Liver and Small Bowel Anatomy PDF

Chapter 16 The Digestive System Sherwood Modified, Edited and Presented by Marios Z Panos Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning  DIGESTIVE SYSTEM OUTLINE - Liver - Structure - Functions - Small Intestine - Sec...

Chapter 16 The Digestive System Sherwood Modified, Edited and Presented by Marios Z Panos Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning  DIGESTIVE SYSTEM OUTLINE - Liver - Structure - Functions - Small Intestine - Secretion - Digestion  Liver Largest and most important metabolic organ in the body Body’s major biochemical factory Importance to digestive system – secretion of bile salts Chapter 16 The Digestive System Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning  Liver Functions not related to digestion – Metabolic processing of the major categories of nutrients – Detoxifying or degrading body wastes and hormones, drugs, and other foreign compounds – Synthesizes plasma proteins – Stores glycogen, fats, iron, copper, and many vitamins – Activates vitamin D – Removes bacteria and worn-out red blood cells – Excretes cholesterol and bilirubin  Liver Bile – Actively secreted by liver and actively diverted to gallbladder between meals – Stored and concentrated in gallbladder – Consists of Bile salts Cholesterol Lecithin Bilirubin – After meal, bile enters duodenum Bile salts – Derivatives of cholesterol – Convert large fat globules into a liquid emulsion – After participation in fat digestion and absorption, most are reabsorbed into the blood  Types of Cells in the Liver Hepatocytes (liver cells) - Specialisation – highly developed organelles Kupffer cells - macrophages - immunity - remove bacteria and worn out red cells Liver Blood Flow  Liver Blood Flow Portal Vein -- > 2/3 liver blood flow Hepatic Artery -- > 1/3 liver blood flow (branch of Coeliac axis) Hepatic Artery - > 3/4 liver Oxygen supply Portal Vein drains: Stomach, Small, Large Intestine, Pancreas & Spleen  Liver Blood Flow Facilitates liver function by enabling flow of blood along rows of hepatocytes Blood from the portal vein (digestive tract) enters liver - > passes along rows of hepatocytes - > central vein - > hepatic vein (systemic circulation) - > to IVC -> R Atrium FIRST PASS METABOLISM  Liver histology- Hepatic sinusoids Hepatocyte plates: 2 layers with bile canaliculus in-between HEPATIC LOBULE Portal triad = Portal tract Liver Sinusoids –Kupffer Cells- Canaliculi Liver Blood Flow Peribiliary glands: serous/mucinous secreting - > regulate enzyme secretion DIGESTIVE SYSTEM - SMALL INTESTINE OUTLINE - Small Intestine - Motility - Secretion - Digestion  Small Intestine Site where most digestion and absorption take place Three segments – Duodenum – Jejunum – Ileum Motility includes – Segmentation – Migrating Motility Complex (MMC)  Small intestine Terminal Ileum  Small bowel - enteroclysis (small bowel contrast enema ) Normal small bowel Chapter 16 The Digestive System Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning  Small Intestine Segmentation – Primary method of motility in small intestine – Consists of ring-like contractions along length of small intestine – Within seconds, contracted segments relax and previously relaxed areas contract – Action mixes chyme throughout small intestine lumen  Segmentation Chapter 16 The Digestive System Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning  Small Intestine Segmentation – Initiated by pacemaker cells in small intestine which produce basic electrical rhythm (BER) – Circular smooth muscle responsiveness is influenced by distension of intestine, gastrin, and extrinsic nerve activity –Functions Mixing chyme with digestive juices secreted into small intestine lumen Exposing all chyme to absorptive surfaces of small intestine mucosa  Segmentation (contd.) Basic Electrical Rhythm (BER) Distension, gastrin, extrinsic n. activity - > influence excitability - > by shifting starting potential of BER away/closer to threshold Absent / slight between meals Vigorous directly after meals Duodenum + ileum start to segment simultaneously - Duodenum in response to local distension (chyme) - Ileum in response to Gastrin secreted by the stomach (even though ileum is empty) = Gastro-ileal reflex  Segmentation (contd.) Extrinsic n. modify strength of segmental contractions - Parasympathetic enhances segmentation - Sympathetic depresses segmental activity Rate of contractions - Duodenum 12 / min - Terminal ileum 9 / min Net result - > chyme moves along distally Small bowel transit time 3-5 hours* *time from entry into the duodenum to exit into the caecum  Small Intestine Migrating Motility Complex (MMC) – Sweeps small bowel clean between meals Active only during periods of fasting Repetitive pattern every 1.5 hours Phase I - Quiet 40-60 min Phase II - Some contractions, variable intervals Phase III - Intense peristaltic contractions from upper stomach to terminal ileum - > lasts 5-10 mins, pylorus relaxes  Motility (contd.) MMC activity Regulated by motilin – hormone secreted by endocrine cells of small intestinal mucosa Released in the unfed state Release inhibited by feeding Ileocaecal valve - sphincter Prevents bacterial contamination of small intestine by colonic bacteria Distension on ileal side - > relaxes Pressure on caecal side - > contracts more strongly Short bowel syndrome - importance of ileo-caecal valve “brake” e.g after resection of length of ileum  Small Intestine Secretion – Juice secreted by small intestine does not contain any digestive enzymes – acqueous salt + mucus solution – Stimulus = presence of chyme in lumen -> secretion watery solution, aids absorption – Synthesized enzymes act within brush-border membrane of epithelial cells Enteropeptidase (enterokinase) Disaccharidases Aminopeptidases  Small Intestine Digestion – Pancreatic enzymes continue carbohydrate and protein digestion within the lumen – Fat is digested entirely within small intestine lumen by pancreatic lipase - Fats - > monoglycerides and FFAs - Proteins - > small peptides + some amino acids - CHOs - > disaccharides, α-limit dextrins, some monosaccharides NB. Pancreatic enzymes act in the lumen, small intestinal enzymes act at the brush border Digestion-Absorption – large surface area Length of small bowel, circular folds, villi, microvilli  Digestion - Brush border Brush-border enzymes (microvilli) complete digestion of carbohydrates and protein Membrane-bound enzymes - Enteropeptidase – activates trypsinogen - Disaccharidases - maltase, sucrase-isomaltase, lactase Maltase - > Maltose (product of amylases) -> glucose Sucrase-isomaltase - > -> glucose - > sucrose - > α-limit dextrins - > glucose Lactase - > lactose - > galactose Starch digestion - 2 products: maltose and α-limit dextrins Dextrins: low-molecular-weight carbohydrates produced by the hydrolysis of starch and glycogen. Dextrins are mixtures of polymers of D-glucose units linked by α-(1→4) or α-(1→6) glycosydic bonds Digestion-Absorption – large surface area Length of small bowel, circular folds, villi, microvilli  IMAGING OF THE SMALL BOWEL Barium contrast studies Magnetic Resonance Enterography Wireless Capsule Endoscopy  Small bowel – jejunal folds “stack of coins” appearance Arrow - superficial ulceration e.g. in Crohn’s disease or NSAID mucosal damage MRI ENTEROGRAPHY MRI : Magnetic Resonance Imaging Wireless Capsule Endoscopy Wireless capsule endoscopy Wireless capsule endoscopy  DIGESTIVE SYSTEM In this lecture we covered - Liver - Structure - Function - Small Intestine - Secretion - Digestion Chapter 16 The Digestive System Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning  DIGESTIVE SYSTEM Next Lecture - Small Intestine - Absorption - CHO, Proteins, Fat - Vitamins - Iron, Calcium - G.I. Hormones - Review  Chapter 16 The Digestive System Sherwood Modified, Edited and Presented by Marios Z Panos Thank you for your attention ! Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning