Facts : 1 Respiration Gas exchange The respiratory system s alveoli are the sites of gas exchange with blood<br />Facts : 2 In humans, the trachea divides into the two main bronchi that enter the roots of the lungs<br />Facts : 3 The bronchi continue to divide within the lung, and after multiple divisions, give rise to bronchioles<br />Facts : 4 The bronchial tree continues branching until it reaches the level of terminal bronchioles, which lead to respiratory bronchioles and alveolar sacs<br />Facts : 5 Alveolar sacs, are made up of clusters of alveoli, like individual grapes within a bunch<br />Facts : 6 The individual alveoli are tightly wrapped in capillaries and it is here that gas exchange actually occurs<br />Facts : 7 Deoxygenated blood from the heart is pumped through the pulmonary artery to the lungs, where oxygen diffuses into blood and is exchanged for carbon dioxide in the hemoglobin of the erythrocytes<br />Facts : 8 The oxygen-rich blood returns to the heart via the pulmonary veins to be pumped back into systemic circulation<br />Facts : 9 Many other non-autonomic nervous and biochemical stimuli, including carbon dioxide and oxygen (acting on the respiratory centers), are also involved in the regulation process<br />Facts : 10 There is also a relationship noted between the pressures in the lung, in the alveoli, in the arteries and in the veins<br />Facts : 11 This is conceptualised into the lung being divided into three vertical regions called the zones of the lung
