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My respiratory physiology > Principles of Gas Exchange; Diffusion of Oxygen and Carbon Dioxide through the Respiratory Membrane > Flashcards

Principles of Gas Exchange; Diffusion of Oxygen and Carbon Dioxide through the Respiratory Membrane Flashcards

1
Q

What does 1 atmosphere equal to in regards to the total pressure of air at sea level?

A

760 mm Hg

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2
Q

The pressure of a gas acting on the surface of the respiratory passages and alveoli is proportional to what?

A

Concentration of gas molecules.

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3
Q

How do gases dissolved in tissue fluid or water exert pressure on surfaces?

A

As they still have kinetic energy and are moving randomly.

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4
Q

what is meant by the solubility coefficient of a gas?

A

The ability to readily dissolve in a liquid without raising excess partial pressure in the solution.

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5
Q

What is Henry’s law

A

Partial pressure= Concentration of dissolved gas

/solubility coefficient

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6
Q

What factor influences net movement of diffusion for O2 and CO2 during gaseous exchange.

A

The difference in partial pressures in the alveoli and the pulmonary capillaries. (i.e high Po2 in alveoli to low po2 in capillaries).

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7
Q

What is vapor pressure?

ii). What is its value at normal body temp?

A

Refers to the partial pressure exerted by water molecules escaping the surfaces of the respiratory passage.

ii 47 mm Hg

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8
Q

What is the term describing the difference in number of molecules moving from high to low and in opposite direction?

A

pressure difference for causing direction

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9
Q

What are the 6 main factors which influence the rate of gas diffusion in a fluid?

A
  1. Pressure differences.
  2. solubility of gas in fluid. More molecules available to diffuse.
  3. cross sectional area of fluid. More molecule allowed to diffuse.
  4. distance for gas to move. Shorter distance=shorter time.
  5. molecular weight of gas. The greater the velocity of kinetic movement of the molecules, which is inversely proportional to the square root of the molecular weight, the greater the rate of diffusion of the gas
  6. temperature of fluid. More Kinetic energy
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10
Q

Why is the diffusion of gases used for respiratory importance through the membranes and tissue is equal to the rate they diffuse in water?

A

As they diffuse very quickly through the membrane yet the limiting factor is the rate they diffuse in water. This is because they are predominantly lipids.

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11
Q

Explain the differences between alveolar air and atmospheric air.

A
  1. Alveolar air is only partially replaced by atmospheric air each breath.
  2. O2 is constantly being absorbed into the pulmonary capillaries
  3. co2 is constantly diffusing into alveoli.
  4. Atmospheric air is completely humidified by the time it reaches alveoli.
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12
Q

By how much does the water vapour lower the partial pressure of Oxygen by at sea level?

ii Nitrogen?

A
  1. 159mm Hg —- 149 mm Hg

2. 593 mm Hg —– 563 mm Hg

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13
Q

Average male’s residual volume?

A

2300 ml

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14
Q

What are the benefits of having a slow change in alveolar air?

A

Doesn’t disrupt the gas concentrations in blood greatly. This allows for respiratory control mechanisms to be more stable. Doesn’t alter tissue pH greatly either.

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15
Q

What are the two factors which control the O2 concentration in the alveoli and its partial pressure?

A
  1. Rate of absorption of oxygen into blood.

2. Rate of new o2 entering the lungs.

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16
Q

What is the normal value for alveolar Po2?

What is Po2 maximum value in humidified air at sea level?

A

104 mm Hg

ii 149 mm Hg

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17
Q

Normal value of alveolar Pco2?

A

40 mm Hg

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18
Q

Describe the relationship of alveolar pco2 in regards to:

i.Rate of co2 excretion

ii Rate of pulmonary ventilation

A

i proportional

ii inversely proportional

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19
Q

Expired air is determined by?

A

i) .The amount of it which is from dead space air.

ii) . The amount of it which is from alveolar air.

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20
Q

How can you collect the amount of alveolar air which is present in expired air?

A

Collect the final portion of expired air from forced expiration. The first section consists of dead space air only. Second section mixture of both.

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21
Q

What does the respiratory unit (lobule) consist of?

A

Respiratory bronchiole, Alveolar ducts, astia and alveoli

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22
Q

How many alveoli are there in both lungs?

A

300 million

23
Q

What is the average diameter of an alveolus?

A

0.2 millimeter

24
Q

Gaseous exchange occurs at all membranes at terminal portions of the lungs and not just in the alveoli true or false?

A

True

25
Q

What is the name given to these membranes where gaseous exchange occurs?

A

Respiratory/pulmonary membranes.

26
Q

Name the layers of which the respiratory membrane consists of.

A
  1. A layer of fluid containing surfactant that lines the alveolus and reduces the surface tension of the alveolar fluid.
  2. The alveolar epithelium, which is composed of thin epithelial cells.
  3. An epithelial basement membrane.
  4. A thin interstitial space between the alveolar epithelium and the capillary membrane.
  5. A capillary basement membrane that in many places fuses with the alveolar epithelial basement membrane.
  6. The capillary endothelial membrane.
27
Q

What is the average thickness of a respiratory membrane?

A

0.6 micrometers

28
Q

What is the total quantity of blood in pulmonary capillaries at any given time

A

60-140 millilitres

29
Q

What is the average diameter of a pulmonary capillary?

ii what are the benefits?

A

5 micrometers

ii). Makes RBCs squeeze in the capillaries meaning O2 and CO2 don’t have to dissolve in plasma in order to pass through the capillary wall. This increases the rate of diffusion.

30
Q

What are the four main factors which affect the rate of gases diffusing via the respiratory membranes?

A
  1. The thickness of the membrane.
  2. surface area of the membrane.
  3. diffusion coefficient of gas.
  4. The difference in partial pressures either side of the membrane.
31
Q

What can affect the thickness of the membrane?

A

Pulmonary oedema, will increase tissue fluid in the interstitial space meaning gases will have to diffuse it thus decreasing rate.

Pulmonary fibrosis also thickens some parts of the respiratory membrane.

32
Q

What can affect the surface area of the membrane?

A
  1. Removal of a lung decrease S.A by half.

2. emphysema causes alveoli to coalesce causing foldings to dissolute. Therefore S.A decreases.

33
Q

What are the two main things the diffusion coefficient relies on?

A

gas solubility

inversely depends on the square root of the molecular weight of the gas.

34
Q

Define what is the diffusing capacity of a membrane.

A

The volume of a gas that will diffuse through the membrane each minute for a partial pressure difference of 1 mm Hg.

35
Q

What is the average diffusing capacity of O2 in a young man at resting conditions

A

21ml/min/mm Hg

36
Q

What is the mean pressure difference of O2 across the respiratory membrane at resting conditions?

A

11 mm Hg

37
Q

What is the average diffusing capacity of O2 in a young man at strenuous exercises?

A

It reaches a maximum value of 65 ml/min/mm Hg.

38
Q

Why does the average diffusing capacity of O2 increase?

A
  1. The surface area of the blood increases via using dormant pulmonary capillaries or increasing dilation of already open ones.
  2. Better ventilation-perfusion ratio.
39
Q

Why is the diffusing capacity of co2 not measured?

A

As it diffuses very quickly and so Pco2 in blood is almost equal to alveolar pco2 and so the difference is too small.

40
Q

The O2 diffusing capacity can be measured by?

A

(1) alveolar PO2,
(2) PO2 in the pulmonary capillary blood
(3) the rate of O2 uptake by the blood.

41
Q

Why is Carbon monoxide used to measure OXYGEN’S diffusing capacity

A
  1. A small amount is breathed in.

This is because it has a very affinity for haemoglobin so its partial pressure in blood practically 0. Therefore, the pressure difference of CO across the respiratory membrane is equal to its partial pressure in the alveolar air sample.

oxygen has a diffusing coefficient which is 1.23 times greater than CO so just multiple the answer by this to get your value.

42
Q

Define what the ventilation perfusion ratio is.

A

It describes the relationship of the respiratory exchange between alveolar ventilation and alveolar blood flow.

43
Q

What is the ratio when both ventilation and perfusion are normal?

A

The ratio is normal.

44
Q

What is the value of the ratio when ventilation is normal but perfusion is zero?

A

The ratio is infinity.

45
Q

What is the value of the ratio when ventilation is zero but perfusion is normal?

A

The ratio is zero.

46
Q

What are the partial pressures of O2 and CO2 when the Ventilation perfusion ratio is zero?

A

Po2= 40 mm Hg

Pco2= 45 mm Hg

The same values as they are in the capillaries as there is no ventilation

47
Q

What are the partial pressures of O2 and CO2 when the Ventilation perfusion ratio is infinity?

A 
Po2= 149 mm Hg
Pco2= 0 mm Hg

The alveolar gases equilibriate with humidified air and not the gases in the capillaries causing the partial pressures to reach these values.

48
Q

What are the partial pressures of O2 and CO2 when the Ventilation perfusion ratio is normal?

A

Po2 = 104 mm Hg

Pco2= 40 mm Hg

49
Q

What does shunted blood mean?

A

Blood which passes through the pulmonary capillaries but is not oxygenated. Due to the fact that the ventilation perfusion ratio is below normal.

Also sometimes refered to blood which may flow through bronchial vessels rather than alveoli capillaries. This accounts for 2% of cardiac output.

50
Q

What is the physiological shunt?

A

Quantitative amount of shunted blood per minute.

51
Q

What does the term physiological dead space mean?

A

Refers to when the ventilation perfusion ratio is above normal. More oxygen is being ventilated then actually being transported in blood.

Refers to alveolar dead space and anatomical dead space.

52
Q

What abnormalities occur regarding the ventilation perfusion ratio?

A
  1. In a normal person in the upright position, both pulmonary capillary blood flow and alveolar ventilation are considerably less in the upper part of the lung than in the lower part; however, the decrease of blood flow is considerably greater than the decrease in ventilation. Therefore, at the top of the lung, is as much as 2.5 times as great as the ideal value, which causes a moderate degree of physiological dead space in this area of the lung.
  2. At the other extreme, in the bottom of the lung, there is slightly too little ventilation in relation to blood flow, with as low as 0.6 times the ideal value. In this area, a small fraction of the blood fails to become normally oxygenated, and this represents a physiological shunt.
53
Q

How does COPD effect the ventilation perfusion ratio?

A
  1. Causes bronchial obstruction effecting ventilation to alveoli.
  2. Emphysema causes damage to alveoli walls. This means while ventilation might be normal perfusion is not.

My respiratory physiology (3 decks)

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