Gas Laws

Question 1

Partial Pressure of a Gas

Answer 1

Pressure an individual gas exerts in a mixture which is a fraction of the total pressure of that mixture (same as when it acts independently

Question 2

Vapour Pressure

Answer 2

When h20 molecules enter a gas (if in a closed system such as alveolus then equilibrium SVP reached)

Question 3

Gas Tension in Solution

Answer 3

Gas exerts tension (like pressure) when in a solution and at equilibrium the tension of a particular gas in water is proportional to partial pressure of gas in adjacent gas mixture

Question 4

Content of a Gas

Answer 4

Physical amount of gas in liquid - dependent on temperature and pressure and at equilibrium gas content is proportional to its solubility in that liquid and the pressure in adjacent gas mixture

Question 5

Boyle’s Law

Answer 5

Pressure is inversely proportionate to volume

Question 6

Charles’ Law

Answer 6

Pressure is directly proportionate to temperature

Question 7

Dalton’s Law

Answer 7

In a mixture of non-reactive gases the total pressure exerted is the sum of the partial pressures of individual gases

Question 8

Universal Gas Law

Answer 8

Pressure and volume are both proportional to temperature

Question 9

Henry’s Law

Answer 9

Physical amount of gas dissolving in a solvent is directly proportional to the pressure of the gas at the solvents surface - related to ability of gas to dissolve in a solvent/liquid

Question 10

In healthy tissue o2 transfer to tissues is perfusion limited. What happens in disease states?

Answer 10

Transfer becomes diffusion limited. Only way you can increase o2 transfer is by increasing blood flow and therefore perfusion, but if diffusion barrier is damaged then this won’t make a difference to Hb o2 saturation in capillaries.

Question 11

What factors determine diffusion of gas across alveolar membrane?

Answer 11

Partial pressure, temperature, molecular weight, solubility

Question 12

Pressure equation and unit

Answer 12

Force per unit area = P=F/A in Pascal (Pa)

Question 13

What happens when gas and fluid meet?

Answer 13

Gas dissolves = fluid phase
Water evaporates = gas phase
Occurs until equilibrium reached where partial pressure and gas tension are equal

Question 14

Relationship between gas and water in body?

Answer 14

Gas always in contact with blood

Question 15

Solubility and what can change it?

Answer 15

Amount of solvent that can dissolve in unit volume of solute - dependent on temperature, pH & pressure

Question 16

Pressure =

Answer 16

The force exerted per unit area

Question 17

Resistance =

Answer 17

A force that tends to oppose the flow of a subsance

Question 18

Pressure gradient =

Answer 18

The difference in forces exerted (per unit area) at either side an object eg either side of a membrane

Question 19

Flow (Q) =

Answer 19

The volume of fluid passing a given level of the circulation/airways per unit time

Question 20

Velocity =

Answer 20

The rate of movement of fluid particles along a vessel/airway

Question 21

Laminar flow =

Turbulent flow =

Answer 21

Laminar = fluid moves in parallel layers without disruption (width of a tube greatly affects its resistance)

Turbulent = changes in velocity and resistance

Question 22

Viscosity =

Answer 22

?

Question 23

Capacitance =

Answer 23

?

Question 24

What’s the rate of flow in the systemic circulation and why does pressure change throughout?

Answer 24

Flow should be constant, at 5l.min-1
Pressure is greatest in large arteries and declines through to veins
Changes in pressure reflects differences in resistance to flow
Heart generates pressure high enough to pump through whole body

Question 25

What does Poiseulle’s law say resistance through a tube is affected by? What’s the clinical application of this

Answer 25

Affected by length and radius of tube and viscosity of fluid

IV catheterisation, endotracheal tubes, disease states that cause a change in vessel/airway radius

Question 26

What’s the relevance of laminar flow through blood vessels?

Answer 26

Cellular component of blood affects viscosity and flow

RBCs tend to move in most rapidly moving stream in centre of tube

Question 27

What factors increase likelihood of turbulent flow?

How can you tell turbulent flow in arteries and airways

Answer 27

Low viscosity (of blood), high velocity, high radius
Damages endothelium lining
Bruits in arteries
Wheeze in airways
= sounds noisy/murmurs

Question 28

What effect does transmural pressure have on the distensibility of blood vessels?

Answer 28

Distensible = able to stretch
Transmural pressure = intravascular pressure - extravascular pressure

Increased intravascular pressure increases transmural pressure so vessels stretch in order to increase blood flow and volume and reduce resistance

Question 29

What would happen if intravascular pressure is near 0?

Answer 29

Transmural pressure will also drop and will cause vessel to collapse and shut at low pressure = flow also majorly reduced

Question 30

What are some roles of gas transport within the cardiorespiratory system?

Answer 30

Transport of hormones/cytokines
Mobility of cell mediated and humoral immunity
Transport of O2 and nutrients to tissues
Remove CO2 and other waste products from tissues

Question 31

Outline the kinetic theory of gases

Answer 31

Molecules are in constant random motion
Pressure is generated by the force of impacts of the molecules on the container walls

More frequent/harder collisions = higher pressure

Question 32

In relation to Daltons law, what is atmospheric pressure?

Answer 32

Daltons law = total pressure is same as sum of all partial pressures

Atmospheric pressure = sum of partial pressures of O2, N2, water vapour etc

Question 33

What’s the pressure called when fluid enters gas? What will happen if gas volume is unlimited?

Answer 33

Fluid evaporates in gas = exerts vapour pressure = Saturated Vapour Pressure (SVP)

Dryness if unlimited gas volume as all will evaporate and equilibrium won’t be reached

Question 34

What happens to saturated vapour pressure with increasing temperature?

What is it known as when vapour pressure = atmospheric pressure?

Answer 34

SVP increases with increasing temp as more kinetic energy and more molecules escape surface

Boiling point when SVP=Atm.Press

Question 35

How is gas exchange at the lungs facilitated?

Answer 35

Through diffusion across gradients

Each alveolus surrounded by capillary plexus

Question 36

What’s the pO2 in atmospheric air and alveolar air?

Answer 36

Atmospheric - 21.1 kPa

Alveolar - 13.3 kPa

Question 37

What’s the pCO2 in atmospheric and alveolar air?

Answer 37

Atmospheric - minimal

Alveolar - 5.3 kPa

Question 38

What’re the partial pressures of O2 and CO2 in mixed venous blood?

Answer 38

O2 - 6 kPa

Co2 - 6.5 kPa

Question 39

What is diffusion proportional to, and inversely proportional to?

Answer 39

Proportional to: surface area of alveoli and partial pressure gradient of individual gases

Inversely proportional to: diffusion rate and barrier

Question 40

What makes up the diffusion barrier?

Answer 40

Through gas to alveolar wall
Epithelial cell of alveolus
Tissue fluid and connective tissue
Endothelial cell of capillary
Plasma
RBC membrane and cytoplasm

Question 41

What’s the relevance of molecular weight of gases to their diffusion rate?

Answer 41

Gases diffuse at a rate inversely proportionate to the square root of their molecular weight = big molecules diffuse slower

Question 42

What diffuses fast, CO2 or O2?

Answer 42

CO2 diffuses slightly slower because of larger molecular weight
BUT gases diffuse through liquids proportionate to solubility and CO2 has a much higher solubility

= CO2 overall diffuses 21x faster than O2

Question 43

How will O2 transfer be affected across the diffusion barrier in disease states?

Answer 43

Normal tissue O2 transfer is perfusion limited (25% along the capillary the Hb will be fully saturated)
In disease states transfer may become diffusion limited, perhaps not being equilibrated by the end of the capillary