Majority of absorption happens here. Divided into three sections: Duodenum, Jejunum, and ileum. Inner mucosal layer, submucosal layer, muscular layer, outer serosal layer. Relative thickness of the layers differs in each segment of intestine. Parasympathetic stimulation involved in small intestinal motility, secretions, and blood flow. Sympathetic stimulation decreases blood flow, little effect on motility.