The major passages and structures of the lower respiratory tract
include the windpipe (trachea) and within the lungs, the bronchi,
bronchioles, and alveoli. Deep in the lungs, each bronchus divides
into secondary and tertiary bronchi, which continue to branch to
smaller airways called the bronchioles. The bronchioles end in air
sacs called the alveoli. Alveoli are bunched together into clusters
to form alveolar sacs. Gas exchange occurs on the surface of each
alveolus by a network of capillaries carrying blood that has come
through veins from other parts of the body.
Review Date: 11/14/2010
Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of
General Medicine, Department of Medicine, University of Washington
School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical
Director, A.D.A.M., Inc.
A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org)
