Lecture 12 2/6/24 Flashcards
What percent of the air is composed of oxygen?
21%
What is a partial pressure?
pressure exerted by a single gas within a mixture
What determines a partial pressure?
barometric pressure and the fraction of oxygen in the mixture (PO2 = barometric pressure x fraction of O2)
What is the impact of water vapor in inspired air?
-lowers the partial pressure of O2
-dilutes concentration of individual gases in the lungs
What is diffusion?
passive movement of gases down a concentration gradient
What is diffusion proportional to?
-partial pressure gradient
-surface area available for diffusion
-solubility of gas in the medium
What is diffusion inversely proportional to?
-thickness
-molecular weight of gas
How does a partial pressure gradient impact diffusion?
greater difference in partial pressure between substances = faster diffusion
How does surface area impact diffusion?
greater cross-sectional area = more space available for molecules to pass
How does solubility differ with temperature?
gas solubility decreases as temperature increases?
How does molecular weight of the gas impact diffusion?
velocity of particle movement is slower for larger particles
How does diffusion coefficient describe diffusibility?
-oxygen is set to a value of 1
-gases with a higher diffusion coefficient diffuse more easily
-gases with a lower diffusion coefficient diffuse less easily
Why does expired air have a higher O2 conc. than alveolar air?
exhaled alveolar air is mixed with dead space air, which has had no O2 extracted
Which forms can oxygen be found in in the blood?
-dissolved
-bound to hemoglobin
What are the characteristics of dissolved O2?
-proportional to the partial pressure
-extremely low amount in the blood
What are the characteristics of hemoglobin?
-has 4 heme sites that can bind oxygen
-if ferrous ion is oxidized to ferric form, it becomes methemoglobin and cannot bind O2
What is O2 saturation of hemoglobin?
percentage of binding sites on Hb that have O2 attached
What is Henry’s law?
concentration dissolved = solubility of gas x pressure
What things cause the O2 dissociation curve to shift right, indicating more unloading of O2 at the tissue level?
-increased CO2
-acidosis
-increased 2,3-DPG
-exercise
-temperature
When is 2,3-DPG increased?
during chronic hypoxia
When is 2,3-DPG decreased?
when blood is stored
What are the characteristics of perfusion?
-gas uptake into alveolar capillary is determined by blood flow
-increased blood flow rate leads to increased rate of gas transfer
-does not depend on diffusion properties
-O2
What are the characteristics of diffusion?
-rate of uptake into the alveolar capillary is determined by rate of diffusion
-partial pressure differences of a gas are influenced by the diffusion properties of the blood-gas barrier
What does the concentration of carbon dioxide depend on?
rate of metabolic production
What does PCO2 in alveoli depend on?
-rate of elimination of CO2 from pulmonary capillary blood
-rate of elimination of CO2 from lungs by exhalation
-perfusion limited
What are the characteristics of carbon monoxide?
-affinity for hemoglobin is 240x greater than that of oxygen
-diffusion limited, since CO grabs hemoglobin as fast as it is diffused
-reduces available hemoglobin for oxygen binding
Why might partial pressures in the alveolus not match those in the arterial blood?
-true right-to-left shunts
-ventilation/perfusion mismatch
What can lead to minor mismatching between ventilation and perfusion?
-bronchial and cardiac circulation
-regional distribution of blood flow to lungs
What are the characteristics of a low V/Q ratio?
-some alveoli are perfused but not well ventilated
-ventilation is not keeping pace with perfusion
-low alveolar and arterial PO2
-high alveolar and arterial PCO2
What are the characteristics of a high V/Q ratio?
-some alveoli are ventilated but not well perfused
-additional alveolar dead space
-reduced pulmonary blood flow
-alveolar O2 is high while capillary O2 is low
-air content within alveolus will be similar to what was breathed in
