BSC2086 A P II Exam 4 Study Guide Lesson 16 18 The Digestive System The Digestive Tract Digestive Tract also called gastrointestinal tract GI or alimentary canal Muscular tube that extends from oral cavity anus o Passes through Pharynx Esophagus Stomach Small large intestines Acquires nutrients from environment o Provides substrates for catabolic reactions break down substances to provide energy cells need to function to perform anabolic reactions that build macromolecules Six 6 Functions of the Digestive System o Ingestion Occurs when materials enter digestive tract via the mouth o Mechanical Processing Crushing shearing makes materials easier to propel along digestive tract o Digestion Chemical breakdown of food into small organic fragments for absorption by digestive epithelium o Secretion The release of water acids enzymes buffers and salts by epithelium of digestive tract or glandular organs o Absorption Movement of organic substrates electrolytes vitamins and water across the digestive epithelium into interstitial fluid of digestive tract o Excretion Removal of waste products from body fluids Defecation Process that removes feces Lining of digestive tract o Protects surrounding tissues from Corrosive effects of digestive acids enzymes Mechanical stresses abrasion Bacteria ingested with food or residing in the digestive tract o Digestive epithelium its secretions provide nonspecific defense Digestive organs peritoneum o Lined with serous membrane consisting of two 2 parts Serosa Visceral Peritoneum Covers organs within peritoneal cavity Parietal Peritoneum Lines inner surfaces of body wall o Peritoneal Fluid Fluid produced by serous membrane lining Provides essential lubrication Reduces friction irritation Separates parietal visceral surfaces Ascites Excess peritoneal fluid causing abdominal swelling Caused by liver kidney heart disease Can distort internal organs cause heartburn indigestion lower back pain 1 BSC2086 A P II Exam 4 Study Guide Mesenteries Double sheets of peritoneal membrane o Suspend portions of digestive tract within peritoneal cavity abdominal cavity by sheets of serous membrane that connect parietal peritoneum with visceral peritoneum o Stabilize positions of attached organs o Prevent intestines from becoming entangled o Peritonitis Inflammation of peritoneal membrane Caused by Physical damage rupture of stomach intestine appendix Chemical irritation Bacterial invasion Can be fatal Four 4 Major Layers of the Digestive Tract o Mucosa Inner mucosa membrane lining composed of epithelium lamina propria muscles Has blood vessels sensory nerves lymphatic vessels smooth Muscularis Mucosae Narrow band of smooth muscle elastic fibers in lamina propria Smooth muscle cells arranged in two 2 concentric layers o Inner circular layer o Outer longitudinal layer Contractions alter shape of lumen o Move epithelial pleats folds Enteroendocrine Cells Secrete hormones that coordinate activities of the digestive tract accessory glands Lining of digestive tract consists of permanent transverse folds plicae circulares to increase surface area for absorption Longitudinal folds disappear as digestive tract fills o Submucosa Layer of dense irregular connective tissue Surrounds muscularis mucosae of mucosa binds it to the Has large blood vessels lymphatic vessels May contain exocrine glands that secrete buffers enzymes into Submucosal Plexus Intrinsic nerve fibers that innervate mucosa Contains sensory neurons sympathetic parasympathetic muscularis externa digestive tract lumen submucosa components o Muscularis Externa Dominated by smooth muscle cells Two 2 muscle layers Inner circular layer Outer longitudinal layer Moves substances along digestive tract Movement coordinated by enteric nervous system ENS Myenteric Plexus Located between circular longitudinal layers 2 BSC2086 A P II Exam 4 Study Guide Innervated primarily by parasympathetic division Parasympathetic stimulation increases muscle tone activity Sympathetic stimulation causes muscular inhibition relaxation o Serosa Serous membrane covering muscularis externa NOT in oral cavity pharynx esophagus rectum Those areas covered by adventitia dense sheath of collagen fibers that firmly attaches the digestive tract to adjacent structures Movement of digestive materials by muscular layers of digestive tract o Visceral smooth muscle tissue along digestive tract with rhythmic cycles of activity Controlled by pacesetter cells located in muscularis mucosae muscularis externa surrounding lumen of digestive tract o Cells undergo spontaneous depolarization Triggers wave of contraction through entire muscular sheet o Peristalsis Waves of muscular contractions of the muscularis externa Moves a bolus along the length of the digestive tract Peristaltic Motion 3 BSC2086 A P II Exam 4 Study Guide Circular muscles contract behind bolus while circular muscles ahead of bolus relax Longitudinal muscles ahead of bolus contract shortening Wave of contractions in circular muscles that forces bolus adjacent segments forward o Segmentation Occurs in most areas of small intestine some areas of large intestine Cycles of contraction Churn fragment the bolus Mix contents with intestinal secretions Doesn t follow a set pattern Does NOT push materials in any one direction Control of Digestive Functions o Local Factors Prostaglandins histamine other chemicals released into interstitial fluid May affect adjacent cells within small segment of digestive tract Ex Histamine release at lamina propria causes increase in stomach acid release 4 BSC2086 A P II Exam 4 Study Guide Coordinate response to changing conditions Variations in local pH Chemical or physical stimuli o Intestine wall stretching causes local contraction Affect only a portion of the GI tract o Neural Mechanisms Motor neurons located in myenteric plexus Short Reflexes Responsible for local reflexes o Operate entirely outside of CNS control o Control smooth muscle contraction peristalsis glandular secretion secretory functions Long Reflexes CNS control of digestive glandular activities o o May involve parasympathetic fibers that synapse onto Involves CNS interneurons and motor neurons myenteric plexus o Controls large scale peristaltic waves At least 18 peptide hormones produced by enteroendocrine cells in o Hormonal Mechanisms digestive tract Affect o Most aspects of digestive function o Activities of other systems Reach target organs after distribution in bloodstream The Oral Cavity Functions of
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