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Digestive System Anatomy Digestive tract Accessory organs Alimentary tract or canal GI tract Primarily glands Regions Mouth or oral cavity Pharynx Esophagus Stomach Small intestine Large intestine Anus Digestive Tract Histology Digestive System Regulation Nervous regulation Involves enteric nervous system Types of neurons: sensory, motor, interneurons Coordinates peristalsis and regulates local reflexes Chemical regulation Production of hormones Gastrin, secretin Production of paracrine chemicals Histamine Help local reflexes in ENS control digestive environments as pH levels Peritoneum and Mesenteries Peritoneum Visceral: Covers organs Parietal: Covers interior surface of body wall Retroperitoneal: Behind peritoneum as kidneys, pancreas, duodenum Mesenteries Routes which vessels and nerves pass from body wall to organs Greater omentum Lesser omentum Oral Cavity Mouth or oral cavity Lips (labia) and cheeks Palate: Oral cavity roof Vestibule: Space between lips or cheeks and alveolar processes Oral cavity proper Hard and soft Palatine tonsils Tongue: Involved in speech, taste, mastication, swallowing Teeth Two sets Primary, deciduous, milk: Childhood Permanent or secondary: Adult (32) Types Incisors, canine, premolar and molars Tooth structure: Salivary Glands Produce saliva Prevents bacterial infection Lubrication Contains salivary amylase Breaks down starch Three pairs Parotid: Largest Submandibular Sublingual: Smallest Pharynx and Esophagus Pharynx Nasopharynx Oropharynx: Transmits food normally Laryngopharynx: Transmits food normally Esophagus Transports food from pharynx to stomach Passes through esophageal hiatus (opening) of diaphragm and ends at stomach Hiatal hernia Sphincters Upper Lower Deglutition (Swallowing) Three phases Voluntary Bolus of food moved by tongue from oral cavity to pharynx Pharyngeal Reflex: Upper esophageal sphincter relaxes, elevated pharynx opens the esophagus, food pushed into esophagus Esophageal Reflex: Epiglottis is tipped posteriorly, larynx elevated to prevent food from passing into larynx Phases of Deglutition (Swallowing) Functions Ingestion: Introduction of food into stomach Mastication: Chewing Propulsion Deglutition: Swallowing Peristalsis: Moves material through digestive tract Stomach Anatomy: Openings Gastroesophageal: To esophagus Pyloric: To duodenum Regions Cardiac Fundus Body Pyloric Stomach Histology: Layers Serosa or visceral peritoneum: Outermost Muscularis: Three layers Outer longitudinal Middle circular Inner oblique Submucosa Mucosa Stomach Histology Rugae: Folds in stomach when empty Gastric pits: Openings for gastric glands Contain cells Surface mucous: Mucus Mucous neck: Mucus Parietal: Hydrochloric acid and intrinsic factor Chief: Pepsinogen Endocrine: Regulatory hormones Hydrochloric Acid Production Phases of Gastric Secretion Movements in Stomach Small Intestine Site of greatest amount of digestion and absorption Divisions Modifications Duodenum Jejunum Ileum: Peyer’s patches or lymph nodules Circular folds or plicae circulares, villi, lacteal, microvilli Cells of mucosa Absorptive, goblet, granular, endocrine Small Intestine Secretions Mucus Digestive enzymes Protects against digestive enzymes and stomach acids Disaccharidases: Break down disaccharides to monosaccharides Peptidases: Hydrolyze peptide bonds Nucleases: Break down nucleic acids Duodenal glands Stimulated by vagus nerve, secretin, chemical or tactile irritation of duodenal mucosa Duodenum and Pancreas Duodenum Anatomy and Histology Liver Lobes Major: Left and right Minor: Caudate and quadrate Ducts Common hepatic Cystic From gallbladder Common bile Joins pancreatic duct at hepatopancreatic ampulla Functions of the Liver Bile production Storage Hepatocytes remove ammonia and convert to urea Phagocytosis Glycogen, fat, vitamins, copper and iron Nutrient interconversion Detoxification Salts emulsify fats, contain pigments as bilirubin Kupffer cells phagocytize worn-out and dying red and white blood cells, some bacteria Synthesis Albumins, fibrinogen, globulins, heparin, clotting factors Blood and Bile Flow Duct System Gallbladder Bile is stored and concentrated Stimulated by cholecystokinin and vegal stimulation Dumps into small intestine Production of gallstones possible Drastic dieting with rapid weight loss Pancreas Anatomy Endocrine Exocrine Pancreatic islets produce insulin and glucagon Acini produce digestive enzymes Regions: Head, body, tail Secretions Pancreatic juice (exocrine) Trypsin Chymotrypsin Carboxypeptidase Pancreatic amylase Pancreatic lipases Enzymes that reduce DNA and ribonucleic acid Bicarbonate Ion Production Gastric hormones: Movement in small intestine: Mixing: Segmental contraction that occurs in small intestine Secretion: Lubricate, liquefy, digest Digestion: Mechanical and chemical Absorption: Movement from tract into circulation or lymph Elimination: Waste products removed from body Large Intestine: Extends from ileocecal junction to anus Consists of cecum, colon, rectum, anal canal Movements sluggish (18-24 hours) Large Intestine Cecum Colon Ascending, transverse, descending, sigmoid Rectum Blind sac, vermiform appendix attached Straight muscular tube Anal canal Internal anal sphincter (smooth muscle) External anal sphincter (skeletal muscle) Hemorrhoids: Vein enlargement or inflammation Secretions of Large Intestine Mucus provides protection Parasympathetic stimulation increases rate of goblet cell secretion Pumps Exchange of bicarbonate ions for chloride ions Exchange of sodium ions for hydrogen ions Bacterial actions produce gases called flatus Histology of Large Intestine Movement in Large Intestine Mass movements Local reflexes in enteric plexus Gastrocolic: Initiated by stomach Duodenocolic: Initiated by duodenum Defecation reflex Common after meals Distension of the rectal wall by feces Defecation Usually accompanied by voluntary movements to expel feces through abdominal cavity pressure caused by inspiration Reflexes in Colon and Rectum: Digestion, Absorption, Transport Digestion Breakdown of food molecules for absorption into circulation Mechanical: Breaks large food particles to small Chemical: Breaking of covalent bonds by digestive enzymes Absorption and transport Molecules are moved out of digestive tract and into circulation for distribution throughout body Liver Histology portal triad Figure 24.20a, b 3. Architecture of the Hepatic Parenchyma The hepatic lobule is the structural unit of the liver. Portal vein Bile duct Sinusoids Central vein Portal area Hepatic artery Liver cells (Hepatocytes) Bile …each day around 600 ml of bile is produced… Bile acid Phospholipids Cholesterol Bilirubin Waste products Electrolytes Mucin Functions of the Liver Bile production Storage Hepatocytes remove ammonia and convert to urea Phagocytosis Glycogen, fat, vitamins, copper and iron Nutrient interconversion Detoxification Salts emulsify fats, contain pigments as bilirubin Kupffer cells phagocytize worn-out and dying red and white blood cells, some bacteria Synthesis Albumins, fibrinogen, globulins, heparin, clotting factors Exocrine Pancreas – Enzymes Trypsinogen Chymotrysinogen Carboxypeptidases Pro-elastase Phospholipase pancreatic lipase Pancreatic amylase Bicarbonate Ion Production Lipoproteins Types Chylomicrons VLDL LDL Enter lymph Transports cholesterol to cells HDL Transports cholesterol from cells to liver Water and Ions: Water Can move in either direction across wall of small intestine depending on osmotic gradients Ions Sodium, potassium, calcium, magnesium, phosphate are actively transported Effects of Aging Decrease in mucus layer, connective tissue, muscles and secretions Increased susceptibility to infections and toxic agents Ulcerations and cancers
