Gas exchange and gas transport Flashcards
What are the 2 functions of the lung?
- Ventilation – the movement of air in and out of the lungs
- Gas exchange – the exchange of oxygen and carbon dioxide between the airspace of the alveoli and the blood
What does the red line show?
Less efficient alveoli caused by fluid overload
What is the lung ventilated by and perfused by?
The lung is ventilated by air and perfused by blood
How does ventilation/perfusion (V/Q) matching work?
- Pulmonary circulation is a low pressure system (15 mmHg)
- Upright position barely enough pressure to perfuse the apices with overperfusion of the bases
THEREFORE
•Uneven distribution throughout the lung – lower zones more compliant
What are steady-state conditions?
The amount of CO2 produced by the body and the amount of O2 absorbed depends upon the metabolic activity of the body – the ‘Respiratory Quotient’ (RQ)
What is the Respiratory Quotient equation?
What is the RQ value for
Fat metabolism
Carbohydrate metabolism
- Fat metabolism 0.7
- Carbohydrate metabolism 1.0
What does the partial pressure of CO2 in alveolar air (PACO2) depend on?
If CO2 is produced at a constant rate by the body then the partial pressure of CO2 (PCO2) of alveolar air (PACO2) is dependant on alveolar ventilation
What is the relationship between alveolar ventilation and PACO2
- Increase in alveolar ventilation -> decrease in PACO2
- Decrease in alveolar ventilation -> increase in PACO2
What is PACO2?
The partial pressure of CO2 of alveolar air
What is PCO2?
Partial pressure of CO2
What is PAO2?
Partial pressure of O2 in alveolar air
What is the relationship between alveolar ventilation and PAO2?
- Increase in alveolar ventilation -> increase in PAO2
- A big enough increase in alveolar ventilation will allow the PAO2 to approach PO2
- Decrease in alveolar ventilation -> decrease in PAO2
How does gas get into the blood?
Diffusion through tissues is described by Fick’s Law
What is Fick’s Law?
The rate of transfer of a gas through a tissue is proportional to the tissue area and the difference in gas partial pressure between the two sides, and inversely proportional to the tissue thickness.
Alveoli have large surface area so gas transfer is quicker.