Respiration Lecture 07: Movement of Gas from Alveoli to Blood

Question 0

increased CO2 –> PO2 in lung?

Answer 0

decreases, because CO2 also occupies space

Question 1

Why is PO2 in lung lower than PO2 in air?

Answer 1

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

Question 2

What is normal net PO2 in the alveolus?

Answer 2

100 mmHg (after equilibrating with PO2 in alveolus and PO2 in arterial blood)

Question 3

normal venous blood returns with a PCO2 of

Answer 3

45 mmHg

Question 4

Normal net PCO2 in alveolus after equilibrating with arterial blood

Answer 4

40mmHg

Question 5

hyperventilation –> PCO2 and PO2?

Answer 5

decrease PCO2, increase PO2

Question 6

hypoventilation –> PCO2 and PO2?

Answer 6

PCO2 increases, PO2 decreases

Question 7

hyperventilation –> alveolar ventilation

Answer 7

increases

Question 8

hypoventilation –> alveolar ventilation

Answer 8

decreases

Question 9

Why do CO2 and O2 diffuse at similar rates even though O2 has a larger gradient than CO2?

Answer 9

O2 is less soluble than CO2 so it needs a greater gradient to achieve the same rate of diffusion

Question 10

What does blood pressure actually measure?

Answer 10

SYSTEMIC arterial pressure from L heart

Question 11

PO2 in venous blood compared to alveolus

Answer 11

PO2 in venous blood = 40mmHg. PO2 in alveolus = 100mmHg (net driving force for O2 to enter venous blood and leave alveolus)

Question 12

Fick’s Law of Diffusion

Answer 12

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

Question 13

VO2

Answer 13

rate at which O2 diffuses

Question 14

VCO2

Answer 14

rate at which CO2 diffuses

Question 15

Layers separating alveolus and the blood (5)

Answer 15

alveolar epithelium
basement membrane
interstitial space
capillary basement membrane
capillary epithelium

Question 16

Diffusing capacity (DL)

Answer 16

DL= Vgas/change in Pgas = (DAa)/X = J/PA

Question 17

Which gas is commonly used to measure DL?

Answer 17

CO

Question 18

What will decrease DLCO?

Answer 18

Any condition that affects the effective alveolar surface area and/or thickness. Ex:

1) Hindrance to the alveolar wall (fibrosis, alveolitis, vasculitis)
2) decrease in total lung area
3) uneven spread of air in lungs (i.e. emphysema)
4) pulmonary embolism
5) cardiac insufficiency
6) pulmonary hypertension
7) anemia due to decrease in blood volume
8) pulmonary edema