Digestive System Student Guide PDF

Student Guide: Digestive System I. Introduction A. Six Functions of the Digestive System 1. Ingestion - aka eating 2. Propulsion - movement 3. Mechanical Digestion - chewing, peristalsis, and segmentation 4. Chemical/Enzymati...

Student Guide: Digestive System I. Introduction A. Six Functions of the Digestive System 1. Ingestion - aka eating 2. Propulsion - movement 3. Mechanical Digestion - chewing, peristalsis, and segmentation 4. Chemical/Enzymatic Digestion - a) Chemical - HCl, Bile (emulsifies fats) b) Enzymes - (1) Amylases - Turn carbohydrates into glucose (2) Lipases - Break fats into glycerol and fatty acids (3) Proteases - Break proteins into amino acids 5. Absorption - of nutrients 6. Defecation - elimination. a) Water b) Solid waste from food c) Dead cells (epithelial) from lining of gut, bacteria, digestive juices d) **No wastes from the blood!** That is the kidneys. B. Nutrients 1. Macronutrients a) Carbohydrates (1) Sugar (2) Starch (3) Fiber b) Proteins c) Lipids (“fat”) (1) Triglycerides (2) Cholesterol d) Water 2. Micronutrients a) Vitamins (1) Water Soluble - B Vitamins and Vitamin C (2) Fat Soluble - A, D, E, and K (a) We can store fat-soluble vitamins b) Minerals (1) E.g. Zinc C. Microbiome - a community of organisms within the body. AKA “Good Bacteria” 1. The “gut microbiome” is made of trillions of bacteria along the digestive tract. 2. Functions: a) Vitamin metabolism - Vitamins B and K b) Immune System Support c) Protection against other microorganisms  3. Antibiotics will also kill the microbiome. a) “Upset Stomach” is a side effect. b) Other “bad” bacteria can take their place. c) One reason to not take unnecessary antibiotics. II. Anatomy A. Abdominal Quadrants - Picture B. Abdominal Regions - Picture C. Alimentary Canal - The whole passage in which food passes from the mouth to the anus. 1. Oral Cavity a) Mastication - chewing b) Salivary Glands: (1) Parotid Glands (2) (2) Submandibular Glands (2) (3) Sublingual Glands (1 large, 8-30 small) (a) Saliva - moistening, cleansing, enzymes, defensins (antimicrobial/innate immunity.) c) Mucosal layer - stratified squamous epithelial tissue (1) Structure = Function (needs to be stratified) 2. Pharynx a) Bolus - a small mass of substance (food, a dose of medicine, etc) b) Soft Palate - keeps bolus from entering the nasopharynx c) Epiglottis - protects larynx. 3. Esophagus a) Upper Esophageal Sphincter b) Upper is skeletal muscle (Somatic) c) In between is the transition between skeletal and smooth muscle. d) Lower is smooth muscle (ANS) e) Lower Esophageal Sphincter/Cardiac Sphincter 4. Stomach a) Chyme - Gastric Juices and Partially Digested Food b) Fundus - part of a hollow organ that is furthest from the opening. c) Body d) Pylorus/Pyloric Region e) Rugae - anatomical folds that allow for stretching f) Pyloric Sphincter 5. Small Intestine (20-23 feet) a) Duodenum (1) 10 - 15” (or about 1 foot) (2) Mixing of chyme with digestive juices and enzymes (3) Entry of hepatopancreatic duct b) Jejunum (1) About 8 feet long (2) Absorption of nutrients into blood or lymphatics (fats)  c) Ileum (1) About 12 feet long (2) Absorption of digestive juices, vitamins (B12), and other products of digestion d) Villi and Microvilli (1) Finger-like projections. (2) Create a “brush border” and increase surface area for absorption (40 fold and 600 fold) 6. Large Intestine a) Cecum (1) A pouch at the beginning of the large intestine (2) Receives chyme via the ileocecal valve and sends it up the ascending colon b) Appendix (1) 3.5-5” (2) A reservoir of gut bacteria (3) Immunity Function c) Colon (1) 5 to 5.5 feet in length (2) 4 Sections (a) Ascending Colon → Hepatic Flexure (b) Transverse Colon → Splenic Flexure (c) Descending Colon → Sigmoid Flexure (d) Sigmoid Colon (3) Absorption of water (4) Haustra - small pouches that give the large intestine its segmented appearance (5) Mass Movements - general contractions that occur a few times per day to move fecal matter along the large intestine. d) Rectum (1) About 5” in length (2) Responsible for holding fecal matter for elimination e) Anal Canal (1) Internal/Interior Anal Sphincter - Smooth Muscle (ANS control) (2) External/Exterior Anal Sphincter - Skeletal Muscle (Somatic NS control) D. Accessory Organs 1. Teeth 2. Tongue 3. Salivary Glands 4. Liver a) Most of RUQ, some in LUQ  b) Right lobe (largest) and Left Lobe (smaller) c) 3-4 lbs, heaviest internal organ, largest glandular organ. d) Major metabolic organ (1) Processes nutrients (and medicines) absorbed by the intestines via the Hepatic Portal Vein. (2) Stores nutrients, glycogen e) Produces Bile (1) Bile - an emulsifier - breaks down fat to make it easier to digest. (2) Biological “Dawn Soap” 5. Gallbladder a) 3-4” by 1.5” b) Inferior to the liver c) Stores bile that it receives from the liver d) Cystic duct moves bile both ways 6. Pancreas a) ULQ, 5-6” b) Exocrine Organ (Releases outside of the blood) c) Releases enzymes to aid in the digestion of nutrients III. Peristalsis and Segmentation A. Smooth muscle contractions that move food through the alimentary canal. B. Table: Peristalsis vs Segmentation Peristalsis Segmentation (Mass Movements) Primary Esophagus Small Intestine Large Intestine Occurrence Speed Fast Slow Fast, but intermittent Direction One Way Both Ways One way Type of Smooth Circular Longitudinal *Type of Muscle peristalsis Contraction Function Move food quickly Food mixing Elimination of stool C. IV. The Peritoneum (Saran Wrap Demonstration) A. The Peritoneal Membrane 1. Lines the Peritoneum to create a physically separate space within the abdominal cavity.  a) Organs completely surrounded by peritoneal membrane are peritoneal organs. b) Organs with only one side lined by peritoneal membrane are considered “retroperitoneal organs.” 2. Becomes a Serous Membrane a) Is “Visceral” if it touches organs. b) Is “Parietal” if it touches a wall c) Peritoneal fluid (only 3mL at any given time) is between the two. 3. Becomes double-folded to form: a) Mesentery (Dorsal Side) - see below b) Omentum (Ventral Side) - see below B. Mesentery - a structurally supportive passageway formed by a fold of the parietal peritoneum that connects the posterior wall to the peritoneal organs and allows the entry and exit of blood vessels, lymphatics, and nerves. C. Omentum - a pouch formed by a fold of the visceral peritoneum that separates peritoneal organs from one another. 1. Greater Omentum - a pouch of visceral peritoneum that is between the stomach and the small intestines, and hangs over the small intestines 2. Lesser Omentum - a pouch of visceral peritoneum that is between the liver and the stomach. V. Blood Flow A. The Splanchnic Circulatory Route describes the flow of blood to the abdominal organs and back. B. The Hepatic Portal System (Portal Vein) supplies nutrient-rich blood from the intestinal wall to the liver before that blood re-enters the general circulation. 1. This is known as, “first pass” because all nutrients absorbed by the intestines will first be filtered through the liver via the hepatic portal vein before they are released into the blood. C. The Aorta supplies: 1. The Celiac Trunk a) Left Gastric Artery → stomach and more b) Common Hepatic Artery → liver c) Splenic Artery → spleen and more 2. Superior Mesenteric Artery → duodenum, small intestine, large intestine 3. Inferior Mesenteric Artery → colon D. The capillary beds of the small intestine wall will absorb nutrients into the blood and send them to the superior mesenteric vein. E. The Splenic Vein, Superior Mesenteric Vein, and Inferior Mesenteric Vein will merge into the Hepatic Portal Vein. F. The Hepatic Portal Vein carries nutrient-rich, deoxygenated blood to the liver for metabolization. G. The Hepatic Vein collects blood from the Hepatic Artery and the Hepatic Portal Vein and sends it to the IVC. VI. Biliary Flow A. Bile is produced by the liver and flows into ductules that merge into the Left and the Right Hepatic Ducts. B. The Left and Right Hepatic Ducts merge into the Common Hepatic Duct, which exits the liver. C. The Common Hepatic Duct can send blood to the Cystic Duct for storage in the gallbladder or directly to the Bile Duct. D. The Cystic Duct can send stored (and concentrated) bile from the gallbladder to the Bile Duct. 1. The merging of the Cystic Duct and Common Hepatic Duct forms the Bile Duct. E. The Bile Duct will Merge with the Pancreatic Duct (coming from the pancreas) at the Hepato-Pancreatic Ampulla. F. The Hepato-Pancreatic Ampulla is surrounded by the Hepato-Pancreatic Sphincter, which controls the release of bile and pancreatic enzymes into the duodenum.