Chapter 26 Lecture Outline PDF

1 Chapter 26 Lecture Outline © 2019 McGraw-Hill Education 26.1 Introduction to the Digestive System Learning Objectives 1 1. Identify the six organs that make up the gastrointestinal (GI) tract. 2. List the accessory organs and structures involved in the digestive process. 3. List and describe...

1 Chapter 26 Lecture Outline © 2019 McGraw-Hill Education 26.1 Introduction to the Digestive System Learning Objectives 1 1. Identify the six organs that make up the gastrointestinal (GI) tract. 2. List the accessory organs and structures involved in the digestive process. 3. List and describe the six general functions of the digestive system. 4. List and describe the four tunics (layers) that make up the gastrointestinal wall. © 2019 McGraw-Hill Education 2 26.1 Introduction to the Digestive System Learning Objectives 2 5. Briefly describe the general process of absorption. 6. Distinguish the action of the muscularis mucosae from that of the muscularis tunic. 7. Describe the general function of the enteric nervous system and autonomic nervous system in the regulation of the digestive system. 8. Compare long reflexes and short reflexes that regulate the digestive system. 9. List the major hormones that regulate the processes of digestion. © 2019 McGraw-Hill Education 3 26.1 Introduction to the Digestive System Learning Objectives 3 10. Describe the structure of the serous membranes associated with the GI tract. 11. Distinguish between intraperitoneal and retroperitoneal organs. 12. Explain the function of the mesentery, and describe the five individual mesenteries of the abdominopelvic cavity. © 2019 McGraw-Hill Education 4 5 Digestive System Figure 26.1 © 2019 McGraw-Hill Education 26.1b General Functions of the Digestive System 1 Six main functions • Ingestion • Introduction of solid and liquid nutrients into the oral cavity • First step in process of digesting and absorbing nutrients • Motility • Voluntary and involuntary muscular contractions • Mixing and moving materials through the GI tract • Secretion • Process of producing and releasing fluid products facilitating digestion • E.g., digestive enzymes, acid, bile © 2019 McGraw-Hill Education 6 26.1b General Functions of the Digestive System 2 Six main functions (continued) • Digestion • Breakdown of ingested food into smaller structures • Mechanical digestion • Material physically broken down by chewing and mixing • Chemical digestion • Involves specific enzymes to break chemical bonds • Change large complex molecules into smaller molecules • Absorption • Transport of digested molecules, electrolytes, vitamins, water • Move from GI tract into blood or lymph • Elimination • Expulsion of indigestible components that are not absorbed © 2019 McGraw-Hill Education 7 8 • Six essential activities 1.Ingestion 2.Propulsion/Motility 3.Secretion 4.Mechanical and Chemical Digestion 5.Absorption 6.Defecation/Elimination © 2019 McGraw-Hill Education 9 26.1c Gastrointestinal Tract Wall GI tract • Hollow tube of 4 concentric layers, tunics • Innermost to outermost: • Mucosa – secretion and absorption • Submucosa – nerves and immune function • Muscularis - motility • Adventitia (or serosa) - support © 2019 McGraw-Hill Education 1 10 Tunics Figure 26.2a © 2019 McGraw-Hill Education 11 Mucosa Innermost layer Functions in absorption and secretion. • Esophagus - the epithelium is stratified, squamous, and nonkeratinizing, for protective purposes. • Stomach - the epithelium is simple columnar, and is organized into gastric pits and glands to deal with secretion. • Small intestine - the epithelium (particularly the ileum) is specialized for absorption, with villi and microvilli increasing surface area. © 2019 McGraw-Hill Education 12 26.1c Gastrointestinal Tract Wall 3 Submucosa • Blood vessels, lymph vessels, nerves • Submucosal nerve plexus • Nerves and ganglia innervating smooth muscle and glands • Houses mucosa-associated lymphatic tissue (MALT) • Prevents ingested microbes from crossing GI tract wall • Peyer patches • Larger aggregates of lymphatic nodules in distal small intestine © 2019 McGraw-Hill Education 13 Mucosa: Absorption Figure 26.2b © 2019 McGraw-Hill Education 14 26.1c Gastrointestinal Tract Wall 4 Muscularis • Inner circular layer of muscle • Smooth muscle cells oriented circumferentially within GI tract • Contraction constricts tube lumen • Outer longitudinal layer • Cells oriented lengthwise along GI tract • Contraction shortens tube • Myenteric nerve plexus • Axons and ganglia between layers control contractions © 2019 McGraw-Hill Education 15 Muscularis: Motility Figure 26.2c © 2019 McGraw-Hill Education peristalsis 16 26.1c Gastrointestinal Tract Wall 7 Serosa or Adventitia • Two membranous structures that cover the external surface of the internal organs. Areolar CT. • Serosa covers the organs that freely move inside a cavity. Found within peritoneal cavity • Adventitia covers the organs that should be bound with the surrounding structures for support. Found outside the peritoneal cavity © 2019 McGraw-Hill Education 26.1d Overview of the Regulation of the Digestive System 17 1 Enteric nervous system (ENS) • Sensory and motor neurons within submucosal plexus and myenteric plexus • Innervates smooth muscle and glands of GI tract • Coordinates mixing and propulsion reflexes Autonomic Nervous System (ANS) • Parasympathetic innervation promotes GI tract activity • Sympathetic innervation opposes GI tract activity © 2019 McGraw-Hill Education 26.1d Overview of the Regulation of the Digestive System 1 • Enteric nervous system -ANS • Controls digestion independent of CNS • Sensory -Detects changes in tract wall and chemical makeup of lumen content • Motor – Changes blood flow and epithelial cell function • Thickened at several points to form a sphincter • Closes off the lumen • Controls movement of materials into next section of GI tract © 2019 McGraw-Hill Education 18 26.1d Overview of the Regulation of the Digestive System 19 2 Nerve reflexes • Baroreceptors detect stretch in GI tract wall • Chemoreceptors monitor chemical contents in lumen • Reflexes (by ANS or ENS) are initiated in response to receptor input • Short reflex – local reflex, only involves ENS; coordinate small segments of GI tract • Long reflex – involves sensory input to CNS and autonomic motor output; coordinate GI tract motility, secretions, and accessory digestive organs Hormonal control • Several hormones participate in regulation of digestion • E.g., Gastrin, secretin, cholecystokinin, motilin © 2019 McGraw-Hill Education 26.1e Serous Membranes of the Abdominal Cavity 1 Peritoneum serous membrane associated with abdominopelvic cavity • Parietal peritoneum • Lines inside surface of abdominal wall • Visceral peritoneum • Serous membrane reflecting over and covering the internal organs’ surface • Peritoneal cavity • Potential space between these two layers • Lubricating serous fluid secreted from both layers • Allows abdominal organs to move freely © 2019 McGraw-Hill Education 20 26.1e Serous Membranes of the Abdominal Cavity 2 Intraperitoneal and retroperitoneal organs • Intraperitoneal organs • Organs completely surrounded by visceral peritoneum • Includes stomach, most of small intestine, parts of large intestine • Retroperitoneal organs • Lie directly against posterior abdominal wall • Only anterolateral portions covered with peritoneum • Includes most of duodenum, the pancreas, ascending and descending colon, the rectum © 2019 McGraw-Hill Education 21 22 26.1e Mesentery 3 Double layer of peritoneum • Supports, suspends, stabilizes intraperitoneal GI tract organs • Blood and lymph vessels, nerves, are sandwiched between the folds • Greater omentum • Covers most abdominal organs • Accumulates large amounts of adipose tissue (fatty apron) • Lesser omentum • Connects surface of stomach and duodenum to the liver • Falciform ligament • Attaches the liver to internal surface of anterior abdominal wall • Mesentery proper • Suspends most of small intestine from posterior abdominal wall • Mesocolon • Attaches part of large intestine to posterior abdominal wall © 2019 McGraw-Hill Education 23 Clinical View: Peritonitis Inflammation of peritoneum Abdominal pain Most common cause, GI tract perforation • Allows contents to contact peritoneum • May result from within (ulcer, ruptured appendix) or without (gunshot wound, surgery) © 2019 McGraw-Hill Education 24 Section 26.1 What did you learn? 1 1. How is the gastrointestinal (GI) tract distinguished from accessory digestive organs? List the structures that compose each category. 2. What is the primary difference between mechanical digestion and chemical digestion? 3. What specific layer(s) must substances cross to enter the blood or lymphatic capillaries during their absorption? 4. How does peristalsis differ from mixing? 5. What purpose is served by muscular sphincters at various locations along the length of the GI tract? © 2019 McGraw-Hill Education 25 Section 26.1 What did you learn? 2 6. How is a short reflex distinguished from a long reflex? 7. What primary hormones regulate digestive processes? 8. What is the difference between intraperitoneal and retroperitoneal organs? List the digestive organs that are intraperitoneal organs. 9. Where is the greater omentum located? © 2019 McGraw-Hill Education 26.2 Upper Gastrointestinal Tract Learning Objectives 1 13. Describe the components of the upper gastrointestinal tract. © 2019 McGraw-Hill Education 26 27 Upper GI tract Figure 26.7a © 2019 McGraw-Hill Education 26.2a Overview of the Upper Gastrointestinal Tract Organs 1 Upper GI tract organs and accessory structures • Oral cavity and salivary glands • Mechanical digestion begins • Saliva secreted from salivary glands in response to food • Contains salivary amylase, enzyme initiating digestion of starch • Mixed with ingested materials to form bolus • Pharynx • Bolus moved to pharynx during swallowing • Mucus secreted to facilitate swallowing © 2019 McGraw-Hill Education 28 26.2a Overview of the Upper Gastrointestinal Tract Organs 29 2 Upper GI tract organs and accessory structures (continued) • Esophagus • Bolus transported from pharynx into stomach • Lubricated by mucus secretions • Stomach • Bolus mixed with gastric secretions by smooth muscle contractions • Secretions produced by epithelial cells of stomach • Chyme formed from mixing • Duodenum also considered part of upper GI tract © 2019 McGraw-Hill Education 26.2 Upper Gastrointestinal Tract Learning Objectives 1 14. Identify the anatomic structures of the oral cavity. 15. Describe the structure and function of salivary glands and how the release of saliva is regulated. © 2019 McGraw-Hill Education 30 31 Oral Cavity, Anterior View Figure 26.4a © 2019 McGraw-Hill Education 32 Oral Cavity and Pharynx, Sagittal Section Figure 26.4b © 2019 McGraw-Hill Education 33 26.2b Oral Cavity and Salivary Glands 1 Oral cavity • Mouth, entrance to GI tract • Two distinct regions: vestibule and oral cavity proper • Vestibule • Space between gum, lips, cheeks • Oral cavity proper • Lies central to the teeth • Leads posteriorly into oropharynx • Cheeks, contains buccinator muscles • Compress cheeks to hold solid material while chewing © 2019 McGraw-Hill Education 34 26.2b Oral Cavity and Salivary Glands Oral cavity (continued) • Lips, formed primarily by orbicularis oris muscle • Reddish hue from superficial blood vessels and reduced keratin • Palate, the roof of the oral cavity • Separates oral cavity from nasal cavity • Soft palate, posterior 1/3, soft and muscular • Hard palate, anterior 2/3 , maxillae and palantine bones © 2019 McGraw-Hill Education 2 35 26.2b Oral Cavity and Salivary Glands Oral cavity (continued) • Uvula, conical projection from posterior soft palate • Elevates with soft palate during swallowing • Closes off posterior entrance into nasopharynx • Fauces • Opening between oral cavity and oropharynx • Palatine tonsils housed between arches • Early line of defense against foreign antigens © 2019 McGraw-Hill Education 3 36 26.2b Oral Cavity and Salivary Glands 5 Oral cavity (continued) • Tongue, on inferior surface of cavity • Primarily from skeletal muscle, with extrinsic and intrinsic muscles • Numerous projections, papillae, involved with taste • Lingual tonsils on posteroinferior tongue region • Manipulates and mixes materials during chewing • Important functions in swallowing and speech © 2019 McGraw-Hill Education 37 26.2b Oral Cavity and Salivary Glands Histology of oral cavity • Stratified squamous epithelium • Protects against abrasion • Mostly nonkeratinized • Keratinized type lines lips, portions of tongue, small region of the hard palate © 2019 McGraw-Hill Education 6 38 26.2b Oral Cavity and Salivary Glands Salivary glands • Produce saliva • Intrinsic salivary glands (within oral cavity) • Unicellular glands • Continuously release secretions independent of food • Contains lingual lipase, enzyme that begins digestion • Extrinsic salivary glands (outside of oral cavity) • Produce most saliva • Parotid, submandibular, and sublingual glands © 2019 McGraw-Hill Education 7 39 26.2b Oral Cavity and Salivary Glands Salivary glands (continued) • Parotid salivary glands, largest salivary glands • 25–30% of saliva • Infection of the parotid glands causes mumps • Submandibular salivary glands • Produces 60–70% of salliva • Sublingual salivary gland • Contribute only 3–5% of saliva © 2019 McGraw-Hill Education 8 40 Salivary Glands © 2019 McGraw-Hill Education 41 26.2b Oral Cavity and Salivary Glands Histology • Two types of secretory cells within salivary glands make saliva • Mucous cells • Secrete mucin - protection from bacteria • Serous cells • Secrete watery fluid containing electrolytes and salivary amylase – begins digestion and allows for taste sensation © 2019 McGraw-Hill Education 10 42 26.2b Oral Cavity and Salivary Glands 11 Saliva Functions of saliva: • Moistens ingested food to help become bolus • Salivary amylase initiates chemical breakdown of starch • Food molecules dissolved here so taste receptors stimulated • Cleanses oral cavity structures • Antibacterial substances inhibit bacterial growth (lysozyme, IgA antibodies) © 2019 McGraw-Hill Education 43 26.2b Oral Cavity and Salivary Glands 12 Regulation of salivary secretions • Regulated within brainstem • Basal level of salivation in response to parasympathetic stimulation • Receptors detect stimuli (especially acids) in oral cavity and stomach • Send signals to salivary nuclei in brainstem • Signals also received from higher brain centers in response to thought of food • Increased parasympathetic output to salivary glands • Sympathetic stimulation results in a more viscous saliva © 2019 McGraw-Hill Education 26.2 Upper Gastrointestinal Tract Learning Objectives 1 16. Explain the process of mastication. 17. Discuss the structure and development of the teeth. © 2019 McGraw-Hill Education 44 45 26.2b Oral Cavity and Salivary Glands 13 Mechanical digestion: mastication • Mastication, chewing • Mechanically reduces bulk to facilitate swallowing • Increases surface area to facilitate exposure to digestive enzymes • Promotes salivation • Requires coordinated activities of teeth, lips, tongue, cheeks, jaws • Controlled by nuclei in medulla and pons, mastication center • Medications composed of small, nonpolar molecules (e.g., nitroglycerin) can be placed under the tongue where they pass through the epithelium by simple diffusion © 2019 McGraw-Hill Education 46 26.2b Oral Cavity and Salivary Glands Teeth • Also known as the dentition • Exposed crown and constricted neck • One or more roots, anchoring it to jaw • Fit tightly into dental alveoli, sockets within alveolar processes • Bound to processes by periodontal ligament • Gomphosis joint: roots, dental alveoli, periodontal ligament © 2019 McGraw-Hill Education 14 Anatomy of a Molar Dentin, primary mass of tooth, harder than bone Enamel, on external surface of dentin, forms crown Calcium phosphate crystals hardest substance in the body Pulp cavity, center of tooth filled with pulp Root canal, continuous with pulp cavity, opens to tissue around root Blood vessels and nerves passing through here Cementum Hardened material ensheathing root Dental caries: damage to dentin, enamel, or cementum Promoted by bacterial production of acids Gingivae, gums Dense irregular CT Overlying nonkeratinized stratified squamous epithelium Covers alveolar processes and surrounds neck of teeth © 2019 McGraw-Hill Education 47 48 26.2b Oral Cavity and Salivary Glands Deciduous and permanent teeth • 20 Deciduous teeth • Erupt between 6 and 30 months • 32 Permanent teeth, replacing deciduous teeth • More anteriorly placed permanent teeth appearing first • Third molars, wisdom teeth, in late teens or 20s • May emerge partially or become impacted © 2019 McGraw-Hill Education 16 Deciduous and Permanent Teeth Figure 26.6b © 2019 McGraw-Hill Education 49 26.2 Upper Gastrointestinal Tract Learning Objectives 2 18. Discuss the anatomy of the pharynx and esophagus and their complementary activities in the process of swallowing. © 2019 McGraw-Hill Education 50 51 The Pharynx and Esophagus Figure 26.7a © 2019 McGraw-Hill Education 52 26.2c Pharynx 1 Gross anatomy of the pharynx • Funnel-shaped muscular passageway • Passageway for air and food/water • Lined with nonkeratinized stratified squamous epithelium • Protection against abrasion © 2019 McGraw-Hill Education 53 26.2c Esophagus 2 Gross anatomy of the esophagus • Esophagus: normally collapsed, tubular passageway • Passageway for food/water • Esophagus lined with nonkeratinized stratified squamous epithelium • Inferior region connecting to the stomach • Passes through opening in diaphragm, esophageal hiatus © 2019 McGraw-Hill Education 54 26.2c Pharynx and Esophagus 3 Gross anatomy of the esophagus (continued) • Superior esophageal sphincter • Contracted ring of circular skeletal muscle at superior end • Area where esophagus and pharynx meet • Closed during inhalation of air • Inferior esophageal sphincter • Contracted ring of circular skeletal muscle at inferior end • Not strong enough by itself to stop stomach contents from regurgitating; diaphragm muscles help © 2019 McGraw-Hill Education 55 26.2c Pharynx and Esophagus 5 Motility: the swallowing process • Swallowing, deglutition • Moving ingested materials from oral cavity to stomach; 3 phases • Voluntary phase, occurring after ingestion • Controlled by cerebral cortex • Bolus formed as ingested materials and saliva mix • Bolus directed posteriorly toward oropharynx • Pharyngeal phase • Involuntary reflex • Tactile sensory receptors stimulated • Initiate sensory input to swallowing center in medulla oblongata • Signals relayed to effectors © 2019 McGraw-Hill Education 56 26.2c Pharynx and Esophagus 6 Motility: the swallowing process (continued) • Effector response of pharyngeal phase • Entry of bolus into oropharynx • Elevation of soft palate and uvula to block passageway between oropharynx and nasopharynx • Move epiglottis to cover laryngeal opening • Prevents ingested material from getting into trachea • Nerve signals sent to medulla oblongata to ensure breath not taken during swallowing © 2019 McGraw-Hill Education 57 26.2c Pharynx and Esophagus 7 Motility: the swallowing process (continued) • Esophageal phase • Involuntary phase when bolus passes through esophagus • Bolus stimulates sequential waves of muscular contraction • Propels bolus toward stomach • Superior and inferior esophageal sphincters closed at rest • Relax when bolus swallowed • Contract again afterwards, preventing reflux of materials © 2019 McGraw-Hill Education 58 Phases of Swallowing Figure 26.8 © 2019 McGraw-Hill Education Clinical View: Reflux Esophagitis and Gastroesophageal Reflux Disease 1 Inflammation of esophagus due to acidic chyme refluxing into esophagus Pain posterior to sternum, heartburn Seen most frequently • Overweight individuals, smokers, after large meals • Hiatal hernias (portion of stomach protruding through diaphragm) Treatment • Lifestyle changes, head elevation, limiting meal size © 2019 McGraw-Hill Education 59 Clinical View: Reflux Esophagitis and Gastroesophageal Reflux Disease 60 2 Can result from chronic reflux esophagitis Erodes esophageal tissue Scar tissue buildup, leading to narrowed lumen May change from stratified squamous to columnar secretory epithelium, Barrett esophagus • Increases risk of cancerous growth May be treated with multiple medications • Includes proton pump inhibitors, histamine blockers © 2019 McGraw-Hill Education 26.2 Upper Gastrointestinal Tract Learning Objectives 2 19. Describe the gross anatomy and histology of the stomach. 20. Explain the two general functional activities of the stomach. 21. Describe the phases that regulate motility and secretion in the stomach. © 2019 McGraw-Hill Education 61 62 26.2d Stomach 1 Stomach • Located in superior left abdominal quadrant, inferior to diaphragm • Chemical and mechanical digestion continues in stomach • Digestion of protein and fat begins in stomach • Ingested materials spending 2 to 6 hours here • Absorption limited to small, nonpolar substances • Serves as “holding bag” for controlled release of partially digest material © 2019 McGraw-Hill Education 63 Gross Anatomy of the Stomach Rugae Figure 26.9a © 2019 McGraw-Hill Education 64 Stomach Wall, Sectional View Figure 26.10a © 2019 McGraw-Hill Education 65 Gastric Pit and Gland Figure 26.10c © 2019 McGraw-Hill Education 66 26.2d Stomach 7 Gastric secretions • Produced by 5 types of secretory cells • 4 produce gastric juice, fifth type secretes hormone • Surface mucous cells • Line stomach lumen and extend into gastric pits • Continuously secrete alkaline product containing mucin • Mucous layer helps to prevent ulceration of stomach lining • Protects from gastric enzymes and high acidity © 2019 McGraw-Hill Education 67 26.2d Stomach 8 • Mucous neck cells • Immediately deep to base of gastric pit • Interspersed among parietal cells • Produce acidic mucin • Help maintain acidic conditions • Both types of mucous cells help protect the stomach lining from abrasion and injury © 2019 McGraw-Hill Education 68 26.2d Stomach 9 • Parietal cells—add two substances to stomach • Intrinsic factor • Required for absorption of vitamin B12 in ileum • Necessary for production of normal erythrocytes • Hydrochloric acid • Forms from H+ and Cl– secreted across cells’ surface • Responsible for low pH of stomach • Hydrochloric acid functions • • • • © 2019 McGraw-Hill Education Helps break down plant cells walls and animal CT Denatures proteins, facilitating chemical digestion Converts inactive enzyme pepsinogen into active pepsin Kills most microorganisms entering stomach 69 26.2d Stomach 10 • Chief cells • Most numerous secretory cells within gastric glands • Produce and secrete packets of zymogen granules • Primarily containing pepsinogen, inactive precursor of pepsin • Pepsin must be in inactive form to prevent destruction of chief cell proteins • Pepsinogen activated by HCl and other active pepsin molecules • Chemically digests denatured proteins into oligopeptides • Produce gastric lipase, playing limited role in fat digestion (digests about 10-15% of ingested fat) © 2019 McGraw-Hill Education 70 26.2d Stomach 11 • G-cells • Enteroendocrine cells that are widely distributed in gastric glands • Secrete gastrin hormone • Stimulates stomach secretions and motility • Other types of enteroendocrine cells produce other hormones • E.g., somatostatin © 2019 McGraw-Hill Education 71 Gastric Secretions Figure 26.12 © 2019 McGraw-Hill Education 72 26.2d Stomach 12 Stomach motility performs two primary functions: mixing the bolus to form chyme and emptying chyme from stomach to small intestine Gastric mixing • Form of mechanical digestion • Changes semidigested bolus into chyme • Churned and mixed, leading to reduction in size of swallowed particles © 2019 McGraw-Hill Education 73 26.2d Stomach 13 Motility in the stomach (continued) Gastric emptying • Movement of acidic chyme from stomach into duodenum • Pressure gradient moving contents toward pylorus • Gradient increasing force against pyloric sphincter • Sphincter opens, with entrance of small volume of chyme • Sphincter closes, with retropulsion • Reverse flow of some contents back toward stomach © 2019 McGraw-Hill Education Motility In the Stomach: Gastric Mixing and Emptying Figure 26.13 © 2019 McGraw-Hill Education 74 75 26.2d Stomach 14 Regulation of the digestive processes in the stomach • Stomach holding bag for partially digested food until the food is moved into the small intestine where digestion is completed • Pacemaker cells in stomach • Spontaneously depolarize • Establish basic rhythm of muscular contraction • Signals spreading through smooth muscle cells in muscularis layer • Force of contraction and gastric gland secretion • Regulated by nervous reflexes and hormones • Organized in three phases: cephalic, gastric, and intestinal © 2019 McGraw-Hill Education Regulation of Digestive Processes In the Stomach Figure 26.14 © 2019 McGraw-Hill Education 76 77 Clinical View: Gastric Bypass Surgical treatment for obesity • Small part of stomach sectioned off and attached to lower part of small intestine • Less nutrients absorbed • Reduced appetite • Altered response to hormones like insulin • Can induce remission of type 2 diabetes within a few days of surgery © 2019 McGraw-Hill Education 78 Clinical View: Peptic Ulcers Peptic ulcer • Solitary erosion of portion of stomach or duodenum • Gastric ulcers in stomach, duodenal ulcers in duodenum • Symptoms of gnawing, burning pain in epigastric region • Nausea, vomiting, bleeding • May erode and cause perforation, medical emergency • Helicobacter pylori causes erosion of gastric lining • Treatment similar to those of gastric reflux © 2019 McGraw-Hill Education 79 Clinical View: Vomiting Vomiting • Rapid expulsion of gastric contents through oral cavity • Controlled by vomiting center in the medulla oblongata • Responds to head injury, motion sickness, infection, toxicity, food irritation • Closure of nasal passages and the glottis • Skeletal muscle contraction increasing intragastric pressure • Gastric contents forced into and through the esophagus • Danger of aspiration © 2019 McGraw-Hill Education 80 Section 26.2 What did you learn? 10. What structures are considered part of the upper GI tract? How is the ingested material referred to as it moves through each of the structures of the upper GI tract? 11. What are the roles of the tongue, teeth, and salivary glands in forming a bolus? 12. How do the tunics of the esophagus differ from the “default” tunic pattern in both the mucosa and muscularis? 13. How is the bolus moved from the oral cavity into the stomach, as described in the three phases of swallowing? 14. List the secretory cell types in the stomach, their products, and the function of the products. 15. Which neural reflex is initiated by food in the stomach, and what does it control? © 2019 McGraw-Hill Education 26.3 Lower Gastrointestinal Tract Learning Objectives 1 22. Describe the three components of the lower gastrointestinal tract. © 2019 McGraw-Hill Education 81 Gross Anatomy of the Lower GI Tract Organs and Accessory Digestive Organs Figure 26.15 © 2019 McGraw-Hill Education 82 26.3a Overview of the Lower Gastrointestinal Tract Organs 1 Lower GI tract organs • Process of digestion and absorption continues • Elimination of indigestible and unabsorbable material • Small intestine • Divided into 3 continuous regions: duodenum, jejunum, ileum • Duodenum, part of upper GI tract • Receives chyme from stomach mixed with accessory organ secretions • Most chemical digestion and absorption happens here © 2019 McGraw-Hill Education 83 26.3a Overview of the Lower Gastrointestinal Tract Organs 2 Lower GI tract organs (continued) • Accessory digestive organs • Secretions of bile and pancreatic juice • Bile produced by liver • Stored, concentrated, released by gallbladder • Pancreatic juice with digestive enzymes secreted from pancreas • Large intestine • Primarily absorbs water, electrolytes, some vitamins • Feces produced and eliminated through anus © 2019 McGraw-Hill Education 84 Clinical View: Inflammatory Bowel Disease and Irritable Bowel Syndrome 85 1 Inflammatory bowel disease • Autoimmune disorders, both with region of inflamed intestine • Crohn disease • Young adults • Intermittent and relapsing episodes of cramping and diarrhea • Ulcerative colitis • Similar to Crohn’s but only involves large intestine © 2019 McGraw-Hill Education Clinical View: Inflammatory Bowel Disease and Irritable Bowel Syndrome 86 2 Irritable bowel disease • More common, affecting 1 in 5 Americans • Abnormal function of colon • More common in women than men • Cramps, bloating, constipation, diarrhea • Treatment with diet, medication, stress reduction © 2019 McGraw-Hill Education 26.3 Lower Gastrointestinal Tract Learning Objectives 1 23. Describe the anatomy of the small intestine. 24. List the glands found in the small intestine and their secretions. 25. Explain motility within the small intestine. © 2019 McGraw-Hill Education 87 88 26.3b Small Intestine 1 Small intestine • Small bowel, long tube inferior to stomach and located medially in abdominal cavity • Ingested nutrients reside in small intestine at least 12 hours • Absorbs most nutrients and large percentage of water, electrolytes, and vitamins © 2019 McGraw-Hill Education 89 Small Intestine • Jejunum • Primary region for chemical digestion and nutrient absorption • Ileum • Longest part of small intestine Duodenum • C-shape around head of pancreas • Receives chyme from stomach • Receives accessory gland secretions from liver, gallbladder, and pancreas © 2019 McGraw-Hill Education • Distal end terminates at ileocecal valve • Sphincter controlling entry of materials into large intestine • Continues absorption of digested material Figure 26.16 © 2019 McGraw-Hill Education 90 91 26.3b Small Intestine 10 Motility of the small intestine • Smooth muscle of small intestine • Mixes chyme with gland secretions, • Segmentation, backward-and-forward motion • Propels contents through small intestine by peristalsis © 2019 McGraw-Hill Education 92 26.3b Small Intestine 11 Regulation of small intestine motility during the intestinal phase • Segmentation is prevalent early in intestinal phase • Mixes chyme, accessory gland secretions, intestinal juice • Peristalsis is prevalent late in intestinal phase • Successive waves of contractions • Repeats until all content moved to large intestine © 2019 McGraw-Hill Education 93 26.3b Small Intestine 12 Moving chyme from small intestine into large intestine • Gastroileal reflex • Ileum contracts • Ileocecal sphincter relaxes (CCK from small intestine helps cause this) and cecum relaxes • Moves contents from ileum to cecum in response to food in stomach • Ileocecal valve contracts to prevent backflow © 2019 McGraw-Hill Education 26.3 Lower Gastrointestinal Tract Learning Objectives 1 26. Describe the accessory digestive organs associated with the small intestine and the contributions of each to digestive processes. 27. Explain how both blood and bile flow through the liver. 28. Discuss the regulation of the accessory digestive glands associated with the small intestine. © 2019 McGraw-Hill Education 94 Gross Anatomy of the Lower GI Tract Organs and Accessory Digestive Organs Figure 26.15 © 2019 McGraw-Hill Education 95 96 Liver Accessory digestive organ and largest internal organ RUQ of abdomen immediately inferior to diaphragm © 2019 McGraw-Hill Education Figure 26.19 What does the liver do? 97 produces glycogen from glucose breaks down glycogen into glucose converts non-carbohydrates to glucose oxidizes fatty acids synthesizes lipoproteins, phospholipids, and cholesterol converts carbohydrates and proteins into fats deaminates amino acids forms urea synthesizes plasma proteins converts some amino acids to other amino acids stores glycogen, vitamins A,D, B12, iron, and blood phagocytosis of old RBCs and foreign substances removes toxins from blood produces and secretes bile – the only digestive function © 2019 McGraw-Hill Education What does the Liver do? 26.3c Accessory Digestive Organs and Ducts 7 Histology of the liver (continued) • Hepatic artery • Branch of celiac trunk • Carries oxygenated blood to liver • Hepatic portal vein • Carries deoxygenated and nutrient-rich blood from capillary beds of GI tract, spleen, pancreas • Brings 75% of blood to liver • Blood mixes as passes through hepatic lobules • Hepatic veins • Empty into inferior vena cava © 2019 McGraw-Hill Education 98 Figure 26.20 © 2019 McGraw-Hill Education 99 26.3c Accessory Digestive Organs and Ducts 8 Function of the liver • As blood is transported through hepatic sinusoids: • Nutrients and oxygen absorbed, enter hepatocytes • Stellate cells (Kupffer cells) macrophages that clear harmful substances Bile • Secreted by liver • Contains: water, bicarbonate ions, bile salts and pigments, cholesterol, lecithin, mucin • Bile salts and lecithin help mechanically digest lipids © 2019 McGraw-Hill Education 100 101 Clinical View: Cirrhosis of the Liver Hepatocytes replaced by fibrous scar tissue Compresses blood vessels • Causes hepatic portal hypertension Compresses bile ducts in liver Caused by chronic injury to hepatocytes • Chronic alcoholism, liver disease, drugs or toxins • Most frequently viral infections from hepatitis B or C Symptoms • Fatigue, weight loss, nausea, pain in right upper quadrant • If advanced: jaundice, edema, ascites, itching, toxin accumulation, dilated veins of esophagus © 2019 McGraw-Hill Education 26.3c Accessory Digestive Organs and Ducts 9 Gallbladder • Saclike organ attached to inferior surface of liver • Stores, concentrates, and releases bile produced in liver • Connected to common bile duct by cystic duct • Sphincter valve • Controls flow of bile into and out of gallbladder © 2019 McGraw-Hill Education 102 103 Ducts of Accessory Digestive Organs iliary apparatus Figure 26.18 © 2019 McGraw-Hill Education 104 Clinical View: Gallstones (Cholelithiasis) Gallstones in gallbladder or biliary apparatus Risk factors • Female sex, obesity, age, Caucasian Condensations of cholesterol or calcium and bile salts Majority asymptomatic until lodged in neck of cystic duct • Gallbladder inflamed, cholecystitis Severe pain in right hypochondriac region Nausea, vomiting, indigestion, bloating Symptoms worse after fatty meal May require surgical removal, cholecystectomy © 2019 McGraw-Hill Education 26.3c Accessory Digestive Organs and Ducts 10 Pancreas • Endocrine function • Produces and secretes insulin and glucagon • Exocrine function • Produces pancreatic juice to assist with digestive activities © 2019 McGraw-Hill Education 105 106 Anatomy of the Pancreas Figure 26.21 © 2019 McGraw-Hill Education (b) ©McGraw-Hill Education/Christine Eckel 107 Histology of the Pancreas Figure 26.22 © 2019 McGraw-Hill Education ©Carolina Biological Supply Company/Medical Images 26.3c Accessory Digestive Organs and Ducts 12 Pancreatic secretions • Pancreatic juice • Formed from secretions of acinar cells and pancreatic duct cells • Alkaline fluid • Mostly water, HCO3–, digestive enzymes • Pancreatic amylase to digest starch • Pancreatic lipase to digest triglycerides • Inactive proteases that digest proteins when activated • Nucleases for digestion of nucleic acids © 2019 McGraw-Hill Education 108 109 Clinical View: Pancreatic Cancer Cancer of the pancreatic cells, typically exocrine cells Prognosis is good with early detection, but early detection is difficult because: • There is no screening test • Absence of signs and symptoms in the early stages of the disease Symptoms in later stages include abdominal pain, jaundice, loss of appetite, weight loss Pancreatic cancer is often fatal because usually detected late © 2019 McGraw-Hill Education 26.3c Accessory Digestive Organs and Ducts 13 Regulation of accessory structures • Cholecystokinin (CCK) • Hormone released from small intestine in response to fatty chyme • Stimulates gallbladder to strongly contract and release bile • Stimulates pancreas to release pancreatic juice • Relax smooth muscle within hepatopancreatic ampulla • Allows entry of bile and pancreatic juice into small intestine • Inhibits stomach motility and release of gastric secretions © 2019 McGraw-Hill Education 110 26.3c Accessory Digestive Organs and Ducts 14 Regulation of accessory structures (continued) • Secretin • Released from small intestine in response to increased chyme acidity • Causes release of alkaline solution containing HCO3– • From liver and ducts of pancreas • Helps neutralize acidic chyme • Inhibits gastric secretions and motility © 2019 McGraw-Hill Education 111 26.3 Lower Gastrointestinal Tract Learning Objectives 2 29. Name the three major regions of the large intestine and four segments of the colon of the large intestine. 30. Explain the distinguishing histologic features of the large intestine. 31. Describe the bacterial action that takes place in the large intestine. © 2019 McGraw-Hill Education 112 113 26.3d Large Intestine 1 Large intestine (large bowel) • Relatively wide tube, shorter than small intestine • Located in abdominal and pelvic cavities • From ileocecal junction to termination at anus • Functions: • Absorbs water and electrolytes from remaining digested material • Watery chyme compacted into feces • Stores feces until eliminated through defecation © 2019 McGraw-Hill Education Figure 26.23 © 2019 McGraw-Hill Education 114 115 26.3d Large Intestine 6 Gross anatomy of the large intestine (continued) • Anal canal • Last few centimeters of large intestine • Lined by stratified squamous epithelium • Passes through opening in levator ani muscles and terminates at anus • Longitudinal ridges, anal columns • Depressions between, anal sinuses • Release mucus when pressure exerted • Internal anal sphincter • Involuntary smooth muscle at base of anal canal • External anal sphincter • Voluntary skeletal muscle • Sphincters normally closed off but relax during defecation © 2019 McGraw-Hill Education 116 Clinical View: Appendicitis Inflammation of appendix Most due to fecal matter obstructing the appendix Appendix swells, blood supply compromised, bacterial growth May burst if untreated • Causing dangerous infection, peritonitis Pain initially referred to T10 around umbilicus from smooth muscle Eventually involves peritoneum • Pain localized to right lower quadrant Nausea or vomiting, abdominal tenderness, fever Surgically removed through appendectomy © 2019 McGraw-Hill Education 117 Large Intestine Tunics Figure 26.24a © 2019 McGraw-Hill Education 118 26.3d Large Intestine 9 Bacterial action in the large intestine • Indigenous microbiota • Normal bacterial flora in large intestine • Breakdown carbohydrates, proteins, and lipids in chyme • Produce carbon dioxide, H+, other substances • Produce B vitamins and vitamin K • Absorbed from large intestine into blood • Feces is final product • Composed of water salts, epithelial cells, bacteria, undigested material © 2019 McGraw-Hill Education 119 26.3d Large Intestine 10 Motility and regulation in the large intestine • Peristalsis is weak and sluggish • Mass movements • Powerful contractions • Propel fecal material toward the rectum • 2–3 times a day, often after a meal © 2019 McGraw-Hill Education 120 26.3d Large Intestine 11 Motility and regulation in the large intestine (continued) • Gastrocolic reflex • Initiated by stomach distension • Causes a mass movement • Defecation reflex • • • • Filling of rectum initiates urge to defecate Receptors signal to spinal cord Increases parasympathetic output to sigmoid colon and rectum Decreases output to internal (involuntary) anal sphincter • Voluntary defecation • Learned about age 3 • Involves Valsalva maneuver • Involves relaxation of external (voluntary) anal sphincter © 2019 McGraw-Hill Education 121 Defecation Figure 26.25 © 2019 McGraw-Hill Education Figure 26.29 Putting it all together © 2019 McGraw-Hill Education 122 123 Clinical View: Colorectal Cancer Second most common type of cancer in U.S. Malignant growth anywhere along large intestine, rectum Most arising from polyps • Outgrowth from colon mucosa Risk factors • Low fiber diet, family history, age, history of ulcerative colitis Rectal bleeding, abdominal pain, weight loss Must be removed surgically Screened with fecal occult blood test, sigmoidoscopy, colonoscopy © 2019 McGraw-Hill Education 124 Clinical View: Fecal Transplant Low-cost, low-risk procedure to treat Clostridium difficile colitis Fecal matter from donor placed in colon of a patient (via enema or colonoscopy) May help treat Crohn disease, ulcerative colitis, irritable bowel syndrome © 2019 McGraw-Hill Education Clinical View: Diverticulosis and Diverticulitis Diverticulosis • Small bulges in intestinal lining, diverticula • Typically formed when colon narrows in response to low fiber Diverticulitis • Inflammation of diverticula • Life-threatening if diverticula rupture and leak intestinal contents into abdominal cavity © 2019 McGraw-Hill Education 125 126 Clinical View: Constipation and Diarrhea Constipation • Temporary impaired ability to defecate • Compacted feces difficult to eliminate • From low fiber, dehydration, lack of exercise, poor bowel habits, anesthesia Diarrhea • Disruption in normal mechanism to absorb intestinal water • E.g., from osmotically active solutes that move large volumes of water into colon © 2019 McGraw-Hill Education 127 Section 26.3 What did you learn? 1 16. What organs are considered part of the lower GI tract? 17. What are the three anatomic structures that increase the surface area of the small intestine? Describe each. 18. Which type of motility is primarily responsible for mixing the chyme and accessory gland secretions within the small intestine—segmentation or peristalsis? Which for propulsion? Explain each. 19. Where do deoxygenated, nutrient-rich blood and oxygenated blood first come together within a liver lobule? © 2019 McGraw-Hill Education 128 Section 26.3 What did you learn? 2 20. Does the liver produce digestive enzymes? If not, what substance does it produce that assists in digestion? 21. What are the primary functions of pancreatic juice? 22. What is the pathway of chyme from its entry into the large intestine until feces is eliminated? 23. What are the general functions of bacteria within the large intestine? 24. Which substances are typically absorbed by the large intestine? © 2019 McGraw-Hill Education 26.4 Nutrients and Their Digestion Learning Objectives 1 32. Name the three classes of carbohydrates. 33. Explain the processing in the oral cavity that initiates carbohydrate digestion. 34. Describe the chemical digestion of carbohydrates that occurs in the small intestine. 35. Identify the enzyme that initiates protein digestion in the stomach, and explain its activation and action. 36. Explain why the proteolytic enzymes of the stomach and pancreas are synthesized in inactive forms. © 2019 McGraw-Hill Education 129 26.4 Nutrients and Their Digestion Learning Objectives 2 37. Describe the chemical digestion of proteins that occurs in the small intestine. 38. Explain the role of bile salts in mechanical digestion of lipids and the role of pancreatic lipase in the chemical digestion of triglycerides. 39. Discuss the process by which lipids are absorbed. 40. Describe the digestion of nucleic acids. 41. Describe the absorption of water, electrolytes, and vitamins. 42. Explain the details of vitamin B12 absorption. © 2019 McGraw-Hill Education 130 131 26.4a Carbohydrate Digestion 1 Carbohydrates • Monosaccharides, e.g., glucose, fructose • Disaccharides, e.g., sucrose, maltose • Polysaccharides, e.g., starch and cellulose • Starch broken down into individual glucose molecules • Disaccharides broken down into individual monosaccharides • Main digestion sites: oral cavity and small intestine © 2019 McGraw-Hill Education Carbohydrate Digestion Figure 26.26a 132 oral cavity • salivary amylase • Breaks starch molecules • Inactivated by low pH of stomach when bolus swallowed • Occurs within 15 to 20 minutes small intestine • Pancreatic amylase • In pancreatic juice • Continues digestion of starch © 2019 McGraw-Hill Education 133 Digestion of Other Disaccharides Digestion of other disaccharides requires one enzyme each • Named for substrate it digests • E.g., lactase digests lactose to glucose and galactose • Reduced amount or lack of lactase lactose intolerant Figure 26.26c © 2019 McGraw-Hill Education Clinical View: Celiac Disease (Gluten-Sensitive Enteropathy) Autoimmune disorder affecting 1% of U.S. population Gluten protein in wheat, rye, barley • Stimulates immune response damages villi of small intestine, interferes with absorption Symptoms: • Abdominal pain, diarrhea, nutrient deficiencies © 2019 McGraw-Hill Education 134 135 26.4b Protein Digestion 1 Proteins • Polymers composed of amino acid subunits linked by peptide bonds • Digestion releases individual amino acids • Broken down by enzymes © 2019 McGraw-Hill Education 136 26.4b Protein Digestion 2 Protein breakdown in the stomach • Begins within stomach lumen with pepsin • Formed from pepsinogen, inactive precursor • Stomach’s low pH • Due to HCl released from parietal cells • Activates pepsinogen to active pepsin • Denatures proteins to facilitate chemical breakdown © 2019 McGraw-Hill Education 137 Protein Digestion in the Small Intestine Figure 26.27 © 2019 McGraw-Hill Education 138 26.4c Lipid Digestion 1 Lipids • Not water-soluble, highly variable structures • Triglycerides • Composed of glycerol and three fatty acids • Enzymes required to break bonds between • Cholesterol • Does not need to be broken down for absorption © 2019 McGraw-Hill Education 139 26.4c Lipid Digestion 2 Lipid breakdown in the stomach • Lingual lipase • Component of saliva in the mouth • Activated when reaches the stomach • Gastric lipase • Produced by chief cells • Together digest 30% of triglycerides to diglyceride and fatty acid • Neither requires participation of bile salts © 2019 McGraw-Hill Education Lipid Digestion and Absorption in the Small Intestine Figure 26.28 © 2019 McGraw-Hill Education 140 26.4d Nucleic Acid Digestion Nucleic acids are polymers of nucleotides Two types: DNA and RNA • Three components: sugar, phosphate group, nitrogenous base Nucleic acid breakdown in the small intestine • Deoxyribonuclease and ribonuclease • Nucleases released by pancreas • Break phosphodiester bond between nucleotides of DNA and RNA © 2019 McGraw-Hill Education 141 142 26.4d Nucleic Acid Digestion 2 Nucleic acid breakdown in the small intestine (continued) • Phosphatase, breaks bonds holding phosphate • Nucleosidase, breaks bond between sugar and nitrogenous base • Components absorbed across epithelium of small intestine • Phosphate, sugar, nitrogenous bases © 2019 McGraw-Hill Education 26.4e Water, Electrolyte, and Vitamin Absorption 1 Small intestine is location of most water, electrolytes, and vitamin absorption from diet Water absorption • Small intestine absorbs almost all ingested water (average 8 out of 9 liters) • Large intestine absorbs some • Rest passed in feces • Absorbed across epithelia and into blood vessels via osmosis © 2019 McGraw-Hill Education 143 26.4e Water, Electrolyte, and Vitamin Absorption 2 Electrolyte absorption • Small intestine absorbs almost all electrolytes that enter • Most absorption is unregulated, dependent on diet • Iron has controlled absorption • Hepcidin is a hormone released from liver • Inhibits iron absorption • If iron levels are low, hepcidin levels are decreased, allowing for greater iron absorption © 2019 McGraw-Hill Education 144 26.4e Water, Electrolyte, and Vitamin Absorption 3 Vitamin absorption • Fat-soluble vitamins (A, D, E, K) absorbed in small intestine along with lipids within micelles • Water-soluble vitamins (B and C) absorbed through diffusion and active transport • B12 is large, so absorbed by receptor-mediated endocytosis • Requires intrinsic factor (formed by parietal cells in stomach) © 2019 McGraw-Hill Education 145 146 Section 26.4 What did you learn? 25. What enzyme is released from the salivary glands to begin the break down starch? What enzyme is released from the pancreas into the small intestine to continue the breakdown of starch? 26. How are proteolytic enzymes activated in the stomach and in the small intestine? Explain why this is necessary. 27. What is the function of bile salts in lipid digestion? Is this considered chemical digestion or mechanical digestion? 28. How do micelles and chylomicrons function in lipid digestion? 29. Where does nucleic acid digestion occur? 30. Explain the details of vitamin B12 absorption. © 2019 McGraw-Hill Education