S3.2 Gas Exchange Flashcards
What physical factors affect diffusion rate of a gas in a fluid?
Pressure difference
Weight of gas
Solubility of gas
Diffusion distance
Describe gas exchange between alveoli and blood
After alveoli are ventilated diffusion occurs across the alveolar membrane; O2 into pulmonary blood, CO2 in opposite direction. This is helped by the large SA and thin memb in the lungs.
What factors does diffusion resistance depend on?
Nature of barrier: permeability, size
Nature of gas
What happens to oxygen once it is moved from alveoli to blood?
pO2 in alveoli > in capillaries, so oxygen diffuses into the blood.
Then oxygen combines with haemoglobin to form oxy-haemoglobin that is transported within the bloodstream.
Describe CO2 transport across alveoli, and in what form CO2 is carried around the body as
pCO2 in capillaries > in alveoli, thus CO2 diffuses into the alveoli where it is exhaled.
90% is carried as bicarbonate ions in the plasma.
What are levels of pO2 and pCO2 in alveoli?
pO2 13.3 kPa, pCO2 5.3 kPa
What factors affect the rate of diffusion through respiratory membranes?
Thickness of membrane
Surface area
Diffusion coefficient of gas
What conditions might impair diffusion of oxygen?
Fibrosis - thickened surface for exchange so slower,
Pulmonary oedema - fluid in interstitial space increases diffusion distance
Emphysema - decreased SA
Explain the difference between the conductive zone and the respiratory zone
Conductive zone: from the mouth to the terminal bronchioles (aka anatomical dead space)
Respiratory zone: respiratory bronchioles, alveolar ducts and sacs
What is ventilation-perfusion matching?
V/Q ratio (alveolar ventilation/ lung perfusion) ideally 1.
Blood pressure in lungs quite low and they don’t perfuse easily so there will be areas of high Q and low Q.
Changing the V/Q ratio of lungs has effects on the concentrations of O2 and CO2 in the alveoli and blood during respiration.
