Ch. 40: Principles of Gas Exchange; Diffusion fo Oxygen and Carbon Dioxide Through the Respiratory Membrane Flashcards
After alveoli are ventilated with fresh air, what is the next step in the respiratory process?
Diffusion of O2 from alveoli into pulmonary blood and diffusion of CO2 in the opposite direction
What is diffusion?
The random motion of molecules
What must be provided to molecules for diffusion to occur?
An energy source is needed for diffusion to occur, which is provided by the kinetic motion of the molecules themselves
Net diffusion of a gas occurs in what direction?
Net diffusion of gas occurs from high-concentration area toward low-concentration area (concentration gradient)
How is the diffusion rate related to the concentration gradient?
The diffusion rate is PROPORTIONAL to the concentration gradient
How do molecules cause gas pressures?
Gas pressures are caused by the impacts of moving molecules against the surface
How is the pressure of a gas acting on the surfaces of airways and alveoli related to the concentration of gas molecules of each gas?
The pressure a gas acting on surfaces of airways and alveoli is directly proportional to concentration of gas molecules
What is the mixture of gases (AIR) inspired into alveoli? (5)
- Nitrogen
- Oxygen
- Carbon Dioxide
- Helium
- Water
The pressure caused by each gas alone is called?
Partial Pressure (P_x)
How is the diffusion rate of each gas related to its partial pressure gradient
Diffusion rate of each gas is DIRECTLY PROPORTIONAL to its partial pressure gradient
By Daltons Law, what is the total gas pressure of a mixture of gasses equal to?
The sum of the all the partial pressures of all the gases of the mixture.
DALTON’s LAW:
Ptot = PO2 + PN2 + PCO2 + Pother
What is the partial pressure of O2 and CO2 in the air?
PN2 = 78.6 % x 760 = 597 mmHg
PO2 = 20.9 % x 760 = 159 mmHg
PCO2 = 0.04 % x 760 = 0.3 mmHg
Pother = 0.46 % x 760 = 3.7 mmHg
The total pressure of the air is:
Ptot = PO2 + PN2 + PCO2 + Pother = 760 mmHg
True or False:
Gas dissolved in water and tissues enters its own partial pressure on surface of membrane in the same way gas does in the gas phase.
ANSWER: TRUE
How is the partial pressure of a dissolved gas determined or considered?
Partial pressure of a dissolved gas is determined not lonely by its CONCENTRATION but also by its SOLUBILITY COEFFICIENT
HENRY’S LAW :
Partial pressure= (concentration of dissolved gas)/(solubility coefficient)
What is the solubility coefficient?
A measure of electro-chemical attraction that a dissolved gas has to water molecules
What does high attraction refer to when talking about gas?
High attraction = high solubility of gas. More gas molecules can be dissolved before partial pressure of that gas within the solution increases
Which gas has the highest solubility coefficient?
CO2
Which gas has the smallest solubility coefficient?
Helium, then Nitrogen.
What are the gases in order of solubility coefficients, high to low? (5)
- Carbon dioxide (0.57)
- Oxygen (0.024)
- Carbon monoxide (0.018)
- Nitrogen (0.012)
- Helium (0.008)
What affects the net rate of diffusion in fluids? (5)
- Pressure difference
- Solubility of gas in fluid
- Distance through which gas must diffuse (AREA)
- Molecular weight of gas
And also…. - Temperature of fluid (in body, remains constant)
Why is diffusion of gas through membrane, not an issue when discussing the main gases that are involved in respiration?
The main gases involved in respiration are highly soluble in lipids; SOLUBLE in cell membranes. And diffusion of gases through tissues will therefore be almost equal to diffusion through water
How is alveolar air exchanged / replaced with each breath? How many breaths (approximately) to make a full exchange of air molecules?
Alveolar air is only partially replaced by atmospheric air with each breath. It will take over 16 breaths to completely exchange the air.
Which gas is constantly being absorbed into the pulmonary blood from alveolar air?
OXYGEN
What gas I constantly diffusing FROM pulmonary blood to alveoli?
CARBON DIOXIDE
What happens to dry atmospheric air, which is inhaled through the airways, before it reaches the alveoli?
Dry atmospheric air that enters airways is humidified before it reaches the alveoli.
How is inspired air humidified in the passageways?
Water vapor humidifies inspire air in passageways, and water vapor pressure varies with temperature of airways in the body.
Water vapor pressure in the airways of the body varies with temperature. What are the PH2O’s at 37°C, 0°C and 100°C?
• At normal body temperature (37o C): PH2O = 47 mmHg
At 0o C: PH2O = 5 mmHg
At 100o C: PH2O = 760 mmHg
What is the partial pressure of O2 and CO2 in the conducting airways?
In the tracheal airways:
N2: 74.09 % x 760 = 563.4 mmHg
O2: 19.67 % x 760 = 149.3 mmHg
CO2: 0.04 % x 760 = 0.3 mmHg
H2O: 6.20 % x 760 = 47.0 mmHg
What is the partial pressure of O2 and CO2 in the alveoli?
N2: 74.90 % x 760 = 569 mmHg
O2: 13.60 % x 760 = 104 mmHg
CO2: 5.3 % x 760 = 40 mmHg
H2O: 6.2 % x 760 = 47 mmHg
What is the average Functional Residual Capacity (FRC)?\
2300 ml
How much air is pulled into the alveoli each normal resting breath?
350 ml
Approximately how much total air remaining in lungs is replace with new air with each breath?
1/7 of total air remaining in lungs is replaced with new air with each breath
The rate of removal of excess gas from alveoli depends on what?
The rate of removal of excess gas from the alveoli depends on the rate of alveolar ventilation (VA)
Why is the concept of slow replacement important when discussing gas concentrations in the blood?
Slow replacement is important in preventing sudden changes in gas concentration in blood and keeping respiratory control mechanisms stabilized.
How long does it take at rest, for half of the gas to be removed (at a normal rate)?
17 seconds
How long would it take to remove half the normal concentration at half the normal alveolar ventilation rate?
Twice as long as normal, 34 seconds
How long would it take to remove 50% of the normal concentration of gas at 2x the normal alveolar ventilation rate?
Half the time, so, about 8 sec.
What is the vapor pressure of water?
47 mmHg
What are the factors that determine the rate of gas diffusion?
D∝∆PAS/(d√MW)
D = rate of diffusion P = Pressure A = area S = solubility MW=molecular weight
