Exchange of gases in lungs
Alveoli
minute air sacs at the end of bronchioles
site of gas exchange
alveolar membrane= gas exchange surface
between the alveoli there are collagen and elastic fibres which allow the alveoli to stretch
expand during inhalation
constrict during exhalation
lined with epithelium
Easily damaged
stored within the organism to protect them
Role of Alveoli
±300 million alveoli in each human lung
surface area is ±70m2
around each alveolus there is a network of pulmonary capillaries
capillary wall is only 1 cell thick
RBC are flattened against the thin capillary wall in order to squeeze through the narrow capillaries
Diffusion of gases between the alveoli and the blood will be very rapid because:
red blood cells are slowed as they pass through pulmonary capillaries, allowing more time for diffusion
the distance between the alveolar air and red blood cells is reduced as the red blood cells are flattened against the capillary walls
the walls of both alveoli and capillaries are very thin and therefore the distance over which diffusion takes place is very short
alveoli and pulmonary capillaries have a very large total surface area
breathing movements constantly ventilate the lungs. and the action of the heart constantly circulates blood around the alveoli. Together. these ensure that a steep concentration gradient of the gases to be exchanged is maintained
blood flow through the pulmonary capillaries maintains a concentration gradient.
