Science Gas Exchange Flashcards
Where is the best perfusion and ventilation in the lung?
Base of lung
Where is the intrapleural pressure most and least negative in the lung?
Less -ve at base
More -ve at apex
What do you want the VA:Q ratio to be for efficient gas exchange?
Close to 1
What is the anatomical dead space?
Does not participate in gas exchange = ventilated alveoli not perfused therefore….
VA:Q = infinity
Why are lungs succeptible to emboli?
Thrombus forms in systemic circ > venous circ > resistance lower in heart > pulmonary circ > capillaries get narrower = increased resistance > clot trapped in lung
What is right to left shunting of blood?
= blood passing through lung without contact with alveolar air (VA:Q = 0) so deoxygenated blood in right mixes with oxygenated in left
- Physiological - bronchial blood supply
- Pathophysiological - fluid filled alveoli
What mechanisms are there to defend VA:Q matching?
Modulation of blood flow rather than ventilation
Vasoconstriction by low PO2 = blood directed away from poorly ventilated areas to prevent shunting
How is breathing controlled?
Medulla = responsible for breathing pattern
What does damage to the medulla result in?
No breathing - resp. failure
What does damage to the pons result in?
Erratic breathing
What happens to stretch receptors when lungs distend?
Fire less to reduce muscle activity
What are J receptors?
Sensitive to pressure + other features in pulmonary circulation
What are proprioreceptors?
Position/length sensors
In joints + rib cage
Sends signals to brain which modifies breathing
What do central chemoreceptors do?
- Brainstem
- Sensitive to pH of CSF = index of CO2
- Slow response
- Insensitive to pO2
What do peripheral chemoreceptors do?
- Near carotid + aortic arteries
- Detect changes in blood stream
- Low pO2 = increased firing to medulla + pons via carotid sinus nerve
- High [H+] or pCO2 = increased firing
- Rapid response
