Menstruation, periodic discharge from the vagina of blood, secretions, and disintegrating mucous membrane that had lined the uterus. 1  The biological significance of the process in humans can best be explained by reference to the reproductive function in other mammals.
Chlamydial (kla-MID-ee-al) infections are caused by three species of microorganisms. Chlamydia trachomatis can cause eye or lung infections and can also infect the urinary and genital areas of both men and women. Chlamydia pneumoniae causes infections of the respiratory tract, and Chlamydia psittaci causes an illness, known as parrot fever, that is similar to the flu.
1 Chlamydia is one of the most common STDs. 2  Chlamydia is caused by a type of bacteria called Chlamydia trachomatis. 3  It can infect the urethra, rectum and eyes in men and women, as well as the cervix in women. 4  Chlamydia is spread via vaginal, anal or oral sex.