Introduction Digestive System Chapter 29 Provides processes to break down molecules into a state easily used by cells - A disassembly line: Starts at the mouth and ends at the anus Digestive functions are initiated by the parasympathetic division - Digestion occurs during periods of low activity - Produces more energy than it uses 1 2 Anatomy The Digestive System Oral cavity Pharynx Esophagus Stomach Small intestine and large intestine Accessory organs: Pancreas, liver, and gallbladder From Herlihy B: The human body in health and illness, ed 4, St. Louis, 2011, Saunders. 3 4 Physiology Gastrointestinal Tract Ingestion: Taking materials into mouth by eating/drinking Digestion: Breaking down food into molecules that can be used by the body - Includes mechanical and enzymatic action Absorption: Simple molecules from the gastrointestinal (GI) tract move into the bloodstream or lymph vessels and then into body cells Defecation: Eliminating indigestible or unabsorbed material from the body Muscular tube throughout digestive system Accessory organs and glands secrete substance to aid in digestion GI tract wall has four layers: - Mucosa - Submucosa - Muscle layer: Responsible for peristalsis - Serosa 5 6 1
Peristalsis Oral Cavity First portion of GI tract Contains: - Teeth - Tongue - Openings for salivary glands From Thibodeau GA, Patton KT: Anatomy & physiology, ed 6, St. Louis, 2007, Mosby. 7 8 Oral Cavity Teeth Where food is chewed (masticated) with help of the teeth and tongue Chewed food becomes a soft mass of food (bolus) Food is then swallowed and propelled toward the stomach via peristalsis Medical term for swallowing is deglutition Used to bite off and break up larger pieces of food into smaller ones Adults: 32 secondary teeth Children: 20 primary teeth - Usually shed between 6 and 12 years of age 9 10 Teeth Tongue Classified according to shape and function - Incisors - Cuspids: Canines - Bicuspids: Premolars - Multicuspids: Molars Third molars are called wisdom teeth Large, strong muscle that: - Mixes food with saliva - Directs bolus toward back of throat 11 12 2
Salivary Glands Salivary Gland Secretions Three pairs: - Submandibular - Sublingual - Parotid Largest Saliva: Clear, watery fluid that keeps mucosa moist and lubricates food Salivary amylase - Digestive enzyme found in saliva - Breaks down carbohydrates Lingual lipase - Breaks down lipids 13 14 Pharynx Esophagus Transports the bolus and liquids during swallowing Passageway for digestive and respiratory system Muscular tube from pharynx to stomach Secretes mucus to aid in transport of food Contains two valves (sphincters) - Upper esophageal sphincter: Keeps air from the stomach during breathing - Lower esophageal sphincter (LES): Trigger for relaxation is food travelling down esophagus and approaching the stomach 15 16 Stomach The Stomach J-shaped, saclike organ Enlargement of GI tract bound at both ends by sphincters - Serves as an expandable food storage tank Rugae: Folds in stomach lining that allow it to enlarge Three regions: Fundus, body, and pylorus - Also contains a greater curvature and lesser curvature From Herlihy B: The human body in health and illness, ed 4, St. Louis, 2011, Saunders. 17 18 3
Stomach Stomach Secretions Gastric juice: Blend of enzymes and acids - Eventually becomes chyme Chyme passes through the pyloric sphincter Body maintains energy needs with only two or three meals per day Hydrochloric acid: - Produced by parietal cells - Breaks down protein and activates many gastric enzymes Instrinsic factor: - Produced by parietal cells - Binds to B 12 ; temporarily protected from deactivation 19 20 Small Intestine Small Intestine Coiled tube bound at both ends by sphincters - Pyloric sphincter: Where digestive materials enter small intestine - Ileocecal sphincter: Where digestive materials leave small intestine Three sections: - Duodenum: Contains ducts from liver, gallbladder, and pancreas - Jejunum: Continues from duodenum (7 to 8 feet) - Ileum: Longest section (about 12 feet) Villi - Fingerlike projections that house blood and lymph capillaries Lacteals - Blood vessels and lymphatic vessels contained in each villus Microvilli: Give the small intestine a brush border 21 22 Small Intestine Wall Absorption Sites From Herlihy B: The human body in health and illness, ed 4, St. Louis, 2011, Saunders. 23 24 4
Large Intestine Large Intestine Sections Digestive materials enter and pass through the ileocecal sphincter Three sections: - Cecum - Colon - Rectum Cecum - Small saclike structure located in right lower quadrant - Vermiform appendix hangs from cecum Contains lymphatic tissue Ascending colon: From cecum to hepatic (right colic) flexure Transverse colon: From hepatic flexure to splenic (left colic) flexure 25 26 Large Intestine Sections Large Intestine Descending colon - From splenic flexure to sigmoid flexure Sigmoid colon - From sigmoid flexure to rectum Rectum - Stores feces; terminal section is the anal canal Anus: Contains anal sphincter From Thibodeau GA, Patton KT: Anatomy & physiology, ed 6, St. Louis, 2007, Mosby. 27 28 Defecation Peritoneum Rectum fills with feces Anal sphincter distends, causing defecation reflex Feces is eliminated - Feces = stool Large serous membrane that envelops abdominal cavity Layers - Parietal peritoneum: Lies against abdominal cavity wall - Visceral peritoneum: Surrounds each abdominal organ Peritoneal cavity lies between the two layers and contains serous fluid 29 30 5
Mesenteries Peritoneum Mesenteries: Connect all divisions of small intestine to each other Contain: - Greater omentum: From stomach and duodenum to transverse colon - Lesser omentum: From stomach and duodenum to the liver From Thibodeau GA, Patton KT: Anatomy & physiology, ed 6, St. Louis, 2007, Mosby. 31 32 Accessory Organs Accessory Organs Consists of the: - Liver - Gallbladder - Pancreas Produce substances that aid digestion 33 34 Liver Liver Functions Largest internal organ Lies beneath diaphragm Most complex internal organ Performs many important functions Metabolizes carbohydrates, proteins, and fats Produces blood cells during fetal development Produces plasma proteins and antibodies Stores many nutrients Detoxifies blood by removing toxic wastes, drugs, and hormones Destroys old red blood cells and platelets Produces bile 35 36 6
Liver Secretions Gallbladder Bile - Breaks apart large fat globules into smaller ones - This creates a larger surface area for fat-digesting enzymes - Gives urine and stool their colors Pear-shaped sac that lies on inferior surface of the liver Stores and concentrates bile produced by liver Rugae enable gallbladder to expand as it fills with bile - Gallbladder sometimes contracts and moves bile into duodenum 37 38 Pancreas Pancreas Secretions Shaped like a fish Pancreatic duct runs length of pancreas and empties into the duodenum Secretes enzymes that break down all categories of digestible foods Pancreatic islets contain alpha and beta cells - Secrete glucagon and insulin Trypsinogen - Becomes trypsin when it enters duodenum Chymotrypsin and carboxypeptidase - Break down proteins Pancreatic amylase - Converts polysaccharides into disaccharides Pancreatic lipase helps convert fats into fatty acids 39 40 Pancreatic Cells Modified from Patton KT: Anatomy & Physiology, ed 8, St. Louis, 2013, Mosby. 41 7