Flashcards in Lecture 29: Gases And Respiration Deck (15):
External respiration involves 4 processes, what are they?
1. Pulmonary ventilation (bulk flow)
2. Gas exchange at lungs (diffusion)
3. O2 and CO2 transport
4. Gas exchange at tissues
Adaptations for gas exchange:
-gas exchange in all organisms relies on diffusion
-diffusion: spread of particles from regions of high concentration to regions of low concentration
-in external respiration, O2 and C2 move by simple diffusion
Factors affecting gas diffusion:
Rate of diffusion depends on:
Diffusion is greatest when pressure gradient, surface area and diffusion coefficient are large BUT diffusion distance is small
1. Pressure gradient:
Pressure represents the number if collisions occurring between the gas molecules themselves and their container walls.
-the greater the number of gas molecules the more collisions that occur, therefore the greater the pressure exerted
Net diffusion of gas will always be from regions of high to regions of low pressure
2. Surface area:
Increased surface area means more oxygen can enter the body over a given time.
Eg lungs have a branching network of airways that gives them 70m 2 surface area
3. Diffusion distance
The thinner the gas exchange membrane, the faster the rate of diffusion.
-gas exchange membranes must be very thin
4. Diffusion coefficient
Diffusion coefficient is dependant on 2 factors:
1. Gas solubility
2. Molecular weight
Those gases which are highly soluble will have a larger diffusion coefficient and diffuse more quickly
The diffusion capacity of CO2 is 20x greater than O2
Factors effecting gas diffusion
1. Pulmonary oedema
1. Pulmonary oedema:
-fluid collected in the interstitial and eventually the alveoli
-fluid on lungs increases diffusion distance
-obstructs normal exchange of gases across respiratory membrane
-progressive destruction of walls of alveoli
-leads to decreased surface area for gas exchange
Name the 6 gas laws
1. Atmospheric pressure and altitude
2. Ideal gas law
3. Dalton's law of partial pressures
4. Henry's law
5. Boyle's law
6. Bulk Air Flow
1. Describe Law 1: atmospheric pressure
Ie why does air pressure decrease with increasing altitude?
Pressure is measured in mm Hg
-the pressure exerted by atmospheric air can push a column of mercury (Hg) to a height of 760 mm.
Patm= 760 mm Hg
Air above us compresses the air around us
-as we ascend, less compression occurs and air I'd less dense.
-at higher altitudes, there are less gas (oxygen) molecules in a given volume ie gas partial pressure decreases
Describe law 2: the ideal gas law
We just need to understand that gas pressure is proportional to the number of gas molecules
Describe law 3: Dalton's law of partial pressures
The total pressure of a mixture of gases is a sum of the partial pressures exerted by each gas
Ptotal= P1 + P2 + P3 etc
Note: increased water vapour pressure (ie humidity) decreases the contribution of the other gases
Describe law 4: Henry's law
The amount of gas that will dissolve in a liquid is determined by its partial pressure and solubility.
-in order to diffuse into a cell, gas molecules in air must first dissolve in liquid.
-the higher the partial pressure and solubility coefficient (dissolving capability), the more soluble gas is.
If a substance is more soluble it means it is attracted to water. More can build up before the pressure is raised. Therefore, if a gas is very soluble, large numbers of molecules will go into solution at low pressures. If gas is less soluble, high partial pressures may cause.
When gas is in contact with a liquid, nett movement will occur between states IF a pressure gradient exists.
This will occur until equilibrium is reached ie PO2 in air=PO2 in liquid
WARNING: equilibrium doesn't mean that numbers of gas molecules in a liquid equals number of gas molecule in air. The final concentration of gas in a liquid will depend on its solubility at equilibrium.
Describe law 5: Boyle's Law
Pressure is inversely related to volume given temp remains constant
-when volume decreases, gas pressure increases