stays the same
Q decreased

V:Q therefore is higher meaning V:Q > 1

V:Q>1

39
Q

What are some conditions that cause a ventilation perfusion mismatch where the ventilation is reduced?
(V:Q < 1)

A

Pneumonia

Asthma

COPD

40
Q

What is a condition that cause a ventilation perfusion mismatch where the perfusion is reduced?
(V:Q > 1)

A

Pulmonary embolism

(The alveoli still gets good air but less blood?)

41
Q

What is Lung Hypoxic vasoconstriction?

A

When blood vessels near poorly ventilated areas vasoconstrict to direct blood away

42
Q

What happens to capillary partial pressures of CO2 and O2 if theres inadequate ventilation?

A

pO2 falls
pCO2 rises

43
Q

Why does lung hypoxic vasoconstriction not fully compensate the gas exchange?

A

The haemoglobin in the well ventilated alveolar capillaries will already be saturated with O2

So the red cells will be unable to bind additional O2 to increase the pO2

44
Q

If pO2 is low in the blood, what can the body try and do to compensate?

How does this affect CO2 levels?

A

Hyperventilation

Can lead to normal or low CO2 levels

45
Q

What is a Shunt?

A

When an alveolus that isn’t ventilated gets perfused with blood leading to no gas exchange occurring

Essentially an area that does undergo gas exchange

Resp (23 decks)

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