Final answer:
A nurse observing tarry stools should conclude the patient is experiencing upper gastrointestinal bleeding, commonly caused by conditions such as gastritis or peptic ulcer disease.
Step-by-step explanation:
If a nurse identifies that a patient has tarry stools, the problem that should be concluded is upper gastrointestinal bleeding. Tarry stools, also known as melena, are caused by the presence of digested blood in the stool, which typically comes from a bleeding source in the upper gastrointestinal tract. Conditions like gastritis, peptic ulcer disease, or a hiatal hernia can lead to such bleeding. Looking at the major accessory organs of digestion, the pancreas and the liver (which includes the gallbladder and bile ducts) do not typically cause melena unless there is associated upper GI tract involvement.
For a patient who has been suffering from chronic, watery diarrhea for 2 months, a blood test might reveal a variety of issues including but not limited to inflammatory markers, signs of infection, anemia or malabsorption which could indicate conditions like inflammatory bowel disease or a gastrointestinal infection. Issues with the pancreas, for example, acute pancreatitis, can lead to digestive problems since it wouldn't be delivering the necessary enzymes to the small intestine. This failure can cause diarrhea due to mal-digestion, but it is not directly associated with tarry stools unless there is concurrent GI bleeding.