Respiratory strand: Lecture 4 - Principles of Gas Exchange

Question 1

How is rate of diffusion, surface area (A) and pressure gradient related?

Answer 1

Rate of diffusion is directly proportional to A x ΔP

Question 2

What is diffusion dependent on?

Answer 2

the physicochemical properties of the gas and nature of the membrane e.g thickness

Question 3

What is the pressure gradient?

Answer 3

the difference in partial pressures of the respective gases in the alveolus and the blood

Question 4

What is the partial pressure of a gas in a mixture of gases?

Answer 4

the pressure that it would exert if it was the only gas in the container

Question 5

How do you calculate the partial pressure of a gas in a gas mixture?

Answer 5

the partial pressure of a gas in a gas mixture = total pressure x fractional concentration of the gas

Question 6

Explain the partial pressures of gas in the atmosphere at sea level and at 5000m altitude

Answer 6

1. Fractional concentration (%) 2. Partial pressure at sea level (kPa)
2. Partial pressure at 5,000 m altitude (kPa)
   Oxygen 1 - 21 2- 21.3 3 - 11.8
   Carbon dioxide 1- 0 2- 0 3- 0
   Nitrogen 1- 79 2- 80 3- 44.2
   Total 1- 100 2- 101.3 3- 56

Question 7

Why is partial pressure of oxygen in the alveoli lower than in room air?

Answer 7

-inspired air is humidified in the upper airway
-in the alveoli, oxygen is taken up while carbon dioxide is added
-the body consumes more 02 molecules than it produces CO2 molecules (typically 1.25x)
(our gases as we breath in mix wth our gases that we breath out)

Question 8

at 37 degrees, what s the partial pressure of water vapour?

Answer 8

6.3 kPa

Question 9

What is a typical value of alveolar pp of CO2?

Answer 9

5 kPa

Question 10

How many O2 molecules are consumed as CO2 molecules produced?

Answer 10

1.25x

Question 11

What is henry’s law?

Answer 11

The partial pressure of gas in solution is equal to the partial pressure of gas above it

Question 12

How is partial pressure of a gas in solution linked to its solubility?

Answer 12

partial pressure of a gas in solution is inversely proportional to its solution

so the greater the solubility, the more molecules can be accommodated for a given partial pressure

high solubility = low partial pressure

Question 13

How many times more soluble Is CO2 in water than oxygen is?

Answer 13

24 times
so for every molecule of oxygen, we can dissolve 24 molecules of CO2
but as CO2 is more soluble, you need more of it to create the same concentration of solution than oxygen

Question 14

What is pulmonary fibrosis?

Answer 14

A restrictive lung condition where fibrous tissue builds up

Question 15

How do we calculate oxygen diffusing capacity?

Answer 15

Oxygen uptake / (alveolar PO2 - mean pulmonary capillary PO2)

Question 16

How do we calculate carbon monoxide diffusing capacity?

Answer 16

carbon monoxide uptake /

alveolar PCO

Question 17

Explain the diffusion pathway from the red blood cell and the capillary membrane?

Answer 17

slide 23 image

Question 18

Give 6 conditions where the alveolar capillary membrane is abnormal

Answer 18

slide 24

Question 19

What is adult respiratory distress syndrome?

Answer 19

White cells in alveoli
Thickened membrane
Opening of pores in capillaries so fluid and macrophages can come and attack

Question 20

What is atelectasis?

Answer 20

lung collapse

Question 21

What is compliance?

Answer 21

the ability of us to expand our lungs