Properties of Respiratory Gases Flashcards
Respiration
mechanisms that promote the delivery of CO2 from active cells to the environment and oxygen from the environment to active cells
How does oxygen primarily leave the body?
H2O and CO2
Respiratory exchange ratio
the ration of CO2 production to oxygen consumption; normally between 0.7-1.0
What are two ways that gases move through a distance?
diffusion and bulk flow
Diffusion
a very efficient process for moving molecules from one area to another as long as the distance is very small
The __ is a gas exchanger that brings oxygen into contact with blood and removes carbon dioxide from the blood to the external environment.
respiratory system
Bulk flow
delivers oxygen rich air to the alveoli (skeletal muscles supply the energy) and to tissues (cardiac muscles supply the energy)
Ventilation
the process by which atmospheric air is delivered into and out of the lungs
Minute ventilation
the amount of air that enters or leaves the lungs per minute and is equal to the tidal volume X rate
Perfusion
the delivery of blood in small capillaries that surround the alveolar spaces in the lungs
Diffusion
the passive movement of gases from an area of high partial pressure to an area of lower partial pressure
Circulation
the bulk flow of blood from one area of the body to another
Differences between pulmonary and systemic circulation?
Lower pressure and lower resistance in pulmonary
The pressure of a gas in a container is dependent upon what 3 things?
- kinetic energy
- the number of gas molecules
- the volume of the container
STPD
Standard Temperature Pressure Dry (0 degrees, 760 mmHg)
BTPS
Body Temperature Pressure Saturated (with water)
Tension
pressure of a gas
Ideal Gas Law
PV = nRT
Boyle’s Law
relationship between P and V at a given temperature
Charles’ Law
relationship between T and V at a given pressure
Dalton’s Law of Partial Pressures
the total pressure exerted by a mixture of gases equals the sum of the individual pressures that each gas would exert individually if it alone occupied the entire volume
The ___ the temperature, the more vapor pressure is exerted and the ___ the temperature, the lower the vapor pressure will be.
higher
lower
Henry’s Law
the volume of a slightly soluble gas that dissolves in a given mass of liquid at a specific temperature is directly proportional to the partial pressure of that gas
The solubility of a gas ___ as the temperature increases.
decreases
The amount of oxygen transported in the ___ state is quite small. However, not all of the oxygen in blood is transferred in this state. Most of it is bound to ___.
dissolved
hemoglobin
A major factor involved in pulmonary gas exchange is __.
simple diffusion
If a specific gas has a higher partial pressure in the gaseous mixture than in the water, the the net transfer will be into the ___. The rate will be affected by 3 things. Name them.
water
- partial pressure gradient
- solubility of the gas in the water
- temperature
What 5 things does the rate of diffusion depend on?
- partial pressure gradient
- cross-sectional area of the diffusion pathway
- the solubility of the gas in the medium
- the distance traveled
- the molecular weight of the gas
D = (P x A x S) / (d x sqr(MW))
Oxygen diffuses more rapidly than carbon dioxide in the alveolar gas phase. Why?
Based on molecular weight, carbon dioxide is 20% slower than oxygen, but based on solubility it is 24 times faster. The bottom line is that the diffusion coefficient for CO2 is over 20 times that of oxygen. The diffusion rate of CO2 in water phase is high compared to that of oxygen. Therefore, CO2 diffuses more rapidly in water than oxygen, although CO2 diffuses more slowly in the alveolar gas phase.
Gas diffusion in the alveoli is __.
fast
How much of the gas enters into solution will depend on ___ of the gas. (HINT: Henry’s Law)
solubility
The gas tensions of the blood leaving the alveolar capillary are roughly equal to the average tensions of the gases in the ___.
alveolus
Respiratory Membrane
number of structures or layers which gases must pass through to move from an alveolar capillary into an alveolus or vice versa
Includes: Alveolar Membrane, Interstitial Fluids, Capillary Membrane, Plasma, RBCs
The movement of gases through a respiratory membrane is dependent on what 4 factors?
surface area, thickness, partial pressure differences, diffusion coefficients
Total respiratory surface area
the sum of the available individual surface areas of all the alveoli in both lungs
Diffusion Coefficient
wholly physical and depends primarily on the molecular weight of the gas and its solubility in the membrane. CO2 diffuses 20 times more than O2 in an aq liquid
Movement of O2 into the blood, as well as transfer of CO2 into the alveoli, is by __ diffusion.
passive
Diffusion capacity
the volume of a gas that diffuses through a membrane per minute down a 1 mmHg pressure gradient across the membrane
Oxygen diffusion capacity in terms of STPD is __ mlmin/mm Hg
20, but during strenuous exercise it can increase up to 65 because of capillary dilation and an increase in the total number of pulmonary capillaries that are open
CO2 retention is rarely a problem, whereas damage to the __ can impair oxygen uptake seriously.
respiratory membrane
Oxygen concentration (PO2) in alveolar air at any moment depends on what 2 things?
- alveolar ventilation rate
2. rate at which O2 is absorbed into pulmonary capillary blood
If cardiac output increases in a normal animal, the point at which equilibrium occurs moves back on the curve However, the time required does not increase as much as cardiac output increases. This is because the lungs have 2 safety mechanisms. Name them.
- recruitment of unperfused capillary beds
2. dilation of previously perfused capillaries
Insufficient time for oxygen equilibration can impair oxygen transport across the alveolar capillary bed under at least 3 kinds of condiions:
- Increased diffusion path length
- Reduction in capillary bed
- Reduced alveolar PO2
The transfer of a gas between perialveolar blood and alveolus requires that the alveolar capillary be __ and that gas ___ takes places across the respiratory membrane.
perfusion
diffusion
__ is more limited than diffusion.
perfusion
Name 2 gases that are perfusion-limited.
oxyen, nitrous oxide
The PCO2 depends on what 2 factors?
- the rate of elimination of CO2 from pulmonary capillary blood
- on the rate at which CO2 is exhaled from the lungs
Alveolar PCO2 __ in direct proportion to the CO2 transfer rate and it __ as the alveolar ventilation rate increases.
increases
decreases
Name a gas that is diffusion-limited.
CO
The affinity of hemoglobin is very high for __ and quickly removes it from the dissolved state.
CO
