Uterus lining. Coloured scanning electron micro- graph (SEM) of the surface lining (endometrium, blue) of the uterus of a 35 year old woman. The lining is seen sectioned at right (green). This is during the early secretory phase of the menstrual cycle. Several rounded pits are seen, the openings of secretory glands in the uterine wall. The uterine lining builds up (proliferation) in the first 14 days of the cycle to prepare for pregnancy, an egg is released, and the lining becomes secretory to nourish the embryo. If no pregnancy occurs, it breaks down at menstruation after 28 days. Magnification: x60 at 6x7cm size.