Normal salivary gland. Coloured scanning electron micrograph (SEM) of the lumen (interior) of a healthy parotid gland, showing the epithelial cells that line it. The parotid glands are the largest of the salivary glands. They produce enzymes and proteins and facilitate mastication and swallowing and to begin the digestion of starches. The lumen is a central opening where the saliva is deposited after being produced by the secretory cells. Magnification: x1500, when printed 15 centimetres wide.