Lecture 12 2/6/24

Question 1

What percent of the air is composed of oxygen?

Answer 1

21%

Question 2

What is a partial pressure?

Answer 2

pressure exerted by a single gas within a mixture

Question 3

What determines a partial pressure?

Answer 3

barometric pressure and the fraction of oxygen in the mixture (PO2 = barometric pressure x fraction of O2)

Question 4

What is the impact of water vapor in inspired air?

Answer 4

-lowers the partial pressure of O2
-dilutes concentration of individual gases in the lungs

Question 5

What is diffusion?

Answer 5

passive movement of gases down a concentration gradient

Question 6

What is diffusion proportional to?

Answer 6

-partial pressure gradient
-surface area available for diffusion
-solubility of gas in the medium

Question 7

What is diffusion inversely proportional to?

Answer 7

-thickness
-molecular weight of gas

Question 8

How does a partial pressure gradient impact diffusion?

Answer 8

greater difference in partial pressure between substances = faster diffusion

Question 9

How does surface area impact diffusion?

Answer 9

greater cross-sectional area = more space available for molecules to pass

Question 10

How does solubility differ with temperature?

Answer 10

gas solubility decreases as temperature increases?

Question 11

How does molecular weight of the gas impact diffusion?

Answer 11

velocity of particle movement is slower for larger particles

Question 12

How does diffusion coefficient describe diffusibility?

Answer 12

-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

Question 13

Why does expired air have a higher O2 conc. than alveolar air?

Answer 13

exhaled alveolar air is mixed with dead space air, which has had no O2 extracted

Question 14

Which forms can oxygen be found in in the blood?

Answer 14

-dissolved
-bound to hemoglobin

Question 15

What are the characteristics of dissolved O2?

Answer 15

-proportional to the partial pressure
-extremely low amount in the blood

Question 16

What are the characteristics of hemoglobin?

Answer 16

-has 4 heme sites that can bind oxygen
-if ferrous ion is oxidized to ferric form, it becomes methemoglobin and cannot bind O2

Question 17

What is O2 saturation of hemoglobin?

Answer 17

percentage of binding sites on Hb that have O2 attached

Question 18

What is Henry’s law?

Answer 18

concentration dissolved = solubility of gas x pressure

Question 19

What things cause the O2 dissociation curve to shift right, indicating more unloading of O2 at the tissue level?

Answer 19

-increased CO2
-acidosis
-increased 2,3-DPG
-exercise
-temperature

Question 20

When is 2,3-DPG increased?

Answer 20

during chronic hypoxia

Question 21

When is 2,3-DPG decreased?

Answer 21

when blood is stored

Question 22

What are the characteristics of perfusion?

Answer 22

-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

Question 23

What are the characteristics of diffusion?

Answer 23

-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

Question 24

What does the concentration of carbon dioxide depend on?

Answer 24

rate of metabolic production

Question 25

What does PCO2 in alveoli depend on?

Answer 25

-rate of elimination of CO2 from pulmonary capillary blood
-rate of elimination of CO2 from lungs by exhalation
-perfusion limited

Question 26

What are the characteristics of carbon monoxide?

Answer 26

-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

Question 27

Why might partial pressures in the alveolus not match those in the arterial blood?

Answer 27

-true right-to-left shunts
-ventilation/perfusion mismatch

Question 28

What can lead to minor mismatching between ventilation and perfusion?

Answer 28

-bronchial and cardiac circulation
-regional distribution of blood flow to lungs

Question 29

What are the characteristics of a low V/Q ratio?

Answer 29

-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

Question 30

What are the characteristics of a high V/Q ratio?

Answer 30

-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