GI Secretion, Digestion & Absorption

By completing this question set, you will be able to map each secretory product to its cell of origin, stimulus, and physiologic target within the gastric secretion system. You will trace the three phases of gastric acid secretion and explain why the intestinal phase is net inhibitory despite a brief stimulatory component. You will apply the complete GI hormone table — identifying source cell, stimulus, and key action for gastrin, secretin, CCK, GIP, motilin, VIP, somatostatin, ghrelin, and GLP-1 — and predict the consequences when tumors oversecrete each. You will explain the zymogen cascade in the pancreas, identify enterokinase as the initiating step, and explain why trypsinogen is activated in the duodenum rather than the pancreas. You will trace bile salt synthesis, enterohepatic recirculation, and the consequence of terminal ileal disease on bile acid pool and fat absorption. You will trace each macronutrient from ingestion to absorption, identifying the specific enzyme deficiencies and transporter failures that disrupt each step. You will apply the D-xylose test and malabsorption anatomical localization framework to identify the site of a malabsorptive lesion.