Stomach 1 PDF

STOMACH 1 Kieron Salmon Learning Objectives Describe the functional anatomy of the oesophagus and its relationship to the stomach Describe the functional anatomy of the simple stomach Explain the motility of the stomach OESOPHAGUS SWALLOWING (Deglutition) Propulsion of food from oral ca...

STOMACH 1 Kieron Salmon Learning Objectives Describe the functional anatomy of the oesophagus and its relationship to the stomach Describe the functional anatomy of the simple stomach Explain the motility of the stomach OESOPHAGUS SWALLOWING (Deglutition) Propulsion of food from oral cavity into oesophagus Food molded into bolus by tongue and moved upwards and backwards to pharynx Under voluntary control Forces soft palette up to seal off nasal cavity Pressure-sensitive sensory cells stimulated Swallowing centre in medulla initiates swallowing reflex Under involuntary control Epiglottis closes off trachea Complicated contraction / relaxation of muscles forces food into oesophagus (to be continued......) Swallowing Swallowing Disorders Failure of soft palette to close off nasal cavity Failure of epiglottis to close off trachea Pharyngeal paralysis Nerve / muscle injury Botulism Clostridial toxins block acetylcholine release Myaestheania gravis Antibodies formed against acetylcholine receptors Anaesthesia Many anaesthetic agents induce vomiting Swallowing process impaired Inhalational pneumonia Anatomy of the Oesophagus Mucosal layer Stratified squamous epithelium Submucosal layer Muscular layer Inner circular / outer longitudinal Composed of striated & smooth muscle Serosal layer Adventitia (loose connective tissue) only in neck Slower healing in surgery True serosal layer in thorax Comparative Anatomy of the Oesophagus Smooth muscle (solid line), striated muscle (dashed line) Innervation Sympathetic via cervical sympathetic chain Parasympathetic SVE/AA via recurrent laryngeal (cranial division of XI) to cranial cervical oesophagus AE/AA via vagus (X) to caudal cervical / thoracic oesophagus Species with striated muscle in caudal oesophagus still innervated by parasympathetic Transport down Oesophagus...... Continued Upper oesophageal sphincter closes behind food bolus (epiglottis opens to allow respiration) Complicated peristaltic contractions force food down oesophagus Animals can swallow upwards Lower oesophageal sphincter opens to allow passage of food into stomach Lower oesophageal sphincter = Cardiac sphincter Physiological sphincter rather than anatomical Except in horses Always closed except during swallowing Oesophagus enters abdomen at oblique angle Higher pressure in abdomen cf thorax causes stomach to exert pressure on diaphragm thus re-inforcing closure Prevents regurgitation of acidic stomach contents Relationship of Oesophagus & Diaphragm Vomiting (emesis) Active propulsion of stomach contents into oral cavity Deep inspiration with simultaneous closure of trachea / nasal cavity Increases intra-abdominal pressure via diaphragm Forceful contraction of abdominal muscles (NOT gastric muscle) Cardiac sphincter opens Food propelled up oesophagus Upper oesophageal sphincter opens Vomiting (emesis) Controlled by vomiting centre in medulla Stimulated by phyaryngeal / gastric distension or irritation Normal in dogs / cats to expel bones / hair Ruminants prefer to regurgitate Horses (& rats) Very well developed cardiac sphincter Exaggerated oblique entry through diaphragm Stomach usually ruptures before vomiting occurs Gastric Torsion Occurs in horses and dogs with wide chests Stomach rotates 90-360˚ Seals off cardiac sphincter thus preventing vomiting Stomach distends further with gas If rotation compromises blood supply gastric tissue becomes oedematous / hypoxic and in severe cases necrotic Stomach dilatation can impair venous return to heart via caudal vena cava resulting in circulatory shock EXTREME EMERGENCY requiring surgical intervention FUNCTIONAL ANATOMY OF SIMPLE STOMACH FUNCTIONAL ANATOMY Functions of simple stomach Digestion Continuation of starch digestion Initiation of protein digestion Protection Stomach acid kills bacteria ingested with food Storage Ensures food delivered to small intestine (main site of digestion / absorption) at controlled rate Mechanical breakdown / mixing Breaks down food and mixes with gastric juice forming a semi- liquid chyme Abomasum is ruminant equivalent of simple stomach (see later) Regions of Stomach Embryological Anatomical Oesophageal region Cardia Non-glandular = entrance to stomach Stratified squamous Physiological valve epithelium Fundus Cardiac region = blind-ending part of Secretes mucous only Fundic region stomach Secretes mucous / gastric Corpus juices = body of stomach Pyloric region Pylorus Secretes mucous only = exit from stomach Regulates stomach emptying Anatomy of Simple Stomach Cell Types Consists of cylindrical glands Mucous (goblet) cells Secrete mucus to protect against HCl Parietal (oxyntic) Cells Secrete HCl to digest protein Chief (peptic) Cells Secrete pepsinogen (pepsin) to digest protein Entero-endocrine Cells Secrete hormones MOTILITY OF STOMACH Motility Serves to: Prepare stomach to receive a meal Mix and mechanically break down chyme Empty stomach contents into small intestine Prevent regurgitation of stomach contents into oesophagus When an animal starts eating there is an initial relaxation of stomach smooth muscle to accommodate the meal (= receptive relaxation) Regulated by swallowing centre via vagus Transmitter = vasoactive intestinal peptide (not acetylcholine) Motility Mainly peristalsis Start in fundus with weak contractions Propogate down corpus Pyloric sphincter opens to allow chyme into duodenum When contractions reach pylorus the pyloric sphincter closes Food forced back into corpus helps mixing Regulation of Stomach Emptying Mainly regulated by strength of contraction Also opening / closing of pyloric sphincter Stimulation of emptying Neural regulation - Expansion of stomach walls increases strength of contraction Hormonal regulation – Release of gastrin increases strength of contraction and dilates pyloric sphincter Inhibition of emptying Factors in duodenum act to inhibit gastric contractions Increased pressure in duodenal walls, Low pH, High fat / peptide concentration, High osmolarity Neural regulation via increased sympathetic activity / decreased parasympathetic activity (via vagus) Hormonal regulation via secretin, cholecystokinin & gastric inhibitory peptide (GIP) Stimulation of Stomach Emptying Inhibition of Stomach Emptying