Chapter 16 The Digestive System PDF

Chapter 16 The Digestive System Sherwood Modified, Edited and Presented by Marios Z Panos Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning  DIGESTIVE SYSTEM OUTLINE - The Mouth - The Oesophagus - The Stomach...

Chapter 16 The Digestive System Sherwood Modified, Edited and Presented by Marios Z Panos Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning  DIGESTIVE SYSTEM OUTLINE - The Mouth - The Oesophagus - The Stomach Chapter 16 The Digestive System Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning  DIGESTIVE SYSTEM Mouth and Oesophagus Chapter 16 The Digestive System Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning  Mouth (Oral Cavity) Lips – Form opening – Help procure, guide and contain food in the mouth – Important in speech – Well-developed tactile sensation Palate – Forms roof of oral cavity (separates mouth from nasal passages) – Uvula (seals off nasal passages during swallowing) Tongue – Forms floor of oral cavity – Composed of skeletal (striated) muscle – Movements aid in chewing and swallowing – Plays important role in speech – Taste buds  Mouth (Oral Cavity) Pharynx – Cavity at rear of throat – Common passageway for digestive and respiratory systems – Tonsils Within side walls of pharynx Lymphoid tissue Teeth – Responsible for chewing (mastication) – First step in digestive process  Mouth (Oral Cavity) Teeth –Functions of chewing Grind and break food into smaller pieces to make swallowing easier and increase food surface area on which salivary enzymes can act Mix food with saliva Stimulate taste buds  Mouth (Oral Cavity) Saliva – Produced largely by three major pairs of salivary glands – Composition 99.5% H2O 0.5% electrolytes and protein (amylase, mucus, lysozyme) – Functions Salivary amylase begins digestion of carbohydrates Facilitates swallowing by moistening food Mucus provides lubrication Antibacterial action – Lysozyme destroys bacteria – Saliva rinses away material that could serve as food source for bacteria Solvent for molecules that stimulate taste buds Aids speech by facilitating movements of lips and tongue Helps keep mouth and teeth clean Rich in bicarbonate buffers Major salivary glands: parotid, submandibular and sublingual There are also hundreds of minor salivary glands in the mouth  Control of Salivary Secretion – Simple and conditioned reflexes Conditioned reflex: Pavlov’s dog experiment In one of his famous experiments, Pavlov observed that dogs naturally salivated when presented with food, an unconditioned stimulus. Through repeated pairings of a neutral stimulus, such as a bell, with the food, the dogs eventually began to associate the bell with the arrival of food.  Swallowing The Four Phases of the Normal Adult Swallow Process Oral Preparatory Phase (chewing and bolus formation) Oral Transit Phase (pushing bolus to back of pharynx) Pharyngeal Phase (closes/protects airway) Esophageal Phase (transfers bolus to stomach) Chapter 16 The Digestive System Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning  Pharynx and Oesophagus Swallowing – Motility associated with pharynx and oesophagus – Sequentially programmed all-or-none reflex – Initiated when bolus is voluntarily forced by tongue to rear of mouth into pharynx – Most complex reflex in body – Can be initiated voluntarily but cannot be stopped once it has begun – Process divided into two stages Oropharyngeal stage -moves bolus from mouth through pharynx and into oesophagus. - airway protection: vocal folds close, larynx rises inside the neck, epiglottis moves to cover it Oesophageal stage – contracts to push the bolus down its length and into the stomach  Pharynx and Oesophagus Oesophagus – Fairly straight muscular tube – Extends between pharynx and stomach – Sphincters at each end Pharyngo-oesophageal sphincter (striated m.) – Keeps entrance closed to prevent large volumes of air from entering esophagus and stomach during breathing Gastro-oesophageal sphincter (smooth m.) – Prevents reflux of gastric contents – Peristaltic waves push food through oesophagus – Secretions (mucus) are entirely protective (and lubricate) Musculature: upper 2/3 of oesophagus is striated & distal 1/3 is smooth The oesophagus is devoid of a serosal layer.  Anatomical relationships of the oesophagus Oesophagus  Anatomical and physiological considerations The two sphincters are at the pharyngo-oesophageal junction (upper) & in the region of the oesophageal opening (hiatus) in the diaphragm (lower). Both have intrinsic & extrinsic components. Upper intrinsic sphincter Main functions (i) prevents access of air to the oesophagus (ii) works in conjunction with laryngeal closure during swallowing to prevent aspiration of food It relaxes on initiation of the swallowing reflex The superior constrictor extrinsic component contracts to expel food or liquid into oesophagus from where a wave of peristalsis carries it downwards. Peristalsis in the Oesophagus  OESOPHAGEAL MANOMETRY Normal Pressure swallow sensors Manometry = measurement of pressure  Physiology of The Oesophagus The function of the esophagus is to transport the ingested material from the pharynx to the stomach by peristaltic waves Primary peristalsis Triggered by the swallowing center in the brain stem and the contraction wave travel at speed 2cm/s Secondary peristalsis Induced by esophageal distension from retained bolus or refluxed material. Its role is to clear the oesophagus form retained bolus.  Physiology of The Oesophagus Tertiary peristalsis Non peristaltic contractions Play no known physiological role. Frequently observed in elderly people - > called presby-oesophagus - > also seen in motility disorders. Presbys:Gk πρέσβυς = senior, elderly  Anatomical and physiological considerations Lower intrinsic sphincter is the circular smooth muscle of the oesophagus. Its role is to prevent GE regurgitation. It is normally closed but relaxes in response to the swallowing wave. The intrinsic sphincter is supplemented by the striated muscle of the right crus, which splits to embrace the lower end of the oesophagus (keeping GEJ closed when intra-abdominal pressure is increased). Also : another factor preventing reflux from the stomach is the acute angle of insertion of the oesophagus into the stomach which brings the gastric and oesophageal walls in contact when intra-abdominal pressure rises. Anatomical disorders at the diaphragmatic hiatus reduce the efficacy of the intrinsic sphincter and may contribute to the phenomenon of gastroesophageal reflux - a common disorder.  PATHOPHYSIOLOGY OF OESOPHAGEAL DISORDERS Chapter 16 The Digestive System Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning  Oesophageal Motility Disorders Spastic oesophageal motility disorders Diffuse oesophageal spasm (DES): This is probably related to fragmental degeneration of vagal nerve fibers Characterized by simultaneous, repetitive high pressure muscular contraction within the oesophagus The muscular wall is thickened, hypertrophied and is hypersensitive to stretching  Normal Barium Swallow Arrow = indentation of the aorta at the level of the aortic arch (normal) Chapter 16 The Digestive System Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning Diffuse oesophageal spasm  Esophageal Motility Disorders Achalasia (failure to relax) Is the only esophageal motility disorder with an established pathology The predominant pathophysiology of achalasia is the loss of Auerbach ganglion cells from the wall of the oesophagus, starting at LES and progress proximally Incidence is 1-3 /100,000 population/year LES = Lower (o)Esophageal Sphincter Gk : χάλασις = chalasis = relaxation  Esophageal Motility Disorders Achalasia (failure to relax) contd. Characterized by failure of LES to relax completely during swallowing The loss of nerve ganglions along the esophageal wall cause aperistalsis leading to stasis of food and subsequent dilatation of the body of the esophagus Manometry may reveal elevated LES pressure > 40 mmHg in 60% of patients and weak peristaltic waves in the body of the oesophagus  Achalasia of the cardia Cardia = region of the lower oesophageal sphincter and gastro-esophageal junction Weak/absent peristalsis in mid-lower-upper oesophagus results in dilation Hypertonic Lower Oesophageal Sphincter with failure to relax “bird’s beak” or “rat tail” sign  Oesophageal Motility disorders Achalasia – bird’s-beak (or rat Diffuse oesophageal tail) sign at lower esophageal spasm sphincter (nutcracker oesophagus) Increased risk of oesophageal corkscrew or rosary beads cancer appearance Primary achalasia Normal oesophagus Achalasia of the oesophagus  Oesophageal Motility Disorders Treatment of Achalasia The primary goal is symptomatic relief directed at relieving the physiologic obstruction at the level of LES by surgical or balloon dilatation Nitrate and Ca channel blockers* are currently used in all patients with esophageal motility disorders. * Nitrate and Ca channel blockers cause relaxation of LES smooth muscle  Oesophageal Motility Disorders Treatment (contd.) Botulinum toxin injection (Botox): Injected endoscopically in 4 quadrants into LES in treating patient with achalasia Botox inhibits acetylcholine release from nerve terminals. Indicated in patients who are not candidates for surgery or refuse surgery Endoscopic balloon dilatation: This is the standard therapy for patients with achalasia The mechanism based on disruption of circular muscle Balloon dilatation response rate is 70%  Oesophageal Motility Disorders Achalasia Treatment (contd.) Surgery (Heller Myotomy): surgical treatment targets to divide (cut) the LES This can be performed by thoracoscopic or laparoscopic methods Outcome is excellent 80-100% response rate Per Oral Endoscopic Myotomy (POEM)  Gastroesophageal reflux disorders Features of reflux occur in association with many different oesophageal conditions, including most of the motility disturbances. Reflux is particularly a symptom of abnormalities at the diaphragmatic hiatus.  Gastroesophageal reflux disorders Pathophysiological features Gastroesophageal reflux: If either acid or strongly alkaline (bile) secretions reach the lower oesophagus → mucosal inflammation Mostly a superficial oesophagitis Stricture – this is usually predominantly an inflammatory reaction in the mucosa & submucosa, but it can, if inflammation takes place, become a fibrous narrowing Metaplastic change – this leads to development of gastric- type columnar epithelium in lower oesophagus ('Barrett's oesophagus‘) It is a premalignant lesion (may lead to adenocarcinoma) Gastroesophageal reflux disorders Clinical syndromes Two main forms Hiatus hernia with reflux Reflux without abnormal anatomy  Types of hiatus hernia Sliding hiatus hernia Paraesophageal (rolling) Hiatus hernia hiatus hernia  Sliding hiatus hernia The proximal stomach ascends into the chest through a lax or enlarged diaphragmatic opening (congenital), taking a circumferential cuff of peritoneum with it The normally acute oesophago-gastric angle is reduced, so that reflux is common even though the intrinsic lower sphincter is normal Aetiology / Contributory factors ↑ intra-abdominal pressure e.g. obesity, increase in abdominal contents (e.g. pregnancy) Ageing Clinical features There is postural reflux, heartburn & occasionally some lower left chest pain Vague indigestion is rarely caused by a sliding hernia  DIGESTIVE SYSTEM In this lecture we covered - The Mouth - The Oesophagus Chapter 16 The Digestive System Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning  Chapter 16 The Digestive System Sherwood Modified, Edited and Presented by Marios Z Panos Thank you for your attention ! Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning