Final answer:
A speculum is the medical instrument used to hold open the walls of the vagina for examination or procedures such as Pap smears.
Step-by-step explanation:
The instrument used to hold open the wall of the vagina in a medical setting, such as an emergency room or during a gynecological exam, is called a speculum. When a female patient experiences vaginal bleeding and requires examination, healthcare providers utilize a speculum to gain visual access to the vagina and cervix, allowing for a proper medical assessment. This tool is essential in diagnosing the cause of the bleeding and for procedures like Pap smears where access to the cervix is necessary.