L11 Diffusion: how gas gets across the blood-gas interface Flashcards
Where are alveoli found?
scattered amongst walls of respiratory bronchioles, forming alveolar ducts and alveolar sacs
What type of epithelium lines alveoli?
Type 1 and Type II alveolar epithelium.
Type I= squamous on basement membrane, allowing passage of gas
Type II= cuboidal and proliferate into Type I&II, producing surfactant from cytoplasmic granules
what is the role of macrophages in alveoli
removing surfactant. Found in inter alveolar space and intravascularly
What is the role of the inter alveolar septa
separate adjacent alveoli, made from collagen + elastic fibres + BV
What constitutes the blood air barrier???
from lumen…
alveolar fluid > alveolar epithelial cells (mostly I) > basement membrane (+/- thin interstitium) > capillary endothelium > capillary endothelial wall
What is a gas partial pressure??
The pressure exerted by a particular gas in a mixture, dependant on it’s proportion contributing to the mixture
what is the partial pressure of O2 at 29.8% of atmospheric pressure?
PO2= 0.209 x 760= 159.5 mmHg
Does respiration change partial pressures n the lungs?
yeah
What factors decrease the PO2 in the lungs??
Pp of water, PP of stale air
P02 drops as the O2 enters circulation in exchange for CO2, meaning PCO2 rises
Why does O2 diffuse from alveoli into blood?!
Gases diffuse down PP gradients. O2 is higher in lungs than blood. CO2 is higher in blood than lungs
Which factors alter the rate of diffusion of gases?
rate of diffusion is proportional to PP gradient across barrier, SA, diffusion constant of the gas and is inversely proportional to thickness it has to travel
What diffuses more rapidly, CO2 or O2 ?
CO2 because it is more soluble
what types of lung pathology would thicken the inter alveolar septum to decrease the rate of diffusion
pulmonary oedema,
fibrosis,
pneumonia
slow blood flow
explain the diffusion reserve
gas transfer takes 1/3 the time that it takes for blood to travel past
if inc, reduced transit time so diffusion reserve is utilised.
what would happen if BF is so fast that the diffusion reserve is exhausted?
hyperaemia without hypercapnia
