Unit 15 The Digestive System PDF

Unit 15: The Digestive System Functions Physical and Chemical Breakdown: o Decomposes ingested food into smaller components. Absorption of Nutrients: o Nutrients move into the bloodstream following digestion. Waste Removal: o Undigested waste is e...

Unit 15: The Digestive System Functions Physical and Chemical Breakdown: o Decomposes ingested food into smaller components. Absorption of Nutrients: o Nutrients move into the bloodstream following digestion. Waste Removal: o Undigested waste is expelled from the body. Housing Symbiotic Bacteria: o Normal flora mainly resides in the large intestine, aiding in digestion. Organs: structure and function Main Organs: Mouth Esophagus Stomach Small Intestine Large Intestine Anus Accessory Organs: Salivary Glands Liver Gallbladder Pancreas Six Digestive Processes and location 1. Ingestion: a. Taking in food through the mouth. b. in mouth 2. Mechanical Digestion:  a. Physically breaking down food into smaller pieces b. mouth, stomach, small intestine 3. Chemical Digestion: a. Utilizing enzymes to break down food components b. Stomach, small intestine 4. Secretion: a. Releasing substances like water, acids, and enzymes into the gastrointestinal tract b. Small intestine 5. Absorption: a. Movement of nutrients and water from the digestive tract into the bloodstream b. Small and large intestine 6. Defecation: a. Elimination of undigested waste (feces) b. Large intestine and rectum The Mouth: Anatomy and Function Parts: o Mandible, maxilla o gums (gingiva) o Tongue: very strong, moves food around while chewing, taste receptors o Uvula – blocks nasal passages  o Epiglottis: in pharynx, blocks trachea o Peristalsis: from mouth to anu, muscle contractions Function: o Chewing (mastication), mixing food with saliva to form bolus, initiating swallowing. o Taste receptors for salty, sweet, bitter, sour, and savory flavors. Salivary Glands 3 parts: Parotid, Submandibular, Sublingual Saliva Composition: 95.5% water, ions, enzymes (amylase, lipase), and mucus. Function: Moisten food, begin starch and fat digestion, and provide a medium for taste by dissolving foods The Stomach Function: o Stores and digests food. Bolus transforms into chyme. Digestion Types: o Mechanical (physical breakdown) and chemical (protein digestion). Sphincters: o Lower esophageal sphincter prevents reflux from stomach to esophagus o pyloric sphincter: holds chyme until its ready to enter the small intestine Divisions: o Cardia, Fundus, Pylorus Rugae: allows expansion Digestive Secretions: o Goblet Cells: Produce mucus for protection of stomach lining o Chief Cells: Produce pepsinogen (activated to pepsin for protein digestion) o Parietal Cells: Produce hydrochloric acid (HCl) to activate pepsin and kill pathogens The Liver Second largest organ  Main cell type: Hepatocytes - involved in nutrient storage and processing Kupffer Cells (Resident immune cells): kill pathogens, breakdown red blood cells and other dead cells Produces bile: fat digestion Stores nutrient during Absorptive Phase: by insulin o glucose into glycogen – glycogenesis o glucose and amino acids into triglycerides – lipogenesis o Produce lipoproteins to transport fats from liver to adipose tissue o Stores excess fat-soluble vitamins – vitamin A, D, E, K o Stores minerals and trace metals Breaks down nutrient during Fasting phase: by glucagon, epinephrine, thyroid hormones, and growth hormone o glycogen into glucose – glycogenolysis o triglycerides into glucose – gluconeogenesis o fatty acids into ketones, which can be converted into acetyl-CoA and can be used to produce ATP o Produces urea from breakdown products of proteins Synthesizes fibrinogen: the protein required for blood clotting Synthesizes angiotensinogen: involved in the renin-angiotensin system to regulate blood pressure Activates vitamin D (kidneys also activate vitamin D): the precursor produced in the skin during sun exposure o Vitamin D is required for calcium homeostasis and immune regulation. Produces insulin-like growth factors (IGFs) in response to growth hormone Secretes complement proteins involved in the immune response The Gallbladder Function: o It stores and concentrates bile, releasing it into the small intestine through cystic duct to aid in fat digestion o Mechanically breaks down fat The Pancreas Also, part of endocrine system: o Endocrine cells: ▪ Alpha islet cells produce glucagon  ▪ Beta islet cells produce insulin o Exocrine cells: ▪ Acini cells secrete pancreatic juice that contains Bicarbonate ions and Enzymes ▪ Pancreatic juice enters the small intestine through the pancreatic duct (with merges with the common bile duct to form hepatopancreatic duct) Function: o Produces enzymes and bicarbonate for digestion, functioning both as an exocrine organ (digestive enzymes) and an endocrine organ (insulin and glucagon). The Small Intestine 3 Regions: o Duodenum: most absorption of nutrients and water o Jejunum o Ileum: absorption of B12 Functions: o Major nutrient absorption and digestion through mechanical and chemical processes. Structural Features: o High surface area due to villi and microvilli for efficient absorption. The Large Intestine Composed of same tissue types Cecum: the first part, very large, where appendix is found Functions: o Absorbs water and ions, stores waste until defecation and supports normal gut flora o Contains normal bacteria Gut Flora Definition:  o Bacteria inhabit the colon, contributing to fecal mass. Functions: o Fermentation of undigested substrates, immune regulation, and synthesis of certain vitamins (e.g., vitamin K). Digestive Enzymes: where it is produced, where it acts, what does it breakdwon Salivary Glands: o Amylase: starch o Lipase: fat Stomach: Pepsin for proteins. Pancreas: enzymes produced in pancreas but activated in small intestine o Amylase for starch o Lipases for fat o Trypsin and Chymotrypsin for proteins. Small Intestine: Maltase, Sucrase, Lactase, peptidases Absorption of Nutrients Locations of Nutrient Absorption: o Mouth: Minimal absorption. o Stomach: Limited absorption; some medications. o Small Intestine: Majority of nutrients, facilitated by villi and microvilli. o Large Intestine: Predominantly water absorption Control mechanisms of the gastrointestinal system are governed by the volume and composition of the luminal contents, rather than by the nutritional state of the body o the body is designed to absorb all the nutrients that are ingested, whether the body really needs them to function 3 Phases of digestion Cephalic phase – digestion stimulated by sight, smell, thought of food, taste, and chewing – body prepares for digestion Gastric phase – initiated by food physically contacting stomach lining, increased acidity (HCl), presence of amino acids or peptides in stomach Intestinal phase – initiated by stimuli in the small intestine – distention, acidity, osmolarity, and nutrient contents Disorders of the Digestive Tract Foodborne and waterborne disease: arise from consuming contaminated food or water, often caused by pathogens like bacteria, viruses, or parasites Irritable bowel syndrome (IBS): cause unknown – may be related to allergies or abnormal gut flora Inflammation of digestive tract: GERD (Gastroesophageal Reflux Disease) – aka heartburn: Stomach acid flows back into the esophagus, causing heartburn and irritation Crohn’s disease: inflammatory disease of small intestine Ulcerative colitis: autoimmune disease of large intestine Physical abnormalities in the digestive tract Hiatal hernia: stomach protrudes through opening in diaphragm Diverticulitis: small pockets of weakened bowel tissue; no known cause or cure; high fiber diet helps Ulcers: sores caused by Helicobacter pylori Gastritis: stomach inflammation (e.g. Norovirus) Hemorrhoids: clusters of swollen veins around anus; caused by constipation Summary Key Takeaways: o The digestive system includes a complex array of organs working together to break down food, absorb nutrients, and eliminate waste. o Accessory organs contribute critical functions, particularly in digestion and metabolism. o Understanding digestive processes and common disorders is essential for maintaining gastrointestinal health.