Physiology of Digestive System 2024-2025 PDF

Physiology of Digestive System Assoc. Prof. Dr. Radiah Abdul Ghani Human Structure & Function 1  Learning Outcomes At the end of this session, you must be able to explain: The basic function of digestive system. The moti...

Physiology of Digestive System Assoc. Prof. Dr. Radiah Abdul Ghani Human Structure & Function 1  Learning Outcomes At the end of this session, you must be able to explain: The basic function of digestive system. The motility and regulation of the system via CNS. The secretion activity in digestive system. The regulation of GIT function and its integrative functions with other systems in human body. Relate the physiological function of digestive system and Islamic view. 2  Gastrointestinal Components GENERAL ORGANIZATION Gastrointestinal (GI) tract consists of 4 anatomical divisions: esophagus, stomach, small intestine, and colon or large intestine. Pancreas and liver play critical roles in digestion and absorption. 3 Overview of the Digestive Tract 4  Overview of the Digestive Tract Accessory Structures: – Teeth – Tongue – Salivary glands – Liver (gall bladder) – pancreas 5  Overview of the Digestive Tract The Digestive System – Consists of the muscular digestive tract assisted by various accessory organs – Digestive system functions include: Digestion Absorption Motility Secretion 6 1 2 3 4 7  Station 1: Oral Cavity Teeth – Participate in mastication of food – Anchored to bone by periodontal ligament – Dentin forms basic shape Enamel covers crown Cementum covers root – 20 deciduous teeth (“baby teeth”) – 32 secondary teeth (“adult teeth”) 8 9 Muscles of Mastication Bruxism? 10  Motility in the mouth Mastication -- Chewing is important : -The food is lubricated by being mixed with saliva -The food is exposed to salivary amylase enzyme, which begins digestion of starch -It breaks the food into small pieces. Swallowing is under the control of extrinsic nerves and the swallowing center (brain stem). 11 Swallowing – simple but significant is the process in the human or animal body that makes something pass from the mouth, to the pharynx, and into the esophagus, while shutting the epiglottis. If the process fails and the material goes through the treachea, then choking or pulmonary aspiration can occur. In the human body the automatic temporary closing of the epiglottis is controlled by the swallowing reflex. 12 13  Swallowing Disorder - Dysphagia Difficulty controlling food in the mouth, inability to control food or saliva in the mouth, difficulty initiating a swallow, coughing, choking, frequent pneumonia. often describes as “becoming stuck” or “held up” before it either passes into the stomach or is regurgitated. 14  The Esophagus Anatomy of the Esophagus – Muscular tube about 25 cm long – Lined by stratified squamous epithelium – Posterior to trachea – Penetrates diaphragm at esophageal hiatus – Possess upper and lower esophageal sphincters – Sphincter—A circular band of muscle that can pinch close a muscular tube 15  Motility of esophagus Movement of Digestive Materials – Involuntary control of smooth muscle of muscularis externa – Two kinds of movement Peristalsis propels material along the tract Segmentation churns material in the small intestine or stomach. Mixing of those two. 16 17  Contraction of circular muscles behind food mass Longitudinal Contraction - Smooth muscle -moving food Circular muscle and muscle From To from mouth to mouth anus cells anus connected by -mechanically gap mixing food to Contraction of longitudinal junctions. muscles ahead of food mass maximize its - Pacemaker. Contraction exposure to - Unique cause enzymes and it can absorptive Contraction contract epithelium. without a Contraction of circular muscle layer forces food mass forward significant change in membrane potential. 18  Station 2: The Stomach Functions of the Stomach – Temporary storage of ingested food – Mechanical breakdown of food Forms chyme, a liquid suspension – Breakage of chemical bonds in food by action of acid and enzymes 19  Functions of Stomach 1) Storage of large quantities of food until the food can be processed. 2) Mixing of food with gastric secretions until it forms a semifluid mixture called chyme. 3) Slow emptying the chyme from the stomach into small intestine. Appear 5 times in Abu Daud Translation 20  Motility in Stomach Peristaltic waves – autorythamic. Autorythamic persist even if stomach is empty – growling and rumbling – hunger. Mixing foods – segmentation. In Islam, it is highly recommended to fill the stomach 1/3 only – why? Function of spinchter – avoid heartburn. 21  Secretion in stomach In a typical day, 9 litres of fluid pass through the lumen of GIT. 2 litre – diet + 7 litre – body water secreted along with mucus and enzymes. (gastric secretion + pancreatic secretion + Intestinal secretion). 22  Secretion of Digestive Enzymes Exocrine gland – salivary and pancreas. Epithelial cells in the mucosa of stomach and small intestine. Zymogen – inactivated form. 23 Gastric Secretion 24  Components of gastric juice Secretory volume: 1~2.5 L/d Character: acidic（pH 0.9-1.5） Component: water inorganic salt: (HCl、 HCO3- 、 Na+、 K+, etc.) organics: (pepsinogen, mucoprotein, intrinsic factor) 25  Function of hydrochloric acid ① Activating pepsinogen ②Supplying acid environment for pepsin decomposing protein； ③ Food protein denaturation and easy decomposition； ④ Kill bacteria in food into the stomach； ⑤ Promoting pancreatic, small intestinal and bile secretion； ⑥ Helping Fe2+、Ca2+ secretion. 26  Regulation of gastric acid secretion Acid secretion is controlled by gastrin, parasympathetic nerves, and histamine. Histamine is released from enterochromaffin-like cells (ECL) and potentiates the stimulatory effects of parasympathetic nerves and gastrin. Acid secretion is inhibited by somatostatin released from stomach cells and by the presence of digested food in the duodenum. Acid secretion is stimulated by signals from the mouth (cephalic phase), stomach (gastric phase) and intestine (intestinal phase). 27 28 29 Helicobacter pylori bacteria on the surface of a human gastric epithelial cell. H. pylori is a Gram-negative spiral-shaped bacterium found in the mucus lining of the stomach. It causes gastritis, and is also the most common cause of stomach ulcers. It may also be a cause or co-factor for gastric cancer as its presence increases the risk of developing stomach tumours. 30  Regulation of stomach emptying - Rate is regulated by signals from both stomach and duodenum. Gastric factors: 1) Effect of gastric food volume on rate of emptying 2) Hormone Gastrin effect 31 32  Station 3: The Small Intestine Regions of the Small Intestine – Duodenum – Jejunum – Ileum – Ileocaecal valve (a sphincter) marks junction with large intestine 34 Secretions of the Small Intestine Intestinal Secretions – Intestinal glands secrete Intestinal juice –Moistens chyme –Buffers stomach acid –Dissolves digestive enzymes –Dissolves products of digestion Mucus Hormones 35 Digestion in small intestines – Most enzymatic digestion and absorption occurs in the small intestine – Digestive enzymes and buffers are released by: Pancreas Liver Gall bladder 36  The Pancreas Anatomy of the Pancreas – Pancreatic duct enters duodenum – Duct delivers pancreatic juice – Duct branches repeatedly – Fine branches end in pancreatic acini – Endocrine cells are found among the acini  The Pancreas Secretions of the Pancreas – Endocrine secretion (hormones) Insulin Glucagon – Exocrine secretion (digestive) Water Ions Enzymes – Carbohydrases – Lipases – Proteases – Nucleases 38  Liver and gall bladder associate with intestine 39 Figure 16-14(b)  The Liver The liver is the largest gland in the body and has four lobes. The liver is composed of liver lobules, which are made of plates of liver cells (hepatocytes). The digestive function of the liver is to produce bile, which is a fat emulsifier. Bile is a yellow-green, alkaline solution containing bile salts, bile pigments (primarily bilirubin), cholesterol, neutral fats, phospholipids, and a variety of electrolytes. The gallbladder stores and concentrates bile that is not needed immediately for digestion. Bile does not usually enter the small intestine until the gallbladder contracts when stimulated by cholecystokinin. 40 Regulation of bile secretion 41 Bile acids and phospholipids are amphipathic molecules, which means that they have both water-soluble and water-insoluble portions. This enables them to dissolve fats in the watery mixture of the small intestine and to form aggregates of lipids called micelles. Both functions greatly facilitate the digestion and absorption of fats. 42  Station 4:The Large Intestine Functions of the Large Intestine – Reabsorbs water and compacts feces – Absorbs vitamins made by bacteria – Stores feces before defecation – Consists of three parts Cecum:Attaches to vermiform appendix Colon Rectum:Terminates in anal canal 43 The Large Intestine 44 45 46 Digestion & Absorption 47 48 49 50 51 1) Digestion of carbohydrate 52  Absorption of carbohydrate The Digestion and Absorption of Carbohydrates Figure 16-18(a) (2 of 2) 53  Ingested carbohydrates in the form of starch are converted to glucose, galactose, or fructose by the combined action of luminal amylase and enzymes on the surface of enterocytes. Carbohydrate metabolites are absorbed by Na- dependent secondary active transport or facilitated diffusion across the luminal surface of enterocytes and by facilitated diffusion across the basolateral surface. Carbohydrates are absorbed as monosaccharides. 54  Glucose intestinal absorption Enterocytes absorb glucose and galactose through an Na-dependent secondary active transport process, while 55 fructose is absorbed by facilitated transport (GLUT) 56 57  Lactose Intolerance Is a milk sugar. Disscharide compose of glucose and galactose. Ingested lactose must be digested before absorbed, a task accomplish by intestinal brush border enzyme lactase. Decrease in lactase activity – intolerance. What happened if person with lactose intolerance drinks/eats dairy product? 58 59  2) Protein digestion and absorption Protein digestion begins in the stomach with the action of pepsin and is completed by proteases (activated by enterokinase) secreted by the pancreas , as well as by those on the surface or within the cytoplasm of enterocytes. Proteins are reduced to small peptides and amino acids prior to absorption. Small peptides and individual amino acids are absorbed by Na-dependent secondary active transport and by facilitated diffusion across the basolateral surface. 60  The Digestion and Absorption of Proteins 61  The Digestion and Absorption of Proteins 62 63 Glucose, galactose and amino acids intestinal absorption Lumen Intestinal Epithelia Blood Glucose Glucose Or Carrier Carrier Galactose Na+ K+ Pump Carrier Na+ Amino Acids Amino Acids Carrier Absorption of Carbohydrates and Amino Acids in the Small Intestine 64  3) Lipid Digestion and Absorption Water insolubility of lipids presents special problems for digestion and absorption, which are overcome by emulsification and formation of micelles. Pancreatic enzymes are primarily responsible for digesting ingested lipids to cholesterol, fatty acids, and monoglycerides. Enterocytes resynthesize triglycerides and phospholipids from absorbed fatty acids and monoglycerides. Within enterocytes, triglycerides, phospholipids, and cholesterol are packaged into chylomicra or very low density lipoproteins (VLDL) and secreted by exocytosis across the basolateral membrane. Chylomicra and VLDL enter the blood through lymphatic vessels draining the small intestine because they are too large to cross the capillary endothelium. 65 Lipid Digestion and Absorption 66 67 68 69 70 71  Special System: Infant System - Born → 6 months old ? - The best food that is easy to digest is breast milk. - As mentioned in Al-Quran. - Link between hyper immunoreaction and digestive system? (at birth, intestinal villi very small and crypts are well expose to laminar content) 72  Special System : Aging Age-Related Changes in the Digestive System – Thinner, more fragile epithelium – Reduced epithelial stem cell division – Weaker peristaltic contraction Reduced smooth muscle tone 73  Flatulence (wind) Wind is also known as flatulence, burping, belching, passing wind, breaking wind, or farting. The wind may emerge from the mouth or the bottom. It is usually made up of carbon dioxide, oxygen, nitrogen, hydrogen and methane. 74  Causes of flatulence Humans cannot digest certain carbohydrates in the small intestine because we may not have - or may not have enough of - the enzymes that can aid their digestion. The food then moves in an undigested state from the small intestine to the large intestine. It is here that the bacteria go to work, producing the gases hydrogen, carbon dioxide and methane, which are then expelled from the body. 75  Not everybody will suffer from wind after eating the same foods. We also swallow a certain amount of air when we eat and drink. This contributes to the production of wind. We usually release swallowed air by burping it out. Whatever isn't released by burping goes into the small or large intestine, where it is eventually released as flatulence. 76  Digestive System from Islamic Perspective http://repository.uinsuska.ac.id/70274/1/Rejuvenating%20Islamic%20Thoug ht%20and%20Civilization.pdf  Rasulullah SAW mentioned: “If you must eat make sure you fill one third of your stomach with food, one third with water and leave one third for air (leave it empty).”(Narrated by Al-Tirmizī) Thank You 79