Gas Laws Flashcards
Partial Pressure of a Gas
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
Vapour Pressure
When h20 molecules enter a gas (if in a closed system such as alveolus then equilibrium SVP reached)
Gas Tension in Solution
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
Content of a Gas
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
Boyle’s Law
Pressure is inversely proportionate to volume
Charles’ Law
Pressure is directly proportionate to temperature
Dalton’s Law
In a mixture of non-reactive gases the total pressure exerted is the sum of the partial pressures of individual gases
Universal Gas Law
Pressure and volume are both proportional to temperature
Henry’s Law
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
In healthy tissue o2 transfer to tissues is perfusion limited. What happens in disease states?
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.
What factors determine diffusion of gas across alveolar membrane?
Partial pressure, temperature, molecular weight, solubility
Pressure equation and unit
Force per unit area = P=F/A in Pascal (Pa)
What happens when gas and fluid meet?
Gas dissolves = fluid phase
Water evaporates = gas phase
Occurs until equilibrium reached where partial pressure and gas tension are equal
Relationship between gas and water in body?
Gas always in contact with blood
Solubility and what can change it?
Amount of solvent that can dissolve in unit volume of solute - dependent on temperature, pH & pressure
Pressure =
The force exerted per unit area
Resistance =
A force that tends to oppose the flow of a subsance
Pressure gradient =
The difference in forces exerted (per unit area) at either side an object eg either side of a membrane
Flow (Q) =
The volume of fluid passing a given level of the circulation/airways per unit time
Velocity =
The rate of movement of fluid particles along a vessel/airway
Laminar flow =
Turbulent flow =
Laminar = fluid moves in parallel layers without disruption (width of a tube greatly affects its resistance)
Turbulent = changes in velocity and resistance
Viscosity =
?
Capacitance =
?
What’s the rate of flow in the systemic circulation and why does pressure change throughout?
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
What does Poiseulle’s law say resistance through a tube is affected by? What’s the clinical application of this
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
What’s the relevance of laminar flow through blood vessels?
Cellular component of blood affects viscosity and flow
RBCs tend to move in most rapidly moving stream in centre of tube
What factors increase likelihood of turbulent flow?
How can you tell turbulent flow in arteries and airways
Low viscosity (of blood), high velocity, high radius Damages endothelium lining Bruits in arteries Wheeze in airways = sounds noisy/murmurs
What effect does transmural pressure have on the distensibility of blood vessels?
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
What would happen if intravascular pressure is near 0?
Transmural pressure will also drop and will cause vessel to collapse and shut at low pressure = flow also majorly reduced
What are some roles of gas transport within the cardiorespiratory system?
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
Outline the kinetic theory of gases
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
In relation to Daltons law, what is atmospheric pressure?
Daltons law = total pressure is same as sum of all partial pressures
Atmospheric pressure = sum of partial pressures of O2, N2, water vapour etc
What’s the pressure called when fluid enters gas? What will happen if gas volume is unlimited?
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
What happens to saturated vapour pressure with increasing temperature?
What is it known as when vapour pressure = atmospheric pressure?
SVP increases with increasing temp as more kinetic energy and more molecules escape surface
Boiling point when SVP=Atm.Press
How is gas exchange at the lungs facilitated?
Through diffusion across gradients
Each alveolus surrounded by capillary plexus
What’s the pO2 in atmospheric air and alveolar air?
Atmospheric - 21.1 kPa
Alveolar - 13.3 kPa
What’s the pCO2 in atmospheric and alveolar air?
Atmospheric - minimal
Alveolar - 5.3 kPa
What’re the partial pressures of O2 and CO2 in mixed venous blood?
O2 - 6 kPa
Co2 - 6.5 kPa
What is diffusion proportional to, and inversely proportional to?
Proportional to: surface area of alveoli and partial pressure gradient of individual gases
Inversely proportional to: diffusion rate and barrier
What makes up the diffusion barrier?
Through gas to alveolar wall Epithelial cell of alveolus Tissue fluid and connective tissue Endothelial cell of capillary Plasma RBC membrane and cytoplasm
What’s the relevance of molecular weight of gases to their diffusion rate?
Gases diffuse at a rate inversely proportionate to the square root of their molecular weight = big molecules diffuse slower
What diffuses fast, CO2 or O2?
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
How will O2 transfer be affected across the diffusion barrier in disease states?
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
