Digestive System

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McMaster University
Danny M.Pincivero

Chapter 24 – The Digestive System What are the parts of the digestive system? - Digestive Tract • GI Tract: stomach and intestines  Accessory organs o Secrete fluids into tract --------------------------------------------------------------------------------------------------- What are the functions of the digestive system? 1. Ingestion: food into stomach 2. Mastication: mechanical digestion (chewing) 3. Propulsion • Deglutition: swallowing • Peristalsis: waves of smooth muscle contraction/relaxation o Propels bolus or chime forward in digestive tract 4. Mixing: segmental contractions (mixing food with enzymes) 5. Secretion: lubricate, liquefy, digest o Bile: emulsifies fats o Enzymes: chemical digestion 6. Digestion: mechanical and chemical 7. Absorption: movement from tract into circulation or lymph 8. Elimination: waste products removed from body as feces (defacation) --------------------------------------------------------------------------------------------------- How is the digestive system regulated? Nervous Regulation Chemical Regulation  Local: Enteric Nervous System - Gastrin (HCL) - Coordinates peristalsis and regulated - Secretin: regulates pH in small local reflexes intestine  General - Serotonin: released by endocrine cells - Coordination with the CNS in digestive tract - Sight, smell, or taste of food - Parasympathetic primarily - Sympathetic inhibits muscle contraction, secretion, and decrease of blood flow to the digestive tract --------------------------------------------------------------------------------------------------- What is the peritoneum and what is it composed of? • Peritoneum: sheets of serous membranes (secretes fluid) o Retroperitoneal: behind the peritoneum  Kidneys, pancreas, urinary bladder, rectum • Mesenteries: two layers of peritoneum w/ thin layer of loose C.T. o Blood vessel and nerve passage o Greater Omentum: connects greater curvature of the stomach to the transverse colon o Lesser Omentum: connects lesser curvature of the stomach and the proximal part of the duodenum to the liver and diaphragm • Ligaments o Coronary: between liver and diaphragm o Falciform: between liver and anterior abdominal wall --------------------------------------------------------------------------------------------------- What makes up the oral cavity? - Bounded by lips, anteriorly, fauces (opening into pharynx) posteriorly • Vestibule: space between lip/cheeks and alveolar processes (maxilla) with teeth • Oral Cavity Proper: medial to alveolar processes • Labial Frenula: mucous folds • Hard Palate: anterior, supported by maxilla and palatine bone • Soft Palate: posterior, consists of skeletal muscle and connective tissue --------------------------------------------------------------------------------------------------- What is mastication? - Chewing - Muscles involved: masseter, temporalis, medial and lateral pterygoids o Elevate mandible  Temporalis, masseter, medial pterygoids o Depress mandible  Lateral pterygoids o Protraction and lateral medial excursion  Pterygoids and masseter o Retraction  Temporalis • Mastication Reflex: medulla oblongata, but descending pathways from cerebrum provide conscious control --------------------------------------------------------------------------------------------------- Salivary Glands • Parotid Gland: largest gland, anterior to ear • Sublingual Gland: smallest What are the functions of saliva? 1. Prevents bacterial infection 2. Lubrication (mucin secreted) 3. Contains salivary amylase that break down startch 4. Helps to form bolus for swallowing 5. Parasympathetic input causes salivary production --------------------------------------------------------------------------------------------------- What are the 3 phases of swallowing (deglutition)? 1. Voluntary o Bolus of food moved by tongue from oral cavity to pharynx 2. Pharyngeal o Reflex o Swallowing center in medulla oblongata o Soft palate elevates, upper esophageal sphincter relaxes, elevated pharynx opens the esophagus o Epiglottis is tipped posterior due to pressure of the bolus, larynx elevated to prevent food from passing in 3. Esophageal o Reflex o Stretching of esophagus causes enteric NS to initiate peristalsis of muscles in the esophagus --------------------------------------------------------------------------------------------------- Describe the breakdown of the stomach. • Gastric Pits: openings for gastric glands  Secretions o Mucus: protects stomach lining from acid and digestive enzymes o Parietal Cells > HCl and intrinsic factor  Intrinsic Factor: assists w/ vitamin B12 absorption o Chief Cells > pepsinogen  Endocrine: regulatory hormones o Histamine: stimulates acid secretion o Gastrin o Somatostatin: inhibits gastrin and insulin secretion What are the 3 phases of stomach secretions? (CGI Friday’s) 1. Cephalic Phase: o Medulla oblongata stimulation (sensations – taste, smell, texture, memory) o Parasympathetic N.S. stimulation (vagus nerve) o Secretion of gastrin and histamine (stimulates HCL and pepsinogen secretion) 2. Gastric Phase (greatest amount of secretion) o Stimulated by stomach volume (presence of food causes distension) o Activation of mechanoreceptors o Amplifies gastric secretions (HCL, pepsinogen) 3. Intestinal Phase o Inhibits gastric secretion o Stimulated by acidic chyme in duodenum (ducts from liver and pancreas) o Secretin released by intestinal cells (inhibits parietal and chief cell
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