Actions of the Digestive System

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Actions of the digestive system Fig. 15-2, Vander’s Human Physiology, 11th edition (2008) • secretion • digestion • absorption • motility Internal vs. external environment Overview of digestive tract function Figure 21.6, p. 667 Components of the digestive system GI TRACT ACCESSORY GLANDS mouth and pharynx salivary glands esophagus stomach small intestine duodenum jejunum liver ileum gallbladder pancreas large intestine rectum Figure 21.1a, p. 656 Structure of the stomach Figure 21.1c, p. 656 Structure of the small intestine Figure 21.1d, p. 656 Digestive secretions entering the duodenum pancreas: • digestive enzymes • bicarbonate liver: • bile salts (solubilize fats) • bicarbonate (gallbladder stores bile) Duodenal papilla: outlet for pancreatic duct and common bile duct Figure 4.109, Gray’s Anatomy for Students Anatomy of the bile ducts cystic bile duct hepatic bile duct common bile duct Adapted from Figure 4.111, Gray’s Anatomy for Students Anatomy of the large intestine From Figure 21.21, p. 686 Structures to identify on the large model of the digestive tract: hard palate common bile duct soft palate small intestine tongue duodenum salivary glands duodenal papilla epiglottis jejunum/ileum esophagus large intestine stomach cecum greater curvature ileocecal valve lesser curvature appendix fundus ascending colon body transverse colon antrum (pylorus) descending colon pyloric sphincter (pyloric valve) sigmoid colon pancreas rectum pancreatic duct anal canal liver external anal sphincter Blood flow to the liver Structures to identify on the model of the liver with gallbladder and duodenum duodenum jejunum gallbladder bile ducts hepatic bile duct cystic bile duct common bile duct pancreas pancreatic duct hepatic portal vein common hepatic artery Structures to identify on the model of the pancreas with spleen and part of the duodenum duodenum plicae circulares duodenal papilla jejunum pancreas pancreatic duct common bile duct hepatic portal vein common hepatic artery Clinical example: bariatric surgery bariatric surgery à weight loss surgery two most common procedures • sleeve gastrectomy • Roux-en-Y gastric bypass treatment for type 2 diabetes mellitus: remission rates following surgery Sleeve gastrectomy “restrictive”—smaller stomach reduces food intake ↓ ghrelin secretion ghrelinàhormone secreted by stomach cells that increases appetite Roux-en-Y gastric bypass (RYGB) Configuration of GI tract after RYGB Endocrine changes after RYGB àreduction or removal of stomach decreases ghrelin secretion àbypass of stomach and upper intestine changes secretion of an unknown hormone àfaster delivery of chyme to distal small intestine increases secretion of GLP-1 and PYY GLP-1 is an incretin • secreted by endocrine cells in small intestine epithelium • secretion stimulated by glucose, fats in small intestine • increase glucose-dependent insulin secretion • incretin-based drugs used in the treatment of type 2 diabetes mellitus • GLP-1 also has effects on CNS control of appetite Secretion and Action of Incretins incretins: GIP, GLP-1 *look for a web page about bariatric surgery by next week.

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BASIC SCIENCE identify the rectosigmoid junction with conﬁdence at operation. The anatomy of the rectum The rectosigmoid junction usually lies approximately 6 cm below the level of the sacral promontory. Approached from the distal and anal canal end, however, as when performing a rigid or ﬂexible sigmoid- oscopy, the rectosigmoid junction is seen to be 14e18 cm from Vishy Mahadevan the anal verge, and 18 cm is usually taken as the measurement for audit purposes. The rectum in the adult measures 10e14 cm in length. Abstract Diseases of the rectum and anal canal, both benign and malignant, Relationship of the peritoneum to the rectum account for a very large part of colorectal surgical practice in the UK. Unlike the transverse colon and sigmoid colon, the rectum lacks This article emphasizes the surgically-relevant aspects of the anatomy a mesentery (Figure 1). The posterior aspect of the rectum is thus of the rectum and anal canal. entirely free of a peritoneal covering. In this respect the rectum resembles the ascending and descending segments of the colon, Keywords Anal cushions; inferior hypogastric plexus; internal and and all of these segments may be therefore be spoken of as external anal sphincters; lymphatic drainage of rectum and anal canal; retroperitoneal. The precise relationship of the peritoneum to the mesorectum; perineum; rectal blood supply rectum is as follows: the upper third of the rectum is covered by peritoneum on its anterior and lateral surfaces; the middle third of the rectum is covered by peritoneum only on its anterior 1 The rectum is the direct continuation of the sigmoid colon and surface while the lower third of the rectum is below the level of commences in front of the body of the third sacral vertebra.
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