What is the difference between a pulmonary acinus and a secondary pulmonary lobule?
The acinus (Latin for “berry”) is a structural unit of the lung distal to a terminal bronchiole, supplied by first-order respiratory bronchioles, which contains alveolar ducts and alveoli. It is 0.6 to 1 cm in size and is the largest unit in which all airways participate in gas exchange.
The secondary pulmonary lobule contains up to 25 acini, is 1 to 2.5 cm in size, is polyhedral in shape, and is the smallest unit of the lung that is surrounded by connective tissue septa. Its centrilobular, or core, structures include bronchioles, pulmonary arterioles, and lymphatic vessels, whereas the peripheral interlobular septa contain pulmonary veins and lymphatic vessels.