Caption

Large intestine lining. Coloured scanning electron micrograph (SEM) of a freeze-fractured section of part of the large intestine (colon). The internal surface of this tube, where water is absorbed, is across top. The plane of the fracture (across bottom) passes down through the lining, revealing three distinct layers. An upper thin layer (across centre) is the columnar epithelium. The columnar nature of these cells is best seen at centre left. The next and largest layer is the tubular glands, the large cylindrical structures. Around five of these are seen. Their primary purpose is secreting a lubricating mucus. Supportive connective tissue is the layer across bottom. Magnification unknown.