3.2.3 Gas Exchange and Acid-Base Flashcards
Why does ventilation and perfusion need to be matched?
To maintain proper concs of O2, CO2, H+ ions in tisue
What determines PO2 in the lungs?
Ration of ventilation to blood flow (V/Q)
What factors effect ventilation and perfusion in a normal animal?
- Regional differences in ventilation
- Regional differences in pulmonary blood flow
- Distribution of V and Q in lungs
How does regional differences in ventilation effect V/Q
Lower regions of lung ventilate better due to gravity reducing intrapleural pressure at lung base.
Alveoli are smaller at the bottom of the lung so have a greater change in volume during inflation, more complient
How does regional differences in pulmonary bloodflow effect V/Q?
Better diffusion at base of lung due to gravity (hydrostatic pressure) , depends on animal size and position of lung compared to heart
When is V/Q < 1?
At the lowest part of lung (V>Q) so SHUNT
When in V/Q > 1?
Upper part of lung (V>Q) so DEADSPACE
What is physiological deadspace?
V/Q = ∞ (Q = 0)
Area being ventilated but no gas exchange occurs because capillaries are not perfused
What is a shunt?
V/Q = 0 (V = 0)
Capillaries are perfused but no gas exchange occurs because alveoli are not ventilated
V/Q mismatch causes?
- Obstructive pulmonary disease
- Compromise of thoracic cavity capacity
- Diseases of pulmonary parenchyma
- Vascular disease
What are the layers of the blood-gas membrane? (8)
- Surfactant
- Alveolar epithelial cells
- Basal lamina
- Connective tissue
- Basal lamina (of the endothelial cell)
- Endothelial cell
- Plasma
- RBC membrane
What is Fick’s Law?
Rate of gas transfer through a sheet of tissue:
- proportional to tissue area and difference in pp between the sides
- inversely proportional to tissue thickness
Factors affecting gas exchange
Ficks law
Adequate ventilation
Perfusion of the lung
Role of haemoglobin in O2 transport
Transports 97% O2
Expressed at volumes per cent
What is the Bohr effect
The shift of )2-heamaglobin dissociation curve to the right due to increased CO2 conc (↑[H+])
Enhances O2 unloading to tissues and increases O2 of blood in lungs
