BIOL 320 1 st Edition Lecture 17 Outline of Last Lecture I Oxygen Carbon Dioxide Exchange II Oxygen Hemoglobin Dissociation Curve III Factors Influencing Hemoglobin Saturation IV Neural Control V Depth and Rate of Breathing VI Hyperventilation VII Hypoventilation VIII Gas Imbalance IX Developmental Aspects I Digestive System II Digestive Process III Regulation of Digestion IV Peritoneum V Histology of the GI Tract VI Oral Cavity VII Tongue Outline of Current Lecture X Salivary Glands XI Teeth XII Pharynx Esophagus XIII Digestive Processes Mouth Esophagus XIV Stomach XV Stomach Mucosa XVI Gastric Secretion Regulation XVII Regulation of HCl Secretion XVIII Gastric Motility XIX Gastric Emptying XX Small Intestine XXI Liver Lobules XXII Accessories to Small Intestine XXIII Bile XXIV Role of the Pancreas XXV Pancreatic Regulation XXVI Digestion Small Intestine XXVII Motility Small Intestine XXVIII Large Intestine XXIX Large Intestine Microscopic Anatomy XXX Motility Defecation XXXI Cancer XXXII Malabsorption of Nutrients XXXIII XXXIV Ulcers Developmental Considerations Current Lecture Salivary Glands Extrinsic glands activated when you smell taste or thinking about food o Parotid have ducts that open into mouth o Submandibular have ducts that open into mouth o Sublingual has 10 12 ducts that open under tongue gleeking Intrinsic glands in oral mucosa all about keeping mouth moist o Buccual glands in oral mucosa keep mouth moist Saliva components 1 97 99 5 water 2 Electrolytes 3 Proteins lysosyme defensins IgA 4 Salivary amylase 5 Metabolic waste Function to produce and secrete saliva Saliva 1 Cleanses the mouth 2 Moistens and dissolves food 3 Aids in bolus formation 4 Contains enzymes to break down starch Regulation o Extrinsic salivary gland secrete saliva in response to 1 Ingested food 2 The thought of food o Strong sympathetic stimulation inhibits salivation Teeth usually you have 32 Function mechanical digestion mastication chewing Incisors cutting Canines tearing and piercing Premolars Molars grinding and crushing Pharynx food goes from oral cavity to oropharynx to laryngopharynx Epithelial lining stratified squamous with mucous glands Muscular layers skeletal muscle Esophagus Pathway pierces diaphragm connects to stomach Layers standard four described before adventia instead of serosa Mucosa stratified squamous ET Typically flattened opens with food passage Mucous secreted as bolus moves through Muscularis changes from upper skeletal to smooth lower this is why swallowing is voluntary and then you have no control Digestive Processes Mouth Esophagus Ingestion Mechanical digestion Begins in the mouth Chewing Chemical digestion salivary amylase begins starch breakdown Propulsion Deglutition Swallowing o Coordinated activity of tongue soft palate pharynx esophagus and 22 muscle groups o Buccal phase bolus forced into oropharynx o Pharyngeal esophageal phase air passages closed off controlled by medulla and pons Stomach Regions o Cardiac surrounds the cardiac orifice where esophagus connects at cardiac sphincter o Fundus and body o Pyloric surrounds pylorus and pyloric sphincter where duodenum leaves stomach Innervation o S ANS and P ANS Layers standard four Muscularis externa three layers longitudinal circular and oblique allows further mechanical digestion Extra o Tissue layers specialized for stomach function o Simple columnar epithelium o Goblet cells mucus secretion o Penetrated by gastric pits which terminate in gastric glands o Fundus body produce gastric juice comprising mucus neck cell secretion hydrochloric acid parietal cell secretion pepsin chief cell secretion Stomach Mucosa Epithelial lining simple columnar with goblet cells Protective properties 1 Mucous layer traps bicarbonate to protect stomach against acid 2 Epithelial cells connected by tight junctions 3 Gastric glands impermeable to gastric juice Gastric pits extend deep into mucosa o Contain gastric glands o That secrete gastric juice o Which allows chemical digestion o Enteroendocrine cells histamine gastrin etc o Neck cells mucous o Parietal cells HCl intrinsic factor allows uptake of vitamin B12 o Chief cells pepsinogen Pepsinogen activation converted to pepsin by HCl Chyme result of chemical and mechanical digestion Gastric Secretion Regulation The cephalic phase is the reflex phase occurs prior to ingestion works through the vagus nerve of PANS o Note the two excitatory stimuli and the two inhibitory stimuli The gastric phase occurs with food in the stomach works through the vagus nerve and by gastrin release o Note the excitatory stimuli know the end result o Note the inhibitory stimuli know the end result The intestinal phase occurs when stomach begins to empty works through gastrin release o Inhibition Distension of duodenum inhibits local reflexes vagus n closes pyloric sphincter inhibit gastric secretion Regulation of HCl Secretion Stimulated by ligand binding ACh histamines and gastrin stimulate parietal cells via 2nd messenger system If one ligand binds to parietal cells low HCl If three ligands bind to parietal cells high HCl Antihistamines bind histamine receptors decrease HCl release Function of HCl pH 1 5 3 5 denatures proteins activates pepsin kills bacteria Gastric Motility Rate of peristaltic waves 3times min pacemaker cells Most vigorous peristalsis mixing pylorus Chyme movement small amounts 3ml at a time Gastric Emptying As peristalsis forces chyme into the duodenum stimulates neural enterogastric reflex hormonal enterogastro mechanism Resulting inhibition gastric secretion duodenal filling Carb rich chyme goes quicker Fat rich chyme travels slower causing it to remain in the stomach longer Small Intestine Proximal opening pyloric sphincter Distal opening ileocecal valve at large intestine Subdivisions o Duodenum proximal 1st foot bile pancreatic duct open here o Jejunum middle 8 ft o Ileum distal 12 ft Suspended by mesentery Covered by greater omentum Small Intestine Histology Surface area increased by modifications 1 Plicae circulares deep circular folds of mucosa submucosa slow chyme via spiralling thru 2 Villi fingerlike extensions of mucosa 3 Microvilli tiny projections of mucosal cells Plasma Membranes Mucosal Epithelium Simple columnar o Absorptive cells goblet cells o Enteroendocrine cells o Intraepithelial lymphocytes T cells release cytokines on Ag challenge Intestinal juice produced in intestinal crypts o Secreted in response to distension or irritation of mucosa o Alkaline o