. During inspiration, the volume of the lungs is actively increased by the action of the diaphragm. As the volume of the lungs increases, the pressure within the lungs falls about 1 mmHg below atmospheric pressure. Air rushes into the lungs due to this pressure difference. Bronchi, Bronchial Tree, and Lungs Larynx Primary bronchi Secondary bronchi Tertiary bronchi Bronchioles Cardiac notch Pulmonary artery Trachea Pulmonary vein Alveolar duct Alveoli This image is part of the Public Domain: https://upload.wikimedia.org/wikipedia/commons/d/db/Illu bronchi lungs.jpg Fig. 1: The bronchi, bronchial trees, and the lungs. (a) The diameter of the trachea (windpipe) is about 17 mm. What net force does the air experience during inhalation? F net = N L (b) The flow rate of air entering the lungs is about 1.1 What is the velocity of air moving S through the windpipe? Vwindpipe cm S (c) The trachea divides into the left and right bronchi. Each main bronchus then divides into lobar bronchi (three on the right and two on the left, each supplying one lung lobe). The lobar bronchi branch into segmental bronchi, and the branching proceeds twenty more times after this! Let's call (c) The trachea divides into the left and right bronchi. Each main bronchus then divides into lobar bronchi (three on the right and two on the left, each supplying one lung lobe). The lobar bronchi branch into segmental bronchi, and the branching proceeds twenty more times after this! Let's call each branch a generation z and assume that the number of branches within a given generation is determined by 2². The chart below gives three different generations, the diameter of an average bronchus or bronchiole in that generation, and the air speed through that region. Does the respiratory system obey the equation of continuity, Q=2² Av = constant? Show this by calculating the flow rate in each branch and verifying that nearly same. Branch Z Diameter (mm) Air speed (cm/s) Segmental Bronchus 4 4.5 392 Terminal Bronchiole 16 0.60 5.40 Alveolar Duct 22 0.41 0.18 Fig. 2: Segmental bronchus has 4 branches, a diameter of 4.5 mm, and an air speed of 392 cm/s. The terminal bronciole has 16 branches, each with a diameter of 0.60 mm, and an average air speed of 5.40 cm/s. The alveolar duct has 22 branches, each with a diameter of 0.41 mm, and an average air speed of 0.18 cm/s. Segmental Bronchus m³ m³ S QTerminal Bronchus QAlveolar Duct = = m³ S S