The Nikon MicroscopyU confocal microscopy image gallery was created with a PCM-2000 confocal scanning system interfaced to a Nikon Eclipse E600 upright microscope. Images were recorded in successive z-axis serial sections with C-Imaging Systems software with excitation illumination provided by an argon-ion and/or a helium-neon laser.

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View a higher magnification confocal sequence of human lung.

The lungs are the essential organs of mammalian respiration. Human lungs are paired in the chest with the heart situated in between. The external surface of a lung is smooth and conforms to the shape and size of the thoracic cavity or chest, bounded by the rib cage and below by the movable diaphragm. Inspiration or breathing air rich in oxygen is achieved by enlarging the chest by contracting the diaphragm, and thereby, reducing the external pressure on the lungs, letting them expand. This creates suction, taking in the fresh air. Expelling depleted air, rich in carbon dioxide, is achieved as the diaphragm returns to its resting place and the thoracic cavity is shortened, adding external pressure to the paired lungs and squeezing air out of them.

The respiratory system branches similarly to a tree, with about 17 levels of branching between the trachea and the bronchioles, and results in about 130,000 bronchioles in the average pair of human lungs. The inner portion of the lungs is where the actual gas exchange occurs between the blood and the external environment. Capillaries allow simple diffusion around the alveoli, small pocket cells, which increase the surface area of the lungs to about 50 to 100 square meters with a typical four-liter volume. Carbon dioxide-rich blood arriving by the pulmonary veins enters the alveolar capillaries and is released, leaving the hemoglobin in the red blood cells available to acquire oxygen from the fresh air taken in via the nose and mouth.

Lung diseases in humans include cancers caused by cigarette smoke and asbestos as well as asthma, bronchitis, pneumonia, and Legionnaire's disease. With cigarette smoke and asbestos, irritating particles of carcinogens such as tar or asbestos fibers lodge in the lung tissue and may result in the formation of cancer cells depending on other environmental and genetic factors. Lung transplants are performed on many afflicted patients and there is some promise for future lung tissue culture using human stem cells.