Lecture 12 - Diffusion in the Lung - Midterm 2

Question 1

where does gas exchange take place

Answer 1

1. Blood and alveoli
2. Blood and tissue

Question 2

Blood and alveoli → uptake _____ and dump ______

Answer 2

O2
CO2

Question 3

Blood and tissue → uptake ______ and dump _______

Answer 3

CO2
O2

Question 4

Gas Exchange in the Lung depends on….

Answer 4

pressure gradients

Question 5

Pressure depends on…

Answer 5

Temperature (for us, this doesn’t matter)

Concentration (# of molecules in a given volume)

Question 6

Diffusion depends on:

Answer 6

Surface area → the more, the better (shape of alveoli)

Distance → the shorter, the better

Concentration difference → ΔP, the greater the better

Question 7

Where Does Gas Exchange Occur?

Answer 7

In alveoli

Question 8

what is alveoli made up of

Answer 8

epithelial cells
1 cell thick; this is good for diffusion since there is a short distance

Question 9

what is Dalton’s Law of Partial Pressure

Answer 9

In a mixture of gases, the pressure of each gas is independent of the others

Pp = total pressure x gas fraction

Question 10

In the lung, total pressure = atmospheric pressure (Patm)

Answer 10

Pgas = Patm x Fgas

Question 11

Atmospheric air is comprised of:

Answer 11

79.04% N2 → FN2 = 0.7904
20.93% O2 → FO2 = 0.2093
0.3% CO2 → FCO2 = 0.003

Question 12

The pressure of O2, atmosphere and Co2 at sea level

Answer 12

Patm = 760 mmHg

PO2 = 760 mmHg x 0.2093 = 159 mmHg (this is the highest amount of oxygen that can get in the blood)

PCO2 = 760 mmHg x 0.003 = 0.23 mmHg

Question 13

The pressure of O2, atmosphere and Co2 on Mount Everest

Answer 13

Patm = 250 mmHg

PO2 = 250 mmHg x 0.2093 = 52 mmHg (this is the highest amount of oxygen that can get in the blood)

The atmospheric pressure is lower, but the gas fractions do not change

Question 14

The pressure of O2, atmosphere and Co2 in expired air

Answer 14

79.07% N2 → FN2 = 0.7907
17.23% O2 → FO2 = 0.1723
3.7% CO2 → FCO2 = 0.037
Patm = 760 mmHg
PO2 = 760 mmHg x 0.1723 = 130.95 mmHg
PCO2 = 760 mmHg x 0.037 = 28.12 mmHg

Question 15

Henry’s Law for Gases Dissolved in Liquids

Answer 15

The volume of gas dissolved in a liquid is proportional to the partial pressure of the gas

Cgas = Pgas x k

Cgas = concentration of gas in a liquid (ml/dl)

K = solubility coefficient of the gas in the liquid

Higher k means less pressure required to dissolve gas

This is important because gases are transmitted between alveoli (air) and blood (liquid)

Example; nitrogen has the lowest K (it is hardest to get into the blood)