Science Gas Exchange Flashcards
(16 cards)
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
Are we more sensitive to hypercapnia or hypoxia?
Hypercapnia = high CO2 in blood
