Salivary gland. Coloured scanning electron micrograph (SEM) of a transverse freeze-fractured section through an acinus (large brown circle) in a salivary gland. The rest of the image comprises several other acini surrounding this acinus. Acini are the smallest unit of a gland. They comprise a circular cluster of cells that secrete fluid into a central duct (hole, centre) that leads to larger ducts. These acini are secreting granules (lumps, brown) of mucus, the natural lubricating fluid found in saliva. Each acini is circled by a layer of connective tissue (pink). Saliva is secreted into the mouth to aid digestion and the process of swallowing. Magnification: x1000 at 6x7cm size.