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Blood Lungs and Heart > Week 1 Gas Laws > Flashcards

Week 1 Gas Laws Flashcards

1
Q

What is kinetic theory? What proportion of a gas is made up by gas molecules?

A

Kinetic theory postulates that gases are made up of submicroscopic particles that are in constant random motion proportional to their energy. Gas molecules form only a small proportion of the total gas volume, most is empty space.

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2
Q

What is generates pressure? What would increase pressure? What is the equation for pressure and the units?

A

Pressure is generated by the force of molecules hitting against the container walls. Faster or harder collisions (Eg increased temp or increased concentration of gas) will increase the pressure. Pressure= Force / unit area and unit is Pascals (Pa). P= F/A

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3
Q

What is Boyle’s Law?

A

Boyle’s law states that the pressure of a gas is inversely proportional to its volume at a constant temperature and constant amount of gas: P= 1/ V therefore PV = a constant therefore P1 xV1= P2 xV2

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4
Q

What is Charle’s law?

A

Charle’s Law states that the volume of a gas is directly proportional to its temperature on an absolute temperature scale and at a constant pressure/ amount of gas. V= T x C Volume= Temp x Constant therefore… V/T= C therefore… V1/T1 = V2/T2

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5
Q

What is the universal gas law/ Ideal gas law?

A

PV= nRT The pressure x volume = no. of moles of gas x Gas constant x Temp in kelvin

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6
Q

What is partial pressure?

A

The partial pressure of a gas is the pressure that would be exerted by one of the gases in a mixture if it occupied the same volume on its own.

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7
Q

What is Dalton’s law?

A

Dalton’s law states that the total pressure of a mixture of gases in a fixed volume is proportional to the sum of the individual partial pressures of each gas in the mixture.

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8
Q

What is gas in constant contact with in biological systems? What occurs at the point of contact? What pressure does evaporated water exert?

A

Gas molecules are in constant contact with water in biological systems. At the point of contact, water molecules evaporate and gas molecules dissolve but there is no reaction between the two. Evaporated water exerts a vapour pressure.

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9
Q

What is reached in closed systems (eg alveoli) when there is a gas/ water interface? What would happen if the volume of gas was unlimited?

A

An equilibrium is reached in closed system such as alveoli (where there is a constant volume of gas) between the amount of water evaporating and entering the gas phase and the amount of gas entering the liquid phase. If there was unlimited gas volume all water would evaporate as no equilibrium could be reached.

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10
Q

What is it called when water reaches an equilibrium between its liquid and gas phase?

A

This is called the saturated vapour pressure (SVP).

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11
Q

Define Saturated vapour pressure

A

The pressure of a vapour which is in equilibrium with its liquid phase.

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12
Q

When is the boiling point of a gas reached?

A

The boiling point of a gas is reached when its saturated vapour pressure is equal to atmospheric pressure (1 atmosphere).

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13
Q

What is saturated vapour pressure dependent on?

A

Saturated vapour pressure is dependent on the temperature only. If you increase the T you increase kinetic energy and the number of molecules able to leave the liquid phase and enter the gas phase.

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14
Q

What is Henry’s Law? What is the proportionality constant for this equation representing?

A

Henry’s Law states that at a constant temperature the amount of gas that will dissolve in a particular volume of solvent is directly proportional to the partial pressure of that gas overlying the gas/ liquid interface (or directly proportional to the partial pressure of that gas in equilibrium with that liquid). The proportionality constant for this equation represents the Solubility of that gas in that particular liquid.

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15
Q

Define solubility What is it dependent on?

A

Solubility is defined as the ability of a certain solute to dissolve in a certain volume of solvent at a constant temperature. It is defined as the amount of solute per volume of solvent and is measured at saturation point where the addition of more solute results in precipitation. The solubility of a substance in a particular solvent is dependent on the individual properties of the solute in that solvent.

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16
Q

Define the solubility of gas What two factors affect the solubility of a gas in a liquid?

A

The solubility of a gas in a given volume of liquid represents its ability to dissolve in that liquid and is constant for specific gas and liquid, depends on the physical properties. Temperature affects solubility as the higher the temperature the more kinetic energy gas molecules have, pushing the equilibrium towards evaporation. Pressure affects solubility of gas as it relates to Henry’s law- the higher the partial pressure of a gas over a liquid interface the more gas will dissolve in that given volume of liquid.

17
Q

What is Gas Tension?

A

Gas molecules entering water exert a pressure- termed the gas tension. The gas tension of a particular gas entering a liquid is proportional to the partial pressure of that gas in equilibrium with that liquid. (Henry’s Law). Gas tension represents the ease with which gas molecules will leave the liquid phase. It is not a measure of the physical amount of gas in the liquid but the partial pressure of that gas within the liquid. Represented in kilopascals e.g. PaCO2- 5.3 kPa in alveoli.

18
Q

What is the content of gas in a liquid? What does the gas content depend on?

A

The content of a gas is the actual physical amount of gas contained within a certain volume of liquid. It is represented by the volume of gas contained within a certain volume of that liquid e.g. O2 mls/ L of blood. It depends on both the solubility of the gas and the partial pressure of the gas in equilibrium with the liquid.

19
Q

What does diffusion require? Define gaseous diffusion

A

Diffusion requires a concentration gradient Gaseous diffusion is by the random movement of gas particles and results in net transfer of gas particles from an area of high concentration to an area of low concentration.

20
Q

Describe the general structure of an alveolus

A

Each alveolus is a thin walled hexagonal structure surrounded by a capillary plexus and supplied by a tiny bronchiole called an alveolar duct.

21
Q

How is blood able to carry O2/CO2 and transfer it from tissues/ lungs?

A

This is due to the properties of haemoglobin in RBC’s.

22
Q

How does the O2 content of blood reach equilibrium? What is total O2 content of the blood made up of?

A

Haemoglobin fully saturates all its binding sites with O2 and reaches equilibrium before the tension of blood can reach equilibrium. Therefore the total O2 content is made up of both reacted O2 with haemoG and dissolved O2 in the plasma.

23
Q

What 3 properties does the final O2 content of blood at equilibrium depend on?

A

1) the gas tension 2) the solubility of O2 in blood 3) the avidity of haemoglobin for O2.

24
Q

Where does gas exchange take place and by what transport mechanism?

What does this transport mechanism depend on?

A

Gas exchange takes place at the alveolar membrane and by diffusion.

Diffusion is dependent on a concentration gradient.

25
Q

What are the gas tensions of alveoli vs venous blood and what does this mean for gas exchange?

A

Alveoli:

  • pAO2= 13.3 kPa
  • pACO2= 5.3 kPa
  • Saturated with water vapour

Venous blood:

  • PaO2= 6kPa
  • PaCO2= 6.5 kPa
  • Varies with metabolism

As pCO2 in venous blood > than alveoli CO2 will diffuse from venous blood into alveolus.

As PO2 in alveolus > than venous blood, O2 will diffuse out the alveolus into blood.

26
Q

What factors affect the rate of diffusion of gas across the alveolar/ capillary membranes?

A
  • Rate of diffusion is directly proportional to:
    • the surface area provided by the alveoli
    • the partial pressure gradient (difference between partial pressures in alveoli vs capillary)
    • the solubility of the gas in blood/ Tissues
  • Rate of diffusion is indirectly proportional to:
    • The resistance to diffusion provided by:
      • Thickness of the alveolar/ capillary barrier - often affected in disease states
      • molecular weight of the gas which affects the solubility (solubility of gas = solubility constant/ square root of molecular weight).
27
Q

How does solubility of gas affect rate of diffusion?

How does the solubility of CO2/O2 differ?

What is the overall effect on the rate of diffusion of CO2 vs O2?

How is this compensated for?

A
  • Solubility of gas is directly proportional to the rate of diffusion. Increased solubility = increased rate of diffusion
  • CO2 is 21x more soluble than O2 in blood and therefore overall has a much higher rate of diffusion compared to O2.
  • This is compensated normally by the large difference in O2 partial pressure between the alveolus and capillary. CO2 in comparision has a much lower partial pressure gradient due to its fast diffusion rate due to its higher solubility.
28
Q

The overall rate of O2 diffusion is slower than that of CO2.

Why does this not matter physiologically?

what does this mean O2 content of blood is limited by normally?

how does this alter in disease states?

Why is the slower rate of O2 diffusion compared to CO2 important in disease?

A
  • The slower rate of diffusion of O2 does not matter physiologically as this is normally compensated for by the large partial pressure gradient between alveolar oxygen and capillary oxygen.
  • O2 has normally saturated haemoglobin around 25% of the distance of the alveolar capillary.
  • This means O2 content of blood is normally perfusion limited under normal circumstances
  • In disease states (which often affect alveolar/ capillary barrier thickness/ SA) oxygen content often becomes diffusion limited.
  • Oxygen transport is often affected first in disease states due to its slower rate of diffusion compared to CO2.
29
Q

Describe the layers of the diffusion barrier

A
  1. Gas needs to diffuse through the alveolus
  2. Through the alveolar epithelial cell
  3. Into the tissue fluid and connective tissue
  4. Across the endothelial cell of the capillary network
  5. Into blood plasma
  6. Across the cell membrane of the RBC
  7. Through RBC cytoplasm to react with haemoglobin.
30
Q

How does the molecular weight of gases affect their rate of diffusion?

A
  • Molecular weight is inversely proportional to the rate of diffusion across the diffusion barrier.
  • Molecules with lower molecular weight diffuse faster and on this basis CO2 would diffuse slower than O2 (however due to higher solubility CO2 diffuses 21x faster overall).
31
Q

What is Fick’s law?

A

Ficks law states that the rate of diffusion of a gas is directly proportional to the surface area over the thickness of the diffusion barrier multiplied by the diffusion constant multplied by the partial pressure gradient.

Where the diffusion constant = the solubility constant of the gas / square root of molecular weight

Blood Lungs and Heart (24 decks)

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