Uterus during secretory phase. Coloured Scanning Electron Micrograph (SEM) of the endometrium of the uterus in the secretory (luteal) phase. The endometrium is the inner lining of the uterus that undergoes changes during the menstrual cycle. Here after ovulation (egg release) the endometrium has formed a thick glandular layer. Its spongy appearance has dark glandular openings. During the secretory phase these glands secrete glycogen, lipids and sugars as nutrients for a possible fertilised egg. The secretory phase is triggered by hormones from the ovary, especially proges- terone. Magnification: x28 at 6x7cm size. x36 at 4x5"~LANDSCAPE"