The two right chambers are responsible for pulmonary circulation while the two left chambers are responsible for systemic circulation. The tricuspid valve prevents blood from returning to the right atrium, the bicuspid prevents blood from returning to the left atrium, the pulmonary semi lunar valve prevents blood from returning to the right ventricle, and the aortic semi lunar prevents blood from returning to the left ventricle. Because the gases to be exchanged need to dissolve in water in order to cross the respiratory surface B. To maintain concentration differences so diffusion of oxygen and carbon dioxide can occur. The medulla sends impulses to the muscles of the diaphragm and rib cage causing them to contract. These contractions cause an increase in the size of the thoracic cavity which creates a vacuum.
Air enters the air passages trying to fill the vacuum, thereby, pulling air into the lungs.
To exhale, the medulla stops sending impulses to the muscles mentioned above causing the thoracic cavity to collapse on the lungs pushing air out of the lungs. The peripheral chemoreceptors and the oxygen receptors monitoring carbonic acid and oxygen levels respectively. They send messages to the medulla causing it to send out impulses faster to increase the breathing rate. The pulmonary artery brings to poorly oxygenated blood which is also high in carbon dioxide to the lungs for gas exchange. The pulmonary vein send the freshly oxygenated blood back to the heart so it may be sent through systemic circulation to all parts of the body.