Anatomy & Physiology

Anatomy & Physiology Study Guide sympathetic innervation. The enterogastric, gastroenteric, and gastroileal reflexes coordinate movement from the stomach to the large intestine. • Intestinal hormones include secretin, cholecystokinin (CCK), gastric inhibitory peptide (GIP), vasoactive intestinal peptide (VIP), gastrin, and enterocrinin. The large intestine is divided into three parts with regional specialization: • The main functions of the large intestine are to reabsorb water and compact materials into feces, absorb vitamins produced by bacteria, and store fecal material before defecation. The large intestine consists of the cecum, colon, and rectum. • The cecum, attached to the appendix, collects and stores material from the ileum and starts the process of compaction. • Compared to the small intestine the colon has a larger diameter and a thinner wall. It bears haustra (pouches), taeniae coli (longitudinal bands of muscle), and sacs of fat (fatty appendices). • The four regions of the colon are the ascending colon, transverse colon, descending colon, and sigmoid colon. • The rectum ends at the anal canal, leading to the anus. • The microscopic anatomy of the colon shows the absence of villi, the presence of mucous cells, and deep intestinal glands. • The large intestine reabsorbs water and other substances (e.g., vitamins, urobilinogen, bile salts, and toxins), and bacteria are responsible for intestinal gas (flatus). • The movement of materials from the ileum to the cecum while you eat is caused by the gastroileal reflex. Mass movements of materials from the transverse colon to the rest of the remaining large intestine and then rectum is caused by the distension of the stomach and duodenum. The passage of fecal material into the anus is controlled by muscular sphincters. Distension of the rectal wall triggers the defecation reflex. Digestion is the mechanical and chemical alteration of food that allows the absorption and use of nutrients: • The digestive system begins by breaking down items physical structure and then disassembles the inherent molecules into smaller fragments by hydrolysis. • Complex carbohydrates are broken down into disaccharides and trisaccharides by salivary and pancreatic amylases. Then they are broken down further into monosaccharides by enzymes at the epithelial surface. By facilitated diffusion or cotransport the intestinal epithelium absorbs the monosaccharides. • Triglycerides are emulsified into lipid droplets that interact with bile salts to form micelles. The fatty acids and monoglycerides resulting from the action of pancreatic lipase diffuse from the micelles across the intestinal epithelium. Then the triglycerides are blended and

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