Primary gas transport mechanism

1. Again carbon dioxide is exchanges for oxygen which travels in exactly the opposite direction (durning inhalation)

2. Respiration

2.1. 1.Deoxygenated blood is carried from the heart(to the lungs) by the pulmonary arteries and arterioles

2.2. 2. Gas exchange take place rapidly at the level of the alveoli

2.3. Alveoli

2.3.1. Alveoli lie against the pulmonary capillary vessels, and as oxygen enters the alveoli from inhalation, it passes freely through tiny passages in the alveolar wall into these capillaries through process of diffusion

2.3.1.1. Carbon dioxide produced by the body's cells return to the lungs in the blood that circulates through and around the alveolar air space

2.3.1.1.1. Carbon dioxide diffuses back into the alveoli and travels back up the bronchial tree and out through the upper airway durning exhalation.

2.4. 3 Oxygenated blood is carried from the lungs (to the heart) by the pulmonary veins and venules.

2.4.1. Through this whole process of respiration the brain stem constantly senses the level of carbon dioxide which causes a healthy person to breath