A 43-year-old male client has presented to the emergency dep…

A 43-year-old male client has presented to the emergency department with complaints of vomiting. The client also states that the emesis has often contained frank blood in the hours prior to admission. His vital signs are stable with temperature 98.3°F (36.8°C), pulse 88, BP 140/87, and respiratory rate 18. He is diagnosed as having acute gastritis.  Which of the following is most likely contributing to this diagnosis?