Chapter 25 Lecture Animation - Digestive System PDF

Chapter 25 *Lecture Animation Outline The Digestive System To run the animations you must be in Slideshow View. Use the buttons on the animation to play, pause, and turn audio/text on or off. Please Note: Once you have used any of the animation functions (such as Play or Pause), you must first cli...

Chapter 25 *Lecture Animation Outline The Digestive System To run the animations you must be in Slideshow View. Use the buttons on the animation to play, pause, and turn audio/text on or off. Please Note: Once you have used any of the animation functions (such as Play or Pause), you must first click in the white background before you can advance to the next slide. *See separate FlexArt PowerPoint slides for all figures and tables preinserted into PowerPoint without notes.  Introduction Most nutrients we eat cannot be used in existing form – Must be broken down into smaller components before the body can make use of them Digestive system—essentially a disassembly line – To break down nutrients into a form that can be used by the body – To absorb them so they can be distributed to the tissues Gastroenterology—the study of the digestive tract and the diagnosis and treatment of its disorders 25-2 Digestive System Overview  Cellular Respiration ATP Carbon Dioxide Oxygen Water Glucose Heat vitamins Acid (H+) minerals water amino acids hormones medicines electrolytes  Digestive Function Processes food Extracts nutrients Eliminates residue 4 Stages of Digestion Ingestion Digestion Absorption Defecation Chemical Digestion (hydrolytic enzymes) Mechanical Digestion  General Anatomy and Digestive Processes Expected Learning Outcomes – List the functions and major physiological processes of the digestive system. – Distinguish between mechanical and chemical digestion. – Describe the basic chemical process underlying all chemical digestion, and name the major substrates and products of this process. 25-7  General Anatomy and Digestive Processes Cont. – List the regions of the digestive tract and the accessory organs of the digestive system. – Identify the layers of the digestive tract and describe its relationship to the peritoneum. – Describe the general neural and chemical controls over digestive function. 25-8  Digestive Function Digestive system—the organ system that processes food, extracts nutrients from it, and eliminates the residue 25-9  Digestive Function Five stages of digestion – Ingestion: selective intake of food – Digestion: mechanical and chemical breakdown of food into a form usable by the body – Absorption: uptake of nutrient molecules into the epithelial cells of the digestive tract and then into the blood and lymph – Compaction: absorbing water and consolidating the indigestible residue into feces – Defecation: elimination of feces 25-10  Digestive Function Mechanical digestion—the physical breakdown of food into smaller particles – Cutting and grinding action of the teeth – Churning action of stomach and small intestines – Exposes more food surface to the action of digestive enzymes 25-11  Digestive Function Chemical digestion—a series of hydrolysis reactions that breaks dietary macromolecules into their monomers (residues) – Carried out by digestive enzymes produced by salivary glands, stomach, pancreas, and small intestine – Results Polysaccharides into monosaccharides Proteins into amino acids Fats into monoglycerides and fatty acids Nucleic acids into nucleotides 25-12  Digestive Function Some nutrients are present in a usable form in ingested food – Absorbed without being digested – Vitamins, free amino acids, minerals, cholesterol, and water 25-13  General Anatomy Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Digestive system has two Oral cavity Parotid anatomical subdivisions Tongue gland Teeth Sublingual gland Pharynx Digestive tract Submandibular gland Esophagus (alimentary canal) – 30 ft long muscular tube extending from mouth to Diaphragm anus Liver Stomach Pancreas – Mouth, pharynx, Gallbladder Bile duct Transverse colon esophagus, stomach, Ascending colon Descending small intestine, and large Small intestine colon intestine Cecum Appendix – Gastrointestinal (GI) Sigmoid colon Rectum tract is the stomach and Anal canal Anus intestines 25-14 Figure 25.1  General Anatomy Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Oral cavity Tongue Parotid Cont. gland Teeth Sublingual gland Pharynx Accessory organs Submandibular gland Esophagus – Teeth, tongue, salivary glands, liver, gallbladder, and pancreas Diaphragm Liver Stomach Pancreas Gallbladder Transverse Bile duct colon Ascending colon Descending colon Small intestine Cecum Appendix Sigmoid colon Rectum Anal canal Anus 25-15 Figure 25.1  General Anatomy Digestive tract is open to the environment at both ends Most material in it has not entered the body tissues – Considered to be external to the body until it is absorbed by the epithelial cells of the alimentary canal On a strict sense, defecated food residue was never in the body 25-16  General Anatomy Most of the digestive tract follows the basic structural plan with digestive tract wall consisting of the following tissue layers, in order from inner to outer surface – Mucosa Epithelium Lamina propria Muscularis mucosae – Submucosa – Muscularis externa Inner circular layer Outer longitudinal layer – Serosa Areolar tissue Mesothelium 25-17  General Anatomy Mucosa (mucous membrane)—lines the lumen and consists of: – Inner epithelium Simple columnar in most of digestive tract Stratified squamous from mouth through esophagus, and in lower anal canal – Lamina propria: loose connective tissue layer – Muscularis mucosa: thin layer of smooth muscle Tenses mucosa creating grooves and ridges that enhance surface area and contact with food Improves efficiency of digestion and nutrient absorption – Mucosa-associated lymphatic tissue (MALT): the mucosa exhibits an abundance of lymphocytes and lymphatic nodules 25-18  General Anatomy Submucosa—thicker layer of loose connective tissue – Contains blood vessels, lymphatic vessels, a nerve plexus, and in some places mucus-secreting glands that dump lubricating mucus into the lumen – MALT extends into the submucosa in some parts of the GI tract 25-19  General Anatomy Muscularis externa—consists of usually two layers of muscle near the outer surface – Inner circular layer In some places, this layer thickens to form valves (sphincters) that regulate the passage of material through the tract – Outer longitudinal layer Responsible for the motility that propels food and residue through the tract 25-20  General Anatomy Serosa—composed of a thin layer of areolar tissue topped by simple squamous mesothelium – Begins in the lower 3 to 4 cm of the esophagus – Ends just before the rectum – Adventitia: a fibrous connective tissue layer that binds and blends the pharynx, most of the esophagus, and the rectum into the adjacent connective tissue of other organs 25-21  Tissue Layers of the Digestive Tract Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Diaphragm Esophageal hiatus Enteric nervous system: Mucosa: Myenteric plexus Stratified squamous epithelium Submucosal plexus Lamina propria Muscularis mucosae Parasympathetic ganglion of myenteric plexus Submucosa: Esophageal gland Lumen Muscularis externa: Inner circular layer Outer longitudinal layer Blood vessels Serosa Figure 25.2 25-22 Digestive Tract 30ft. (9m) in cadaver Length  General Anatomy Enteric nervous system—a nervous network in the esophagus, stomach, and intestines that regulated digestive tract motility, secretion, and blood flow – Thought to have over 100 million neurons – More than the spinal cord – Functions completely independently of the central nervous system CNS exerts a significant influence on its action Enteric nervous system contains sensory neurons that monitor tension in gut wall and conditions in lumen 25-24  General Anatomy Composed of two networks of neurons – Submucosal (Meissner) plexus: in submucosa Controls glandular secretion of mucosa Controls movements of muscularis mucosae – Myenteric (Auerbach) plexus: parasympathetic ganglia and nerve fibers between the two layers of the muscularis interna Controls peristalsis and other contractions of muscularis externa 25-25  Relationship to the Peritoneum Mesenteries—connective tissue sheets that loosely suspend the stomach and intestines from the abdominal wall – Allows stomach and intestines to undergo strenuous contractions – Allow freedom of movement in the abdominal cavity – Hold abdominal viscera in proper relationship to each other 25-26  Relationship to the Peritoneum Mesenteries—connective tissue sheets that loosely suspend the stomach and intestines from the abdominal wall – Allow stomach and intestines to undergo strenuous contractions – Allow freedom of movement in the abdominal cavity – Hold abdominal viscera in proper relationship to each other – Prevent the intestines from becoming twisted and tangled by changes in body position and by its own contractions – Provide passage of blood vessels and nerves that supply digestive tract – Contain many lymph nodes and lymphatic vessels 25-27  Relationship to the Peritoneum Parietal peritoneum—a serous membrane that lines the wall of the abdominal cavity – Turns inward along posterior midline – Forms dorsal mesentery: a translucent two-layered membrane extending to the digestive tract – The two layers of the mesentery separate and pass around opposite sides of the organ forming the serosa – Come together on the far side of the organ and continue as another sheet of tissue, called the ventral mesentery May hang freely in the abdominal cavity May attach to the anterior abdominal wall or other organs 25-28  Relationship to the Peritoneum Lesser omentum—a ventral mesentery that extends from the lesser curvature of the stomach to the liver Greater omentum—hangs from the greater curvature of the stomach – Covers the small intestines like an apron – The inferior margin turns back on itself and passes upward – Forming a deep pouch between its deep and superficial layers – Inner superior margin forms serous membranes around the spleen and transverse colon 25-29  Relationship to the Peritoneum Mesocolon—extension of the mesentery that anchors the colon to the posterior abdominal wall Intraperitoneal—when an organ is enclosed by mesentery on both sides – Considered within the peritoneal cavity – Stomach, liver, and other parts of small and large intestine Retroperitoneal—when an organ lies against the posterior body wall and is covered by peritoneum on its anterior side only – Considered to be outside the peritoneal cavity – Duodenum, pancreas, and parts of the large intestine 25-30  Serous Membranes Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Liver Stomach Gallbladder Lesser omentum Greater omentum Ascending colon Small intestine Figure 25.3a (a) Lesser omentum—attaches stomach to liver Greater omentum—covers small intestines like an apron 25-31  Serous Membranes Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Greater omentum (retracted) Transverse colon Mesocolon Descending colon Mesentery Jejunum Sigmoid colon Figure 25.3b (b) Mesentery of small intestines holds many blood vessels Mesocolon anchors colon to posterior body wall 25-32  Lesser and Greater Omentum 25-33  Mesentery 25-34  Regulation of the Digestive Tract Motility and secretion of the digestive tract are controlled by neural, hormonal, and paracrine mechanisms Neural control – Short (myenteric) reflexes: stretch or chemical stimulation acts through myenteric plexus Stimulates parastaltic contractions of swallowing – Long (vagovagal) reflexes: parasympathetic stimulation of digestive motility and secretion 25-35  Regulation of the Digestive Tract Hormones – Chemical messengers secreted into bloodstream, and stimulate distant parts of the digestive tract – Gastrin and secretin Paracrine secretions – Chemical messengers that diffuse through the tissue fluids to stimulate nearby target cells 25-36  The Mouth Through Esophagus Expected Learning Outcomes – Describe the gross anatomy of the digestive tract from the mouth through the esophagus. – Describe the composition and functions of saliva. – Describe the neural control of salivation and swallowing. 25-37  The Mouth The mouth is known as the oral, or buccal cavity Functions – Ingestion (food intake) – Other sensory responses to food: chewing and chemical digestion – Swallowing, speech, and respiration Mouth enclosed by cheeks, lips, palate, and tongue 25-38  The Mouth Oral fissure—anterior opening between lips Fauces—posterior opening to the throat Stratified squamous epithelium lines mouth – Keratinized in areas subject to food abrasion: gums and hard palate – Nonkeratinized in other areas: floor of mouth, soft palate, and insides of cheeks and lips 25-39  The Oral Cavity Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Upper lip Vestibule Superior labial frenulum Palatine raphe Palatoglossal Hard palate arch and palatine Palatopharyngeal rugae arch Palatine tonsil Soft palate Tongue Uvula Lingual frenulum Salivary duct Lower lip Figure 25.4 orifices: Sublingual Submandibular Inferior labial frenulum 25-40  The Cheeks and Lips Cheeks and lips – Retain food and push it between the teeth for chewing – Essential for articulate speech – Essential for sucking and blowing actions, including suckling by infants – Fleshiness due to subcutaneous fat, buccinator muscle of the cheek, and the orbicularis oris of the lips – Labial frenulum: median fold that attaches each lip to the gum between the anterior incisors – Vestibule: the space between cheek or lips and the teeth 25-41  The Cheeks and Lips Lips divided into three areas – Cutaneous area: colored like the rest of the face Has hair follicles and sebaceous glands – Red (vermillion) area: hairless region where lips meet Tall dermal papilla that allows blood vessels and nerves to come closer to epidermal surface Redder and more sensitive than cutaneous area – Labial mucosa: the inner surface of the lips facing the gums and teeth 25-42  The Tongue Tongue—muscular, bulky, but remarkably agile and sensitive organ – Manipulates food between teeth while it avoids being bitten – Can extract food particles from the teeth after a meal – Sensitive enough to feel a stray hair in a bite of food 25-43  The Tongue Cont. – Nonkeratinized stratified squamous epithelium covers its surface – Lingual papillae: bumps and projections on the tongue that are the sites of the taste buds – Body: anterior two-thirds of the tongue occupies oral cavity – Root: posterior one-third of the tongue occupies the oropharynx 25-44  The Tongue Cont. – Vallate papillae: a V-shaped row of papillae that mark the boundary between the body and root of the tongue – Terminal sulcus: groove behind the V-shaped vallate papillae – Lingual frenulum: median fold that attaches the body to the floor of the mouth – Intrinsic muscles are contained entirely within the tongue Produce the subtle tongue movements of speech 25-45  The Tongue Cont. – Extrinsic muscles: with origins elsewhere and insertions in the tongue Produce stronger movements of food manipulation Genioglossus, hyoglossus, palatoglossus, and styloglossus – Lingual glands: serous and mucous glands amid the extrinsic muscles Secrete a portion of the saliva – Lingual tonsils: contained in the root 25-46  The Tongue Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Epiglottis Intrinsic muscles of the tongue Lingual Buccinator m. Root tonsils 1st molar Palatine Styloglossus m. tonsil Terminal sulcus Vallate Hyoglossus m. papillae Genioglossus m. Foliate Mandible papillae Sublingual gland Body Fungiform Submandibular gland papillae Mylohyoid m. Hyoid bone (a) Superior view (b) Frontal section, anterior view Figure 25.5a,b 25-47  The Palate Palate—separates the oral cavity from the nasal cavity – Makes it possible to breathe while chewing food Hard (bony) palate—anterior portion that is supported by the palatine processes of the maxillae and the palatine bones – Palatine rugae: transverse ridges that help the tongue hold and manipulate food 25-48  The Palate Soft palate—posterior with a more spongy texture – Composed of skeletal muscle and glandular tissue – No bone – Uvula: conical medial projection visible at the rear of the mouth – Helps retain food in the mouth until one is ready to swallow Pair of muscular arches on each side of the oral cavity – Palatoglossal arch: anterior arch – Palatopharyngeal arch: posterior arch – Palatine tonsils are located on the wall between the arches 25-49  The Teeth Dentition—the teeth Masticate food into smaller pieces – Makes food easier to swallow – Exposes more surface area for action of digestive enzymes speeding chemical digestion 25-50  The Teeth 32 adult teeth; 20 deciduous (baby) teeth – 16 in mandible – 16 in maxilla – From midline to the rear of each jaw 2 incisors—chisel-like cutting teeth used to bite off a piece of food 1 canine—pointed and act to puncture and shred food 2 premolars—broad surface for crushing and grinding 3 molars—even broader surface for crushing and grinding 25-51  The Teeth Alveolus—tooth socket in bone Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Names of teeth Age at eruption (months) 6–9 – Gomphosis joint formed between Central incisor Lateral incisor 7– 11 Canine 16–20 tooth and bone 1st molar 12–16 2nd molar 20–26 Periodontal ligament—modified periosteum whose collagen fibers (a) Deciduous (baby) teeth penetrate into the bone on one side Names of teeth Age at eruption (years) and into the tooth on the other Central incisor 6–8 Lateral incisor 7–9 – Anchors tooth firmly in alveolus Canine 9–12 – Allows slight movement under 1st premolar 10–12 2nd premolar 10–12 pressure of chewing 1st molar 6–7 2nd molar 1–13 3rd molar 17–25 Gingiva (gum)—covers the (wisdom tooth) alveolar bone (b) Permanent teeth Figure 25.6 25-52  The Teeth Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Names of teeth Age at eruption (months) Central incisor 6–9 Lateral incisor 7– 11 Regions of a tooth Canine 16–20 1st molar 12–16 – Crown: portion above the gum 2nd molar 20–26 – Root: the portion below the gum, embedded in alveolar bone (a) Deciduous (baby) teeth – Neck: the point where crown, Names of teeth Age at eruption (years) root, and gum meet Central incisor 6–8 Lateral incisor 7–9 – Gingival sulcus: space between Canine 9–12 1st premolar 10–12 the tooth and the gum 2nd premolar 10–12 Hygiene in the sulcus is 1st molar 6–7 important to dental health 2nd molar 1–13 3rd molar 17–25 (wisdom tooth) (b) Permanent teeth Figure 25.6 25-53  The Teeth Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Dentin—hard yellowish tissue that makes up most Enamel of the tooth Dentine Crown Pulp in pulp cavity Enamel—covers crown Gingival sulcus and neck Gingiva Neck Cementum—covers root Alveolar bone Periodontal ligament Cementum and dentin are Root canal living tissue and can Cementum Root regenerate Apical foramen Artery, nerve, vein Figure 25.7 25-54  The Teeth Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Enamel is noncellular Enamel secretion formed during Dentine Crown development Pulp in pulp cavity Gingival sulcus Root canal in the roots Gingiva Neck leading to pulp cavity in Alveolar bone the crown Periodontal ligament – Nerves and blood vessels Root canal Root – Apical foramen: pore at the Cementum basal end of each root canal Occlusion—meeting of the teeth with the mouth Apical foramen closed Artery, nerve, vein Figure 25.7 25-55 Permanent and Deciduous Teeth Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. * * * * © The McGraw-Hill Companies, Inc./Rebecca Gray, photographer/Don Kincaid, dissections Figure 25.8 25-56  The Teeth 20 deciduous teeth (milk teeth or baby teeth) Teeth develop beneath the gums and erupt in a predictable order – Erupt from 6 to 30 months – Beginning with incisors – Between 6 and 32 years of age, are replaced by 32 permanent teeth Third molars (wisdom teeth) erupt from age 17 to 25 years – May be impacted: crowded against neighboring teeth and bone so they cannot erupt 25-57  Tooth and Gum Disease The human mouth is home to more than 700 species of microorganisms, especially bacteria Plaque—sticky residue on the teeth made up of bacteria and sugars – Calculus: calcified plaque – Bacteria metabolize sugars and release acids that dissolve the minerals of enamel and dentin to form dental caries (cavities) Root canal therapy is necessary if cavity reaches pulp 25-58  Tooth and Gum Disease Calculus in the gingival sulcus wedges the tooth and gum apart – Allows bacterial invasion of the sulcus – Gingivitis: inflammation of the gums – Periodontal disease: destruction of the supporting bone around the teeth which may result in tooth loss 25-59  Mastication Mastication (chewing)—breaks food into smaller pieces to be swallowed and exposes more surface to the action of digestive enzymes – First step in mechanical digestion – Food stimulates oral receptors that trigger an involuntary chewing reflex – Tongue, buccinator, and orbicularis oris manipulate food – Masseter and temporalis elevate the teeth to crush food – Medial and lateral pterygoids, and masseter swing teeth in side-to-side grinding action of molars 25-60  Saliva and the Salivary Glands Saliva – Moisten mouth – Begin starch and fat digestion – Cleanse teeth – Inhibit bacterial growth – Dissolve molecules so they can stimulate the taste buds – Moisten food and bind it together into bolus to aid in swallowing 25-61  Saliva and the Salivary Glands Hypotonic solution of 97.0% to 99.5% water and the following solutes: – Salivary amylase: enzyme that begins starch digestion in the mouth – Lingual lipase: enzyme that is activated by stomach acid and digests fat after the food is swallowed – Mucus: binds and lubricates the mass of food and aids in swallowing – Lysozyme: enzyme that kills bacteria – Immunoglobulin A (IgA): an antibody that inhibits bacterial growth – Electrolytes: Na+, K+, Cl−, phosphate, and bicarbonate pH: 6.8 to 7.0 25-62  Saliva and the Salivary Glands Intrinsic salivary glands—small glands dispersed amid other oral tissues – Lingual glands: in the tongue; produce lingual lipase – Labial glands: inside of the lips – Buccal glands: inside of the cheek – All secrete saliva at a fairly constant rate 25-63  Saliva and the Salivary Glands Extrinsic salivary glands—three pairs connected to oral cavity by ducts – Parotid: located beneath the skin anterior to the earlobe Mumps is an inflammation and swelling of the parotid gland caused by a virus – Submandibular gland: located halfway along the body of the mandible Its duct empties at the side of the lingual frenulum, near the lower central incisors – Sublingual glands: located in the floor of the mouth Has multiple ducts that empty posterior to the papilla of the submandibular duct 25-64  The Extrinsic Salivary Glands Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Parotid gland Parotid duct Tongue Sublingual ducts Figure 25.9 Masseter muscle Submandibular duct Lingual Submandibular frenulum gland Sublingual Opening of gland Mandible submandibular duct 25-65  Salivary Glands Parotid Sublingual Submandibular  Histology of Salivary Glands Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Compound tubuloacinar Mucous acinus Mucous cells Serous cells glands – Branched ducts ending in acini Salivary duct Mucous cells secrete mucus Serous Serous demilune acinus Mixed acinus on mixed (a) acinus Serous cells secrete thin fluid rich in amylase and Mucous cells electrolytes Serous demilune Stroma Duct Mixed acinus has both (b) b: © The McGraw-Hill Companies, Inc./Dennis Strete, photographer mucous and serous cells 25-67 Figure 25.10a,b  Salivation Extrinsic salivary glands secrete about of 1 to 1.5 L of saliva per day Cells of acini filter water and electrolytes from blood and add amylase, mucin, and lysozyme Salivary nuclei in the medulla oblongata and pons respond to signals generated by presence of food – Tactile, pressure, and taste receptors – Salivary nuclei receive input from higher brain centers as well Odor, sight, thought of food stimulates salivation 25-68  Salivation Cont. – Send signals by way of autonomic fibers in the facial and glossopharyngeal nerves to the glands Parasympathetics stimulate the glands to produce an abundance of thin, enzyme-rich saliva Sympathetic stimulation stimulates the glands to produce less, and thicker, saliva with more mucus Bolus—mass swallowed as a result of saliva binding food particles into a soft, slippery, easily swallowed mass 25-69  The Pharynx Pharynx—a muscular funnel that connects oral cavity to esophagus and allows entrance of air from nasal cavity to larynx – Digestive and respiratory tracts intersect 25-70  The Pharynx Pharyngeal constrictors (superior, middle, and inferior)—circular muscles that force food downward during swallowing – When not swallowing, the inferior constrictor remains contracted to exclude air from the esophagus – This constriction is considered to be the upper esophageal sphincter although it is not an anatomical feature – Disappears at the time of death when the muscles relax, so it is a physiological sphincter, not an anatomical structure 25-71  Pharynx Upper Esophageal Sphincter  Pharynx Nasopharynx Oropharynx Laryngopharynx Esophagus Upper esophageal sphincter – inferior pharyngeal constrictor Esophageal hiatus Lower esophageal sphincter Esophageal glands - mucus  The Esophagus Esophagus—a straight muscular tube 25 to 30 cm long – Begins at level between C6 and the cricoid cartilage – Extends from pharynx to cardiac orifice of stomach passing through esophageal hiatus in diaphragm – Lower esophageal sphincter: food pauses at this point because of this constriction Prevents stomach contents from regurgitating into the esophagus Protects esophageal mucosa from erosive effect of the stomach acid Heartburn—burning sensation produced by acid reflux into the esophagus 25-75  The Esophagus Cont. – Nonkeratinized stratified squamous epithelium – Esophageal glands in submucosa secrete mucus – Deeply folded into longitudinal ridges when empty – Skeletal muscle in upper one-third, mixture in middle one-third, and only smooth muscle in the bottom one- third – Meets stomach at level of T7 – Covered with adventitia 25-76  Deglutition (Swallowing)  Swallowing Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Soft palate Uvula Epiglottis Relaxation Bolus of food Esophagus Pharynx Tongue 2 Bolus passes into pharynx. Misdirection Epiglottis of bolus is prevented by tongue blocking oral cavity , soft palate blocking nasal cavity, and epiglottis blocking larynx. Glottis 1 Tongue compresses food against palate Trachea to form a bolus. 3 Upper esophageal sphincter constricts and bolus passes downward. Constriction Peristaltic 4 Peristalsis drives bolus down wave esophagus. Esophagus constricts above bolus and Bolus dilates and shortens below it.Upper esophagus Relaxation Shortening Peristaltic contraction Figure 25.11a,b Bolus of ingested matter passing down esophagus 5 Lower esophageal sphincter relaxes to admit bolus to stomach. (b) Constriction Stomach Cardiac Lower esophageal orifice sphincter (a) Relaxation 25-78 b: © The McGraw-Hill Companies, Inc.,/Jim Shaffer, photographer  Swallowing Swallowing (deglutition)—a complex action involving over 22 muscles in the mouth, pharynx, and esophagus – Swallowing center: pair of nuclei in medulla oblongata that coordinates swallowing Communicates with muscles of the pharynx and esophagus by way of trigeminal, facial, glossopharyngeal, and hypoglossal nerves 25-79  Swallowing Swallowing occurs in two phases – Buccal phase: under voluntary control Tongue collects food, presses it against the palate forming a bolus, and pushes it posteriorly Food accumulates in oropharynx in front of “blade” of the epiglottis Epiglottis tips posteriorly and food bolus slides around it through the laryngeal opening Bolus enters laryngopharynx and stimulates tactile receptors and activates next phase 25-80  Swallowing Cont. – Pharyngoesophageal phase: involuntary Three actions prevent food and drink from reentering the mouth or entering the nasal cavity or larynx – Root of the tongue blocks the oral cavity – Soft palate rises and blocks the nasopharynx – Infrahyoid muscles pull the larynx up to meet the epiglottis while laryngeal folds close the airway Food bolus is driven downward by constriction of the upper, then middle, and finally the lower pharyngeal constrictors Bolus enters esophagus, stretches it, and stimulates peristalsis 25-81  Swallowing Peristalsis—wave of muscular contraction that pushes the bolus ahead of it – Entirely involuntary reflex When standing or sitting upright, the food and liquid drops through the esophagus by gravity faster than peristalsis can keep up with it Peristalsis ensures you can swallow regardless of body position Liquid reaches the stomach in 1 to 2 seconds Food bolus in 4 to 8 seconds When it reaches lower end of the esophagus, the lower esophageal sphincter relaxes to let food pass into the stomach 25-82  Swallowing Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Upper esophagus Peristaltic contraction Figure 25.11b Bolus of ingested matter passing down esophagus (b) 25-83 © The McGraw-Hill Companies, Inc.,/Jim Shaffer, photographer  The Stomach Expected Learning Outcomes – Describe the gross and microscopic anatomy of the stomach. – State the function of each type of epithelial cell in the gastric mucosa. – Identify the secretions of the stomach and state their functions. – Explain how the stomach produces hydrochloric acid and pepsin. – Describe the contractile responses of the stomach to food. – Describe the three phases of gastric function and how gastric activity is activated and inhibited. 25-84  The Stomach Stomach—a muscular sac in upper left abdominal cavity immediately inferior to the diaphragm – Primarily functions as a food storage organ Internal volume of about 50 mL when empty 1.0 to 1.5 L after a typical meal Up to 4 L when extremely full and extend nearly as far as the pelvis 25-85  The Stomach Mechanically breaks up food particles, liquefies the food, and begins chemical digestion of protein and fat – Chyme: soupy or pasty mixture of semidigested food in the stomach Most digestion occurs after the chyme passes on to the small intestine 25-86  Gross Anatomy Stomach—J-shaped muscular organ with lesser and greater curvatures – Nearly vertical in tall people, and horizontal in short people – Divided into four regions Cardiac region (cardia)—small area within about 3 cm of the cardiac orifice Rundic region (fundus)—dome-shaped portion superior to esophageal attachment Body (corpus)—makes up the greatest part of the stomach 25-87  Gross Anatomy Cont. – Pyloric region: narrower pouch at the inferior end Subdivided into the funnel-like antrum Narrower pyloric canal that terminates at pylorus Pylorus: narrow passage to duodenum Pyloric (gastroduodenal) sphincter—regulates the passage of chyme into the duodenum 25-88  Gross Anatomy Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Diaphragm Fundic region Lesser omentum Cardiac region Lesser curvature Body Pyloric region: Longitudinal Antrum muscle Pyloric canal Circular muscle Pylorus Pyloric sphincter Oblique muscle Gastric rugae Figure 25.12a Greater curvature Greater omentum Duodenum (a) Note the bulge of fundus, narrowing of pyloric region, thickness of pyloric sphincter, and greater and lesser curvatures 25-89  Gross Anatomy Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Esophagus Fundic region Lesser curvature Cardiac orifice Cardiac region Duodenum Body Pyloric region: Gastric rugae Pylorus Pyloric sphincter Pyloric canal Antrum Greater curvature © The McGraw-Hill Companies, Inc./Rebecca Gray, photographer/Don Kincaid, dissections (b) Figure 25.12b Longitudinal wrinkles called rugae can be seen in empty stomach wall 25-90  Stomach Parasympathetics – vagus nerve Sympathetics – Celiac Ganglia Stomach Stomach  Innervation and Circulation Stomach receives: – Parasympathetic fibers from vagus – Sympathetic fibers from celiac ganglia Supplied with blood by branches of the celiac trunk All blood drained from stomach and intestines enters hepatic portal circulation and is filtered through liver before returning to heart 25-94  Microscopic Anatomy Simple columnar epithelium covers mucosa – Apical regions of its surface cells are filled with mucin – Swells with water and becomes mucus after it is secreted Mucosa and submucosa flat when stomach is full, but form longitudinal wrinkles called gastric rugae when empty Muscularis externa has three layers instead of two – Outer longitudinal, middle circular, and inner oblique layers 25-95  Microscopic Anatomy Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lumen of stomach Epithelium Gastric pit Mucosa Gastric gland Lamina propria Submucosa Lymphatic nodule Muscularis Muscularis mucosae externa Serosa Artery Vein Oblique layer of muscle Circular layer of muscle Longitudinal layer of muscle (a) Stomach wall Figure 25.13a 25-96  Microscopic Anatomy Gastric pits—depressions in gastric mucosa – Lined with simple columnar epithelium – Two or three tubular glands open into the bottom of each gastric pit Cardiac glands in cardiac region Pyloric glands in pyloric regions Gastric glands in the rest of the stomach 25-97 The Opening of a Gastric Pit Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Visuals Unlimited 25-98 Figure 25.13d  Microscopic Anatomy Mucous cells—secrete mucus Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. – Predominate in cardiac and pyloric glands – In gastric glands, called mucous neck Mucous neck cell cells since they are concentrated at the Parietal cell neck of the gland Regenerative (stem) cells—found in the base of the pit and in the neck of the gland Chief cell – Divide rapidly and produce a continual supply of new cells to replace cells that die G cell Parietal cells—found mostly in the upper (c) Gastric gland half of the gland – Secrete hydrochloric acid (HCl), intrinsic factor, and a hunger hormone Figure 25.13c called ghrelin 25-99  Microscopic Anatomy Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mucous neck cell Chief cells—most numerous Parietal cell – Secrete gastric lipase and pepsinogen – Dominate lower half of gastric glands – Absent in pyloric and cardiac glands Enteroendocrine cells—concentrated in lower end of gland Chief cell – Secrete hormones and paracrine messengers that regulate digestion G cell (c) Gastric gland Figure 25.13c 25-100 Pyloric and Gastric Glands Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mucous neck cell Parietal cell Mucous cell Chief cell G cell (b) Pyloric gland (c) Gastric gland Figure 25.13b,c 25-101  Gastric Secretions Gastric juice—2 to 3 L per day produced by the gastric glands Mainly a mixture of water, hydrochloric acid, and pepsin 25-102  Hydrochloric Acid Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Blood Parietal cell Lumen of gastric gland Alkaline tide Cl– Cl– Stomach HCO3 – HCO3 – K+ H+ acid Figure 25.14 H+–K+ ATPase CO2 CO2+ H2O H2CO3 Gastric juice has a high concentration of hydrochloric acid – pH as low as 0.8 25-103  Hydrochloric Acid Parietal cells produce HCl and contain carbonic anhydrase (CAH) CAH – CO + H O H CO HCO − + H+ 2 2 2 3 3 – H+ is pumped into gastric gland lumen by H+–K+ ATPase pump Antiporter uses ATP to pump H+ out and K+ in – HCO3− exchanged for Cl− (chloride shift) from blood plasma Cl− (chloride ion) pumped into the lumen of gastric gland to join H+ forming HCl Elevated HCO3− (bicarbonate ion) in blood causes alkaline tide increasing blood pH 25-104  Hydrochloric Acid Activates pepsin and lingual lipase Breaks up connective tissues and plant cell walls – Helps liquefy food to form chyme Converts ingested ferric ions (Fe3+) to ferrous ions (Fe2+) – Fe2+ absorbed and used for hemoglobin synthesis Contributes to nonspecific disease resistance by destroying most ingested pathogens 25-105 Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.  Pepsin Zymogens—digestive enzymes secreted as inactive proteins – Converted to active enzymes by removing some of their amino acids Pepsinogen—zymogen secreted by the chief cells – Hydrochloric acid removes some of its amino acids and forms pepsin that digests proteins – Autocatalytic effect—as some pepsin is formed, it converts more pepsinogen into more pepsin Pepsin digests dietary proteins into shorter peptide chains – Protein digestion is completed in the small intestine 25-107 The Production and Action of Pepsin Parietal cell Removed Dietary peptide proteins HCl Pepsin (active enzyme) Chief cell Pepsinogen (zymogen) Partially digested protein Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Gastric gland Figure 25.15 25-108  Gastric Lipase Gastric lipase—produced by chief cells Gastric lipase and lingual lipase play a minor role in digesting dietary fats – Digests 10% to 15% of dietary fats in the stomach – Rest digested in the small intestine 25-109  Intrinsic Factor Intrinsic factor—a glycoprotein secreted by parietal cells Essential to absorption of vitamin B12 by the small intestine – Binds vitamin B12 and then intestinal cells absorb this complex by receptor-mediated endocytosis 25-110  Intrinsic Factor Vitamin B12 is needed to synthesize hemoglobin – Prevents pernicious anemia Secretion of intrinsic factor is the only indispensable function of the stomach – Digestion can continue if stomach is removed (gastrectomy), but B12 supplements will be needed 25-111  Chemical Messengers Gastric and pyloric glands have various kinds of enteroendocrine cells that produce as many as 20 chemical messengers – Some are hormones that enter blood and stimulate distant cells – Others are paracrine secretions that stimulate neighboring cells 25-112  Chemical Messengers Cont. – Several are peptides produced in both the digestive tract and the central nervous system: gut–brain peptides Substance P, vasoactive intestinal peptide (VIP), secretin, gastric inhibitory peptide (GIP), cholecystokinin, and neuropeptide Y (NPY) 25-113  Gastric Motility Swallowing center of medulla oblongata signals stomach to relax Food stretches stomach activating a receptive- relaxation response – Resists stretching briefly, but relaxes to hold more food 25-114  Gastric Motility Soon stomach shows a rhythm of peristaltic contractions controlled by pacemaker cells in longitudinal layer of muscularis externa – Gentle ripple of contraction every 20 seconds churns and mixes food with gastric juice – Becomes stronger contraction at pyloric region – After 30 min. or so these contractions become quite strong They churn the food, mix it with gastric juice, and promote its physical breakup and chemical digestion 25-115  Gastric Motility Cont. – Antrum holds about 30 mL of chyme – As a parastaltic wave passes down the antrum, it squirts about 3 mL of chyme into the duodenum at a time – Allowing only a small amount into the duodenum enables the duodenum to: Neutralize the stomach acid Digest nutrients little by little – If duodenum is overfilled it inhibits gastric motility – Typical meal emptied from stomach in 4 hours Less time if the meal is more liquid As long as 6 hours for a high-fat meal 25-116  Vomiting Vomiting—the forceful ejection of stomach and intestinal contents (chyme) from the mouth Emetic center in the medulla oblongata integrates multiple muscle actions Vomiting induced by: – Overstretching of the stomach or duodenum – Chemical irritants such as alcohol and bacterial toxins – Visceral trauma – Intense pain or psychological and sensory stimuli 25-117  Vomiting Vomiting is usually preceded by nausea and retching Retching—thoracic expansion and abdominal contraction creates a pressure difference that dilates the esophagus – Lower esophageal sphincter relaxes while the stomach and duodenum contract spasmodically – Chyme enters esophagus but then drops back to the stomach as the stomach relaxes – Does not get past the upper esophageal sphincter – Usually accompanied by tachycardia, profuse salivation, and sweating 25-118  Vomiting Vomiting—occurs when abdominal contractions and rising thoracic pressure force the upper esophageal sphincter to open – Esophagus and body of the stomach relax – Chyme is driven out of the stomach and mouth by strong abdominal contractions combined with reverse peristalsis of gastric antrum and duodenum Projectile vomiting—sudden vomiting with no prior nausea or retching – Common in infants after feeding 25-119  Vomiting Chronic vomiting causes: – Dangerous fluid, electrolyte, and acid–base imbalances – Bulimia: eating disorder in which the tooth enamel becomes eroded by the hydrochloric acid in the chyme – Aspiration (inhalation) of acid is very destructive to the respiratory tract – Surgical anesthesia may induce nausea and must be preceded by fasting until the stomach and small intestine are empty 25-120  Digestion and Absorption Salivary and gastric enzymes partially digest protein and lesser amounts of starch and fat in the stomach Most digestion and nearly all absorption occur after the chyme has passed into the small intestine 25-121  Digestion and Absorption Stomach does not absorb any significant amount of nutrients – Aspirin – Some lipid-soluble drugs Alcohol is absorbed mainly by small intestine – Intoxicating effects depend partly on how rapidly the stomach is emptied 25-122  Protection of the Stomach Living stomach is protected in three ways from the harsh acidic and enzymatic environment it creates – Mucous coat: thick, highly alkaline mucus resists action of acid and enzymes – Tight junctions: between epithelial cells prevent gastric juice from seeping between them and digesting the connective tissue of the lamina propria and beyond 25-123  Protection of the Stomach Cont. – Epithelial cell replacement: stomach epithelial cells live only 3 to 6 days Sloughed off into the chyme and digested with the food Replaced rapidly by cell division in the gastric pits Breakdown of these protective measures can result in inflammation and peptic ulcer 25-124  Peptic Ulcer Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 25.16a,b (a) Normal (b) Peptic ulcer CNR/SPL/Photo Researchers, Inc. Gastritis, inflammation of the stomach, can lead to a peptic ulcer as pepsin and hydrochloric acid erode the stomach wall. Most ulcers are caused by acid-resistant bacteria Helicobacter pylori, that can be treated with antibiotics and Pepto-Bismol. 25-125  Regulation of Gastric Function Nervous and endocrine systems collaborate – Increase gastric secretion and motility when food is eaten; suppresses them when the stomach empties Gastric activity is divided into three phases – Cephalic phase: stomach being controlled by brain – Gastric phase: stomach controlling itself – Intestinal phase: stomach being controlled by small intestine Phases overlap and can occur simultaneously 25-126  Regulation of Gastric Function Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sensory and Long (vagovagal) reflex: mental input Sensory fibers Motor fibers Vagus nerve Vagus nerve Vagus nerve Sympathetic nerve – + Intestinal gastrin + 0 + + Gastrin Histamine Secretin – – and CCK + Short Enterogastric (myenteric) reflex reflex 1 Cephalic phase 2 Gastric phase 3 Intestinal phase Vagus nerve stimulates Food stretches the stomach and Intestinal gastrin briefly stimulates the gastric secretion even activates myenteric and stomach, but then secretin, CCK, and the before food is swallowed. vagovagal reflexes. These enterogastric reflex inhibit gastric secretion reflexes stimulate gastric and motility while the duodenum processes Key secretion. Histamine and gastrin the chyme already in it. Sympathetic nerve + Stimulation also stimulate acid and enzyme fibers suppress gastric activity, while vagal secretion. (parasympathetic) stimulation of the – Inhibition stomach is now inhibited. 0 Reduced or no effect Figure 25.17 25-127 Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.  Regulation of Gastric Function Cephalic phase – Stomach responds to sight, smell, taste, or thought of food – Sensory and mental inputs converge on the hypothalamus Relays signals to medulla oblongata – Vagus nerve fibers from medulla oblongata stimulate the enteric nervous system of stomach In turn, stimulates gastric secretion 25-129  Regulation of Gastric Function Gastric phase – Period in which swallowed food and semidigested protein activate gastric activity Two-thirds of gastric secretion occurs in this phase – Ingested food stimulates gastric activity in two ways By stretching the stomach – Activates short reflex mediated through myenteric nerve plexus – Activates long reflex mediated through the vagus nerves and the brainstem By increasing the pH of its contents 25-130  Regulation of Gastric Function Cont. – Gastric secretion is stimulated by three chemicals Acetylcholine (ACh)—secreted by parasympathetic nerve fibers of both reflexes Histamine—a paracrine secretion from enteroendocrine cells in the gastric glands Gastrin—a hormone produced by the enteroendocrine G cells in pyloric glands 25-131  Regulation of Gastric Function Intestinal phase – Stage in which the duodenum responds to arriving chyme and moderates gastric activity through hormones and nervous reflexes – Duodenum initially enhances gastric secretion, but soon inhibits it Stretching of the duodenum accentuates vagovagal reflex that stimulates the stomach Peptides and amino acids in chyme stimulate G cells of the duodenum to secrete more gastrin which further stimulates the stomach 25-132  Regulation of Gastric Function Enterogastric reflex—duodenum sends inhibitory signals to the stomach by way of the enteric nervous system and signals to the medulla oblongata; triggered by acid and semidigested fats in the duodenum – Inhibits vagal nuclei: reducing vagal stimulation of the stomach – Stimulate sympathetic neurons: send inhibitory signals to the stomach 25-133  Regulation of Gastric Function Chyme also stimulates duodenal enteroendocrine cells to release secretin and cholecystokinin – They stimulate the pancreas and gallbladder – Also suppress gastric secretion 25-134  Regulation of Gastric Function Pyloric sphincter contracts tightly to limit chyme entering duodenum – Gives duodenum time to work on chyme Enteroendocrine cells also secrete glucose- dependent insulinotropic peptide (GIP) originally called gastrin-inhibiting peptide – Stimulates insulin secretion in preparation for processing nutrients about to be absorbed by the small intestine 25-135 Feedback Control of Gastric Secretion Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Pyloric gland Gastric gland Mucous cell Figure 25.18 Parietal cell Chief cell Chief cells secrete Gastrin pepsinogen stimulates chief cells Ingested food and buffers parietal Parietal stomach acid cells cells secrete G cells secrete HCI Elevated pH gastrin stimulates G cells G cell Oligopeptides Oligopeptides and amino directly acids buffer stimulate stomach acid G cells HCI converts Pepsin digests pepsinogen dietary protein to pepsin Partially digested protein Pepsin (active enzyme) HCI Pepsinogen (zymogen) 25-136 The Liver, Gallbladder, and Pancreas Expected Learning Outcomes – Describe the gross and microscopic anatomy of the liver, gallbladder, bile duct system, and pancreas. – Describe the digestive secretions and functions of the liver, gallbladder, and pancreas. – Explain how hormones regulate secretion by the liver and pancreas. 25-137 The Liver, Gallbladder, and Pancreas Small intestine receives chyme from stomach Also secretions from liver and pancreas – Enter digestive tract near the junction of stomach and small intestine Secretions are so important to the digestive process of the small intestine 25-138  The Liver Liver—reddish brown gland located immediately inferior to the diaphragm The body’s largest gland – Weighs about 1.4 kg (3 lb) Variety of functions – Secretes bile which contributes to digestion 25-139  Gross Anatomy Four lobes—right, left, quadrate, and caudate – Falciform ligament separates left and right lobes Sheet of mesentery that suspends the liver from the diaphragm – Round ligament (ligamentum teres)—fibrous remnant of umbilical vein Carries blood from umbilical cord to liver of the fetus From inferior view, squarish quadrate lobe next to the gallbladder and a tail-like caudate lobe posterior to that 25-140  Gross Anatomy Porta hepatis—irregular opening between these lobes – Point of entry for the hepatic portal vein and proper hepatic artery – Point of exit for the bile passages – All travel in lesser omentum Gallbladder—adheres to a depression on the inferior surface of the liver, between right and quadrate lobes Bare area on superior surface where it attaches to diaphragm 25-141  Gross Anatomy of the Liver Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Inferior vena cava Bare area Caudate lobe Posterior Right lobe Left lobe Falciform ligament Round ligament Porta hepatis: Hepatic portal vein Proper hepatic artery Common hepatic duct Anterior Quadrate lobe Gallbladder Right lobe (b) Anterior view (c) Inferior view Figure 25.19b,c 25-142 Liver  Liver Gall Bladder Rt. & Lt. Hepatic Common hepatic duct Bile duct Pancreatic duct ducts Duodenal papilla  Liver Right Left Caudate Lobe Quadrate Lobe Lobe Lobe  Microscopic Anatomy of the Liver Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Hepatocytes Bile canaliculi Stroma Central vein Hepatic triad: Hepatic Branch of sinusoid hepatic portal vein Branch of proper hepatic Stroma artery Bile ductule (a) Figure 25.20a 25-146  Microscopic Anatomy Hepatic lobules—tiny innumerable cylinders that fill the interior of the liver – About 2 mm long and 1 mm in diameter – Central vein: passing down the core – Hepatocytes: cuboidal cells surrounding central vein in radiating sheets or plates Each plate of hepatocytes is an epithelium one or two cells thick – Hepatic sinusoids: blood-filled channe