The Respiratory System

The function of the respiratory system is to move air in and out of the lungs in a process known as ventilation, respiration, or breathing. The exchange of oxygen and carbon dioxide in the lungs is called external respiration. The same exchange within the hemoglobin of red blood cells is internal respiration. The larynx contains the vocal cords, which stretch between the thyroid and cricoids cartilages. The muscles of the lower vocal cords stretch and relax to produce different sounds which allow you to sing. The lungs contain connective tissue, the bronchial tree, nerves, lymphatic vessels and blood vessels. The left lung consist of two lobes, upper and lower and the right lung consist of three lobes, upper, middle, and lower. Within each lung are the primary, secondary, and tertiary branches of the bronchi, the bronchioles, and the alveoli.  The lungs are covered by, and the chest cavity is line with the pleura. The outer membrane is the parietal pleura and the inner membrane is the visceral pleura.

During inspiration, the diaphragm contracts and the intercostals muscles raise the ribs, increasing the space in the thoracic cavity. This decreases the pressure within the cavity so that the air outside the body passively flows into the thoracic cavity. During expiration, the diaphragm relaxes, pushing up into the thoracic cavity, and the intercostals muscles lower the rib, forcing the air flow out of the body.  Breathing is controlled by the respiratory center of the brain, located in the pons and medulla oblongate. 

Thoracic- chest cavity