A&P ch22 Lecture PDF

22 The Digestive System Lecture Presentation by Lori Garrett © 2018 Pearson Education, Inc.  Note to the Instructor: For the third edition of Visual Anatomy & Physiology...

22 The Digestive System Lecture Presentation by Lori Garrett © 2018 Pearson Education, Inc.  Note to the Instructor: For the third edition of Visual Anatomy & Physiology, we have updated our PowerPoints to fully integrate text and art. The pedagogy now more closely matches that of the textbook. The goal of this revised formatting is to help your students learn from the art more effectively. However, you will notice that the labels on the embedded PowerPoint art are not editable. You can easily import editable art by doing the following: Copying slides from one slide set into another You can easily copy the Label Edit art into the Lecture Presentations by using either the PowerPoint Slide Finder dialog box or Slide Sorter view. Using the Slide Finder dialog box allows you to explicitly retain the source formatting of the slides you insert. Using the Slide Finder dialog box in PowerPoint: 1. Open the original slide set in PowerPoint. 2. 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Slides will place immediately after the slide you have selected in the Slides tab in Normal view. © 2018 Pearson Education, Inc.  Section 1: Organization of the Digestive System Learning Outcomes 22.1 Name the major and accessory organs of the digestive system. 22.2 Describe the functional histology of the digestive tract. 22.3 Describe the structural and functional features of smooth muscle tissue. 22.4 Explain the processes by which materials move through the digestive tract. © 2018 Pearson Education, Inc.  Module 22.1: The digestive system consists of the digestive tract and accessory organs Digestive system  Provides nutrients for cell maintenance and growth  Consists of muscular tube called digestive tract— also called gastrointestinal (GI) tract, or alimentary canal © 2018 Pearson Education, Inc.  Module 22.1: Digestive system organization Digestive system (continued)  Supports tissues with no direct contact with the outside environment Cardiovascular system Respiratory system – Works with the cardiovascular system to supply oxygen to and remove carbon dioxide from cells Urinary system – Removes organic wastes generated by cell activity © 2018 Pearson Education, Inc.  Digestive system works with other systems © 2018 Pearson Education, Inc.  Module 22.1: Digestive system organization Digestive system (continued)  Composed of: Digestive tract – Food passes along length from mouth to anus Accessory organs – Secrete products into the digestive tract © 2018 Pearson Education, Inc.  Module 22.1: Review A. Which other systems work with the digestive system to support the cells and tissues of the human body? B. Starting at the mouth, identify the major organs of the digestive tract. C. List the accessory organs of the digestive system. Learning Outcome: Name the major and accessory organs of the digestive system. © 2018 Pearson Education, Inc.  Module 22.2: The digestive tract is a muscular tube lines by a mucous epithelium Digestive tract description  Long muscular tube  Lined with permanent ridges and temporary folds Both features increase surface area for absorbing nutrients © 2018 Pearson Education, Inc.  Module 22.2: Digestive tract structure Mesentery  Double sheets of peritoneal membrane Areolar tissue lies between mesothelial layers – Provides access route for blood vessels, nerves, and lymphatics Stabilizes attached organs Prevents entanglement of intestines © 2018 Pearson Education, Inc.  Module 22.2: Digestive tract structure Four major layers of the digestive tract 1. Mucosa (inner lining) Mucous membrane of epithelium, moistened by glandular secretions, and lamina propria of areolar tissue © 2018 Pearson Education, Inc.  Module 22.2: Digestive tract structure Four major layers of the digestive tract (continued) 2. Submucosa Layer of dense irregular connective tissue Contains blood vessels and lymphatic vessels Also contains exocrine glands in some regions – Secrete buffers and enzymes into the digestive tract © 2018 Pearson Education, Inc.  Module 22.2: Digestive tract structure Four major layers of the digestive tract (continued) 3. Muscular layer Smooth muscle in two layers (inner circular layer; outer longitudinal layer) Involved in mechanical processing and movement along tract © 2018 Pearson Education, Inc.  Module 22.2: Digestive tract structure Four major layers of the digestive tract (continued) 4. Serosa Layer of visceral peritoneum along the digestive tract in the abdominal cavity No serosa in oral cavity, pharynx, esophagus, and rectum – Covered instead by adventitia (sheath formed from a dense network of collagen fibers) – Firmly attaches tract to adjacent structures © 2018 Pearson Education, Inc.  Module 22.2: Digestive tract structure Components of the mucosa  Mucosal epithelium Tract begins and ends with stratified squamous epithelium Stomach, small and large intestines are simple columnar with goblet cells © 2018 Pearson Education, Inc.  Module 22.2: Digestive tract structure Components of the mucosa (continued)  Villi (singular, villus) Small mucosal projections that increase surface area for absorption © 2018 Pearson Education, Inc.  Module 22.2: Digestive tract structure Components of the mucosa (continued)  Lamina propria Areolar tissue containing blood vessels, sensory nerve endings, lymphatic vessels, smooth muscle cells, lymphoid tissue, and some mucous glands © 2018 Pearson Education, Inc.  Module 22.2: Digestive tract structure Components of the mucosa (continued)  Muscularis mucosae Two concentric layers of smooth muscle 1. Inner circular layer 2. Outer longitudinal layer Alter shape of lumen and move the circular folds and villi – Circular folds (plicae circulares) o Permanent transverse folds in the intestinal lining © 2018 Pearson Education, Inc.  Module 22.2: Digestive tract structure Nerve plexuses  Involved in local control of digestive activities Parasympathetic stimulation increases digestive muscle tone and activity Sympathetic stimulation decreases muscle tone and activity  Submucosal neural plexus Located in the submucosal layer Innervates the mucosa and submucosa Contains sensory neurons, autonomic nerve fibers © 2018 Pearson Education, Inc.  Module 22.2: Digestive tract structure Nerve plexuses (continued)  Myenteric plexus (mys, muscle + enteron, intestine) Network of sensory neurons and autonomic nerve fibers Located in the muscularis externa between the circular and longitudinal layers Works with the submucosal plexus to coordinate local control of digestive activity © 2018 Pearson Education, Inc.  Module 22.2: Review A. What is the importance of the mesenteries? B. Name the four layers of the digestive tract beginning from the lumen of the digestive tract. C. Compare the submucosal neural plexus with the myenteric plexus. Learning Outcome: Describe the functional histology of the digestive tract. © 2018 Pearson Education, Inc.  Module 22.3: Smooth muscle tissue is found throughout the body, but it plays a particularly prominent role in the digestive tract Smooth muscle  Found throughout the body  Forms sheets, bundles, or sheaths around tissues Around blood vessels, regulates blood flow Ring-shaped sphincters regulate movement along passageways in the digestive and urinary systems  In the digestive tract, organized into inner circular layer and outer longitudinal layer Within each layer, cells are aligned parallel to each other © 2018 Pearson Education, Inc.  Smooth muscle of the digestive tract © 2018 Pearson Education, Inc.  Module 22.3: Smooth muscle in the digestive tract Smooth muscle cells  Relatively long and slender Diameter 5–10 µm; length 30–200 µm  Contain actin and myosin filaments Organization of actin and myosin filaments differs from skeletal and cardiac muscle Contain no T tubules Sarcoplasmic reticulum forms loose network throughout the sarcoplasm Have no myofibrils or sarcomeres No striations, giving the tissue a “smooth” microscopic appearance © 2018 Pearson Education, Inc.  Module 22.3: Smooth muscle in the digestive tract Smooth muscle cell contraction  Thin filaments are attached to dense bodies Distributed throughout sarcoplasm Similar to Z lines of skeletal muscle tissue Attachment points for adjacent smooth muscle cells  Thick filaments scattered throughout the sarcoplasm More myosin heads per thick filament than in skeletal or cardiac muscle © 2018 Pearson Education, Inc.  Module 22.3: Smooth muscle in the digestive tract Smooth muscle cell contraction (continued)  Contraction still involves interaction of thin and thick filaments Cell shortens, but not in a straight line Cell twists like a corkscrew as it contracts © 2018 Pearson Education, Inc.  Module 22.3: Smooth muscle in the digestive tract Two types of smooth muscle 1. Multi-unit smooth muscle cells Innervated in motor units like skeletal muscle – But each cell may be connected to more than one motor neuron Locations – Iris of eye (regulates diameter of the pupil) – Portions of male reproductive system – Walls of large arteries – Arrector pili muscles of skin © 2018 Pearson Education, Inc.  Module 22.3: Smooth muscle in the digestive tract Two types of smooth muscle (continued) 2. Visceral smooth muscle cells Lack any direct connection with motor neuron Arranged in sheets or layers Electrically connected by gap junctions and mechanically connected by dense bodies – Cells contract in a wave as a single unit Stimulation can be neural, hormonal, or chemical – Some rhythmically stimulated by pacesetter cells Located in digestive tract walls, the gallbladder, urinary bladder, and many other internal organs © 2018 Pearson Education, Inc.  Types of smooth muscle © 2018 Pearson Education, Inc.  Module 22.3: Smooth Muscle in the digestive tract Functional characteristics of smooth muscle  Plasticity Ability to function over a wide range of lengths – Due to the scattered arrangement of thick and thin filaments – Tension development and resting length are not directly related Important for digestive tract and other organs that change size and shape  Smooth muscle tone Normal background activity and tension due to various stimulations © 2018 Pearson Education, Inc.  Module 22.3: Review A. Describe the orientation of smooth muscle fibers in the muscular layer of the digestive tract. B. Identify the structural characteristics of smooth muscle fibers. C. Why can smooth muscle contract over a wider range of resting lengths than skeletal muscle? Learning Outcome: Describe the structural and functional features of smooth muscle tissue. © 2018 Pearson Education, Inc.  Module 22.4: Smooth muscle contractions produce motility of the digestive tract... Peristalsis  Wave of muscle contraction  Food enters the digestive tract as a bolus Moist, compact mass of material  Bolus is propelled along the tract by contractions of the muscularis externa (peristalsis) Circular muscles contract behind bolus Longitudinal muscles ahead of bolus contract Process repeats © 2018 Pearson Education, Inc.  Peristalsis © 2018 Pearson Education, Inc.  Module 22.4: Movement along the digestive tract Segmentation  Cycles of contraction  Churn and fragment bolus  Mix contents with intestinal secretions  No set pattern of contractions, so no particular direction of movement  Occurs in most areas of the small intestine and some portions of the large intestine © 2018 Pearson Education, Inc.  Segmentation © 2018 Pearson Education, Inc.  Module 22.4:... and local factors interact with neural and hormonal mechanisms to regulate digestive activities Digestive regulation mechanisms 1. Local factors Primary stimulus for digestive activities Examples: – Changes in pH of contents in lumen – Physical distortion of digestive tract wall – Presence of chemicals (specific nutrients or chemical messengers released by the mucosa) © 2018 Pearson Education, Inc.  Module 22.4: Movement along the digestive tract Digestive regulation mechanisms (continued) 2. Neural control mechanisms Short reflexes (myenteric reflexes) – Triggered by chemoreceptors or stretch receptors in digestive tract walls – Controlling neurons located in the myenteric plexus Long reflexes – Higher level of control involving interneurons and motor neurons of the CNS o Generally control large-scale peristalsis, moving material from one region of the tract to another – May involve parasympathetic motor fibers that synapse in the myenteric plexus © 2018 Pearson Education, Inc.  Module 22.4: Movement along the digestive tract Digestive regulation mechanisms (continued) 3. Hormonal control mechanisms Involve at least 18 hormones that affect digestive function – Some affect other systems as well Hormones are peptides produced by enteroendocrine cells (endocrine cells in the epithelium of the digestive tract) © 2018 Pearson Education, Inc.  Digestive regulation mechanisms © 2018 Pearson Education, Inc.  Module 22.4: Movement along the digestive tract Congenital megacolon (Hirschsprung disease)  Characterized by absences or marked reduction in number of ganglion cells in the myenteric plexus of rectum  Causes paralysis of smooth muscle (absence of peristaltic movement) Abnormal dilation and hypertrophy of colon Chronic constipation, bloating, abdominal pain © 2018 Pearson Education, Inc.  Module 22.4: Review A. Which is more efficient in propelling intestinal contents along the digestive tract: peristalsis or segmentation? Why? B. Cite the major mechanisms that regulate and control digestive activities. C. Describe enteroendocrine cells. Learning Outcome: Explain the processes by which materials move through the digestive tract. © 2018 Pearson Education, Inc.  Section 2: Digestive Tract Learning Outcomes 22.5 Name the structures and primary functions of the digestive tract organs. 22.6 Describe the anatomy of the oral cavity, and discuss the functions of its structures. 22.7 Describe the types of teeth, and differentiate between deciduous teeth and permanent teeth. 22.8 Describe the anatomy and functions of the pharynx and esophagus, and explain the swallowing process. © 2018 Pearson Education, Inc.  Section 2: Digestive Tract Learning Outcomes (continued) 22.9 Explain the embryonic development of the mesenteries, and describe the mesenteries that remain in adulthood. 22.10 Describe the anatomy of the stomach and its histological features. 22.11 Describe the anatomy of the stomach relating to its role in digestion and absorption. 22.12 Describe the anatomy of the intestinal tract and its histological features. © 2018 Pearson Education, Inc.  Section 2: Digestive Tract Learning Outcomes (continued) 22.13 Describe the anatomy and physiology of the small intestine. 22.14 Discuss the major digestive hormones and their primary effects. 22.15 Explain the regulation of gastric activity by central and local mechanisms. 22.16 Describe the gross anatomy of the three segments of the large intestine. © 2018 Pearson Education, Inc.  Section 2: Digestive Tract Learning Outcomes (continued) 22.17 Describe the large intestine’s histology and role in fecal compaction, and explain the defecation reflex. © 2018 Pearson Education, Inc.  Module 22.5: The digestive tract begins with the mouth and ends with the anus Description and major organs  Muscular tube about 10 m (33 ft) long  Major organs and their functions Oral cavity (mouth) – Mechanical processing (with the teeth and tongue), moistening, mixing with salivary secretions Pharynx – Muscular propulsion of food into the esophagus Esophagus – Transport of materials to the stomach © 2018 Pearson Education, Inc.  Module 22.5: The digestive tract Description and major organs (continued)  Stomach Chemical breakdown and mechanical processing  Small intestine Enzymatic digestion and absorption  Large intestine Dehydration and compaction of indigestible materials © 2018 Pearson Education, Inc.  Digestive organs © 2018 Pearson Education, Inc.  Module 22.5: The digestive tract Functions of the digestive tract  Ingestion Occurs when solid food and liquid enter the oral cavity  Mechanical digestion and propulsion Involves crushing and shredding of food in the oral cavity and mixing and churning in the stomach  Chemical digestion Chemical and enzymatic breakdown of food into small organic molecules that can be absorbed by the digestive epithelium © 2018 Pearson Education, Inc.  Module 22.5: The digestive tract Functions of the digestive tract (continued)  Secretion The release of water, acids, enzymes, buffers, and salts by the digestive tract epithelium and by accessory digestive organs  Absorption Movement of nutrients across the digestive epithelium and into the bloodstream  Defecation Indigestible food is compacted into material waste called feces, which are eliminated by defecation © 2018 Pearson Education, Inc.  Module 22.5: Review A. Define ingestion. B. Distinguish between chemical digestion and absorption. C. Describe the function of the large intestine. Learning Outcome: Name the structures and primary functions of the digestive tract organs. © 2018 Pearson Education, Inc.  Module 22.6: The oral cavity is a space that contains the tongue, teeth, and gums Oral cavity (mouth)  Lined by oral mucosa (stratified squamous epithelium) Keratinized in areas that are exposed to severe abrasion (superior tongue surface, hard palate) Thin, nonkeratinized lining on cheeks, lips, and inferior tongue surface – Thin mucosa inferior to the tongue allows for rapid absorption of lipid-soluble drugs (example: nitroglycerin)  Nutrients are not absorbed here  Digestion of carbohydrates and lipids begins here © 2018 Pearson Education, Inc.  Module 22.6: The oral cavity Oral cavity boundaries  Superior boundary Hard palate – Formed by the palatine processes of the maxillary bones and horizontal plates of the palatine bones Soft palate – Muscular region posterior to the hard palate © 2018 Pearson Education, Inc.  Module 22.6: The oral cavity Oral cavity boundaries (continued)  Anterior and lateral boundary Cheeks – Form the lateral walls of the oral cavity o Supported by pads of fat and the buccinator muscles – Anteriorly, cheek mucosa is continuous with the labia Labia (lips) – Form anterior boundary © 2018 Pearson Education, Inc.  Module 22.6: The oral cavity Oral cavity boundaries (continued)  Posterior boundary Uvula – Dangling process extending from the soft palate – Helps prevent food from entering pharynx prematurely – Swings upward during swallowing to prevent food from entering the nasopharynx Palatine tonsils (one located on either side of the oropharynx) © 2018 Pearson Education, Inc.  Module 22.6: The oral cavity Oral cavity boundaries (continued)  Posterior boundary (continued) Root of tongue – Fixed portion projecting into the oropharynx – Marked by a V-shaped line of vallate papillae Lingual tonsils (located in the root of the tongue) © 2018 Pearson Education, Inc.  Module 22.6: The oral cavity Oral cavity boundaries (continued)  Inferior boundary Body of the tongue – Anterior, mobile portion Geniohyoid and mylohyoid muscles provide extra support to the inferior boundary © 2018 Pearson Education, Inc.  Module 22.6: The oral cavity Oral cavity structures  Oral vestibule The space between the cheeks (or lips) and teeth  Frenulum of the upper lip (frenulum, a small bridle) Attaches gums to upper lip  Thick mucosa with ridges covering the hard palate Provides traction for compression of food by the tongue  Frenulum of the lower lip Attaches gums to lower lip © 2018 Pearson Education, Inc.  Module 22.6: The oral cavity Oral cavity structures (continued)  Gingivae (gums) Ridges of oral mucosa surrounding the base of each tooth Firmly attached to the periostea of the underlying bone  Palatal arches Located on either side of the uvula Palatoglossal arch – Extends between soft palate and base of tongue Palatopharyngeal arch – Extends from soft palate to pharyngeal wall © 2018 Pearson Education, Inc.  Module 22.6: The oral cavity Oral cavity structures (continued)  Fauces Space between oral cavity and oropharynx  Tongue Manipulates materials inside the mouth Surface flushed by secretions of small glands – Secretions contain water, mucins, and lingual lipase (an enzyme that starts the digestion of lipids) Attached to the floor of the mouth by the frenulum of the tongue (lingual frenulum) © 2018 Pearson Education, Inc.  Oral cavity © 2018 Pearson Education, Inc.  Module 22.6: The oral cavity Ankyloglossia (tongue-tie)  Present at birth  Frenulum of tongue is too short  Interferes with breastfeeding in newborns  Interferes with learning to speak in toddlers © 2018 Pearson Education, Inc.  Module 22.6: Review A. The oral cavity is lined by which type of epithelium? B. Name the structure that forms the roof of the mouth. C. Describe the location of the fauces. D. What effects might a shortened frenulum of tongue cause? Learning Outcome: Describe the anatomy of the oral cavity, and discuss the functions of its structures. © 2018 Pearson Education, Inc.  Module 22.7: Teeth in different regions of the jaws vary in size, shape, and function Components of a tooth  The bulk of each tooth is composed of dentin Mineralized matrix similar to bone but contains no cells  Pulp cavity The interior chamber of the tooth © 2018 Pearson Education, Inc.  Module 22.7: Teeth Components of a tooth (continued)  Occlusal surface Portion of the crown used for crushing, slicing, or chewing  Enamel Covers the dentin of the crown Hardest biologically manufactured substance Composed of calcium phosphate – Requires calcium, phosphate, and vitamin D for formation and resistance to decay © 2018 Pearson Education, Inc.  Module 22.7: Teeth Components of a tooth (continued)  Gingival sulcus Shallow groove surrounding the base of the neck Epithelial attachment blocks bacteria from accessing deeper tissues around the root © 2018 Pearson Education, Inc.  Module 22.7: Teeth Components of a tooth (continued)  Cement Covers the dentin in the root Less resistant to erosion than dentin  Periodontal ligament Creates gomphosis articulation between root dentin and alveolar bone  Root canal Narrow tunnel within the root of the tooth Passageway for blood vessels and nerves to the pulp cavity Opening into the root canal is the apical foramen © 2018 Pearson Education, Inc.  Module 22.7: Teeth Regions of a tooth  Crown Portion projecting into the oral cavity from the surface of the gums  Neck The boundary between the crown and root  Root Portion below the gum line Sits in a bony tooth socket called an alveolus © 2018 Pearson Education, Inc.  The tooth © 2018 Pearson Education, Inc.  Module 22.7: Teeth Four types of teeth  Each with a distinctive shape and root pattern 1. Incisors Blade-shaped teeth with a single root Located at the front of the mouth Useful for clipping or cutting © 2018 Pearson Education, Inc.  Module 22.7: Teeth Four types of teeth (continued) 2. Canines (or cuspids) Conical with a sharp ridgeline and pointed tip Used for tearing or slashing Have a single root © 2018 Pearson Education, Inc.  Module 22.7: Teeth Four types of teeth (continued) 3. Premolars (or bicuspids) Have flattened crowns with prominent ridges Used for crushing, mashing, or grinding Have one or two roots © 2018 Pearson Education, Inc.  Module 22.7: Teeth Four types of teeth (continued) 4. Molars Very large flattened crowns with prominent ridges Adapted for crushing and grinding Typically have three roots (upper jaw) or two roots (lower jaw) © 2018 Pearson Education, Inc.  Module 22.7: Teeth Two sets of teeth  Formed during embryonic development 1. Deciduous teeth Also called primary teeth, milk teeth, or baby teeth At 2 years of age – 20 deciduous teeth – 5 on each side of upper and lower jaws o 2 incisors, 1 canine, 2 deciduous molars © 2018 Pearson Education, Inc.  Unerupted permanent teeth exposed in child skull © 2018 Pearson Education, Inc.  Module 22.7: Teeth Two sets of teeth (continued) 2. Permanent teeth Gradually replace deciduous teeth – Periodontal ligaments and roots of primary teeth erode – Primary teeth fall out or are pushed aside by secondary teeth Three additional molars appear on each side of the upper and lower jaws – Third molars are called wisdom teeth 32 total permanent teeth © 2018 Pearson Education, Inc.  Permanent teeth © 2018 Pearson Education, Inc.  Module 22.7: Teeth Impacted tooth  Fails to erupt because of overcrowding from adjacent teeth or from twisting and tilting within jaw bone  Most commonly happens with wisdom teeth  Treatment ranges from nothing to tooth extraction © 2018 Pearson Education, Inc.  Module 22.7: Review A. Name the three main parts of a typical tooth. B. What is the name sometimes given to the third set of molars? Learning Outcome: Describe the types of teeth, and differentiate between deciduous teeth and permanent teeth. © 2018 Pearson Education, Inc.  Module 22.8: The muscular walls of the pharynx and esophagus play a key role in swallowing Pharynx (throat)  Membrane-lined cavity posterior to the nose and mouth  Continuous with the esophagus  Common passageway for solid food, liquids, and air  Three regions 1. Nasopharynx 2. Oropharynx 3. Laryngopharynx © 2018 Pearson Education, Inc.  The pharynx © 2018 Pearson Education, Inc.  Module 22.8: The pharynx and esophagus Esophagus  Function Actively moves food and liquids to the stomach  Structure Hollow, muscular tube ~25 cm (10 in.) long and 2 cm (0.8 in.) wide Narrowest point at the beginning (posterior to cricoid cartilage) – Descends posterior to the trachea – Enters the abdominopelvic cavity through the esophageal hiatus (opening in the diaphragm) © 2018 Pearson Education, Inc.  Module 22.8: The pharynx and esophagus Esophagus (continued)  Innervation By the parasympathetic and sympathetic fibers from the esophageal plexus Maintain resting muscle tone in circular muscle layer – Keeps the lumen closed, except when you swallow © 2018 Pearson Education, Inc.  Module 22.8: The pharynx and esophagus Esophagus (continued)  Control of movement Upper esophageal sphincter – Band of smooth muscle that functions as sphincter – Prevents air from entering the esophagus Lower esophageal sphincter (cardiac sphincter) – At the inferior end of the esophagus – Normally contracted (prevents backflow of stomach contents) © 2018 Pearson Education, Inc.  Module 22.8: The pharynx and esophagus Esophagus (continued)  Layers of the esophageal wall features Mucosa (nonkeratinized stratified squamous epithelium) and submucosa form large folds extending the length of the esophagus – Allow for expansion with passage of a bolus Muscularis externa – Superior third is composed of skeletal muscle – Middle third is a mix of skeletal and smooth muscle – Inferior third is composed of smooth muscle only No serosa – Adventitia of connective tissue anchors esophagus to posterior body wall © 2018 Pearson Education, Inc.  The esophagus © 2018 Pearson Education, Inc.  Module 22.8: The pharynx and esophagus Swallowing, or deglutition  Initiated voluntarily but proceeds automatically  Three phases of swallowing 1. Buccal phase (strictly voluntary) – Begins with compression of bolus against hard palate – Tongue forces bolus into the oropharynx o Also elevates soft palate (sealing off nasopharynx) – Entry into the oropharynx triggers reflex response © 2018 Pearson Education, Inc.  Module 22.8: The pharynx and esophagus Three phases of swallowing (continued) 2. Pharyngeal phase Begins with stimulation of tactile receptors in uvula and palatine arches Motor commands from the swallowing center (in medulla oblongata) coordinate muscle contraction in pharyngeal muscles – Larynx is elevated; epiglottis is folded; uvula and soft palate are elevated Bolus is moved through the pharynx into the esophagus © 2018 Pearson Education, Inc.  Module 22.8: The pharynx and esophagus Three phases of swallowing (continued) 3. Esophageal phase Begins as bolus is forced through the entrance to the esophagus Bolus is pushed toward the stomach by peristalsis Approach of bolus triggers the opening of the lower esophageal sphincter – Bolus enters the stomach Typical travel time is 9 seconds – Liquids may travel faster A dry (poorly lubricated) bolus may require secondary peristaltic waves © 2018 Pearson Education, Inc.  The esophageal phase © 2018 Pearson Education, Inc.  Module 22.8: Review A. Name the regions and functions of the pharynx. B. Describe the muscular layer of the esophagus. C. Describe the major event in each of the three phases of swallowing. Learning Outcome: Describe the anatomy and functions of the pharynx and esophagus, and explain the swallowing process. © 2018 Pearson Education, Inc.  Module 22.9: The stomach and most of the intestinal tract are suspended by mesenteries and covered by the peritoneum Peritoneal cavity  Encloses stomach and most of intestine  Lined by a serous membrane called the peritoneum Serous membrane divided into: – Serosa, or visceral peritoneum o Covers organs enclosed by the peritoneal cavity – Parietal peritoneum o Lines the inner surface of the peritoneal cavity © 2018 Pearson Education, Inc.  Module 22.9: Mesenteries Peritoneal cavity (continued)  Serous membrane Continuously secretes peritoneal fluid into peritoneal cavity ~7 liters/day secreted and reabsorbed Volume at any one time is about 50 mL – Thin layer separates parietal and visceral surfaces – Allows sliding movements without friction or irritation Rate of fluid moving into the cavity is accelerated by liver disease, kidney disease, and heart failure – Accumulation of peritoneal fluid can create abdominal swelling (ascites) © 2018 Pearson Education, Inc.  Module 22.9: Mesenteries Dorsal and ventral mesenteries  Formed during embryonic development  Suspend the digestive tract and accessory organs  Develop into other adult connections © 2018 Pearson Education, Inc.  Module 22.9: Mesenteries Dorsal and ventral mesenteries (continued)  Dorsal mesentery becomes: Greater omentum (omentum, fat) – Attached to stomach and transverse colon – Forms a large pouch extending inferiorly between anterior body wall and anterior surface of the small intestine – Contains adipose tissue that provides padding and protection © 2018 Pearson Education, Inc.  Module 22.9: Mesenteries Dorsal and ventral mesenteries (continued) Mesentery proper – Connects small intestine to posterior body wall Mesocolon – Connects large intestine to posterior body wall © 2018 Pearson Education, Inc.  Module 22.9: Mesenteries Dorsal and ventral mesenteries (continued)  Ventral mesentery becomes: Lesser omentum – Connects the stomach to the liver – Provides an access route for blood vessels and other structures entering/leaving the liver Falciform ligament – Connects the liver to the anterior body wall © 2018 Pearson Education, Inc.  Module 22.9: Mesenteries Changing position of the mesenteries  With elongation of the digestive tract, position of the mesenteries changes Some segments of the tract become fixed in position Segments of the mesentery proper come into contact and fuse together Much of the mesocolon fuses to the dorsal body wall © 2018 Pearson Education, Inc.  Mesenteries © 2018 Pearson Education, Inc.  Orientation of the mesenteries © 2018 Pearson Education, Inc.  Module 22.9: Review A. What is the falciform ligament? B. What is the function of the lesser omentum? C. Explain the significance of peritoneal fluid. Learning Outcome: Explain the embryonic development of the mesenteries, and describe the mesenteries that remain in adulthood. © 2018 Pearson Education, Inc.  Module 22.10: The stomach is a muscular, expandable, J-shaped organ with three layers in the muscular layer Stomach  Highly variable shape depending on contents Empty: muscular tube with constricted lumen Full: can expand to contain 1–1.5 liters of material (chyme) – Viscous, highly acidic, soupy mixture formed from the combination of food, saliva, and gastric gland secretions © 2018 Pearson Education, Inc.  Module 22.10: The stomach Stomach (continued)  Lesser curvature forms the medial surface Attached to the mesentery of the lesser omentum  Greater curvature forms the lateral and inferior surfaces Attached to the mesentery of the greater omentum © 2018 Pearson Education, Inc.  Module 22.10: The stomach Stomach regions 1. Fundus Superior to the junction between the stomach and esophagus © 2018 Pearson Education, Inc.  Module 22.10: The stomach Stomach regions (continued) 2. Cardia Superior, medial portion within 3 cm of gastroesophageal junction Secretes mucus to protect esophagus from stomach acid/enzymes © 2018 Pearson Education, Inc.  Module 22.10: The stomach Stomach regions (continued) 3. Body Largest region Between the fundus and pylorus Functions as a mixing bowl © 2018 Pearson Education, Inc.  Module 22.10: The stomach Stomach regions (continued) 4. Pylorus Sharp curve of “J” of the stomach Frequently changes shape with mixing movements © 2018 Pearson Education, Inc.  Cadaver dissection with stomach © 2018 Pearson Education, Inc.  Module 22.10: The stomach Muscle layers and rugae  Layers of the muscularis externa Oblique layer – Strengthens the stomach wall – Assists in mixing and churning to form chyme Circular layer Longitudinal layer © 2018 Pearson Education, Inc.  Module 22.10: The stomach Muscle layers and rugae (continued)  Rugae (wrinkles) Prominent, temporary mucosal folds Allow gastric expansion by flattening out with stomach expansion © 2018 Pearson Education, Inc.  Module 22.10: The stomach The pyloric part  Pyloric antrum (antron, cavity) Portion connected to stomach body  Pyloric canal Empties into the duodenum (proximal segment of small intestine) © 2018 Pearson Education, Inc.  Module 22.10: The stomach The pyloric part (continued)  Pyloric sphincter Smooth muscle band regulating release of chyme into the duodenum  Pyloric orifice Stomach outlet © 2018 Pearson Education, Inc.  Module 22.10: Review A. Name the four major regions of the stomach in order from its junction with the esophagus to the small intestine. B. What anatomical feature of the stomach allows the organ to form chyme? C. Describe the lining of the stomach. Learning Outcome: Describe the anatomy of the stomach and its histological features. © 2018 Pearson Education, Inc.  Module 22.11: The stomach receives food and liquids from the esophagus and aids in mechanical and chemical digestion Functions of the stomach 1. Temporary storage of ingested food 2. Mechanical digestion of ingested food 3. Chemical digestion of food through the action of acid and enzymes 4. Production of intrinsic factor © 2018 Pearson Education, Inc.  Module 22.11: The stomach wall and functions Layers of the stomach wall  Mucosa Composed of simple columnar epithelium – Produces layer of alkaline mucus o Protects epithelial cells against acid and enzymes in gastric lumen – Life span of a gastric epithelial cell is only 3–7 days © 2018 Pearson Education, Inc.  Module 22.11: The stomach wall and functions Layers of the stomach wall (continued) Submucosa Muscular layer – Oblique, circular, and longitudinal layers Serosa © 2018 Pearson Education, Inc.  Module 22.11: The stomach wall and functions Gastric glands  Glands in the fundus and body Secrete most of the acid and enzymes enabling gastric digestion Dominated by parietal cells and chief cells Secrete ~1.5 L of gastric juice each day  Glands in the pylorus Secrete mucus and hormones that coordinate and control digestive activity © 2018 Pearson Education, Inc.  Module 22.11: The stomach wall and functions Gastric pits  Shallow depressions opening onto the gastric surface  Active stem cells at the base of each pit replace superficial cells shed into the chyme  Each pit communicates with several gastric glands © 2018 Pearson Education, Inc.  Gastric pits and glands © 2018 Pearson Education, Inc.  Module 22.11: The stomach wall and functions Cells of gastric glands  Parietal cells secrete: Intrinsic factor – Glycoprotein that aids in vitamin B12 absorption Hydrochloric acid (HCl) – Activates pepsinogen – Keeps stomach at pH 1.5–2 © 2018 Pearson Education, Inc.  Module 22.11: The stomach wall and functions Cells of gastric glands (continued)  G cells (enteroendocrine cells) Produce variety of hormones © 2018 Pearson Education, Inc.  Module 22.11: The stomach wall and functions Cells of gastric glands (continued)  Chief cells secrete: Pepsinogen – Activated by HCl to become pepsin o Active proteolytic (protein-digesting) enzyme Newborns also produce rennin and gastric lipase – Enzymes important for the digestion of milk © 2018 Pearson Education, Inc.  Module 22.11: The stomach wall and functions HCl production  Parietal cells do not create HCl in their cytoplasm (it would destroy the cell) H+ and Cl– are transported and secreted separately H+ is generated as carbonic anhydrase converts CO2 and H2O to carbonic acid – Carbonic acid dissociates into bicarbonate ions and hydrogen ions – CO2 + H2O → H2CO3 → HCO3– + H+ © 2018 Pearson Education, Inc.  HCl production © 2018 Pearson Education, Inc.  Module 22.11: The stomach wall and functions HCl production (continued)  Bicarbonate ejected into the interstitial fluid in exchange for a chloride ion From the interstitial fluid, bicarbonate enters the bloodstream – If gastric glands very active, amount of bicarbonate released is enough to increase the pH of the blood – Sudden influx of bicarbonate ions is called the alkaline tide  Chloride ions diffuse across cell and exit into the lumen of the gastric gland  Hydrogen ions are also actively transported into the gastric gland lumen © 2018 Pearson Education, Inc.  HCl production © 2018 Pearson Education, Inc.  Module 22.11: Review A. Explain the significance of the alkaline mucous layer lining the interior surface of the stomach. B. What is the function of parietal cells? C. Describe the alkaline tide. Learning Outcome: Describe the anatomy of the stomach relating to its role in digestion and absorption. © 2018 Pearson Education, Inc.  Module 22.12: The intestinal tract is specialized to absorb nutrients Specialized structures  Many intestinal structures add surface area to increase absorption Circular folds (plicae circulares) – Series of transverse folds along the intestinal lining – Permanent features – Roughly 800 folds in the small intestine – Mostly in the jejunum © 2018 Pearson Education, Inc.  Module 22.12: Intestinal tract structures Specialized structures (continued)  Intestinal villi (singular, villus) Fingerlike projections of mucosa Covered by epithelial cells – Surfaces covered with microvilli © 2018 Pearson Education, Inc.  Module 22.12: Intestinal tract structures Intestinal glands  Located at the bases of villi © 2018 Pearson Education, Inc.  Module 22.12: Intestinal tract structures Intestinal glands (continued)  Near base, stem cells divide and produce epithelial cells  Paneth cells at the base have a role in innate immunity Release defensins and lysozyme © 2018 Pearson Education, Inc.  Module 22.12: Intestinal tract structures Internal structure of a villus  Extensive capillary network in the lamina propria Carries absorbed nutrients to the hepatic portal circulation © 2018 Pearson Education, Inc.  Module 22.12: Intestinal tract structures Internal structure of a villus (continued)  Lymphatic capillary, or lacteal (lacteus, milky) Transports materials that cannot enter blood capillaries Example: – Absorbed fatty acids assembled into protein–lipid packages (chylomicrons) too large to diffuse into bloodstream – Transported by lymphatic system to venous circulation © 2018 Pearson Education, Inc.  Module 22.12: Intestinal tract structures Internal structure of a villus (continued)  Smooth muscle in muscularis mucosae and within the villi Moves villi back and forth, exposing surfaces to intestinal contents Squeezes lacteal, assisting in lymph movement © 2018 Pearson Education, Inc.  Module 22.12: Intestinal tract structures Internal structure of a villus (continued)  Brush border Carpet of microvilli on the surface of the epithelial cells Increases surface area for absorption Contains enzymes that digest materials – Epithelial cells can then absorb breakdown products © 2018 Pearson Education, Inc.  Module 22.12: Review A. Name the layers of the small intestine from superficial to deep. B. Describe the anatomy of the intestinal mucosa. C. Explain the function of lacteals. Learning Outcome: Describe the anatomy of the intestinal tract and its histological features. © 2018 Pearson Education, Inc.  Module 22.13: The small intestine is divided into the duodenum, jejunum, and ileum The small intestine  Plays key role in nutrient digestion and absorption 90 percent of nutrient absorption occurs in small intestine Most of remaining 10 percent occurs in large intestine  Average overall length = 6 m (19.7 ft)  Diameter ranges from 4 cm (1.6 in.) near stomach to 2.5 cm (1 in.) near large intestine  Three segments 1. Duodenum 2. Jejunum 3. Ileum © 2018 Pearson Education, Inc.  The small intestine © 2018 Pearson Education, Inc.  Module 22.13: Segments of the small intestine Segments of the small intestine 1. Duodenum 25 cm (10 in.) in length Segment closest to the stomach Acts as a “mixing bowl” – Receives chyme from stomach and digestive secretions from liver, gallbladder, and pancreas Mostly retroperitoneal Duodenal glands produce mucous secretions Has few circular folds and small villi Main function is to neutralize acidic chyme © 2018 Pearson Education, Inc.  Module 22.13: Segments of the small intestine Segments of the small intestine (continued) 2. Jejunum Between the duodenum and ileum Marked by a sharp bend at its beginning ~2.5 m (8.2 ft) in length In the peritoneal cavity Has numerous circular folds and abundant, long villi Majority of chemical digestion and nutrient absorption occurs in jejunum © 2018 Pearson Education, Inc.  Module 22.13: Segments of the small intestine Segments of the small intestine (continued) 3. Ileum Final segment of small intestine ~3.5 m (11.5 ft) in length Ends at the ileocecal valve – Sphincter controlling flow from the ileum into the cecum of the large intestine Has few circular folds (none in the distal portion) Villi are relatively stumpy Submucosa contains aggregated lymphoid nodules © 2018 Pearson Education, Inc.  Segments of the small intestine © 2018 Pearson Education, Inc.  Module 22.13: Review A. Name the three segments of the small intestine from proximal to distal. B. Identify the segment of the small intestine found within the epigastric region. C. What is the primary function of the duodenum? D. A traumatic injury to the umbilical region could affect which segments of the small intestine? Learning Outcome: Describe the anatomy and physiology of the small intestine. © 2018 Pearson Education, Inc.  Module 22.14: Several hormones regulate digestion Multiple major hormones regulate digestive activities  Several of them are produced by the duodenum Duodenum coordinates gastric activity and digestive secretion according to characteristics of the arriving chyme © 2018 Pearson Education, Inc.  Hormones of the duodenum, part 1 © 2018 Pearson Education, Inc.  Hormones of the duodenum, part 2 © 2018 Pearson Education, Inc.  Hormone action of the digestive system © 2018 Pearson Education, Inc.  Module 22.14: Review A. Name the major hormones that regulate digestive activities. B. How would the pH of the intestinal contents be affected if the small intestine did not produce secretin? C. Does a high-fat meal raise or lower the level of cholecystokinin (CCK) in the blood? Learning Outcome: Discuss the major digestive hormones and their primary effects. © 2018 Pearson Education, Inc.  Module 22.15: Central and local mechanisms coordinate gastric… Phases of gastric secretion 1. Cephalic phase Begins when you see, smell, taste, or think of food Directed by the CNS to prepare stomach to receive food Parasympathetic impulse down the vagus nerve stimulates the submucosal plexus – Postganglionic fibers innervate gastric gland cells © 2018 Pearson Education, Inc.  Module 22.15: Central and local mechanisms coordinate gastric… Phases of gastric secretion (continued) 1. Cephalic phase (continued) Gastric juice production increases (~500 mL/h) Phase generally lasts only minutes © 2018 Pearson Education, Inc.  Module 22.15: Central and local coordination of digestive activities Phases of gastric secretion (continued) 2. Gastric phase Begins with stimuli as food arrives in the stomach Stimuli include: 1. Distention of stomach 2. Increase in gastric content pH 3. Presence of undigested materials (especially proteins and peptides) in stomach Gastrin secretion – Increases mixing waves of stomach muscle contraction – Increases secretion by parietal and chief cells Phase may last 3–4 hours © 2018 Pearson Education, Inc.  Gastric phase © 2018 Pearson Education, Inc.  Module 22.15: …and intestinal activities Phases of gastric secretion (continued) 3. Intestinal phase Begins when chyme enters duodenum (usually after several hours of mixing) Distention of the duodenum initiates the enterogastric reflex © 2018 Pearson Education, Inc.  Module 22.15: …and intestinal activities Phases of gastric secretion (continued) 3. Intestinal phase (continued) – Inhibits gastrin production – Decreases gastric motility and secretion – Stimulates contraction of pyloric sphincter, decreasing chyme release into duodenum Mucus production is increased in the duodenum © 2018 Pearson Education, Inc.  Module 22.15: Central and local coordination of digestive activities Gastric central reflexes  Triggered by the stimulation of stretch receptors in the stomach wall as it fills  Accelerate movements along the small intestine Rate of chyme movement into small intestine is fastest when the stomach is greatly distended © 2018 Pearson Education, Inc.  Module 22.15: Review A. Name and briefly describe an important characteristic of each of the three phases of gastric secretion. B. Describe two central reflexes triggered by stimulation of the stretch receptors in the stomach wall. C. Why might severing the branches of the vagus nerves that supply the stomach provide relief for a person who suffers from chronic gastric ulcers (sores on the stomach lining)? Learning Outcome: Explain the regulation of gastric activity by central and local mechanisms. © 2018 Pearson Education, Inc.  Module 22.16: The large intestine stores and concentrates fecal material The large intestine  Also known as large bowel  Average length is ~1.5 m (4.9 ft), and diameter is 7.5 cm (3 in.)  Major functions 1. Reabsorbing water and compacting intestinal contents into feces 2. Absorbing important vitamins generated by bacterial action 3. Storing fecal material prior to defecation  Three segments: cecum, colon, rectum © 2018 Pearson Education, Inc.  The Large Intestine © 2018 Pearson Education, Inc.  Module 22.16: The large intestine Large intestine segments  Cecum Expanded pouch distal to the ileum Collects and stores material Begins the process of compaction – Compression into feces Opening between the cecum and ileum is the ileocecal valve © 2018 Pearson Education, Inc.  Module 22.16: The large intestine Large intestine segments (continued)  Cecum (continued) Attached to the appendix (also called the vermiform appendix) – ~9 cm (3.6 in.) in length, but size and shape are variable – Contains numerous lymphoid nodules o Functions as a lymphoid organ – Appendicitis is inflammation of the appendix © 2018 Pearson Education, Inc.  Module 22.16: The large intestine Large intestine segments (continued)  Colon Larger diameter and thinner wall than the small intestine Subdivided into four regions 1. Ascending colon 2. Transverse colon 3. Descending colon 4. Sigmoid colon Ascending and descending colon are retroperitoneal and attached to the abdominal wall Transverse and sigmoid colon are suspended by remnants of the embryonic mesocolon © 2018 Pearson Education, Inc.  Module 22.16: The large intestine Large intestine segments (continued)  Colon (continued) 1. Ascending colon – From the cecum along the right margin of the peritoneal cavity to the inferior surface of the liver – Bends sharply to the left at the right colic (hepatic) flexure © 2018 Pearson Education, Inc.  Module 22.16: The large intestine Large intestine segments (continued)  Colon (continued) 2. Transverse colon – Crosses the abdomen from right to left – Supported by the transverse mesocolon – Makes a 90º turn at the left colic (splenic) flexure © 2018 Pearson Education, Inc.  Module 22.16: The large intestine Large intestine segments (continued)  Colon (continued) 3. Descending colon – Moves inferiorly along the body’s left side to the iliac fossa – Ends at the sigmoid flexure © 2018 Pearson Education, Inc.  Module 22.16: The large intestine Large intestine segments (continued)  Colon (continued) 4. Sigmoid colon (sigmeidos, Greek letter S) – S-shaped segment – About 15 cm (6 in.) long – Empties into the rectum © 2018 Pearson Education, Inc.  Module 22.16: The large intestine Large intestine segments (continued)  Rectum Forms last 15 cm (6 in.) of digestive tract Expandable for temporary feces storage Movement of fecal material into the rectum triggers the urge to defecate © 2018 Pearson Education, Inc.  Module 22.16: The large intestine Other large intestine structures  Omental (fatty) appendices Teardrop-shaped sacs of fat in the serosa of the colon  Tenia coli Three longitudinal bands of smooth muscle Run along outer colon surface deep to the serosa Correspond to the outer layer of the muscularis externa in other digestive tract portions © 2018 Pearson Education, Inc.  Module 22.16: The large intestine Other large intestine structures (continued)  Haustra Series of pouches in the colon wall Also produce internal folding in the intestinal lumen Created by muscle tone of the tenia coli Allow for expansion and elongation of colon © 2018 Pearson Education, Inc.  Module 22.16: The large intestine Mass movements  Powerful peristaltic contractions  Occur a few times each day in response to distention of the stomach and duodenum  Begin at the transverse colon and push materials along the distal portion of the large intestine © 2018 Pearson Education, Inc.  Module 22.16: Review A. Name the major functions of the large intestine. B. Identify the four regions of the colon. C. Describe mass movements. Learning Outcome: Describe the gross anatomy of the three segments of the large intestine. © 2018 Pearson Education, Inc.  Module 22.17: The large intestine compacts fecal material; the defecation reflex coordinates the elimination of feces Major characteristics of the large intestine wall  Lacks villi  Contains distinctive intestinal glands Dominated by mucin-secreting goblet cells Mucus lubricates feces as it becomes drier and more compact  Mucosa does not produce enzymes © 2018 Pearson Education, Inc.  Large intestine wall © 2018 Pearson Education, Inc.  Module 22.17: Compaction and elimination of feces Characteristic features of the rectum  Anal canal (distal portion of rectum) Contains small longitudinal folds called anal columns Epithelium transitions from columnar to stratified squamous epithelium Network of veins in the lamina propria and submucosa – Increased venous pressure can distend the veins, producing hemorrhoids o Increased pressure caused by pregnancy or straining during defecation © 2018 Pearson Education, Inc.  The rectum © 2018 Pearson Education, Inc.  Module 22.17: Compaction and elimination of feces Characteristic features of the rectum (continued)  Internal anal sphincter Inner circular smooth muscle layer Not under voluntary control  External anal sphincter Outer skeletal muscle layer Under voluntary control © 2018 Pearson Education, Inc.  Module 22.17: Compaction and elimination of feces Characteristic features of the rectum (continued)  Anus (exit of the anal canal) Epidermis here becomes keratinized © 2018 Pearson Education, Inc.  Module 22.17: Compaction and elimination of feces Absorption in the large intestine  Accounts for