The document summarizes the mechanics of respiration. It describes the respiratory cycle as consisting of inspiration, expiration, and pause. Inspiration is an active process involving contraction of the diaphragm and intercostal muscles to increase the vertical, anteroposterior, and transverse diameters of the thoracic cage. Expiration can be passive due to lung elasticity and muscle relaxation, or active using abdominal and other muscles. The document also outlines changes in lung position and circulation during the respiratory cycle.