The-microanatomy of the alveolar duct system

Observations made on wet and dry slices of inflated human lungs taken at necropsy have been used to give a more complete account of the alveolar duct system, the basic respiratory structure. This includes consideration of the central spiral alveolar duct fibre, which is thought to consist of elastic and collagen, the spiral arrangement of alveoli and the special nature of the terminal alveolus, the interdigitation of alveoli from adjacent alveolar ducts and the arrangement of pulmonary arterioles. This suggests that the alveolar duct system is specifically designed so that changes in volume are not accompanied by changes in alveolar surface area. Of the small holes seen in the cut surface of the fixed inflated lung (Fig. 1) the vast majority are found to be alveolar ducts, separated by trans-lucent brownish alveolar tissue. The structure of the alveolar ducts, which, with the alveoli open-ing off them, make up the basic respiratory unit of the lung, has been considered by many authors. The diagrams of Miller (1947) represent an olde