Lungs

lung The respiratory organ of air-breathing vertebrates. A pair of lungs is situated in the thorax, within the ribcage. Each consists essentially of a thin moist membrane that is folded to increase its surface area. Exchange of oxygen and carbon dioxide takes place between blood capillaries on one side of the membrane and air on the other. The lung is supplied with air through a bronchus. The lungs are covered by a thin tissue layer called the pleura. The same kind of thin tissue lines the inside of the chest cavity -- also called pleura. A thin layer of fluid acts as a lubricant allowing the lungs to slip smoothly as they expand and contract with each breath.

Pneumocystis pneumonia

Pneumocystis pneumonia (PCP) is an infection caused by Pneumocystis jiroveci, a microscopic fungus that lives in the lungs of many people. PCP is a rare disease in healthy people. However, it can cause a serious pneumonia in infants who have AIDS, cancer, or other conditions that weaken the immune system.
PCP is the most common pediatric illness associated with AIDS, especially in babies younger than 6 months old, and its prevention is very important in AIDS care since it is an important cause of mortality in people with AIDS.