The cervical canal. False-colour scanning electron micrograph of the epithelium of the cervical canal through which the uterus is linked to the vagina. This epithelium is composed of columnar cells which may be ciliated or, as shown here, secretory (purple and orange). The apical surface of the secretory cells is covered by microvilli and yellow droplets of mucus. Mucus is secreted in response to estrogen hormones and it is maximal at the time of ovulation. During the menstrual cycle the mucus is highly viscous but at mid-cycle it becomes more hydrated in order to ease sperm migration. Magnification: x2470 at 6x7cm size. Magnification: x3940 at 4x5 inch size.