Unit 3 digestive system Chapter 25 Anatomy Physiology II Unit 3 digestive system Chapter 25

Digestive System

Digestion: breakdown into small and simple. Prepare for absorption. Objective #1 Digestion: breakdown into small and simple. Prepare for absorption. Mechanical Digestion: physical breakdown by mashing, grinding, churning, etc. Chemical Digestion: chemical (molecular) breakdown by using enzymes, water, acid, etc. Absorption: transport and movement of food molecules from gastrointestinal (GI) tract into blood or lymph.

5 functions of digestive system are: Objective #2 5 functions of digestive system are: Ingestion; Propulsion; Digestion ; Absorption; Defecation Parts: a. Alimentary Canal: mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, anus b. Accessory organs: teeth, tongue, salivary glands, liver, pancreas, gall bladder. c. Peritoneum: lines abdominopelvic cavity- visceral and parietal layers. Mesenteries (two layers of Peritoneum) bind organs to walls and to each other and make a path for blood vessels and nerves.

Parts of the mouth and pharynx: Saliva: moistens food, has Amylase that begins starch digestion in mouth. Cleans mouth by digesting food particles. Salivary glands are: a. Parotid: between skin and masseter muscle, near ear. b. Submandibular: medial to mandible body. c. Sublingual: anterior to submandibular, under tongue. Parts of the mouth and pharynx: Teeth: for chewing (mastication) Cheeks and tongue: to form the bolus (balling up food), tasting food Pharynx: four-way crossing for air and food Uvula (part of soft palate): closes the nasopharynx Epiglotis: covers entrance to larynx during swallowing Esophagus: propels bolus to stomach Tonsils: lymphoid organs to expose immune system to various microbes present in food

Disaccharides (maltose) Objective #4 Enzyme Source Substrates Products Optimum pH Salivary Amylase Salivary Glands Starches Disaccharides (maltose) 6.35- 6.8 Objective 3 Teeth are for biting and mastication. Teeth types: Incisors: chisel-shaped, for cutting and biting. Canines (eyeteeth): fang-like, conical, for tearing, piercing, and shredding. Premolars Broad crown, round tips, for grinding and crushing d. Molars

Enamel: Calcium and salts, hardest substance in body. Dentin: under enamel, bonelike, bulk of tooth. Pulp cavity: surrounded by dentin. Contains connective tissue, blood vessels, and nerve fibers.

Objective 5 Peristalsis: wave-like contractions for propelling chyme distally. Segmentation: Ring-like contractions for mixing chyme. Objective 6 The five layers of the digestive tract from inside out are: Mucosa, Submucosa, Muscularis externa, Serosa, Mesentery

Objective 8, & 11 Gastroesophageal (Cardiac) Sphincter allows the bolus from esophagus to enter stomach and prevents backflow into esophagus. In stomach a lot of mechanical digestion and mixing takes place and chemical breakdown of proteins begin here. Stomach juices contain pepsinogen (from chief cells), hydrochloric acid (from parietal cells), and mucus (from mucus cells). Pepsinogen is activated into pepsin which catalyses breakdown of proteins to polypeptides. It requires a low pH of 1-2 which is provided by HCl. Mucus secretions prevent self-digestion. Gastrin: Hormone from stomach mucosa, released in response to protein or alcohol. It increases HCl and pepsinogen secretion, causes contraction of cardiac sphincter, and increases peristalsis. Pyloric Sphincter controls movement of chyme into small intestine. Substances absorbed in stomach are: H2O, ions, alcohol, and drugs into blood stream.

The three parts of the small intestine are: duodenum, jejunum, and ileum Acid chyme entering duodenum is quickly neutralized by sodium bicarbonate in pancreatic juices and bile from liver helps emulsify fat (makes fat soluble by breaking it up into small droplets). Secretions of small intestine, pancreatic juice, and bile work on the chyme and digest it to an absorbable form. Absorption of AA’s, ions, water, water soluble vitamins, and monosaccharides is into blood stream. Lipids are broken up into fatty acids and glycerol. Lipids and Lipid Soluble vitamins are absorbed into Lymph by way of lacteals.

Disaccharides (maltose) Carbohydrates Enzyme Source Substrates Products Optimum pH Salivary Amylase Salivary glands Starches Disaccharides (maltose) 6.35- 6.8 Pancreatic Amylase Pancreas Polysach. 7.6 Maltase Small intestine Maltose Glucose Lipids Lipase Pancreas Fats F.A.+ glycerol 7.6 Proteins Pepsin Stomach Proteins Polypeptides 1-2 Trypsin Pancreas Dipeptides 7.6 Polypeptidase Dipep. + AA’s Dipeptidase Small Intest. AA’s

Objective #12 Sugars, AA’s, water, and water soluble substances are absorbed into the blood stream. This blood loaded with nutrients flows into the Hepatic Portal Vein. This vein takes its blood through liver tissue where some nutrients are taken out, bacteria are filtered, and adjustments are made before this blood flow into the Inferior Vena Cava by way of the Hepatic Veins. Lipids including fatty acids, and glycerol, and fat soluble vitamins are absorbed into the lymph through the lacteals. Fatty acids and glycerol combined with bile salts to form tiny droplets called micelles. The fats in micelles are then absorbed into the intestinal cells. Inside the cells, fatty acids and glycerol combine to form triglycerides. Triglycerides, cholesterol, and phospholipids combine to form Chylomicron droplets. Chylomicrons leave these cells, but they are too large to be absorbed into the blood capillaries and instead enter lacteals.

To facilitate absorption, small intestine has villi and microvilli that increase surface area for absorption. Absorption is by diffusion, facilitated diffusion, and active transport. Large molecules such as proteins are too large to be absorbed before being digested. Newborns and infants, having not fully developed systems, can absorb these macromolecules by endocytosis and exocytosis. This is how IgA (antibodies) in mother’s milk enters baby’s blood stream for protection. This can also be the reason for early allergies caused by proteins and other substances in formulas and other foods that are not natural to the newborn.

Objective 9, 10, & 14

Sphincter of Oddi (Hepatopancreatic Sphincter): valve that controls entry of bile and pancreatic juices into duodenum. Pancreas: secretes insulin and digestive enzymes Liver: stores sugar, builds many proteins and secretes bile a. makes bile which helps with fat digestion and absorption. b. Neutralizes toxins and poisons, and makes nitrogen waste, urea c. Storage place for vitamins, glycogen, and poisons such as DDT d. Converts glucose to glycogen for storage e. Can make glucose from non-sugar substances such as fats and proteins. f. Determines body’s nutrient needs. All nutrients absorbed in intestine pass through liver by way of Hepatic Portal Vein.

Secretin: From duodenum mucosa in response to acidic chyme from stomach. It causes a rise in HCO3- levels in pancreatic juices, and a rise in bile and intestinal secretions. It inhibits gastric activities. Cholecystokinin: From duodenum mucosa in response to fatty chyme from stomach. Stimulates release of pancreatic juices, and contraction of gall bladder causing release of bile. Inhibits release of gastric juices and GI mobility.

Objective #13 Large Intestine (Colon): It has a length of about 5 feet and a diameter of 2.5 inches. Bacteria in colon produce vitamin K. A lot of water and minerals are absorbed and waste materials are expelled. Ileocecal Valve: Guards the entrance from small intestine and controls flow from small to large intestine. Cecum: dead-end pouch. Appendix: Small structure on cecum that functions as a lymphoid organ. Ascending Transverse, Descending, and Sigmoid Colon, are sections of colon through which feces are propelled. Rectum (Anal Canal): Stores and eliminates feces with anus as the voluntary sphincter valve to outside. Haustra: bulges Taenia Coli: Long muscles running the length of colon.

Objective # 15 (on handout) Unit 3: Digestion Objective # 15 (on handout) Peptic ulcer: Raw, open sore in stomach or duodenum mucousa due to excessive gastric juice. Perforates and sometimes bleeds. Constipation: caused by slow peristalsis in colon. Diarrhea: loose stool, high mobility of GI tract Peritonitis: inflammation of peritoneum due to ulceration and rupture of appendix. Appendicitis: inflammation of appendix due to obstructions or kinking. If ruptured can cause peritonitis. Flatulence: results form excessive bacterial action on foods in colon producing H2, CO2, and CH4 gases. flatus = gas Diverticulitis: inflammation of a weakened haustra (colon pouches). May perforate and cause peritonitis. Gall stones: crystallization of cholesterol in bile. Hepatitis: inflammation of liver due to infection, chemicals, or drugs. Cirrhosis: destruction of liver tissue caused by alcohol Jaundice: liver is unable to remove bile pigments (bilirubin) which build up in tissues and in blood. Cystic Fibrosis: genetic disorder in which thick mucus builds up in the ducts of pancreas and prevents release of pancreatic juices into the duodenum. This may prevent digestion of fats and other substances. Emesis: vomiting from stomach or upper duodenum. Results in acid/base imbalance and fluid loss Bulimia: bench-purge behavior--overeating followed by self-induced vomiting. It results in loss of tooth enamel and damage to esophagus and stomach and causes electrolyte imbalances that can result in abnormal heart activity. Anorexia: lack of appetite due to apprehensiveness and tension. Lifestyle, perspective on one’s career and social status, and overall state of mind are major factors for anorexia.