FILL IN EVALUATION FORM

GASEOUS EXCHANGE IN THE ALVEOLI

Scanning electron micrograph of alveoli Image reproduced from Respiratory System, BioNet Permission granted by Mike Mahon, University of Manchester

Gas exchange at the respiratory membrane is rapid due to several factors:

• The large surface area available for diffusion due to the high number of alveoli in the lungs. There are between 300-500 million alveoli with an internal surface area approximately equivalent to the size of a tennis court.

• The distance for diffusion is short as the respiratory membrane is thin

The membrane consists of an alveolar epithelial cell, a capillary endothelial cell and the fused basement membranes of the two cells Image reproduced from Mammalian Physiology lecture notes, Permission granted by Domnica Marghescu, Chief Technician, Physiology Department, McGill University

• The vast network of pulmonary capillaries that surrounds the alveoli

Image reproduced from Asthma, Pharma-CAL-ology Permission granted by Jeff Claudius, British Pharmacological Society

• The small diameter of the pulmonary capillaries means that the red blood cells have to "squeeze" through. The red blood cells therefore come into contact with the capillary wall so respiratory gases do not have to travel through a lot of plasma to reach them

Undergraduates click here for more information on partial pressures and gas exchange