external os

The external os is the opening of the cervix into the vagina. The cervix itself is the lowest part of the uterus, connecting it to the vagina and serving as a passageway between the two cavities. It is approximately 4 centimeters long and projects about 2 centimeters into the vaginal cavity.1

The endocervical canal runs through the cervix, transporting sperm into the uterus, allowing menstrual blood to exit, and producing mucus for lubrication. This mucus changes in consistency throughout the menstrual cycle, becoming more watery during ovulation to facilitate sperm passage and thicker at other times. Cervical mucus also contains lysozyme, an enzyme that helps protect against bacterial infections. The cervix is composed of dense, fibrous tissue with some muscle, making it more rigid than other parts of the uterus. During pregnancy, the cervix remains closed and sealed by a thick mucus plug to prevent infection.1