Smooth muscle in human uterus. Coloured Transmission Electron Micrograph (TEM) of smooth muscle in the outer wall of the human uterus (or womb). These cells make up the myometrium, part of the uterus which encloses the inner wall or endometrium. The cells are arranged in regular rows with enlarged & elongated nuclei (orange). The rest of the cell mainly contains a protein used to make the muscle contract. The shape of this muscle tissue reflects its function of making rhythmic contractions. These are regulated by female hormones which are present at particular stages of the menstrual cycle and pregnancy. Magnification: x1880 at 6x7cm size.