Alveolar Gas Exchange Flashcards
blood entering the pulmonary capillary is (what type of blood)
- mixed venous
blood leaving the pulmonary capillary is
- arterial
rate of movement of gas through tissue over time directly proportional to
- permeability
- partial pressure gradient
- tissue surface area
rate of movement of gas through tissue over time inversely proportional to
- tissue thickness
gas permeability is directly proportional to
- solubility of gas in barrier tissue and blood
gas permeability is inversely proportional to
- molecular weight
which gas is more permeable in the lung (O2 or CO2)
- CO2
alveolar type I epithelial cell and pulmonary microvascular endothelial cell share
- opposite sides of a common basement membrane
which gradient is higher for O2 and CO2
- O2 but CO2 is more soluble
alveoli are richly supplied with
- capillaries
the diffusing distance from oxygen extends from
- alveolus to hemoglobins molecules within erythrocytes
what does the diffusion barrier consist of?
- alveolar air
- surfactant and fluid layer
- alveolar type I cell
- lung interstitial
- endothelial cell
- blood plasma
- RBC hemoglobin
what is the thickness of the blood-gas barrier?
- miniscule
what drives diffusion across the blood gas barrier
- differences in partial pressures
which gas molecules can exert a partial pressure
- free, unbound gas molecules
how long does it take for an erythrocyte to traverse the capillary across the width of an alveolus
- about .75 seconds
how long does it take O2 and CO2 to equilibrate across the blood gas barrier
what does this mean?
- about .25 seconds
- there is reserve time for additional gas exchange
does O2 bound to Hb exert a partial pressure?
- no
in what forms can oxygen exist in the blood
what form has greater existence
- dissolved O2
- O2 bound to hemoglobin
- O2 bound to hemoglobin
N2O permeability
does it bind to hemoglobin?
considered in partial pressure determination
- highly permeable
- it does not.
considered in partial pressure determination
CO permeability
does it bind to hemoglobin
considered in partial pressure determination?
- low permeability
- it does. almost irreversibly.
- takes it out of partial pressure determination
the greater the perfusion
- the greater the uptake of gas by the lung
what is a perfusion limitation
- blood leaves pulmonary capillary fully equilibrated with a gas
what is diffusion limitation
- when blood leaves pulmonary capillary before it is equilibrated with a gas
which gasses are perfusion limited under normal conditions?
- N2O
- O2
- CO2
which gasses are diffusion limited under normal conditions
- CO
when can O2 or CO2 become diffusion limited
- heavy exercise in elite athletes
- high altitudes
- severe pulmonary disease
approximately half of the overall resistance to O2 loading of the alveolar capillary blood due to
- kinetics of Hb-O2 binding reaction
result of pulmonary fibrosis
effect on O2 equilibrium
- thickened interstitium due to collagen deposition
- increases time for O2 equilibration
result of pulmonary edema
effect on O2 equilibrium
- interstitiium thickened by excess fluid
- increase O2 equilibration time
conditions that impair diffusion at rest
what about exertion
- may allow O2 equilibration
- will probably cause disequilibration
high hydrostatic pressure favors
- fluid out of capillary into intersitium
- does not push out protein
as you go down the capillary, what will happen with the colloid osmotic pressure
- as fluid leaves the vessel, colloid oncotic pressure increases down vessel length
- will draw water back into the capillary at the pulmonary vein
pulmonary edema on capillary permeability
- increases capillary permeability
pulmonary edema on capillary hydrostatic pressure
- increases capillary hydrostatic pressure
pulmonary edema on plasma oncotic pressure
- decreases plasma oncotic pressure
how can we measure how well diffusion is happening?
- diffusion capacity of the lung for CO
factors affecting diffusion of CO across the lung
- surface area
- permeability of blood-gas barrier
- Hb status
- body position
- exercise
what parts of Hb status would affect CO diffusion across the lung?
- anything that reduces Hb
- anemia
- carboxy-Hb (smoking)
- oxyhemoglobin (O2 therapy)
2/3 of O2 consumed goes to
- skeletal muscle
- brain
- liver
slope of Hb-O2 dissociation curve
- sigmoid
hemoglobin is nearly saturated with O2 at partial pressures as low as
- 70 mmHg
large amount of O2 are ________ in response to small decrements in PO2 in the ___________
- unloaded
- metabolizing tissues
affinity of Hb for O2 is modified by
- pH
- pCO2
- temperature
- 2,3 DPG (glycolytic product)
what is the Bohr effect
- low pH and CO2 shifting Hb-O2 curve to the right
rightward shift means Hb affinity for O2 is _______ at a given PO2
- lower
CO2 is carried in what forms
which one mainly
- dissolved gas
- bound to Hb as carbamino Hb
- bicarbonate (HCO3-) (mainly)
bicarbonate reaction
- CO2 + H2O -> H2CO3 -> HCO3 + H+
what is the chloride shift
- exchange of HCO3- for Cl- that occurs in red blood cells
- how bicarb gets into the plasma
protons generated in the bicarbonate reaction help to
- dissociate O2 from Hb so it can be delivered to the tissues
high PO2 in the lungs helps to
what is this known as
- remove CO2 to deliver to alveolus
- Haldane effect
CO2 dissociation curve
- much more linear over a wide range
what happens to deoxygenated hemoglobin
- it picks up CO2
CO2 is directly proportion to ______ ventilation
- lung ventilation
result of hypoventilation on alveolar PCO2
- alveolar PCO2 will increase
result of hyperventilation of alveolar PCO2
- alveolar PCO2 will decrease
what does pulse oximetry provide us
- pulse
- Hb saturation
oxygenated hemoglobin absorbs which light
which light passes
- infrared light
- red light passes
deoxygenated hemoglobin absorbs which light
which light passes
- absorbs red light
- infrared light passes
what does pulse oximetry measure
- ratios of red and infrared light
when would hemoglobin not bind to oxygen normally
- CO poisoning
- heme iron in ferric instead of ferrous state
