In session two of this module you have learnt the administration of anesthetics in different methods, one method of induction and maintenance of general anesthesia is inhalation anesthesia which is administered via a patent airway and the air way may again be affected by the depressant effects of anesthesia and muscle relaxants. The respiratory system is essential for life. The goals of respiration are to provide oxygen to the tissues and to remove carbon dioxide. The respiratory system consists of mouth or nose, palate, nose, pharynx, larynx, trachea and bronchial and the lungs. Normal lung function requires a balanced interrelationship between the respiratory (the upper and lower airway), nervous, and cardiovascular systems. The brain receives and sends out stimuli to maintain a normal oxygen and carbon dioxide balance. The medulla and the pons are the major brain centers that affect respiration. The body's respiratory center in the medulla is normally stimulated by an increased concentration of carbon dioxide, and to a lesser extent, by decreased levels of oxygen in arterial blood. In this session you will learn the relevant anatomy and physiology of respiratory system which helps the anesthetist. This session will give you the necessary knowledge to anatomy and physiology of respiratory system and base line to skill and right attitude for assessment of anesthetized patient.