Gonorrhea and chlamydia can only be transmitted from infected sites. Someone with urethral gonorrhea can infect a partner only from his penis, i.e. by insertive vaginal, anal or oral sex. Contact with his rectum, for example, is risk free. Similarly, if a woman has only cervical infection, she cannot transmit it by oral sex. And in your example, a rectally infected person is infectious only by contact with his rectum. The same is true for most STDs:  HPV and herpes are only spread from infected anatomical sites.

Syphilis and HIV are exceptions, in a sense. While the STDs just discussed generally do not spread through the body to sites other than those initially infected, syphilis and HIV are systemic, body-wide infections. No matter where HIV was acquired (e.g. by receptive anal sex), before long the virus is throughout the body, including sites not initially infected.

I hope these comments are helpful. Let me know if you have specific exposures, symptoms, or other aspects that concern you -- or if a partner does. Or anything else that might need clarification.

HHH, MD