BSC 2086 1st Edition Lecture 19Outline of Last Lecture I. Gas TransportII. Respiration ControlIII. Effects of AgingIV. Digestive Tract Outline of Current Lecture I. Layers of Digestive TractII. Movement of Materials in Digestive Tract III. Control of Digestive FunctionsIV. Oral CavityV. PharynxVI. EsophagusVII. StomachCurrent LectureI. Layers of Digestive Tracta. Mucosa i. Inner mucous membrane liningii. Has epithelium and lamina propria 1. Lamina propria has blood vessels, sensory nerves, lymphatics, andsmooth musclesiii. 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 layer1. Contractions will alter the lumens shape and move the epithelial pleats and folds v. Enteroendocrine cells: secrete hormones which coordinate digestive tractand accessory gland activities vi. Plicae circularis: permanent transverse folds located in the lining of the digestive tract 1. Increases surface area to increase absorption2. Has longitudinal folds that disappear as the digestive tract fillsb. Submucosa i. Layer made of dense, irregular connective tissueii. Surrounds the muscularis mucosae of the mucosa and binds it to the muscularis externaiii. 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 componentsc. Muscularis externa i. Smooth muscle cells inner circular layer and outer longitudinal layerii. Moves substances along the digestive tractiii. Enteric nervous system (ENS): coordinates movement1. Myenteric plexus: located between circular and longitudinal layersa. Innervated mainly by parasympathetic division which increases muscle tone and activityb. Sympathetic stimulation will cause muscular inhibition andrelaxation d. Serosa i. Serous membrane which covers the muscularis externaii. Oral cavity, pharynx, esophagus and membrane are not covered by serousmembrane, instead they are covered by adventitia 1. Adventitia: dense sheath of collagen fibers which firmly attaches the digestive tract to adjacent structure II. Movement of Materials in Digestive Tract a. Movement due to muscular layers of digestive tracti. Have visceral smooth muscle tissue along the digestive tract ii. Rhythmic cycles of activity controlled by pacesetter cells1. Located in muscularis mucosae and muscularis externa, surrounding the lumen of the digestive tractiii. Spontaneous depolarization of cells, which triggers wave of contraction through the entire muscular sheet b. Peristalsisi. Waves of contractions of the muscularis externaii. Helps move bolus along the length of digestive tract iii. Peristaltic motion1. Circular muscles will contract behind bolus while the circular muscles ahead of bolus relax2. Longitudinal muscles ahead of the bolus will contract, shortening adjacent segments3. 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 intestineii. Cycles of contraction:1. Churn and fragment the bolus, and mix the contents with intestinal secretions2. Does not follow a set pattern or push materials in any one directionIII. Control of Digestive Functionsa. Local factorsi. 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 release2. Response is coordinated with changing conditionsa. Variations in local pH, as well as in chemical or physical stimulib. Intestine wall stretching will cause a local contractionc. Affects only a small portion of tractb. Neural mechanisms i. Control movement of materials along the digestive tract and secretionsii. Motor neurons control smooth muscle contraction and glandular secretion 1. Located in myenteric plexusiii. Short reflexes1. Myenteric plexus is responsible for local reflexes a. Operates entirely out of the control of the CNS b. Controls small segments of tractiv. Long reflexes1. Higher level of control of digestive and glandular activitiesa. Control of large scale peristaltic wavesb. Involve motor neurons and interneurons in CNSc. May involve parasympathetic motor fibers that synapse in the myenteric plexus i. Examples include glossopharyngeal, vagus or pelvic nervesc. Hormonal mechanismsi. At least 18 peptide hormones affect most aspects of digestive function and activities of other systemsii. Produce by enteroendocrine cells in digestive tractiii. Reach target organs after distribution in bloodstreamiv. No hormones in the lumenIV. Oral Cavitya. Functionsi. Sensory analysis of materials before swallowingii. Mechanical process done by teeth, tongue and palatal surfacesiii. Lubrication through mixing with mucus and salivary gland secretionsiv. Limited carb digestion by salivary amylase and lipids by lingual lipaseb. Tongue i. Functions1. Mechanical process by compression, abrasion and distortion2. Manipulation to help with chewing and to prepare materials for swallowing3. Sensory analysis through the use of touch, temperature and taste receptors. 4. Secretion of mucins and lingual lipasec. Salivary glandsi. Produce saliva with different propertiesii. 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 lubricant3. Submandibular salivary glands: makes buffer, glycoproteins and salivary amylasea. Mucins made of glycoproteins give saliva its lubricating propertyiii. Saliva 1. Glands make 1.0-1.5 liters per daya. 70% submandibular glandsb. 25% parotid glandsc. 5% sublingual glands2. Made up of:a. 99.4% waterb. 0.6% includesi. Electrolytes (Na+, Cl-, and HCO3-)ii. Buffersiii. Glycoproteins or mucinsiv. Antibodiesv. Enzymesvi. Wastes3. Functions:a. Lubrication of the mouthb. Moistening and lubrication of materials in the mouthc. 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 secretionsa. By the autonomic nervous systemi. Parasympathetic innervation: accelerates
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