Flashcards in Respiration Lecture 07: Movement of Gas from Alveoli to Blood Deck (19):
Why is PO2 in lung lower than PO2 in air?
air in lung is saturated with water vapor, which occupies some of the total gas volume. PO2 in lung = FO2 * (Pb - 47). PO2 in air = FO2 * Pb
increased CO2 --> PO2 in lung?
decreases, because CO2 also occupies space
What is normal net PO2 in the alveolus?
100 mmHg (after equilibrating with PO2 in alveolus and PO2 in arterial blood)
normal venous blood returns with a PCO2 of
Normal net PCO2 in alveolus after equilibrating with arterial blood
hyperventilation --> PCO2 and PO2?
decrease PCO2, increase PO2
hypoventilation --> PCO2 and PO2?
PCO2 increases, PO2 decreases
hyperventilation --> alveolar ventilation
hypoventilation --> alveolar ventilation
Why do CO2 and O2 diffuse at similar rates even though O2 has a larger gradient than CO2?
O2 is less soluble than CO2 so it needs a greater gradient to achieve the same rate of diffusion
What does blood pressure actually measure?
SYSTEMIC arterial pressure from L heart
PO2 in venous blood compared to alveolus
PO2 in venous blood = 40mmHg. PO2 in alveolus = 100mmHg (net driving force for O2 to enter venous blood and leave alveolus)
Fick's Law of Diffusion
The rate at which a molecule crosses a membrane is determined by the properties of the molecule and the membrane. J = DAa[change in P/X] where J= rate of molecular movement (flux), D= diffusion constant, A= area of membrane, a= solubility, and X = membrane thickness. Aka the consumption rate of O2, VO2, and release rate of CO2 and VCO2
rate at which O2 diffuses
rate at which CO2 diffuses
Layers separating alveolus and the blood (5)
capillary basement membrane
Diffusing capacity (DL)
DL= Vgas/change in Pgas = (DAa)/X = J/PA
Which gas is commonly used to measure DL?