Development of the acinus in the human lung

Abstract

Development and remodeling of the acinus (those structures distal to the terminal bronchiolus) occurs during fetal life and childhood. Multiplication of the acinar air spaces and the structural changes they undergo are described and represented schematically by summarizing previous studies, particularly those of the last 2 decades. Most acinar airways are present before birth. Future respiratory bronchioli are represented by the 19 intrauterine week; alveolar ducts are present as saccules by the 28th week. Alveolar sacs and alveoli, as properly described, do not appear until after birth: alveoli increase in number particularly in the first 7 or so years of life, and in size with thoracic growth.