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.

Breathlessness

Breathlessness is a sensation of air hunger and an uncomfortable awareness of one's own breathing at rest or on exertion due to low oxygenation of tissues and the respiratory receptors in the human brain. Other similar terms are "dyspnea" and shortness of breath. Breathlessness and labored breathing are common in people with chronic diseases, such as advanced diabetes, cancer, cystic fibrosis, HIV-AIDS, heart disease, COPD, bronchitis, and many other conditions. It can appear on exertion, after meals, during night sleep, or at pregnancy.