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PowerPoint® Lecture Slide Presentation by Vince Austin Human Anatomy & Physiology FIFTH EDITION Elaine N. Marieb Chapter 24 The Digestive System Part A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Digestive System • Takes in food • Breaks food down into nutrient molecules • Absorbs these molecules into the blood stream • Rids the body of indigestible remains 2 Digestive System: Overview • The alimentary canal or gastrointestinal (GI) tract digests and absorbs food • Alimentary canal – mouth, pharynx, esophagus, stomach, small intestine, and large intestine: a long tube • Accessory digestive organs – teeth, tongue, gallbladder, salivary glands, liver, and pancreas; not part of the tube but help with digestion 3 4 Figure 22.1 Digestion • Mechanism for nourishing the body • Most nutrients in food require either degradation ( break apart) or release prior to absorption • Digestion occurs in GI Tract • Digestion – Mechanical • chewing and peristalsis – Chemical • enzymes, HCl • The GI tract is a “disassembly” line • Nutrients become more available to the body in each step 6 7 Digestive Process • There are six essential activities: • Ingestion • Propulsion • Mechanical digestion • Chemical digestion • Absorption • Defecation Figure 22.2 8 Essential Activities of Digestion • Ingestion – taking food in • Propulsion – swallowing and peristalsis • Peristalsis – waves of contraction and relaxation of muscles in organ walls, esophagus and intestine • Mechanical digestion – chewing; mixing; churning food 9 Movement of digestive materials • Visceral (organ) smooth muscle shows rhythmic cycles of activity • Pacemaker cells • Peristalsis • Waves that move a bolus (rounded mass of food that is swallowed) • Segmentation • Churn and fragment a bolus 10 Figure 22.4 Peristalsis 11 Figure 22.4 Essential Activities of Digestion bolus 12 Figure 22.3a, b Essential Activities of Digestion • Chemical digestion – catabolic breakdown of food • Absorption – movement of nutrients from GI tract to blood or lymph • Defecation – elimination of indigestible solid wastes 13 14 Figure 22.2 Figure 22.2 GI Tract • External environment for the digestive process; open to outside at both ends • Regulation of digestion involves: • Mechanical and chemical stimuli • Extrinsic control by CNS centers • Intrinsic control by local centers 15 Receptors of the GI Tract • Mechano- and chemoreceptors respond to: • Stretch by food in lumen • Osmolarity(solute concentration) and pH • Presence of substrate or • End products of digestion • They initiate reflexes that: • Activate or inhibit digestive glands • Mix lumen contents and move them along 16 Control of the digestive system • Movement of materials along the digestive tract is controlled by: • Neural mechanisms • Parasympathetic and local reflexes • Hormonal mechanisms • Enhance or inhibit smooth muscle contraction • Local mechanisms • Coordinate response to changes in pH or chemical stimuli 17 Nervous Control of the GI Tract • Intrinsic controls • Nerve plexuses near the GI tract initiate short reflexes • Short reflexes are mediated by local enteric plexuses (gut brain) • Extrinsic controls • Long reflexes arising within or outside the GI tract • Involve CNS centers and extrinsic autonomic nerves 18 Nervous Control of the GI Tract 19 Figure 22.4 Figure 22.5 The Regulation of Digestive Activities 20 Figure 22.5 Digestive System Organs and Peritoneum • Peritoneum – serous membrane of the abdominal cavity • Visceral – covers external surface of most digestive organs • Parietal – lines the body wall 21 Figure 22.5a Digestive System Organs and Peritoneum • Peritoneal cavity • Lubricates digestive organs • Allows them to slide across one another 22 Figure 22.5a Digestive System Organs and Peritoneum • Mesentery – double layer of peritoneum • Vascular(blood) and nerve supplies to the viscera • A means to hold digestive organs in place and store fat • Retroperitoneal organs – organs outside the peritoneum • Peritoneal organs (intraperitoneal) – organs surrounded by peritoneum 23 Figure 22.5b 24 The digestive system organs and the peritoneum • Mesenteries • Sheets of serous membranes that support portions of the digestive tract • Greater omentum lies anterior to abdominal viscera • Provides padding, protection, insulation, and energy reserves • Lesser omentum 25 26 Figure 24.2 Mesenteries 27 Figure 24.2b Figure 24.2 Mesenteries 28 Figure 24.2c Figure 24.2 Mesenteries 29 Figure 24.2d PowerPoint® Lecture Slide Presentation by Vince Austin Human Anatomy & Physiology FIFTH EDITION Elaine N. Marieb Chapter 24 The Digestive System Part B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Blood Supply: Splanchnic Circulation • Arteries that branch off abdominal aorata and the organs they serve include • The hepatic: liver, splenic:spleen, and left gastric: stomach • Inferior and superior mesenteric: small and large intestines • Hepatic portal circulation: • Collects nutrient-rich venous blood from the digestive viscera (organs) • Delivers it to the liver for metabolic processing and storage 31 Histology of the Alimentary Canal • From esophagus to the anal canal the walls of the GI tract have the same four tunics • From the lumen outward they are the: • mucosa • submucosa • muscularis externa • and serosa • Note: serosa is technically not present on the esophagus • Each tunic has a predominant tissue type and specific digestive function 32 Histology of the Alimentary Canal 33 Figure 24.6 Figure 24.3 The Structure of the Digestive Tract 34 Figure 24.3 Mucosa • Moist epithelial layer -- lines the lumen of the alimentary canal • Its three major functions are: • Secretion of mucus • Absorption of the end products of digestion • Protection against infectious disease • Consists of three layers: • lining epithelium • lamina propria • muscularis mucosae 35 Mucosa: Epithelial Lining • Consists of simple columnar epithelium and mucus-secreting goblet cells • The mucus secretions: • Protect digestive organs from digesting themselves • Ease food along tract • Stomach and small intestine mucosa contain: • Enzyme-secreting cells • Hormone-secreting cells 36 Mucosa: Lamina Propria and Muscularis Mucosae • Lamina Propria • Loose areolar and reticular connective tissue • Nourishes the epithelium and absorbs nutrients • Contains lymph nodes (part of MALT-Mucosa Associated Lymphatic Tissue) important in defense against bacteria • Muscularis mucosae– smooth muscle cells that produce local movements of mucosa 37 Mucosa: Other Sublayers • Submucosa – dense connective tissue containing: • elastic fibers • blood and lymphatic vessels • lymph nodes • nerves • Muscularis externa – responsible for segmentation and peristalsis • Serosa – the protective visceral peritoneum • Replaced by the fibrous adventitia in the esophagus 38 • Retroperitoneal organs have both an adventitia and serosa Enteric Nervous System • Composed of two major intrinsic nerve plexuses • Submucosal nerve plexus – regulates glands and smooth muscle in the mucosa • Myenteric nerve plexus: • Major nerve supply that controls GI tract mobility • Segmentation and peristalsis • Linked to the CNS via long autonomic reflex arc • Parasympatheitic enhances • Sympathetic inhibits 39 Enteric nevous system or “gut brain” 100 million neurons-more than the spinal cord PowerPoint® Lecture Slide Presentation by Vince Austin Human Anatomy & Physiology FIFTH EDITION Elaine N. Marieb Chapter 24 The Digestive System Part C Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Mouth • Oral or buccal cavity: • Is bounded by lips, cheeks, palate, and tongue • Has the oral orifice as its anterior opening • Is continuous with the oropharynx posteriorly • To withstand abrasions: • The mouth is lined with stratified squamous epithelium • The gums, hard palate, and dorsum of the tongue are slightly keratinized 41 Mouth 42 Figure 24.7a Lips and Cheeks • Have a core of skeletal muscles • Lips: orbicularis oris • Cheeks: buccinators • Vestibule – bounded by the lips and cheeks externally and teeth and gums internally • Oral cavity proper– area that lies within the teeth and gums • Labial frenulum – median fold that joins the internal aspect of each lip to the gum 43 Figure 24.7b Lips and Cheeks 44 Figure 24.7b Palate • Hard palate – underlain by palatine bones and palatine processes of the maxillae • Assists the tongue in chewing • Slightly corrugated on either side of the raphe (midline ridge) • Soft palate – mobile fold formed mostly of skeletal muscle • Closes off the nasopharynx during swallowing • Uvula projects downward from its free edge • Palatoglossal and palatopharyngeal arches form the borders of the fauces 45 Cleft palate Tongue • Occupies the floor of the mouth and fills the oral cavity when mouth is closed • Functions include: • Gripping and repositioning food during chewing • Mixing food with saliva and forming the bolus • Initiation of swallowing, and speech • Intrinsic muscles change the shape of the tongue • Extrinsic muscles alter the tongue’s position • Lingual frenulum secures the tongue to the floor of the mouth 47 Homeostatic Imbalance • Ankyloglossia – congenital situation where the lingual frenulum is extremely short • Commonly referred to as being “tongue-tied” • Corrected surgically by cutting the frenulum 48 Tongue • Superior surface bears three types of papillae • Filiform – give the tongue roughness and provide friction • Fungiform – scattered widely over the tongue and give it a reddish hue • Circumvallate – V-shaped row in back of tongue • Sulcus terminalis – groove that separates the tongue into two areas: • Anterior 2/3 residing in the oral cavity • Posterior third residing in the oropharynx 49 Tongue 50 Figure 24.8a Taste and taste buds • Most of the 10,000 or so taste buds are found on the tongue • Taste buds are found in papillae of the tongue mucosa • Fungiform and circumvallate papillae contain taste buds Five taste sensations • There are five basic taste sensations • Sweet – sugars, saccharin, alcohol, and some amino acids • Salt – metal ions • Sour – hydrogen ions • Bitter – alkaloids such as quinine and nicotine • Umami – elicited by the amino acid glutamate • Taste is 80% smell Salivary Glands • Produce and secrete saliva that: • Cleanses the mouth • Moistens and dissolves food chemicals • Aids in bolus formation • Contains enzymes that breakdown starch • Three pairs of extrinsic glands – • parotid • submandibular • sublingual • Intrinsic salivary glands (buccal glands) – scattered throughout the oral mucosa 54 Salivary Glands • Parotid – lies anterior to the ear between the masseter muscle and skin • Parotid duct – opens into the vestibule next to the second upper molar • Submandibular – lies along the medial aspect of the mandibular body • Its ducts open at the base of the lingual frenulum • Sublingual – lies anterior to the submandibular gland under the tongue • It opens via 10-12 ducts into the floor of the mouth 55 Salivary Glands II 56 Figure 24.9a Homeostatic Imbalance • Mumps – inflammation of the parotid glands caused by myxovirus • Signs and symptoms – moderate fever and pain in swallowing acidic foods • In adult males, mumps carries 25% risk that testes may become infected, leading to sterility 57 58 Saliva: Source and Composition • Secreted from serous and mucous cells of salivary glands • A 97-99.5% water, hypo-osmotic, slightly acidic solution containing • Electrolytes – Na+, K+, Cl–, PO42–, HCO3– • Digestive enzyme – salivary amylase • Proteins – mucin, lysozyme, defensins, and IgA • Metabolic wastes – urea and uric acid 59 Control of Salivation • Intrinsic glands keep the mouth moist • Extrinsic salivary glands secrete serous, enzymerich saliva in response to: • Ingested food which stimulates chemoreceptors and pressoreceptors • The thought of food • Strong sympathetic stimulation inhibits salivation and results in dry mouth 60 Teeth • Primary and permanent dentitions have formed by age 21 • Primary – 20 deciduous teeth that erupt at intervals between 6 and 24 months • Permanent – enlarge and develop causing the root of deciduous teeth to be resorbed and fall out between the ages of 6 and 12 years • All but the third molars have erupted by the end of adolescence • There are usually 32 permanent teeth 61 Teeth 62 Figure 24.10.2 Classification of Teeth • Teeth are classified according to their shape and function • Incisors – chisel-shaped teeth adapted for cutting or nipping • Canines – conical or fanglike teeth that tear or pierce • Premolars (bicuspids) and molars – have broad crowns with rounded tips and are best suited for grinding or crushing • During chewing, upper and lower molars lock together generating crushing force = 170N 63 Tooth Structure Two main regions – crown and the root • Crown – exposed part of the tooth above the gingiva (gum) encapsulaed by enamel • Enamel – acelluar, brittle material composed of calcium salts and hydroxyapatite crystals;the hardest substance in the body • Root – portion of the tooth embedded in the jawbone 64 Tooth Structure • Neck – constriction where the crown and root come together • Cementum – calcified connective tissue • Covers the root • Attaches it to the periodontal ligament • Periodontal ligament • Anchors the tooth in the alveolus of the jaw • Forms the fibrous joint called a gomaphosis • Gingival sulcus – depression where the gingival borders the tooth 65 Tooth Structure • Dentin – bonelike material deep to the enamel cap that forms the bulk of the tooth • Pulp cavity – cavity surrounded by dentin that contains pulp • Pulp – connective tissue, blood vessels, and nerves • Root canal – portion of the pulp cavity that extends into the root • Apical foramen – proximal opening to the root canal • Odontoblasts – secrete and maintain dentin throughout life 66 Tooth Structure 67 Figure 24.11 Homeostatic Imbalance • Root canal therapy – blows to the teeth can cause swelling and consequently pinch off the blood supply to the tooth. The nerve dies and may become infected with bacteria • the cavity is sterilized and filled with an inert material • The tooth is capped 68 Tooth and Gum Disease • Dental caries or cavities – gradual demineralization of enamel and dentin by bacterial action • Dental plaque, a film of sugar, bacteria, and mouth debris, adheres to teeth • Acid produced by the bacteria in the plaque dissolves calcium salts • Without these salts, organic matter is digested by proteolytic enzymes • Daily flossing and brushing help prevent caries by removing forming plaque 69 Dental Caries 70 Tooth and Gum Disease: Periodontitis • Gingivitis –plaque accumulates, calcifies and forms calculus, or tartar • Accumulation of tartar: • Disrupts the seal between the gingivae and the teeth • Puts the gums at risk for infection • Periodontitis – serious gum disease resulting from an immune response • Attack of the immune system against intruders: • Also carves pockets around the teeth and • Dissolves bone away 71 • Can cause heart problems including heart attack!! Periodontitis 72 Pharynx • From the mouth, the oro- and laryngopharynx allow passage of: • Food and fluids to the esophagus • Air to the trachea • Lined with stratified squamous epithelium and mucus glands • Has two skeletal muscle layers • Inner longitudinal • Outer pharyngeal constrictors 73 Esophagus • Muscular tube going from the laryngopharynx to the stomach • Travels through the mediastinum and pierces the diaphragm • Joins the stomach at the cardiac orifice 74 Homeostatic Imbalance • Heartburn (gastroesophageal reflux disease or GERD) – burning, radiating substernal pain caused by acidic gastric juice regurgitated into the esophagus • Caused by excess eating or drinking, and conditions that force abdominal contents superiorly (e.g., extreme obesity, pregnancy, and running) • Hiatus hernia – structural abnormality in which the superior part of the stomach protrudes slightly above the diaphragm • Prolonged episodes can lead to esophagitis, ulcers, and cancer 75 Esophageal Characteristics • Esophageal mucosa – nonkeratinized stratified squamous epithelium • The empty esophagus is folded longitudinally and flattens when food is present • Glands secrete mucus as a bolus moves through the esophagus • Muscularis changes from skeletal (superiorly) to smooth muscle (inferiorly) 76 Digestive Processes in the Mouth • Food is ingested • Mechanical digestion begins (chewing) or mastication • Propulsion is initiated by swallowing • Salivary amylase begins chemical breakdown of starch • The pharynx and esophagus serve as conduits to pass food from the mouth to the stomach 77 Deglutition (Swallowing) • Involves the coordinated activity of the tongue, soft palate, pharynx, esophagus and 22 separate muscle groups • Buccal phase – bolus is forced into the oropharynx • Pharyngeal-esophageal phase – controlled by the medulla and lower pons • All routes except into the digestive tract are sealed off • Peristalsis moves food through the pharynx to the esophagus 78 Deglutition (Swallowing) 79 Figure 24.13a-c Deglutition (Swallowing) 80 Figure 24.13d, e Stomach 81 Figure 24.14a Digestion in the Stomach • The stomach: • Holds ingested food • Degrades it both physically and chemically • Chemical breakdown of proteins begins and food is converted to chyme • Delivers chyme to the small intestine • Enzymatically digests proteins with pepsin • Secretes intrinsic factor required for absorption of vitamin B12 82 Microscopic Anatomy of the Stomach • Muscularis – has an additional oblique layer that • Allows the stomach to churn, mix and pummel food physically • Breaks down food into smaller fragments • Epithelial lining is composed of: • Goblet cells that produce a coat of alkaline mucus • Gastric pits containing gastric glands that secrete: • Gastric juice • Mucus • Gastrin 83 Glands of the Stomach Fundus and Body • Gastric glands of the fundus and body have a variety of secretory cells • Mucous neck cells – secrete acid mucus • Parietal (oxyntic) cells – secrete HCl and intrinsic factor • Chief (zymogenic) cells – produce pepsinogen • Pepsinogen is activated to pepsin by: – HCl in the stomach – Pepsin itself by a positive feedback mechanism • Enteroendocrine cells – secrete gastrin, histamine, endorphins, serotonin, cholecystokinin (CCK), and somatostatin into the lamina propria 84 85 Stomach Lining • The stomach is exposed to the harshest conditions in the digestive tract • To keep from digesting itself, the stomach has a mucosal barrier with: • A thick coat of bicarbonate-rich mucus on the stomach wall • Epithelial cells that are joined by tight junctions • Gastric glands that have cells impermeable to HCl • Damaged epithelial cells are quickly replaced 86 Regulation of Gastric Secretion • Neural and hormonal mechanisms regulate the release of gastric juice • Stimulatory and inhibitory events occur in three phases • Cephalic (reflex) phase: prior to food entry • Gastric phase: once food enters the stomach • Intestinal phase: as partially digested food enters the duodenum 87 Cephalic Phase • Excitatory events include: • Sight or thought of food • Stimulation of taste or smell receptors • Inhibitory events include: • Loss of appetite or depression • Decrease in stimulation of the parasympathetic division 88 Gastric Phase • Excitatory events include: • Stomach distension • Activation of stretch receptors (neural activation) • Activation of chemoreceptors by peptides, caffeine, and rising pH • Release of gastrin to the blood • Inhibitory events include: • A pH lower than 2 • Emotional upset which overrides the parasympathetic division 89 Intestinal Phase • Excitatory phase – low pH and partially digested food enters the duodenum • Inhibitory phase – distension of duodenum, presence of fatty, acidic, or hypertonic chyme, and/or irritants in the duodenum • Closes the pyloric sphincter • Releases enterogastrones that inhibit gastric secretion 90 Release of Gastric Juice 91 Figure 24.16 92 93 94 Regulation and Mechanism of HCl Secretion • HCl secretion is stimulated by ACh, histamine, and gastrin • Release of hydrochloric acid: • Is low if only one ligand binds to parietal cells • Is prolific if all three ligands bind to parietal cells • Antihistamines and cimetidine (Tagamet) block H2 receptors and decrease HCl release; proton pump inhibitors like Prilosec interupt HCl production at pump and stop production. 95 Regulation and Mechanism of HCl Secretion 96 Figure 24.17 Response of the Stomach to Filling • Stomach pressure remains constant until about 1L of food is ingested • Relative unchanging pressure results from reflexmediated relaxation and plasticity • Reflex-mediated events include: • Receptive relaxation – as food travels in the esophagus, stomach muscles relax • Adaptive relaxation – the stomach dilates in response to gastric filling • Plasticity – intrinsic ability of smooth muscle to exhibit the stress-relaxation response 97 Gastric Contractile Activity • Peristaltic waves move toward the pylorus at the rate of 3 per minute • This basic electrical rhythm (BER) is initiated by pacemaker cells (cells of Cajal) • Most vigorous peristalsis and mixing occurs near the pylorus • Chyme is either: • Delivered in small amounts to the duodenum or • Forced backward into the stomach for further mixing 98 Gastric Contractile Activity 99 Figure 24.18 Regulation of Gastric Emptying • Gastric emptying is regulated by: • The neural enterogastric reflex • Hormonal (enterogastrone) mechanisms • These mechanisms inhibit gastric secretion and duodenal filling • Carbohydrate-rich chyme moves through the duodenum quickly • Fat-laden chyme is digested more slowly causing food to remain in the stomach longer 100 1 Regulation of Gastric Emptying Figure 24.19 Homeostatic Imbalance • Vomiting (emesis) – the stomach empties via a different route (oral) • Causes include extreme stretching, irritants such as bacterial toxins, excessive alcohol, spicy foods, and certain drugs • The emetic center of the medulla initiates a number of motor responses • Diaphragm and abdominal wall muscle contract • Cardiac sphincter relaxes and soft palate closes off the nasal passages • Excessive vomiting can cause dehydration and upset electrolyte and pH balance 102 Small Intestine: Gross Anatomy • Runs from pyloric sphincter to the ileocecal valve • Has three subdivisions: duodenum, jejunum, and ileum • The bile duct and main pancreatic duct: • Join the duodenum at the hepatopancreatic ampulla • Are controlled by the sphincter of Oddi • The jejunum extends from the duodenum to the ileum • The ileum joins the large intestine at the ileocecal valve 103 104 Microscopic Anatomy of the Small Intestine • Structural modifications of the small intestine wall increase surface area • Plicae circulares: deep circular folds of the mucosa and submucosa • Villi: fingerlike extensions of the mucosa • Microvilli: tiny projections of absorptive mucosal cells’ plasma membranes 105 Microscopic Anatomy of the Small Intestine 106 Figure 24.21a-c Small Intestine: Histology of the Wall • The epithelium of the mucosa is made up of: • Absorptive cells and goblet cells • Interspersed T cells (intraepithelial lymphocytes), and • Enteroendocrine cells • Intestinal crypts cells secrete intestinal juice • Peyer’s patches are found in the submucosa • lymphoid tissue; fights infection causing bacteria • Brunner’s glands in the duodenum secrete alkaline mucus 107 Intestinal Juice • Secreted by intestine glands in response to distension or irritation of the mucosa • It is slightly alkaline and isotonic with blood plasma • Is largely water, enzyme-poor, but contains mucus 108 Liver • The largest gland in the body • Superficially has four lobes – right, left, caudate, and quadrate • The falciform ligament: • Separates the right and left lobes anteriorly • Suspends the liver from the diaphragm and anterior abdominal wall • The ligamentum teres: • Is a remnant of the fetal umbilical vein • Runs along the free edge of the falciform ligament 109 Liver: Associated Structures • The lesser omentum anchors the liver to the stomach • The hepatic blood vessels enter the liver at the porta hepatis • The gallbladder rests in a recess on the inferior surface of the right lobe • Bile leaves the liver via • Bile ducts which fuse into the common hepatic duct • The common hepatic duct fuses with the cystic duct • These two ducts form the bile duct 110 Liver: Associated Structures 111 Figure 24.20 The Liver 112 p.286 Microscopic Anatomy of the Liver • Hexagonal-shaped liver lobules are the structural and functional units of the liver • Composed of hepatocyte (liver cell) plates radiating outward from a central vein • Portal triads are found at each of the six corners of each liver lobule • Portal triads consist of • a bile duct and • Hepatic artery – supplies oxygen-rich blood to the liver • Hepatic portal vein – carries venous blood with nutrients from digestive viscera 113 Microscopic Anatomy of the Liver 114 Figure 24.24c, d Microscopic Anatomy of the Liver • Liver sinusoids – enlarged, leaky capillaries located between hepatic plates • Kupffer cells – hepatic macrophages found in liver sinusoids • Hepatocytes’(liver cells) functions include: • Production of bile • Processing blood borne nutrients • Storage of fat-soluble vitamins • Detoxification • Secreted bile flows between hepatocytes toward the bile ducts in the portal triads 115 Microscopic Anatomy of the Liver Figure 24.24c, d 116 Homeostatic Imbalance • Hepatitis – inflammation of the liver often due to viral infection • Viruses causing hepatitis are catalogued has HVA through HVF • HVA and HVE are transmitted enterically and cause self-limiting infections • Hepatitis B is transmitted via blood transfusions, contaminated needles, and sexual contact, and increases the risk of liver cancer • Hepatitis C produces chronic liver infection • Nonviral hepatitis is caused by drug toxicity and wild mushroom poisoning 117 Homeostatic Imbalance • Cirrhosis – diffuse and progressive chronic inflammation of the liver • Typically results from chronic alcoholism or severe chronic hepatitis • The liver becomes fatty and fibrous and its activity is depressed • Scar tissue obstructs blood flow in the hepatic portal system causing portal hypertension 118 Composition of Bile • A yellow-green, alkaline solution containing bile salts, bile pigments, cholesterol, neutral fats, phospholipids, and electrolytes • Bile salts are cholesterol derivatives that: • Emulsify fat • Facilitate fat and cholesterol absorption • Help solubilize cholesterol • Enterohepatic circulation recycles bile salts • The chief bile pigment is bilirubin, a waste product of heme 119 The Gallbladder • Thin-walled, green muscular sac on the ventral surface of the liver • Stores and concentrates bile by absorbing its water and ions • Releases bile via the cystic duct which flows into the bile duct 120 Regulation of Bile Release • Acidic, fatty chyme causes the duodenum to release: • Cholecystokinin (CCK) and secretin into the bloodstream • Bile salts and secretin transported in blood stimulate the liver to produce bile • Vagal stimulation causes weak contractions of the gallbladder • Cholecystokinin causes: • The gallbladder to contract • The hepatopancreatic sphincter to relax • As a result, bile enters the duodenum 121 Regulation of Bile Release 122 Figure 24.25 Homeostatic Imbalance • Gallstones – crystallization of cholesterol which can obstruct the flow of bile • Current treatments include: dissolving the crystals with drugs, pulverizing them with ultrasound, vaporizing them with lasers, and surgical removal of the gallbladder • cholecystectomy : surgery to remove gall bladder • Obstructive jaundice – yellowish skin caused by bile pigments deposited in the skin • Due to blocked bile ducts 123 Pancreas • Location • Lies deep to the greater curvature of the stomach • The head is encircled by the duodenum and the tail abuts the spleen • Exocrine function • Secretes pancreatic juice which breaks down all categories of foodstuff • Acini (clusters of secretory cells) contain zymogen granules with digestive enzymes • The pancreas also has an endocrine function – release of insulin and glucagon 124 Pancreas 125 Figure 24.26a Composition and Function of Pancreatic Juice • Water solution of enzymes and electrolytes (primarily HCO3) • Neutralizes acid chyme • Provides optimal environment for pancreatic enzymes • Enzymes are released in inactive form and activated in the duodenum 126 Composition and Function of Pancreatic Juice • Examples include • Trypsinogen is activated to trypsin • Procarboxypeptidase is activated to carboxypeptidase • Active enzymes secreted • Amylase, lipases, and nucleases • These enzymes require ions or bile for optimal activity 127 Regulation of Pancreatic Secretion • Secretin and CCK are released when fatty or acidic chyme enters the duodenum • CCK and secretin enter the bloodstream • Upon reaching the pancreas: • CCK induces the secretion of enzyme-rich pancreatic juice • Secretin causes secretion of bicarbonate-rich pancreatic juice • Vagal stimulation also causes release of pancreatic juice 128 Regulation of Pancreatic Secretion 129 Figure 24.28 Digestion in the Small Intestine • As chyme enters the duodenum • Carbohydrates and proteins are only partially digested • No fat digestion has taken place • Digestion continues in the small intestine • Chyme is released slowly into the duodenum • Because it is hypertonic and has low pH, mixing is required for proper digestion • Required substances needed are supplied by the liver • Virtually all nutrient absorption takes place in the small intestine 130 • Incorporated in the plasma membrane of the microvilli are a number of enzymes that complete digestion: • aminopeptidases attack the amino terminal (N-terminal) of peptides producing amino acids. • disaccharidases These enzymes convert disaccharides into their monosaccharide subunits. • maltase hydrolyzes maltose into glucose. • sucrase hydrolyzes sucrose (common table sugar) into glucose and fructose. • lactase hydrolyzes lactose (milk sugar) into glucose and galactose. • Fructose simply diffuses into the villi, but both glucose and galactose are absorbed by active transport. • Fatty acids and monoglycerides. These become resynthesized into fats as they enter the cells of the villus. The resulting small droplets of fat are then discharged by exocytosis into the lymph vessels, called lacteals, draining the villi. 131 Motility of the Small Intestine • The most common motion of the small intestine is segmentation • It is initiated by intrinsic pacemaker cells (Cajal cells) • Moves contents steadily toward the ileocecal valve • After nutrients have been absorbed: • Peristalsis begins with each wave starting distal to the previous • Meal remnants, bacteria, mucosal cells, and debris are moved into the large intestine 132 Control of Motility • Local enteric neurons of the GI tract coordinate intestinal motility • Cholinergic neurons cause: • Contraction and shortening of the circular muscle layer • Shortening of longitudinal muscle • Distension of the intestine • Other impulses relax the circular muscle • The gastroileal reflex and gastrin: • Relax the ileocecal sphincter • Allow chyme to pass into the large intestine 133 Large Intestine • Has three unique features: • Teniae coli – three bands of longitudinal smooth muscle in its muscularis • Haustra – pocketlike sacs caused by the tone of the teniae coli • Epiploic appendages – fat-filled pouches of visceral peritoneum • Is subdivided into the cecum, appendix, colon, rectum, and anal canal • The saclike cecum: • Lies below the ileocecal valve in the right iliac fossa • Contains a wormlike vermiform appendix 134 Large Intestine 135 Figure 24.29a The Large Intestine 136 Silv. p.686 Homeostatic Imbalance • Appendicitis – inflammation of the appendix resulting from blockage that traps infectious bacteria in its lumen • If the appendix ruptures, feces containing bacteria spray over the abdominal contents causing peritonitis • Treatment is surgical removal of the appendix 137 PowerPoint® Lecture Slide Presentation by Vince Austin Human Anatomy & Physiology FIFTH EDITION Elaine N. Marieb Chapter 24 The Digestive System Part F Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Colon • Has distinct regions: ascending colon, hepatic flexure, transverse colon, splenic flexure, descending colon, and sigmoid colon • The transverse and sigmoid portions are anchored via mesenteries called mesocolons • The sigmoid colon joins the rectum • The anal canal, the last segment of the large intestine, opens to the exterior at the anus 139 Valves and Sphincters of the Rectum and Anus • Three valves of the rectum stop feces from being passed with gas • The anus has two sphincters: • Internal anal sphincter composed of smooth muscle • External anal sphincter composed of skeletal muscle • These sphincters are closed except during defecation 140 Mesenteries of Digestive Organs 141 Figure 24.30b Mesenteries of Digestive Organs 142 Figure 24.30c Mesenteries of Digestive Organs 143 Figure 24.30d Large Intestine: Microscopic Anatomy • Colon mucosa is simple columnar epithelium except in the anal canal • Has numerous deep crypts lined with goblet cells • Anal canal mucosa is stratified squamous epithelium • Anal sinuses exude mucus and compress feces • Superficial venous plexuses are associated with the anal canal • Inflammation of these veins results in itchy varicosities called hemorrhoids 144 Mechanical Digestion • Haustral contractions • propel and mix from pouch to pouch 145 146 147 Large Intestine: Microscopic Anatomy 148 Figure 24.29b Bacterial Flora • The bacterial flora of the large intestine consist of: • Bacteria surviving the small intestine that enter the cecum and • Those entering via the anus • These bacteria: • Colonize the colon • Ferment indigestible carbohydrates • Release irritating acids and gases (flatus) • Synthesize B complex vitamins and vitamin K 149 Functions of the Large Intestine • Other than digestion of enteric bacteria, no further digestion takes place • Vitamins, water, and electrolytes are reclaimed • Its major function is propulsion of fecal material toward the anus • Though essential for comfort, the colon is not essential for life 150 Motility of the Large Intestine • Haustral contractions • Slow segmenting movements that move the contents of the colon • Haustra sequentially contract as they are stimulated by distension • Presence of food in the stomach: • Activates the gastrocolic reflex • Initiates peristalsis that forces contents toward the rectum 151 Homeostatic Imbalance • Diverticulosis – small herniation (diverticula) of the mucosa of the colon walls caused by lack of bulk in the colon • Most common in the sigmoid colon in people over 70 • Diverticulitis – inflamed diverticula that can be life threatening if the diverticula rupture 152 Figure 24.23 The Large Intestine 153 Figure 24.23b, c Defecation • Distension of rectal walls caused by feces • Stimulates contraction of the rectal walls • Relaxes the internal anal sphincter • Voluntary signals stimulate relaxation of the external anal sphincter and 154 defecation occurs Figure 24.32 The Defecation Reflex 155 Figure 24.25 Figure 24.27 Digestive Secretion and Absorption of Water 156 Figure 24.27 Homeostatic Imbalance • Diarrhea – watery stool resulting from any condition that rushes food residue through the large intestine too quickly • This causes insufficient time for water absorption • Prolonged diarrhea may result in dehydration and electrolyte imbalance • Constipation – hard stool that is difficult to pass resulting from residues staying in the intestine too long • May result from lack of fiber in the diet 157 Food Poisoning: Salmonella • Salmonella is spread by: • Contaminated eggs and egg products • Infected food handlers with feces-contaminated hands • Salmonella can cause: • Bacteremia 4 to 7 days after infection • Endocarditis, thrombi, bone infections, arthritis, and meningitis • Diagnosis is by positive stool samples • Salmonellosis is treated symptomatically 158 Chemical Digestion: Carbohydrates • Absorption: via cotransport with Na+, and facilitated diffusion • Enter the capillary bed in the villi • Transported to the liver via the hepatic portal vein • Enzymes used: salivary amylase, pancreatic amylase, and brush border enzymes 159 Chemical Digestion: Proteins • Absorption: similar to carbohydrates • Enzymes used: pepsin in the stomach • Enzymes acting in the small intestine • Pancreatic enzymes – trypsin, chymotrypsin, and carboxypeptidase • Brush border enzymes – aminopeptidases, carboxypeptidases, and dipeptidases 160 Chemical Digestion: Proteins 161 Figure 24.34 Chemical Digestion: Fats • Absorption: Diffusion into intestinal cells where they • Combine with proteins and extrude chylomicrons • Enter lacteals and are transported to systemic circulation via lymph • Glycerol and short chain fatty acids • are absorbed into the capillary blood in villi • transported via the hepatic portal vein • Enzymes/chemicals used: bile salts and pancreatic lipase 162 Chemical Digestion: Fats 163 Figure 24.35 Fatty Acid Absorption • Fatty acids and monoglycerides enter intestinal cells via diffusion • They are combined with proteins within the cells • Resulting chylomicrons are extruded • They enter lacteals and are transported to the circulation via lymph 164 Fatty Acid Absorption 165 Figure 24.36 Chemical Digestion: Nucleic Acids • Absorption: active transport via membrane carriers • Absorbed in villi and transported to liver via hepatic portal vein • Enzymes used: pancreatic ribonucleases and deoxyribonuclease in the small intestines 166 Electrolyte Absorption • Most ions are actively absorbed along the length of small intestine • Na+ is coupled with absorption of glucose and amino acids • Ionic iron is transported into mucosal cells where it binds to ferritin • Anions passively follow the electrical potential established by Na+ 167 Electrolyte Absorption • K+ diffuses across the intestinal mucosa in response to osmotic gradients • Ca2+ absorption: • Is related to blood levels of ionic calcium • Is regulated by Vitamin D and parathyroid hormone (PTH) 168 Water Absorption • 95% of water is absorbed in the small intestines by osmosis • Water moves in both directions across intestinal mucosa • Net osmosis occurs whenever a concentration gradient is established by active transport of solutes into the mucosal cells • Water uptake is coupled with solute uptake, and as water moves into mucosal cells, substances follow along their concentration gradients 169 Malabsorption of Nutrients • Results from anything that interferes with delivery of bile or pancreatic juice • Factors that damage the intestinal mucosa (e.g., bacterial infection) • Gluten enteropathy (adult celiac disease) – gluten damages the intestinal villi and reduces the length of microvilli • Treated by eliminating gluten from the diet (all grains but rice and corn) 170 Embryonic Development of the Digestive System • 3rd week – endoderm has folded and foregut and hindgut have formed • The midgut is open and continuous with the yolk sac • Mouth and anal openings are nearly formed • 8th week – accessory organs are budding from endoderm 171 Embryonic Development of the Digestive System 172 Figure 24.37 Homeostatic Imbalance • Peritonitis – inflammation of the peritoneum caused by a piercing wound, perforating ulcer, or burst appendix • Often, infected membranes tend to stick together localizing the infection • Generalized or widespread peritonitis is dangerous and often lethal • Treatment includes removing infectious debris and massive doses of antibiotics 173 Homeostatic Imbalance • Cleft palate – palatine bones, palatine process of the maxillae (or both) fail to fuse • Tracheoesophageal fistula – opening between the esophagus and trachea • Cystic fibrosis – impairs pancreatic activity 174 Developmental Aspects • During fetal life, nutrition is via the placenta, but the GI tract is stimulated toward maturity by amniotic fluid swallowed in utero • At birth, feeding is an infant’s most important function and is enhanced by • Rooting reflex (helps infant find the nipple) and sucking reflex (aid in swallowing) • Digestive system has few problems until the onset of old age • During old age the GI tract activity declines, absorption is less efficient, and peristalsis is slowed 175 176 Overview of GI Tract • Upper GI Tract – Mouth and pharnyx provide entryway – Lead to Esophagus • Esophagus wall consists of same layers found in remainder of GI tract – epithelium (mucosa), submucosa (submucosal plexus), muscularis externa (circular and longitudinal muscles + myenteric plexus); serosa – Secretory glands found throughout GI except colon • exocrine glands (ducted) and endocrine (ductless) glands Upper GI Tract Continued • Sphincters – circular muscles located throughout digestive tract • Lower Esophageal Sphincter – allows passage of food into stomach • Pyloric Sphincter – Controls release of chyme from stomach to duodenum • Ileocecal sphincter • Stomach – J shaped organ – volume ranges from 50 to 1500 mL (2 -52 oz) Lower GI tract and Accessory Organs • Small Intestine – Duodenum (< 1 ft), jejunum and ileum (~9 ft) – main site for nutrient digestion and absorption – duodenum receives secretions from liver, gallbladder and pancreas • Liver – hepatocytes make bile from cholesterol – right and left hepatic bile ducts join to form common hepatic duct • unites with cystic duct leading to gallbladder Lower GI tract and Accessory Organs • Gallbladder – capacity to hold 40-50 mL of bile – functions to concentrate and store bile – Common hepatic bile duct goes to duodenum (Sphincter of Oddi) • Pancreas – 2 types of active tissue • Acini or ducted exocrine tissue – produces digestive enzymes • secreted into small ducts within pancreas which leads to common hepatic bile duct • empties into duodenum via Sphincter of Oddi • Ductless endocrine tissue – secretes hormones, glucagon and insulin into blood Structure of SI • Epithelial surface (mucosa) structured to maximize surface area – Large folds of mucosa (folds of Kerckring) – Villi • projections lined with 100s of absorptive cells • contain blood capillaries and central lacteal – Microvilla • • • • extensions of plasma membrane of absorptive cells possess surface coat of glycocalyx forms brush border most digestive enzymes produced by SI found here. Structure of SI • Crypts of Lieberkuhn – pits located between villi – epithelial cells in these crypt migrate upward and out of crypts toward tips of villi – turnover every 3-5 days – Cells include • paneth cells secrete proteins with unknown function • globlet cells secrete mucus • Enterochromaffin cells with endocrine functions Structure of SI • Gut Associated Lymphoid Tissue (GALT) – mucosa and submucosa – Leukocytes (white blood cells) • Found between intestinal absorptive cells – T-lymphocytes, Natural Killer cells, Microfold cells • Peyer’s Patches – Aggregates of lymphoid tissue underneath M cells – T-lymphocytes, B-lymphocytes and macrophages – provide defense against bacteria and foreign bodies • Ileocecal valve – allows unabsorbed materials to leave ileum and enter cecum Colon • Cecum • Ascending, transverse and descending sections • Sigmoid sections • Haustra or pouches – created by contraction of 1 or 3 muscular strips (tenaie coli) along with contraction of circular muscles • Absorbs water and lytes Regulation Of Digestive Process • Regulatory Peptides (GI hormones and neuropeptides) – Gastrin (hormone) • produced mainly by gastric (G) cells in stomach (pyloric gland) • released upon entry of food into stomach – stimulates HCl release – gastric and intestinal motility – pepsinogen release – Cholecystokinin (CCK, hormone) • produced by SI cells • released upon entry of chyme into stomach – amino acids, fat • targets pancreas and gallbladder Regulatory Peptides • Secretin (hormone) – – – – produced by cells of SI secreted in response to chyme (acid) into duodenum targets pancreas (HCO-3) may inhibit GI motility • Gastric Inhibitory Polypeptide (GIP; hormone) – produced by SI cells – Inhibits gastric secretions and motility – Simulates intestinal and insulin secretions Regulatory Peptides • Somatostatin – Produced by pancreatic and SI cells – Paracrine • released by endocrine cells but diffuse through extracellular space to gastric juice – Inhibits gastrin secretion – Increases release of GIP, secretin, motilin – Inhibits gastric acid release, gastric motility, pancreatic exocrine secretions and gall bladder secretions Regulatory Peptides • Motilin – Small intestine – Contraction of intestinal smooth muscle • Vasoactive intestinal peptide (VIP; Neurocrine) – Neurons within gut – Stimulates intestinal secretions, relaxes most GI sphincters, inhibits gastric acid secretion and stimulates HCO3- • Gastrin-releasing pepetide (GRP; Neurocrine) – Released from nerves, stimulates release of HCL, gastrin and CCK 188 Neural Regulation • Enteric Nervous System – located in wall of GI tract – begins in esophagus and ends at anus – controls peristaltic activity/GI motility (myenteric plexus) • affected by parasympathetic and sympathetic nervous systems – Acetylcholine increase GI motility – Norepinephrine and epinephrine inhibit GI activity – Also influences GI secretions (submucosal plexus) Process of Digestion • Oral Cavity and Salivary Glands – mastication of food – mixed with salivary gland secretions • parotid glands – water, lytes and enzymes • submandibular and sublingual glands – water, lytes, enzymes and mucus – Enzymes • alpha amylase and lingual lipase Process of Digestion • Esophagus – Entry of food results in peristalsis • acetylcholine – LES • LES pressure decreases upon swallowing • Neural and hormonal regulation • functions to prevent gastric reflux Process of Digestion • Stomach – Body extends from LES to angular notch • includes fundus • serves as reservoir as well as producer of gastric juice – Antrum (Pyloric Portion) • extends from angular notch to duodenum • grinds and mixes food with digestive juice (chyme) • provides strong peristalsis Stomach • Gastric Juices – produced by 3 different gastric glands • Cardiac glands (fundus) – mucus cells (HCO3- and mucus) and endocrine cells – no parietal (oxyntic cells) • Parietal glands (body) – mucus cells, oxyntic cells (secrete HCl and IF), chief cells (secrete pepsinogen upon stimulation by acetylcholine) • Pyloric glands (antrum) – both mucus and oxyntic cells – G cells that produce gastrin – Acetylcholine stimulates chief, oxyntic and other gastric cells Gastric Juices • HCl – – – – activates inactive zymogen pepsinogen to active pepsin denatures proteins serves as bactericide nutrient release • Mucus – lubricates and protects gastric lining • Intrinsic Factor (IF) – necessary for vitamin B12 absorption HCl • Release from oxyntic cells stimulated by – acetylcholine, gastrin, CCK, histamine – Histamine • secreted from mast cells • paracrine that binds to H2 receptors on parietal cells to stimulate HCl release • mechanism used in drug therapy to lower acid – Drugs (tagamet) prevent histamine from binding to H2 receptors – decreases acid release – Parietal cells contain • Potassium chloride transport system • Hydrogen (proton) potassium ATPase exchange system – Proton pump • Result: secretion of hydrogen and chloride • Proton pump targetted/exploited in drug therapy to lower acid – Prilosec binds to proton pump Gastric Emptying • GI hormones and neuropeptides affect a pacemaker (between fudnus and body of stomach) – determines frequency and rate of contractions – 1-5 mL (<1 tsp) chyme allowed to enter duodenum every 30 seconds – Fat appears to slow gastric emptying • Inhibitors – Secretin, GIP, Somatostatin, CCK Small Intestine • Chyme has low pH – SI protected by pancreatic secretions and secretions from Brunner’s glands (located in mucosa and submucosa of the first few centimeters of the duodenum) – Secretin and CCK • Digestive juices – Glands within crypts of Lieberkuhn – Pancreas • Responsible for enzymes that digest 50% CHO, 50% protein, 90% lipids Digestive Juice • Pancreatic Proteases – trypsinogen, chymotrypsinogen, procarboxypeptidases, proelastase, collagenase – secreted in vesicles – must be activated • trypinsogen converted to trypsin by enteropeptidase (enterokinase) and by free trypsin – hydrolyze peptide bonds either internally or from ends – mono, di and some tri can be absorbed • Brush border aminopeptidases to hydrolyze further Digestive Juice • CHO – Pancreatic alpha amylase • hydrolyzes alpha 1-4 bonds – Alpha dextrinase to hydrolyze 1-6 branches – Brush border enzymes (isomaltase, maltase, sucrase, lactase) • Lipids – Pancreatic lipase hydrolyzes TG to yield MG, FFA and glycerol – Phospholipase and cholesterol esterase – Bile required and sometimes pancreatic colipase (binds TG and pancreatic lipase displacing bile) Bile Synthesis • Made in liver cells from cholesterol – cholesterol oxidized • chenodeoxycholic acid and cholic acid – conjugated to glycine or taurine • glycocholic acid and taurocholic acid – conjugation of bile acids with amino acids improves its ability to form micelles – cholesterol and PLs secreted into bile • bile acid dependent frx – Water, Lytes and bilirubin secreted in bile Bile Storage • Gallbladder – Concentrates bile by removing 90% of water – Stores bile – Stimulated to release bile by CCK • CCK secreted in response to amino acids and lipids – Bile is secreted into duodenum Function of Bile • Digestion – Bile acids are amphipathic • Contain polar (hypdrophic) and non-polar (hydrophobic) areas – Decrease surface tension of fat • Hydrophobic part surrounds and dissolves into the ingested fat molecule and helps break apart – Permits emulsification of fat • Increases exposed surface area of lipids – Allow digestive enzymes (lipase) to get close to fat • Absorption – Micelle Formation Micelles • Contain ~ 40 bile salt molecules – Hydrophobic centers, hydrophilic periphery • Fatty acids, MAGs, cholesterol, fat soluble vitamins enter micelles – Mixed Micelles • Micelles travel to brush border – Contents diffuse through unstirred water layer and into enterocytes – Bile acids released back to lumen for reuse Enterohepatic Circulation • > 90% of bile acids secreted in duodenum are reabsorbed into ileum • Enters portal vein for transport via blood back to liver • Reabsorbed bile acids are secreted in bile along with newly made bile acids • New bile mixed with recirculated bile is sent via cystic duct for storage in gallbladder • Pool of bile (2-4 g) may recycle 1-2 times/meal Secondary Bile Acids • Bile acids not reabsorbed in ileum may be deconjugated by bacteria in colon – deconjugated bile acids form secondary bile acids • cholic acid is converted to deoxycholic acid which may be reabsorbed • chenodeoxycholic acid is converted to lithocholic acid which is excreted in feces – ~ 0.5 g of bile salts are lost in feces daily – Some fibers bind bile salts and acids and prevent conversion to secondary bile acids (possible risk factor in colon cancer?) Decreasing Blood Cholesterol • Only route of cholesterol excretion is in feces • By increasing excretion of bile in feces, one can lower blood cholesterol levels – necessitates use of body cholesterol for synthesis of new bile acids – drugs (powdered resins) bind bile and enhance excretion from body (cholestyramine) – soluble fiber behaves like resins Role of Intestinal Brush Border in Digestion • CHO Digestion – Isomaltase • 1-6 bonds in oligosaccharides and dextrins – Sucrase • alpha 1-4 bonds in sucrose and maltose – Glucoamylase, glucosidase, maltase • alpha 1-4 bonds in oligosaccharides, maltotriose and maltose – Maltase, Lactase and Sucrase Role of Intestinal Brush Border in Digestion • Protein Digestion – Aminopeptidases hydrolyze N terminal amino acids from oligopeptides, tripeptides and dipeptides – Tripeptidases = 1 free aa + dipeptide – Dipeptidases = 2 free aa Absorption • Begins in duodenum • Continues throughout jejunum and ileum • May be accomplished by – simple diffusion – facilitated diffusion – active transport – pinocytosis or endocytosis – paracellular absorption • Mechanism depends on – nutrient solubility; electrical gradient; size Colon • Greater absorption of sodium, chloride and water – 90-95% of water and sodium reabsorbed • Secretion of bicarbonate into colon – neutralize acids produced by colonic anaerobic bacteria via action on CHO • Progressive dehydration of unabsorbed materials – 1 L of chyme reduced to < 200 mL of defecated material Colon • Bacteria – synthesize small amounts of vitamin K, biotin and folate – CHO digestion (fiber) • Produce acids in colon include short chain fatty acids – acetate, butyrate (preferred energy source for colon cells; regulate cell growth), propionate – may be absorbed by colonocyte – Protein digestion • Ammonia (must be controlled in those with liver disease) • Probiotics and Prebiotics – Increase populations with no adverse health effects and decrease populations with adverse health effects (pathogenic strains) 211 212 The Large Intestine Silv. p.686 213 214 NaCl Absorption by the Colon Silv. p.687 215 216 Digestive Secretions: (7 L / Day From Tissues into Lumen) • • • • • • • • Salivary glands Pancreas Water Enzymes Mucus Ions: H+, K+, Na+ HCO3-, ClMass Balance (H2O) 217 Enzymatic digestion in the human digestive system 218 Motility: Smooth Muscle Contractions • Tonic – support • Phasic – move products – Parastalsis – moves – Segmentation – mixes Figure 21-4: Contractions in the GI tract 219 Digestion of fats 220 Regulating Digestion: CNS and Enteric Nervous System (ENS) 221 Gastric Phase: The Stomach Figure 21-15: The mucus-bicarbonate barrier of the gastric mucosa 222 PowerPoint® Lecture Slide Presentation by Vince Austin Human Anatomy & Physiology FIFTH EDITION Elaine N. Marieb Chapter 24 Pathology Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Digestive Health: Protection & Problems • Immune defense: M-cells, Peyer's patches, lymphocytes • Irritable bowel disease – chronic inflammation • Diarrhea: leads to dehydration (4 million deaths/yr) – Osmotic-solutes prevent H2O reabsorption – Secretory- bacterial toxins ("flush out' pathogens) • Vomiting (emesis) can lead to alkalosis • Ulcers- Helicobacter pylori • "heart-burn" acid reflux disease (GERD) 224 Peptic Ulcer •Lesions in the wall of the stomach or duodenum. •Primarily caused by bacteria. •Treated with antacids AND antibiotics. 225 Appendicitis •Usually caused by fecal obstruction or anatomical “kinking” of the appendix. •A rupture leads to peritonitis. 226 Peritonitis (Inflammation of the Peritoneum) •Usually results from an infection caused by a external or internal penetrating wound. •Bacteria enter the sterile areas of the body surrounding the digestive system. •May become lethal if not treated with high doses of antibiotics. 227 Hepatitis (Inflammation of the liver) •Caused by drugs, chemicals, viruses, alcohol, etc. •Viral “Hepatitis A” is usually caused by the ingestion of food. •Viral “Hepatitis B” and “Hepatitis C” are “blood-borne” pathogens. 228 Homeostatic Imbalance • Hepatitis – inflammation of the liver often due to viral infection • Viruses causing hepatitis are catalogued has HVA through HVF • HVA and HVE are transmitted enterically and cause self-limiting infections • Hepatitis B is transmitted via blood transfusions, contaminated needles, and sexual contact, and increases the risk of liver cancer • Hepatitis C produces chronic liver infection • Nonviral hepatitis is caused by drug toxicity and wild mushroom poisoning 229 Diverticulitis •Small herniations of the mucosa in the large intestine. •These areas can become inflamed and possibly rupture. •Prevention is the treatment of choice. A diet high in fiber will help prevent diverticulitis. 230 231 Diverticulosis 232 Emesis (Vomiting) •Can be caused by microbes, allergies, gluttony, poisons, etc. 233 Diarrhea •Movement of fecal material through the GI Tract too rapidly. •May be caused by microbes, spicy foods, stress, etc. 234 Constipation •Infrequent defecation of fecal material. •Usually caused by a diet low in fiber and water. 235 Cirrhosis of the Liver •Condition where liver cells are destroyed and replaced by fibrous connective tissue. •Alcoholism is a common cause of cirrhosis. 236 Gall Stones (Biliary Calculi) •Crystalization of cholesterol and bile salts. •Blocks the bile duct or fills the gall bladder. 237 Jaundice •Build-up of bile in the skin and conjunctiva causing a yellowing of the skin. •May be caused by damage to the liver, gall bladder, or any of the ducts that service these organs. 238 Jaundice 239 Bulemia Nervosa •Condition where a patient binges on food and then purges with either laxatives or vomiting. •Considered a psychological disorder where the patient has a fear of gaining weight. •Treated with psychotherapy. 240 Anorexia Nervosa •Psychological disorder where the patient has a false perception of their own weight. •Patient denies their own appetite. •Patients are usually 15 - 20 % below normal body weight. •Extreme cases are lethal. •Closely associated with bulimia nervosa. 241 Flatulence •Excessive intestinal gas resulting from bacteria in the intestines, diet, or swallowing air. 242 Cystic Fibrosis •Genetic disorder where excess mucous is produced. •Causes a blocking of the pancreatic duct, therefore enzymes cannot enter the duodenum from the pancreas. •Treated by giving digestive enzymes orally. 243 NaCl Secretion by the Colon Silv. p.688 244 Cancer • Stomach and colon cancers rarely have early signs or symptoms • Metastasized colon cancers frequently cause secondary liver cancer • Prevention is by regular dental and medical examinations • Colon cancer is the 2nd largest cause of cancer deaths in males (lung cancer is 1st) • Forms from benign mucosal tumors called polyps whose formation increases with age • Regular colon examination should be done for all those over 50 245 Malabsorption of Nutrients • Results from anything that interferes with delivery of bile or pancreatic juice • Factors that damage the intestinal mucosa (e.g., bacterial infection) • Gluten enteropathy (adult celiac disease) – gluten damages the intestinal villi and reduces the length of microvilli • Treated by eliminating gluten from the diet (all grains but rice and corn) 246 Food Poisoning: Salmonella • Salmonella is spread by: • Contaminated eggs and egg products • Infected food handlers with feces-contaminated hands • Salmonella can cause: • Bacteremia 4 to 7 days after infection • Endocarditis, thrombi, bone infections, arthritis, and meningitis • Diagnosis is by positive stool samples • Salmonellosis is treated symptomatically 247 Homeostatic Imbalance • Hiatal hernia • structural abnormality in which the superior part of the stomach protrudes slightly above the diaphragm • Prolonged episodes can lead to esophagitis, ulcers, and cancer 248 Age related changes in the digestive system include: • Thinner, more fragile epithelium • Reduction in epithelial stem cells • Weaker peristaltic contractions • Effects of cumulative damage • Increased cancer rates 249 Digestive Disorders • Anorexia Nervosa • Emesis • Appendicitis • Gall Stones • Barrett’s esophagus • GERD • Buliemia Nervosa • Gingivitis • Cancer • Hepatitis • Cavities • Hiatal Hernia • Celiac Disease (gluten enteropathy) • Jaundice • Cirrhosis of the Liver • Lactose Intolerance • Constipation • Mumps • Crohn’s Disorder • Peptic Ulcer • Cystic Fibrosis • Periodontitis • Diarrhea • Peritonitis • Diverticulitis 250