In Some Species, Air Travels Between Adjacent Regions of Lung Through Collateral Pathways

The lungs of mammalian species differ in the degree to which they are subdivided by connective tissue into secondary lobules. In the lungs of pigs and cattle, there is complete separation of lobules, and in dogs and cats there is no separation. In horses and sheep there is partial separation. The connective tissue septa prevent collateral ventilation (i.e., movement of air between adjacent lobules) in cattle and pigs. Collateral ventilation is extensive in dogs and intermediate in horses. Collateral ven­tilation provides air to alveoli when their main parent bron­chus is obstructed. The differences in collateral ventilation mean that gas exchange abnormalities that follow airway obstruc­tion are more serious in pigs and cattle than in dogs.