Physiology 2: Gas Exchange (L-3) Flashcards
Define anatomical dead space
- The volume of the airways in the lungs (Non-alveolar space)
- Gas exchange doesn’t occur
Define pulmonary ventilation
The volume ventilated per minute
breath volume x Resp rate
Define alveolar ventilation
- Volume of air exchanged between the atmosphere and alveoli per minute
- Represents the new air available for alveolar/blood gas exchange
Why is the alveolar ventilation less than the pulmonary ventilation?
Due to the presence of anatomical dead space
Is it more beneficial to increase resp rate or breathing depth to increase oxygen uptake?
Why?
It is more beneficial to increase breathing depth
Because as you increase resp rate the alveolar ventilation decreases, as air in the anatomical dead space is ventilated first
Ventilation is best at which area in the lung?
The apex of the lungs
Is blood perfusion better at the top or bottom of the lungs?
Better in the inferior part of the lungs
What is meant by the V/Q ratio?
The ratio between lung ventilation and perfusion
Why does the V/Q ratio vary in different parts of the lungs?
Due to their differing perfusion and ventilation
Define alveolar dead space
- Ventilated alveoli that are not adequately perfused
- Gas exchange is not effective
Define physiological dead space
Anatomical dead space
+
Alveolar dead space
(Total volume not actively exchanging gases)
Which local controls act to match ventilation and perfusion?
Smooth muscles in the airways and arterioles
vasodilation/constriction
bronchodilation/constriction
Describe what happens if the perfusion is greater than the ventilation
- Alveolar carbon dioxide increased
- So airway dilation, increased airflow
- Alveolar oxygen decreased
- So pulmonary vasoconstriction, blood flow decreases
Describe the response to high alveolar carbon dioxide
- airway smooth muscle relaxes
- Increases airway size, decreased airway resistance
- Increased airflow
- Reduced carbon dioxide
Describe the response to high alveolar oxygen
- Pulmonary vasodilation
- Increased blood flow to alveoli
- The increase in oxygen can now be transferred to the blood
Describe what happens if the ventilation is greater than the perfusion
- Alveolar carbon dioxide decreased
- So airway constriction, decreased airflow
- Alveolar oxygen increased
- Pulmonary vasodilation, increased blood flow
Describe the effects on pulmonary and systemic arterioles of decreased alveolar oxygen
Pulmonary arterioles:
- Vasoconstriction
- To get a better V/Q ratio
Systemic arterioles:
- Vasodilation
- Increase oxygen supply to tissues
Describe the effects on pulmonary and systemic arterioles of increased alveolar oxygen
Pulmonary arterioles:
- Vasodilation
- To get a better V/Q ratio
Systemic arterioles:
- Vasoconstriction
Describe the 4 factors that affect the rate of alveolar gas exchange
- Partial pressure gradient of oxygen and carbon dioxide
- Diffusion coefficient for oxygen and carbon dioxide
- Alveolar surface area
- Alveolar membrane thickness
Define the partial pressure of a gas
The pressure that one gas in a gas mixture would exert if it were the only gas present in the volume occupied by the gas mixture
(at a constant temp.)
Describe how gases move with regards to partial pressures
Gases move down partial pressure gradients
High partial pressure –> Low partial pressure
Give the alveolar gas equation
PAO2 = PiO2 - [PaCO2 / 0.8]
0.8 = The resp exchange ratio
Which has a greater partial pressure gradient CO2 or oxygen?
Why?
Carbon dioxide has a much smaller partial pressure gradient
Due to CO2 being more soluble in membranes than oxygen (has a greater diffusion coefficient)
Which has a greater diffusion coefficient CO2 or oxygen?
Means what?
- CO2 has a greater diffusion coefficient
- 20 times greater
- So CO2 more membrane soluble
Describe the normal gradient between alveolar and arterial PO2
- Usually a small gradient
- Gradient exists as V/Q ratio isn’t perfect
Define:
- PAO2
- PaO2
PAO2 - Alveolar PO2
PaO2 - Arterial PO2
What percentage of the cardiac output is received by the pulmonary circulation
100%
Describe the effect of surface area and membrane thickness on gas diffusion (Fick’s Law)
Gas movement is:
- Proportional to surface area
- Inversely proportional to thickness
List non-respiratory functions of the respiratory system
- Heat elimination
- Water loss
- Maintaining acid-base balance
- Phonation
- Olfaction
