Describe the process of gas exchange in the lungs, including the section of the ciculatory system that pertains to respiration, starting with the nose and mouth.
Your diaphragm moves down when inhaling and creates a partial vacuum in the lungs. Air is therefore forced into the nasal cavity or mouth and travels down the trachea into the bronchus, which splits into the left and right lung. Once inside the lung, air moves into smaller and smaller tissues until it comes to the smallest, the aveoli. Arterial and venous tissues meet at the aveoli; here is where the diffusion of gasses occurs. Oxygen from the air moves from the aveoli into the pulmonary capillaries, while at the same time carbon dioxide, the result of metabolic processes in the body, moves from the pulmonary capillaries into the aveoli. The reason this exchange of gasses occurs is due to the partial pressure gradients of CO2 and O2 in the pulmonary capillary; higher concentrations of either gas moves to where there's a lower concentration of that gas. The oxygenated blood in the lungs then moves to heart, where it is circulated throughout the rest of the body. See graphics at the link: