Alveolar cell. Black and white electron micrograph (TEM) of a section through a type II alveolar cell. This cell is found in the alveoli (air sacs) of the lungs. At centre is the cell nucleus, which contains the cell's genetic information. In the cell's cytoplasm are mitochondria, which provide the cell with energy, and lamellar bodies (mainly clear), which contain surfactant. The lamellar bodies are secreted onto the epithelial cell surface of the alveoli where the surfactant decreases the surface tension, allowing the alveoli to inflate during inspiration and preventing their collapse during expiration. Alveolar capillaries containing red blood cells and platelets surround the alveolar cell. Magnification: x4000 when printed at 10 centimetres wide.