Gas exchange in lungs Flashcards
What is the pO2 of inhaled air?
The same as the pO2 of the atmospheric air
What is the calculation for the inhaled pO2?
21% x 101kPa
How does the pO2 change in the upper respiratory tract? Why?
Decreases
as the inhaled air is humidified with water in the airways evaporating into water vapour
dilutes the oxygen in the air
What is the actual vapour pressure in the upper respiratory tract?
6.28kPa
What is the calculation for the pO2 in the upper respiratory tract?
21% x (101 - 6.28kPa)
How does the pO2 change in the alveoli? Why?
Decreases
as oxygen diffuses from the alveoli into the pulmonary capillaries
What is the pO2 in the alveoli?
13.3kPa
What is the pO2 in the pulmonary capillaries? Why?
13.3kPa
because oxygen diffuses into the pulmonary capillaries until the pO2 in the pulmonary capillaries is equal to the pO2 in the alveoli
How long does it take for the pO2 in the pulmonary capillaries to increase to 13.3kPa?
A third of the time that the blood is in the pulmonary capillaries
What is the advantage of the pO2 in the pulmonary capillaries increasing to 13.3kPa so quickly?
So that during exercise
when there is increased blood flow through pulmonary capillaries
still enough time for pO2 in pulmonary capillaries to increase to 13.3kPa
How does the pO2 of air in the alveoli compare with the pO2 of expired air?
Higher pO2 in expired air
because expired are includes air from anatomical dead space, conducting part of respiratory tract
which wasn’t involved in gas exchange
therefore contains more oxygen
What is the pCO2 in the pulmonary capillaries?
5.3kPa
What is the pCO2 in the alveoli? Why?
5.3kPa
because carbon dioxide diffuses from the pulmonary capillaries into alveoli until the pCO2 in the alveoli is the same as the pCO2 in the pulmonary capillaries
How does the pCO2 change from the upper respiratory tract to the alveoli? Why?
Increases
as carbon dioxide diffuses from the pulmonary capillaries into the alveoli
What is meant by diffusion barriers in the lungs?
Structures that oxygen and carbon dioxide have to pass through as they diffuse between the alveoli and the pulmonary capillaries
What are the factors affecting gas exchange across the respiratory membrane?
Partial pressure difference of gas across membrane
Diffusion coefficient of gas
Surface area of membrane
Thickness of membrane
What are the actual diffusion barriers in the lungs?
Fluid lining alveolus
Alveolar epithelium
Alveolar basement membrane
Tissue fluid
Pulmonary capillary basement membrane
Pulmonary capillary endothelium
Plasma
Red blood cell membrane
How do the partial pressure gradients of oxygen and carbon dioxde in the alveoli and pulmonary capillaries compare to each other? Why?
Need a larger partial pressure gradient for same rate of diffusion of oxygen
because it has a lower solubility coefficient
so it has a lower diffusion coefficient
What is the solubility coefficient of oxygen at 37C?
0.01
What is the solubility coefficient of carbon dioxide at 37C?
0.2
Does oxygen or carbon dioxide have a faster rate of diffusion between the alveoli and pulmonary capillaries? Why?
Carbon dioxide
because it has a higher solubility coefficient
so it has a higher diffusion coefficient
How are the lungs adapated to increase the rates of diffusion of oxygen and carbon dioxide?
Thin membrane
shorter diffusion distance between alveoli and red blood cells in pulmonary capillaries
Large surface area of alveoli
Large surface area of pulmonary capillaries
What is meant by the ventilation:perfusion ratio?
The amount of alveolar ventilation compared to blood flow into the lungs
How does normal alveolar ventilation compare to normal cardiac output?
They are both approximately 5L/min
What is the normal ventilation:perfusion ratio?
1
What are the pO2 and pCO2 of the alveoli and pulmonary capillaries when the ventilation:perfusion ratio is 1?
pO2 - 13.3kPa
pCO2 - 5.3kPa
