Final answer:
The pathophysiologic mechanism that supports the client's clinical presentation is intestinal scar tissue buildup from a chronic condition.
Step-by-step explanation:
The pathophysiologic mechanism that supports the adolescent client's clinical presentation of severe, colicky abdominal pain, nausea, vomiting, and abdominal distention is intestinal scar tissue buildup from a chronic condition. Intestinal scar tissue, also known as intestinal adhesions, can develop as a result of various conditions such as previous abdominal surgeries, inflammatory bowel disease, or abdominal infections. These adhesions can cause partial or complete intestinal blockage, leading to the symptoms described in the question.