WEBVTT 1 00:00:01.828 --> 00:00:07.940 In the course of pulmonary respiration, the air in the lungs must constantly be renewed. 2 00:00:07.941 --> 00:00:11.440 This is what is called pulmonary ventilation. 3 00:00:11.441 --> 00:00:14.862 But how is it that air enters and leaves the lungs? 4 00:00:14.863 --> 00:00:18.127 This is done thanks to the movements of the thoracic cage 5 00:00:18.128 --> 00:00:22.856 which includes the ribs and the sternum, the intercostal muscles 6 00:00:22.857 --> 00:00:25.860 and a large muscle called the diaphragm. 7 00:00:27.350 --> 00:00:31.946 The lungs are fixed to the interior of the thoracic cage by the pleura. 8 00:00:33.358 --> 00:00:38.190 During inspiration, the intercostal muscles and the diaphragm contract 9 00:00:38.191 --> 00:00:41.298 causing an enlargement of the thoracic cage. 10 00:00:41.299 --> 00:00:43.675 This results in the expansion of the lungs 11 00:00:43.676 --> 00:00:49.344 and, consequently, the flow of air into the lungs via the respiratory passages. 12 00:00:49.345 --> 00:00:55.535 in the reverse process, during expiration the intercostal muscles and the diaphragm relax 13 00:00:55.536 --> 00:00:58.879 and the volume of the thoracic cage decreases. 14 00:00:58.880 --> 00:01:04.913 This results in a deflation of the lungs and, consequently, the exiting of air from the lungs. 15 00:01:04.914 --> 00:01:10.921 To measure the amount of air entering and leaving the lungs we must use a spirometer. 16 00:01:10.922 --> 00:01:14.526 In an adult, one can thereby measure the entry and exiting 17 00:01:14.527 --> 00:01:19.776 of 0.5 liters of air under normal breathing conditions. 18 00:01:21.293 --> 00:01:23.225 As for forced respiration 19 00:01:23.226 --> 00:01:28.188 this involves the inspiration and expiration of the maximum amount of air. 20 00:01:28.189 --> 00:01:31.189 In this case, the spirometer measures more than 3 liters of air.