Medical Physiology Lectures (1+2+3) - Digestive System & Organs - PDF

Medical physiology Lectures (1 +2 +3) Physiology of digestion system , organs , it’s accessory organs & steps of digestion. Uruk university Health and medical technology college Anesthesia technology dept....

Medical physiology Lectures (1 +2 +3) Physiology of digestion system , organs , it’s accessory organs & steps of digestion. Uruk university Health and medical technology college Anesthesia technology dept. 1 DR.RAAD H.H.  Physiology of Digestion and absorption: Digestion is the process in which complex food substances (carbohydrates, proteins, and lipids) are degraded to products that can be absorbed into a blood stream. Absorption (or uptake) of these products occur when they are transported into absorptive cells in the small intestine. Several major organs contribute to the digestion and absorption of food substances. They include the mouth, Esophagus ,stomach, small intestine, Large Intestine , Rectum , liver, pancreas, and the gall bladder. Each organ is responsible for degrading and/or absorbing food substances. They contain enzymes and other substances that allow this process to occur. 2 Main organ associated with food metabolism ? Mouth: carbohydrates Stomach: Proteins, lipids, (histones) Small intestine: Proteins, lipids, and carbohydrate & nucleic acids. 3 Which organ contains Digestive Enzyme & Secretion substances? Mouth: amylase, saliva, and mucins Stomach: HCl , pepsinogen (pepsin), gastric lipases, and mucins. Liver: Bile Gall Bladder: Bile (concentrated) Pancreas: pancreatic juices (ex. Lipases, peptidases, (chymo) trypsinogen, amylase, and etc…) Small Intestine: Bile (from the gall bladder), pancreatic juices 4 Three types of secreted substances in digestive system : 1) Neurotransmitters: acetylcholine: (salivary, gastric & pancreatic secretions) 2) Biologic amines: histamine: (stimulates HCl secretion in stomach) 3) Hormones of whole GIT :- aldosterone: (electrolyte composition of saliva) gastrin: (stimulates HCl and pepsinogen), cholecystokinin: (gall bladder contraction, pancreatic secretions, & inhibits gastric motility) Secretin: (helps neutralize stomach acids by stimulating pancreatic secretion of NaHCO3) vasoactive intestinal peptide (VIP): (stimulates NaCl secretion in small intestine) 5 Overview of the Digestive System The Digestive System Consists of ; a)Long hollow muscular tube or canal or tract called gastrointestinal tract or (GIT): it is about 9 meters long b) Accessory glands: include: Salivary glands Liver and gall bladder Pancreas 6 Oral cavity (Mouth) : 1) In humans, digestion begins in the Mouth, also known as the "Buckle Cavity", where food is chewed. 2) Saliva is secreted in large amounts (1-1.5 liters/day) , by three pairs of Exocrine Salivary Glands : ( Parotid , Submandibular and Sublingual ) 3) Saliva cleans the oral cavity, moistens the food, and contains Digestive Enzymes such as salivary Amylase, which aids in chemical breakdown of Polysaccharides such as Starch into Disaccharides. It also contains mucus, a Glycoprotein that helps soften the food and form it into a bolus. 4) An additional enzyme, Lipase, hydrolyzes long-chain Triglycerides into partial Glycerides and Fatty Acids. 7 4 major (Main Functions) activities of Digestive Tract (GI tract): 1.Motility drive ingested food from mouth toward rectum 2.Secretion of juices e.g. saliva Aid in digestion and absorption 3.Digestion Food broken down into absorbable molecules 4.Absorption Nutrients, electrolytes, and water are absorbed or transported from lumen of GIT to blood stream 8 Motility Functions (Motor) of GIT parts : 1. Motility in the mouth Two types: a) Chewing or Mastication: It is reflex in nature b) Swallowing: Swallowing is the transport of food from mouth to stomach ; It consists of 3 phases or steps 1) Buccal Phase: food is pushed back into pharynx from mouth 2) Pharyngeal Phase: food pass through pharynx to esophagus 3) Esophageal Phase: food pass through esophagus to stomach by peristaltic movements. 9 10  Pharynx The pharynx is the part of the neck and throat situated immediately behind the mouth and nasal cavity, and superior to the digestive system and esophagus. It is also part of the respiratory system: Because both food and air pass through the pharynx. 11  2. Motility of Esophagus The esophagus is 25 cm ms tube which starts at the pharynx at the back of the mouth, passes through the thoracic diaphragm, and ends at the cardiac orifice of the stomach. At the top of the esophagus, is a flap of tissue called the Epiglottis that closes during swallowing to prevent food from entering the Trachea. It is guarded by 2 sphincters; a) Upper esophageal sphincter prevents air from entering the GIT b) Lower esophageal sphincter prevents gastric contents from re-entering the esophagus from the stomach Esophageal Peristalsis Motility sweeps down the esophagus 12 3. Motility of Stomach The stomach is a small, J - shaped pouch with walls made of thick, distensible muscles, which stores and helps break down food. The stomach consists of fundus, body & pylorus parts. Proximal area (fundus and body) has a thin wall & contracts weakly & infrequently → holds large volumes of food (to store food) because of receptive relaxation. Distal area (pylorus) has thick wall with strong & frequent peristaltic contractions that mix & drive emptying food into the duodenum. After being processed in the stomach, food is passed to the small intestine via the pyloric sphincter. 13 4. Motility of Small intestine Small intestine ; measuring about 22 feet (or 7 meters) ; It has three parts: the Duodenum, Jejunum, & Ileum. The majority of digestion & absorption occurs here after the milky Chyme enters the duodenum. Here Food is further mixed with three different liquids: a) Bile: which emulsifies fats to allow absorption. b) Pancreatic juice: made by the pancreas, which secretes enzymes such as Pancreatic Amylase, Pancreatic Lipase, & Trypsinogen (Inactive Form Of Protease). c) Intestinal juice :secreted by the intestinal glands in the small intestine. It contains enzymes such as Enteropeptidase, Erepsin, Trypsin, Chymotrypsin, Maltase, Lactase & Sucrase. Motility of Small intestine Motility of Small intestine : Two basic motility patterns exist segmentation & peristalsis 14  The site of absorption in the Small Intestine is : A small finger-like structures called Villi , and their epithelial cells is covered with numerous Microvillus to improve the absorption of nutrients by increasing the surface area of the intestine and enhancing the speed of absorption. 15 Large intestine In humans, the large intestine is roughly 1.5 meters long, with three parts: a) The cecum: at the junction with the small intestine. b) The colon : has 4 parts, the ascending colon, the transverse colon, the descending colon, & the sigmoid colon. c) The rectum : Food products that cannot pass through the villi, such as cellulose (dietary fiber), are mixed with other waste products from the body & become hard & concentrated feces. The feces is stored in the rectum & then eliminated from the body by the contraction & relaxation through the anus. The exit of this waste material (stool) is regulated by the anal sphincter. 16 5. Motility Types of Large intestine or colon: a) Segmentation in the large intestine causes the contents to be continuously mixed b) Mass movement drives the contents of one segment of the large intestine into the next downstream segment. c) Defecation involves involuntary reflexes and voluntary reflexes → evacuation of colonic content through anal canal. 17 Secretory Functions (Secretions) of GIT: The total volume of GIT secretions is about 6-8 L/day Secretions arise from specialized cells lining the GI tract, the pancreas, liver & gallbladder. GIT secretions functions to lubricate (water and mucus), protect (mucus), sterilize (HCl), neutralize (HCO3-), & digest (enzymes). 18 Secretions of Mouth (in GIT): Salivary Glands : Three pairs of glands. Parotid Sublingual Submandibular Functions of saliva 1.Lubricates, cleanse oral cavity 2.Dissolves chemicals 3.Suppresses bacterial growth 4.Digest starch by amylase salivary glands of the oral cavity. Human salivary mucins are glycoproteins secreted through epithelial cells of the salivary mucins is to provide a protective coating about the hard and soft tissues of the mouth. It also contains mucus, a Glycoprotein that helps soften the food and form it into a bolus. An additional enzyme , Lipase, hydrolyzes long-chain Triglycerides into partial Glycerides and Fatty Acids. 19 Nervous Regulation of salivary secretion 20 GIT secretions in Stomach Stomach: HCl, pepsinogen (pepsin), gastric lipases, and mucins. 21 Function of Gastric HCL : 1. Activates pepsinogen into pepsins to digest proteins. 2. Provides optimum for pH for action of pepsins 3. Denatures protein denaturation→help its digestion 4. Kills bacteria in food 5. Help Fe2+、Ca2+absorption. 6. Promotes pancreatic, small intestinal and bile secretion. 22 Function of Gastric mucous and intrinsic factor : Soluble and insoluble mucus are secreted by cells of the stomach. Soluble mucus mixes with the contents of the stomach and helps to lubricate chyme. Insoluble mucus forms a protective barrier against the high acidity of the stomach content. Intrinsic Factor : Help absorption of vitamin B12 23 Pancreatic Secretion: Pancreas has 2 functions: a) Endocrine functions: secretes insulin and glucagon hormones from islets of Langerhans for regulation of proper level of sugar in the blood. b) Exocrine function: secretion of pancreatic juice called enzymes that will exit the body through the digestive system ; and secreted in duodenum to assist in the digestion It has 2 components: aqueous and enzymatic components. Aqueous component (contains HCO3) is important for neutralizing stomach acid in the duodenum so pancreatic enzymes can function properly Enzymatic component is essential for the proper digestion and absorption of carbohydrates, fats, and proteins ; Pancreatic enzymes include trypsin, chemotrypsin, lipase, and amylase 24 Bile Bile is a greenish-yellow fluid released by the liver and stored in the gallbladder (a small organ) that aids in the digestion of fats. After being produced by cells in the liver, the bile travels down through the bile ducts which merge with the cystic duct to form the common bile duct. 25 liver 26 27 28 Absorption of Water 29 General Human digestion process: The whole digestive system is around 9 meters long. In a healthy human adult this process can take between 24 and 72 hours. Food digestion physiology varies between individuals and upon other factors such as the characteristics of the food and size of the meal. 30 Phases of gastric secretion: 1. Cephalic phase : This phase occurs before food enters the stomach and involves preparation of the body for eating and digestion. Sight and thought stimulate the cerebral cortex. Taste and smell stimulus is sent to the Hypothalamus And Medulla Oblongata. After this it is routed through the Vagus Nerve and release of acetylcholine. 2. Gastric phase : This phase takes 3 to 4 hours. It is stimulated by Distension of the stomach, presence of food in stomach and Decrease in pH. This activates the release of Acetylcholine, which stimulates the release of more Gastric Juices. As Protein enters the stomach, it binds to hydrogen ions, which Raises the pH of the stomach. 31 Protein digestion and absorption steps: 1) Protein digestion occurs in the stomach and duodenum in which 3 main enzymes: 2) Pepsin secreted by the stomach and Trypsin and Chymotrypsin secreted by the pancreas. 3) They break down food proteins into polypeptides that are then broken down into amino acids. 32 Fat digestionand absorption steps: 1) Lipid digestion is the enzymatic degradation of Dietary Fats Triacylglycerols (TAG’s) to monoacylglycerols and fatty acids. 2) Digestion of some fats can occur in the stomach where Gastric lipase breaks down some short chain lipids. 3) Then, the presence of fat in the small intestine produces hormones that stimulate the release of Pancreatic lipase from the Pancreas and bile from the Liver for breakdown of fats into fatty acids. 4) The bile emulsifies the fat into fat droplets (miscelles) while the action of Colipase and Pancreatic lipase act on the product to produce monoacylglycerol and 2 fatty acid chains. 5) Complete digestion of one molecule of fat (a triglyceride) results in 3 fatty acid molecules and one glycerol molecule. 6) Monoacylglycerol and long chain fatty acids are packaged into mixed Micelles ‫ ( مذيلة‬a combination of protein and cholesterol, bile salts, and fat soluble vitamins) and diffuse across the cellular membrane of the jejunum). 33 Carbohydrate digestion and absorption steps : 1) Carbohydrate digestion involves the enzymatic degradation of di-, tri, & polysaccharides to monosaccharides (glucose, fructose, & galactose). 2) Digestion begins in the mouth with salivary amylase 3) Polysaccharides are then further broken down by pancreatic amylase in the small intestine. 4) Final degradation occurs on the surface (brush border) of the absorptive cells in the jejunum. The brush border secretes amylo-1,6-glucosidase ,lactase, sucrase, & maltase 5) Once carbohydrates are broken down into monosaccharides, then absorbed into the intestinal cells by facilitated (membrane carrier) or active transport (membrane carrier, Na+, and ATP). 6) Fructose – by facilitative transport 7) Glucose and galactose – by active transport 8) Lactose intolerance: Caused by deficiency in lactase. Lactose is not hydrolyzed & accumulates in the intestine where it is fermented by intestinal microorganisms. 34 DNA & RNA digestion : DNA & RNA are broken down into Mononucleotides by : Nucleases, Deoxyribonuclease & Ribonuclease (DNase & RNase) from the pancreas. Occurs in the duodenum where diesterases hydrolyzes oligonucleotides to mononucleotides & phosphatase hydrolyzes mononucleotides to nucleotides. by Transport Passive diffusion. 35 Basic Concepts of Metabolism Metabolism consists of two types of reactions: Catabolism & Anabolism Catabolism: Process in which macromolecules are broken up to yield energy & simple organic compounds. Catabolic reactions mainly involve oxidative degradation. Anabolism: Process in which simple organic compounds & energy are used to form macromolecules. Anabolic reactions mainly involve reductive bio-syntheses. Free Energy that is utilized by an organism is in the form of free energy Carriers: ATP, NADH, NADPH, FADH2, & CoA. ATP: is the universal energy carrier. It’s synthesized during glucose metabolism & is used to maintain homeostasis (muscle contraction, active transport, anabolic processes, & signal transduction). 36  The Digestive Enzymes Enzyme Source Major actions Salivary amylase Salivary glands Starch to maltose Pepsin Stomach glands Proteins to polypeptides Renin Milk casein to milk curd Gastric lipase Fats to fatty acids and glycerol Pancreatic amylase Pancreas Starch to maltose Pancreatic lipase Fats to fatty acids and glycerol Trypsin Proteins to polypeptides Chymotrypsin Proteins to polypeptides Carboxypeptidase Polypeptides to amino acids Maltase Small intestine Maltose to glucose and glucose Sucrase Sucrose to glucose and fructose Lactase Lactose to glucose and galactose Aminopeptidase Polypeptides to amino acids 37 38