Which system is affected by issues like unusual bleeding and STDs?

The reproductive system is directly affected by issues such as unusual bleeding and sexually transmitted diseases (STDs) because these conditions are specifically associated with the reproductive organs and their functions. Unusual bleeding can be a symptom of various reproductive health issues, including menstrual irregularities, fibroids, or more serious conditions like endometriosis or cancers of the reproductive organs. STDs, on the other hand, are infections that can significantly impact reproductive health, leading to consequences such as pelvic inflammatory disease, infertility, or complications during pregnancy.

The other systems listed are not typically associated with these specific issues. The digestive system primarily deals with food processing and absorption, the urinary system relates to the elimination of waste and regulation of fluids, and the respiratory system is concerned with gas exchange and breathing. Each of these can have their own set of health issues, but they do not encompass the reproductive-related complications that are mentioned in the question.