Lecture 4: Diffusion + Alveolar Ventilation Flashcards
Alveoli
Gas exchange cells; lined by AT1 cells and interspersed w/ thicker AT2 cells
Respiratory quotient
RQ = CO2 produced:O2 consumed (~0.8 on average)
Dalton’s Law of Partial Pressures
Partial P depends on temperature and concentration; each gas’s partial P is independent of one another and sum together to equal the total P
Factors for alveolar partial P (O2, CO2)
- Atmospheric PO2
- Rate of alveolar ventilation
- Rate of total body O2 consumption/CO2 production
Hypo/hyperventilation
Ventilation relative to metabolism; hypo = increased CO2 production relative to alveolar ventilation, hyper = reduced CO2 production relative to alveolar ventilation.
Partial pressure gradient
Partial P gradient drives gas diffusion
Impairment of gas diffusion factors
- Reduced surface area
- Thickened alveolar walls
Bulk flow gradient
Bulk flow moves air down the total P gradient from outside into the lungs
Particulate deposition in lungs
Air velocity becomes 0 in respiratory zones due to branching; movement by diffusion here. Particulate diffusion starts at 16th gen and is removed by macrophages.
Rate limiting step in respiration
Perfusion is the rate limiting factors in normal lungs, NOT diffusion (can be different w/ disease)
Venous partial pressures
PO2 = 40 mmHg
PCO2 = 46 mmHg
Arterial partial pressures
PO2 = 100 mmHg
PCO2 = 40 mmHg
Alveolar air partial pressures
PO2 = 100 mmHg
PCO2 = 40 mmHg
Carbon monoxide blood partial P
CO does NOT build up partial P in blood due to tight Hb binding; diffusion is thus limited
Transfer factor (diffusion capacity)
D_L = DAS / Δx = gas ventilation / ΔP
How is lung diffusion capacity controlled?
By changing perfusion via vessel recruitment/distension to perfuse more alveoli
Alveolar ventilation equation
Alveolar vent. = VCO2 x (P_B - 47 mmHg) / PCO2
Consumption times barometric P (47 mmHg = H2O) divided by partial P
Respiratory Exchange Ratio
RER = VCO2 / VO2 = 0.8
O2 consumption and CO2 production nearly balance out
Alveolar Gas Equation; effect of ventilation on PO2
PO2 = PO2_inspired - PCO2 / R
PO2 = inspired PO2 - consumed O2; thus increasing ventilation means PO2 increases by the absolute amount which PCO2 decreases.
Matching ventilation and metabolism
Increasing ventilation increases PO2 and decreases PCO2
Increasing metabolism does the opposite
Ventilation and metabolism changes will match PO2 with PCO2 changes.
