Consequences of the bidirectional flow of air within lung structures: dead space definition, composition of ambient air, exhaled air and alveolar air. The Law of Dalton: partial pressure of each component in a gas mixture. Dynamics of respiration: laminar and turbulent flow. The respiratory muscles. Effect of air motion and lung volume on the airway size. Measurement of lung volumes: spirometers of Benedict, Tissot and body plethysmograph. Flowmeter. Divisions of total lung capacity. Metabolism: basal and energetic. Methods of measurement of metabolism. The oxygen debt. Statics of the respiratory system. Pressure-volume diagram of living lung: area-surface tension diagram. Pulmonary hysteresis. Intrathoracic and intrapleuric pressure. Pressure-volume diagram of the combined system lungs-chest wall: the relaxation curve. Maximal expiratory and inspiratory pressures. Graphic and arithmetic representation of the respiratory work: optimal breathing frequency. Diffusion of gases: derivation of the first Fick’s law. Resistances to diffusion: gas-gas, through tissues from air to hemoglobin, limited velocity to hemoglobin oxygenation and backpressure. Breathing at high altitude: maximal altitude attainable by humans. Equation of alveolar air. Diving in apnea and with a respirator. Pneumothorax. Ventilation-perfusion ratio. Gas transport in blood: oxygen and carbon dioxide. Acid-base equilibrium.