To better understand bronchiolitis, it helps to understand the anatomy of the lungs.
Inside the chest, the windpipe, or trachea, divides into two smaller tubes: the right bronchus and the left bronchus. The right bronchus enters the right lung and the left bronchus enters the left lung. The right bronchus and left bronchus branch into smaller and smaller tubes.
The smallest tubes, called bronchioles, end in tiny air sacs, called alveoli. Blood flows very close to the walls of the alveoli. Oxygen and carbon dioxide pass between the air and the bloodstream through the wall of the alveoli.
- Domachowske JB, Rosenberg HF. Advances in the treatment and prevention of severe viral bronchiolitis. Pediatr Ann. 2005 Jan;34(1):35-41. 
- Flores G, Horwitz RI: Efficacy of beta2-agonists in bronchiolitis: a reappraisal and meta-analysis. Pediatrics 1997 Aug; 100(2 Pt 1): 233-9. 
- Kellner JD, Ohlsson A, Gadomski AM, Wang EE: Efficacy of bronchodilator therapy in bronchiolitis. A meta-analysis. Arch Pediatr Adolesc Med 1996 Nov; 150(11): 1166-72. 
- Lozano JM. Bronchiolitis. Clin Evid. 2004 Dec;(12):370-84. 
- Shay DK, Holman RC, Newman RD, et al: Bronchiolitis-associated hospitalizations among US children, 1980-1996. JAMA 1999 Oct 20; 282(15): 1440-6.