Pulmonary Circulation

of these cells to neutralize pathogens or particles as well as to recruit both neutrophils and other types of mononuclear cells.

The alveoli contain about ten percent lymphocytes, including helper T cells, cytotoxic T cells, and NK cells. About 5 percent are B lymphocytes. They get activated by the dendritic cells in the lungs. Neutrophils get activated in bacterial infections and become the most active cells when the alveolar macrophages fail.

PULMONARY CIRCULATION

While ventilation is the movement of air into and outside of the lungs, perfusion is the flow of blood through the pulmonary vasculature. The ventilation and perfusion should be roughly equal and balanced in order to have adequate exchange of oxygen and carbon dioxide. When ventilation is not sufficient for a particular alveolus, blood is redirected to alveoli that are receiving enough ventilation. This happens by constricting flow in the arterioles away from the malfunctioning alveolus. Vasodilation happens in normal alveoli in order to have adequate perfusion to these alveoli.

The pulmonary circuit is the system of blood vessels that supply the lungs. This circuit starts at the right atrium and passes through the right ventricle. It is a single vessel that leaves the right ventricle as the pulmonary trunk. The pulmonary semilunar valve will prevent backflow of blood during diastole into the right ventricle. Shortly after the blood leaves the pulmonary trunk it bifurcates into the left and right pulmonary artery. These branch several times to end in multiple pulmonary capillaries. After exchanging oxygen and carbon dioxide, the blood vessels enlarge to end within the pulmonary veins. There are four pulmonary veins, two on the right and two on the left.