Flashcards in Gas Exchange Deck (37)
How big is the gas exchange area?
what is the alveolar capillary diffusion distance?
Where does respiration occur?
What are the 3 different kinds of dead space VD?
1. anatomic dead space
2. alveolar dead space
3. physiological dead space
alveolar dead space
the volume of inspired air that is delivered to alveoli in which there is no gas exchange or gas exchange is incomplete
anatomic dead space
volume of all non-gas exchange airways from the nose (or mouth, during mouth breathing) down to the respiratory bronchioles
physiologic dead space
the sum of anatomic dead space and alveolar dead space
*defines the portion of each inspiration that does not participate in gas exchange
why is alveolar ventilation less than pulmonary ventilation?
less because of anatomical dead space
What is convection?
convection is the bulk movement of gas due to pressure gradients and requires mechanical power input
What two transport processes occur by means of convection?
1. transport from the environment to terminal bronchioles
2. transport of erythrocytes between pulmonary capillaries and peripheral capillaries
what is diffusion?
transport based on random motion of thermally energetic particles situated in a concentration gradient
What transport processes occur by means of convection?
1. transport between terminal bronchioles to erythrocytes
2. transport between erythrocytes and peripheral mitochondria
Whats the difference between convection and diffusion?
in convection, gas moves from high pressure to low pressure. In diffusion, there is no pressure or mechanical movement
the movement of particles by convection is driven by what?
the pressure gradient between the atmosphere and terminal bronchioles
The mechanical work required for convection is a function of what 3 factors?
1. resistance of the transport path to air flow (diameter and cross-sectional area of airways)
2. the viscosity and density of air being moved
3. the compliance of the lung and chest wall
The movement of particles by diffusion is driven by what two factors?
1. concentration gradient
What is diffusivity?
a measure of the tendency of a molecule to avoid getting hung up in the surrounding media, specific for solute, solvent, temperature.
the total pressure of a gas mixture is the sum of the partial pressures of its constituents
the partial pressure of a gas in equilibrium with a volume of liquid is proportional to the amount of gas dissolved in the liquid
k = constant
c = [ ] of the gas
the pressure exerted by each type of gas in a mixture
What determines the concentration of a gas in a liquid
1. partial pressure
2. diffusivity (solubility coefficient)
How do gases dissolve in fluids?
by moving down a partial pressure gradient rather than a concentration gradient
what is the partial pressure of oxygen and carbon dioxide in the pulmonary artery?
oxygen: 40 mmHg
carbon dioxide: 46 mmHg
what is the partial pressure of oxygen and carbon dioxide in the lungs?
oxygen: 105 mmHg
carbon dioxide: 40 mmHg
what is the partial pressure of oxygen and carbon dioxide in the pulmonary vein?
oxygen: 100 mmHg
carbon dioxide: 40 mmHg
what is the A-a gradient?
alveoli - artery gradient
It is the difference between oxygen content in alveolus gas (measured during exhalation) and the oxygen content in arterial blood (equivalent to that leaving the lungs)
what is abnormal A-a?
What are the factors contributing to the A - a gradient?
1. blood shunts
2. blood mixing
what 3 things does gas diffusion in the lung depend on?
1. area of the respiratory membrane
2. distance of the diffusion
3. V/Q (ventilation and perfusion)