Blood supply, gas exchange, ventilation & perfusion Flashcards
What is the function of the pulmonary artery?
Carries de-oxygenated blood away from the heart, towards the lungs
What is the function of the pulmonary vein?
Carries oxygenated blood towards the heart, away from the lungs
Describe bronchial circulation
Nutritive - supplied via bronchial arteries arising from systemic circulation to supply oxygenated blood to smooth muscle, nerves and lung tissue
Describe pulmonary circulation
Gas exchange - consistis of L&R pulmonary artery originating from right ventricle. CArries entire cardiac output from right ventricle. Supplies the dense capillary network surrounding the alveoli and returns oxygenated blood to the left atrium via pulmonary vein. High flow, low pressure system.
The rate of diffusion of gases:
- directly proportional to partial pressure
- directly proportional to gas solubility
- directly proportional to surface area
- inversely proportional to thickness of membrane
- most rapid over short distances.
What effect does emphysema have on gas exchange?
Destruction of alveoli; reduces surface area
What effect does fibrosis have on gas exchange?
Thickened alveolar membrane; slows rate of diffusion. Loss of compliance may reduce alveolar ventilation
What effect does oedema have on gas exchange?
Fluid on interstitial space increases space for diffusion. . Aterial PCO2 may be normal due to higher solubility in water
What effect does asthma have on gas exchange?
Constriction of bronchioles - Increased resistance; decreases ventilation
What is ventilation?
Volume of air reaching alveoli (L/min)
What is perfusion?
Local blood flow (L/min)
What is ventilation-perfusion relationship?
Ventilation and perfusion match each other
Where in the lungs is blood flow the highest (any why?)
At the bottom of lung. At bottom of lung arterial pressure exceeds alveolar pressure and vascular resistance is therefore low. Opposite in case of apex of lung
What is Ventilation-perfusion mismatch (“shunt”)?
When ventalation < blood flow. If ventilation decreases in a group of alveoli, PCO2 increases, and PO2 decreases = blood flowing past these areas does not get oxygenated.
How does the blood supply to the lungs compensate for Ventilation-perfusion mismatch?
Decreased tissue PO2 around under ventilated alveoli constricts their arterioles, diverting to a better ventilated area (constriction due to hypoxia only occurs in the lungs, systemic vessels dilate)
