Pathogenesis of Emphysema.

protease-antiprotease imbalance hypothesis

α1-Antitrypsin, normally present in serum, tissue fluids, and macrophages, is a major inhibitor of proteases (particularly elastase) secreted by neutrophils during inflammation

Most common is the normal (M) allele and the corresponding phenotype

Pts homozygous for the Z allele have markedly decreased serum levels of α1-antitrypsin

In smokers, neutrophils and macrophages accumulate in alveoli due to direct chemoattractant effects of nicotine

Accumulated neutrophils are activated and release their granules, rich in a variety of cellular proteases (neutrophil elastase, proteinase and metalloproteinases

macrophage elastase is not inhibited by α1-antitrypsin and, indeed, can proteolytically digest this antiprotease

oxidant-antioxidant imbalance hypothesis

reactive oxygen species contained in smoke

Oxygen species released by the inflammatory cells

Morphology of lungs in emphysema:

pale, voluminous lungs that often obscure the heart, esp with panacinar emphysema

Less dramatic appearance in centriacinar type

M/E shows thinning and destruction of alveolar walls

adjacent alveoli become confluent, creating large airspaces

With the loss of elastic tissue in the surrounding alveolar septa, there is reduced radial traction on the small airways. As a result, they tend to collapse during expiration-an important cause of chronic airflow obstruction.