after a partial gastrectomy or pyloroplasty, clinical manifestations that include increased pulse, hypotension, weakness, pallor, sweating, and dizziness are a result of: a. hemorrhage postoperatively in which a large volume of blood is lost, causing hypotension with compensatory tachycardia. b. an anaphylactic reaction in which chemical mediators, such as histamine, prostaglandins, and leukotrienes, relax vascular smooth muscles causing shock. c. a rapid gastric emptying and creation of a high osmotic gradient in the small intestine that causes a sudden shift of fluid from the blood vessels to the intestinal lume