BSC 2086 1st Edition Lecture 19 Outline of Last Lecture I Gas Transport II Respiration Control III Effects of Aging IV Digestive Tract Outline of Current Lecture I II III Layers of Digestive Tract Movement of Materials in Digestive Tract Control of Digestive Functions IV Oral Cavity V Pharynx VI Esophagus VII Stomach Current Lecture I Layers of Digestive Tract a Mucosa i Inner mucous membrane lining ii Has epithelium and lamina propria 1 Lamina propria has blood vessels sensory nerves lymphatics and smooth muscles iii Muscularis mucosae narrow band made of smooth muscle and elastic fibers in the lamina propria iv Smooth muscle cells are arranged in an inner circular layer and an outer longitudinal layer II 1 Contractions will alter the lumens shape and move the epithelial pleats and folds v Enteroendocrine cells secrete hormones which coordinate digestive tract and accessory gland activities vi Plicae circularis permanent transverse folds located in the lining of the digestive tract 1 Increases surface area to increase absorption 2 Has longitudinal folds that disappear as the digestive tract fills b Submucosa i Layer made of dense irregular connective tissue ii Surrounds the muscularis mucosae of the mucosa and binds it to the muscularis externa iii Contains large blood vessels and lymphatic vessels and may contain exocrine glands that secrete buffers and enzymes iv Submucosal plexus group of intrinsic nerve fibers that innervates the mucosa and submucosa 1 Has sensory neurons and both sympathetic and parasympathetic components c Muscularis externa i Smooth muscle cells inner circular layer and outer longitudinal layer ii Moves substances along the digestive tract iii Enteric nervous system ENS coordinates movement 1 Myenteric plexus located between circular and longitudinal layers a Innervated mainly by parasympathetic division which increases muscle tone and activity b Sympathetic stimulation will cause muscular inhibition and relaxation d Serosa i Serous membrane which covers the muscularis externa ii Oral cavity pharynx esophagus and membrane are not covered by serous membrane instead they are covered by adventitia 1 Adventitia dense sheath of collagen fibers which firmly attaches the digestive tract to adjacent structure Movement of Materials in Digestive Tract a Movement due to muscular layers of digestive tract i Have visceral smooth muscle tissue along the digestive tract ii Rhythmic cycles of activity controlled by pacesetter cells 1 Located in muscularis mucosae and muscularis externa surrounding the lumen of the digestive tract iii Spontaneous depolarization of cells which triggers wave of contraction through the entire muscular sheet b Peristalsis III i Waves of contractions of the muscularis externa ii Helps move bolus along the length of digestive tract iii Peristaltic motion 1 Circular muscles will contract behind bolus while the circular muscles ahead of bolus relax 2 Longitudinal muscles ahead of the bolus will contract shortening adjacent segments 3 Wave of contraction in circular muscles force the bolus forward c Segmentation i Occurs in most areas of small intestine and some areas of large intestine ii Cycles of contraction 1 Churn and fragment the bolus and mix the contents with intestinal secretions 2 Does not follow a set pattern or push materials in any one direction Control of Digestive Functions a Local factors i Chemicals released into interstitial fluid such as histamine and prostaglandins 1 May affect adjacent cell walls within a small segment of the digestive tract a Histamine released at the lamina propria will cause increase in stomach acid release 2 Response is coordinated with changing conditions a Variations in local pH as well as in chemical or physical stimuli b Intestine wall stretching will cause a local contraction c Affects only a small portion of tract b Neural mechanisms i Control movement of materials along the digestive tract and secretions ii Motor neurons control smooth muscle contraction and glandular secretion 1 Located in myenteric plexus iii Short reflexes 1 Myenteric plexus is responsible for local reflexes a Operates entirely out of the control of the CNS b Controls small segments of tract iv Long reflexes 1 Higher level of control of digestive and glandular activities a Control of large scale peristaltic waves b Involve motor neurons and interneurons in CNS IV c May involve parasympathetic motor fibers that synapse in the myenteric plexus i Examples include glossopharyngeal vagus or pelvic nerves c Hormonal mechanisms i At least 18 peptide hormones affect most aspects of digestive function and activities of other systems ii Produce by enteroendocrine cells in digestive tract iii Reach target organs after distribution in bloodstream iv No hormones in the lumen Oral Cavity a Functions i Sensory analysis of materials before swallowing ii Mechanical process done by teeth tongue and palatal surfaces iii Lubrication through mixing with mucus and salivary gland secretions iv Limited carb digestion by salivary amylase and lipids by lingual lipase b Tongue i Functions 1 Mechanical process by compression abrasion and distortion 2 Manipulation to help with chewing and to prepare materials for swallowing 3 Sensory analysis through the use of touch temperature and taste receptors 4 Secretion of mucins and lingual lipase c Salivary glands i Produce saliva with different properties ii Three pairs 1 Parotid salivary glands produces serous secretions which have salivary amylase a Breaks down starches 2 Sublingual salivary glands produce mucous secretions that act as buffer and lubricant 3 Submandibular salivary glands makes buffer glycoproteins and salivary amylase a Mucins made of glycoproteins give saliva its lubricating property iii Saliva 1 Glands make 1 0 1 5 liters per day a 70 submandibular glands b 25 parotid glands c 5 sublingual glands 2 Made up of a 99 4 water b 0 6 includes i Electrolytes Na Cl and HCO3 ii Buffers iii Glycoproteins or mucins iv Antibodies v Enzymes vi Wastes 3 Functions a Lubrication of the mouth b Moistening and lubrication of materials in the mouth c Dissolving chemicals which stimulate taste buds and provide sensory information d Initiate digestion of complex carbs by salivary amylase ptyalin or alpha amylase 4 Control of secretions a By the autonomic nervous system i Parasympathetic innervation accelerates secretion by all salivary glands ii Sympathetic division unclear effects some evidence shows it produces
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