1 Fundamentals of Anatomy & PhysiologyEleventh Edition Chapter 24 The Digestive System Lecture Presentation by Deborah A. Hutchinson Seattle University

2 Learning Outcomes 24-1 Identify the organs of the digestive system, list their major functions, describe the histology of the digestive tract, and outline the mechanisms that regulate digestion Discuss the anatomy of the oral cavity, and list the functions of its major structures and regions Describe the structure and functions of the pharynx and the esophagus Describe the anatomy of the stomach, including its histology, and discuss its roles in digestion and absorption Describe the structure, functions, and regulation of the accessory digestive organs Describe the anatomy and histology of the small intestine, and explain the functions and regulation of intestinal secretions.

3 Learning Outcomes 24-7 Describe the gross and histological structures of the large intestine, including its regional specializations and role in nutrient absorption List the nutrients required by the body, describe the chemical events responsible for the digestion of organic nutrients, and describe the mechanisms involved in the absorption of organic and inorganic nutrients Summarize the effects of aging on the digestive system Give examples of interactions between the digestive system and other body systems studied so far.

4 An Introduction to the Digestive SystemAcquires nutrients from environment Used to synthesize essential compounds (anabolism) Broken down to provide energy to cells (catabolism)

5 24-1 The Digestive System Digestive system Digestive tractGastrointestinal (GI) tract or alimentary canal Muscular tube Extends from oral cavity to anus Accessory organs Teeth, tongue, and various glandular organs

6 Figure 24–1 Organs of the Digestive System (Part 1 of 2).Major Organs of the Digestive Tract Oral Cavity (Mouth) Ingestion, mechanical digestion with accessory organs (teeth and tongue), moistening, mixing with salivary secretions Pharynx Muscular propulsion of materials into the esophagus Esophagus Transport of materials to the stomach Stomach Chemical digestion of materials by acid and enzymes; mechanical digestion through muscular contractions Small Intestine Enzymatic digestion and absorption of water, organic substrates, vitamins, and ions Large Intestine Dehydration and compaction of indigestible materials in preparation for elimination Anus

7 Figure 24–1 Organs of the Digestive System (Part 2 of 2).Accessory Organs of the Digestive System Teeth Mechanical digestion by chewing (mastication) Tongue Assists mechanical digestion with teeth, sensory analysis Salivary Glands Secretion of lubricating fluid containing enzymes that break down carbohydrates Liver Secretion of bile (important for lipid digestion), storage of nutrients, many other vital functions Gallbladder Storage and concentration of bile Pancreas Exocrine cells secrete buffers and digestive enzymes; endocrine cells secrete hormones

8 24-1 The Digestive System Integrated processes of digestive systemIngestion Mechanical digestion and propulsion Chemical digestion Secretion Absorption Defecation

9 24-1 The Digestive System IngestionOccurs when food enters oral cavity Mechanical digestion and propulsion Crushing and shearing of food Propelling food along digestive tract

10 24-1 The Digestive System Chemical digestionChemical breakdown of food into small organic fragments for absorption by digestive epithelium Secretion Release of water, acids, enzymes, buffers, and salts By epithelium of digestive tract, glandular organs, and gallbladder

11 24-1 The Digestive System AbsorptionMovement of organic molecules, electrolytes, vitamins, minerals, and water Across digestive epithelium Into interstitial fluid of digestive tract Defecation Elimination of wastes from body Compacted, dehydrated wastes are called feces

12 24-1 The Digestive System Lining of digestive tractSafeguards surrounding tissues against Corrosive effects of digestive acids and enzymes Mechanical stresses, such as abrasion Bacteria either ingested with food or that reside in digestive tract

13 24-1 The Digestive System PeritoneumSerous membrane lining peritoneal cavity Superficial mesothelium covering a layer of areolar tissue Visceral peritoneum (serosa) Covers organs within peritoneal cavity Parietal peritoneum Lines inner surfaces of body wall

14 24-1 The Digestive System Peritoneal fluidProduced by serous membrane lining Allows sliding of parietal and visceral surfaces without friction or irritation About 7 liters produced and absorbed daily, but very little in peritoneal cavity at one time Ascites—abdominal swelling due to buildup of peritoneal fluid

15 24-1 The Digestive System MesenteriesDouble sheets of peritoneal membrane Suspend portions of digestive tract within peritoneal cavity Connect parietal peritoneum with visceral peritoneum Provide a route to and from digestive tract for blood vessels, nerves, and lymphatic vessels Stabilize positions of attached organs Prevent intestines from becoming entangled

16 24-1 The Digestive System During embryonic developmentDigestive tract and accessory organs are suspended in peritoneal cavity by Dorsal mesentery Ventral mesentery Ventral mesentery later disappears along most of digestive tract Persists in adults only as lesser omentum and falciform ligament

17 Figure 24–2a The Mesenteries.Neural tube Notochord Mesoderm Parietal peritoneum Dorsal mesentery Coelomic cavity Peritoneal cavity Digestive tract Developing liver Visceral peritoneum Digestive tract 4 weeks Ventral mesentery 5 weeks a During embryonic development, the digestive tube is initially suspended by dorsal and ventral mesenteries. In adults, the ventral mesentery is lost except at the lesser omentum between the stomach and liver and the falciform ligament between the liver and diaphragm (see part d).

18 24-1 The Digestive System Lesser omentumStabilizes position of stomach Provides access route for blood vessels and other structures entering or leaving liver Falciform ligament Helps stabilize position of liver relative to diaphragm and abdominal wall

19 24-1 The Digestive System Dorsal mesenteryEnlarges to form an enormous pouch, the greater omentum Extends inferiorly between body wall and anterior surface of small intestine Hangs like an apron from lateral and inferior borders of stomach

20 24-1 The Digestive System Adipose tissue in greater omentumConforms to shapes of surrounding organs Pads and protects surfaces of abdomen Provides insulation to reduce heat loss Stores lipid energy reserves Contributes to “beer belly”

21 24-1 The Digestive System Mesentery proper Thick mesenterial sheetProvides stability Permits some independent movement Suspends all but first 25 cm of small intestine Mesentery associated with duodenum and pancreas Fuses with abdominal wall, locking organs in place Posterior to peritoneal cavity—retroperitoneal

22 24-1 The Digestive System MesocolonMesentery associated with part of large intestine During development, mesocolon of ascending colon, descending colon, and rectum Fuse to posterior body wall Lock regions in place

23 Figure 24–2b The Mesenteries.Lesser omentum Greater omentum (cut) Stomach Mesocolon of ascending and descending colons fused to posterior portion of the parietal peritoneum Transverse colon Transverse mesocolon Ascending colon Descending colon Mesentery proper (mesenterial sheet) Small intestine Sigmoid colon b A diagrammatic view of the organization of mesenteries in an adult. As the digestive tract enlarges, mesenteries associated with the proximal portion of the small intestine, the pancreas, and the ascending and descending portions of the colon fuse to the body wall.

24 Figure 24–2c The Mesenteries.Falciform ligament Diaphragm Inferior vena cava Esophagus Coronary ligament of liver Pancreas Right kidney Left kidney Duodenum Attachment of transverse mesocolon Superior mesenteric artery and vein Position of ascending colon Position of descending colon Root of mesentery proper Attachment of sigmoid mesocolon Rectum Urinary bladder Parietal peritoneum c An anterior view of the empty peritoneal cavity, showing the attachment of mesenteries to the posterior body wall. Some visceral organs that were originally suspended within the peritoneal cavity are now retroperitoneal due to fusion of the serosa with the parietal peritoneum.

25 Figure 24–2d The Mesenteries.Diaphragm Falciform ligament Visceral peritoneum Liver Liver Lesser omentum Stomach Pancreas Transverse mesocolon Duodenum Transverse colon Mesentery proper Greater omentum Sigmoid mesocolon Parietal peritoneum Rectum Small intestine Urinary bladder Uterus d A sagittal section showing the mesenteries of an adult. Notice that the pancreas, duodenum, and rectum are retroperitoneal.

26 24-1 The Digestive System Histology of digestive tractMajor layers of digestive tract Mucosa Submucosa Muscular layer Serosa Lining of digestive tract varies by region Longitudinal folds in empty stomach Permanent transverse folds in small intestine

27 Mesenteric artery and vein Circular folds Muscular layerFigure 24–3 Histological Organization of the Digestive Tract (Part 1 of 2). Mesenteric artery and vein Circular folds Mesentery Mucosa Submucosa Muscular layer Serosa

28 Mucosa Circular fold Mucosal epithelium Lamina propria MuscularisFigure 24–3 Histological Organization of the Digestive Tract (Part 2 of 2). Circular fold Mucosa Mucosal epithelium Lamina propria Muscularis mucosae Villi Intestinal glands Submucosal gland Lymphatic vessel Mucosa Artery and vein Submucosa Submucosal neural plexus Muscular layer Circular muscle layer Myenteric plexus Serosa Longitudinal muscle layer

29 24-1 The Digestive System Mucosa Inner lining of digestive tractMucous membrane consisting of Epithelium, moistened by glandular secretions Lamina propria of areolar tissue Muscular muscularis mucosae

30 24-1 The Digestive System Digestive epitheliumMucosal epithelium is simple or stratified Depending on location, function, and stresses Oral cavity, pharynx, esophagus, anal canal Stratified squamous epithelium Stomach, small intestine, most of large intestine Simple columnar epithelium Enteroendocrine cells Secrete hormones that coordinate activities of digestive tract and accessory glands

31 24-1 The Digestive System Lamina propriaA layer of areolar tissue that contains Blood vessels Sensory nerve endings Lymphatic vessels Smooth muscle cells Scattered lymphatic tissue

32 24-1 The Digestive System Muscularis mucosaeIn most areas of digestive tract, deep to lamina propria Narrow sheet of smooth muscle and elastic fibers Smooth muscle cells are arranged in two concentric layers Inner layer encircles lumen (circular muscle) Outer layer contains cells arranged parallel to long axis of tract (longitudinal layer)

33 24-1 The Digestive System SubmucosaLayer of dense irregular connective tissue Binds mucosa to muscular layer Numerous blood vessels and lymphatic vessels May contain exocrine glands Secrete buffers and enzymes into digestive tract Submucosal neural plexus Innervates mucosa and submucosa Sensory neurons, parasympathetic ganglionic neurons, and sympathetic postganglionic fibers

34 24-1 The Digestive System Muscular layerDominated by smooth muscle cells Inner circular layer and outer longitudinal layer Involved in mechanical digestion and moving materials along digestive tract Movements coordinated by enteric nervous system (ENS) Innervated primarily by parasympathetic division Also by sympathetic postganglionic fibers

35 24-1 The Digestive System Muscular layer Myenteric plexusNetwork of parasympathetic ganglia, sensory neurons, interneurons, and sympathetic postganglionic fibers Between circular and longitudinal muscle layers

36 24-1 The Digestive System SerosaSerous membrane covering muscular layer Along most portions of digestive tract enclosed by peritoneal cavity In areas where serosa is lacking Adventitia (dense network of collagen fibers) firmly attaches digestive tract to adjacent structures

37 24-1 The Digestive System Motility of digestive tractVisceral smooth muscle tissue Rhythmic cycles of activity Controlled by pacesetter cells that undergo spontaneous depolarization Wave of contraction spreads throughout entire muscular sheet

38 24-1 The Digestive System PeristalsisWaves of muscular contractions that move a bolus along length of digestive tract Circular muscles behind bolus contract While circular muscles ahead of bolus relax Longitudinal muscles ahead of bolus contract Shortening adjacent segments Wave of contraction in circular muscle layer Forces bolus forward

39 Figure 24–4 Peristalsis (Part 1 of 4).

40 Figure 24–4 Peristalsis (Part 2 of 4).

41 Figure 24–4 Peristalsis (Part 3 of 4).

42 Figure 24–4 Peristalsis (Part 4 of 4).

43 24-1 The Digestive System SegmentationCycles of contraction that churn and fragment the bolus Mixing contents with intestinal secretions Does not follow a set pattern Does not push materials in any one direction

44 24-1 The Digestive System Regulation of digestive functionsLocal factors Neural mechanisms Hormonal mechanisms

45 24-1 The Digestive System Local factorspH, volume, or chemical composition of intestinal contents Can have direct, localized effects on digestive activity Stretching of intestinal wall Can stimulate localized contractions Local factors may stimulate release of chemicals Prostaglandins, histamine, and other chemicals may affect adjacent cells

46 24-1 The Digestive System Neural mechanisms Visceral motor neuronsControl smooth muscle contraction and glandular secretion Located in myenteric plexus

47 24-1 The Digestive System Neural mechanismsShort reflexes (local reflexes) Control small segments of digestive tract Operate entirely outside of CNS control Long reflexes Involve interneurons and motor neurons in CNS Provide higher level control Stimulate large-scale peristalsis Parasympathetic motor fibers synapse in myenteric plexus

48 24-1 The Digestive System Hormonal mechanismsEnteroendocrine cells in digestive tract produce many peptide hormones Affect almost every aspect of digestion Some also affect other systems Travel through bloodstream to reach target organs

49 Figure 24–5 The Regulation of Digestive Activities.Neural Control Mechanisms The movement of materials along the digestive tract, as well as many secretory functions, is primarily controlled by local factors. Short reflexes are triggered by chemoreceptors or stretch receptors in the walls of the digestive tract; the controlling neurons are located in the myenteric plexus. These reflexes are often called myenteric reflexes. Long reflexes involving interneurons and motor neurons in the CNS provide a higher level of control over digestive and glandular activi- ties, generally controlling large-scale peristalsis that moves materials from one region of the digestive tract to another. Long reflexes may involve parasympa- thetic motor fibers in the glossopharyn- geal (IX), vagus (X), or pelvic nerves that synapse in the myenteric plexus. CNS Long reflex Myenteric plexus Short reflex Peristalsis and segmentation movements Stretch receptors, chemoreceptors Buffers, acids, enzymes released Secretory cells 3 Hormonal Control Mechanisms The digestive tract produces numerous hormones that affect almost every aspect of diges- tion, and some of them also affect the activities of other systems. These hormones are peptides produced by entero- endocrine cells, endocrine cells in the epithelium of the digestive tract. We consider these hormones as we proceed down the digestive tract. 1 Local Factors Local factors are the primary stimulus for digestion. They coordinate the responses to changes in the pH of the contents of the lumen, physical distor- tion of the wall of the digestive tract, or the presence of chemicals—either specific nutrients or chemical messen- gers released by cells of the mucosa. Carried by bloodstream Enteroendocrine cells Hormones released

50 24-2 The Oral Cavity Functions of oral cavity Sensory analysisOf food before swallowing Mechanical digestion Through actions of teeth, tongue, and palatal surfaces Lubrication By mixing with mucus and saliva Limited chemical digestion Of carbohydrates and lipids

51 24-2 The Oral Cavity Oral mucosa Lining of oral cavityStratified squamous epithelium Relatively thin and nonkeratinized on cheeks, lips, and inferior surface of tongue Thin, vascular mucosa inferior to tongue can rapidly absorb lipid-soluble drugs Mucosae of cheeks Supported by pads of fat and buccinator muscles Continuous with those of lips

52 24-2 The Oral Cavity Oral vestibuleSpace between cheeks (or lips) and teeth Gingivae (gums) Ridges of oral mucosa Surround base of each tooth on alveolar processes of maxillae and mandible

53 24-2 The Oral Cavity Uvula Dangling process at posterior margin of soft palate Prevents food from entering pharynx too soon Palatoglossal arch Extends between soft palate and base of tongue Fauces Space between oral cavity and pharynx Bounded by soft palate and base of tongue Palatopharyngeal arch Extends from soft palate to pharyngeal wall

54 Figure 24–6a Anatomy of the Oral Cavity.Hard palate Soft palate Palatoglossal arch Nasal cavity Pharyngeal tonsil Opening of parotid duct Entrance to auditory tube Upper lip Nasopharynx Cheek Uvula Dorsum of tongue Palatine tonsil Lower lip Fauces Palatopharyngeal arch Gingiva Oral vestibule Oropharynx Lingual tonsil Body of tongue Epiglottis Root of tongue Hyoid bone Laryngopharynx Geniohyoid Mylohyoid a A sagittal section of the oral cavity

55 Figure 24–6b Anatomy of the Oral Cavity.Frenulum of upper lip Hard palate Soft palate Fauces Uvula Palatoglossal arch Palatopharyngeal arch Palatine tonsil Tongue Tongue Frenulum of tongue Gingiva Oral vestibule Frenulum of lower lip Openings of submandibular ducts b An anterior view of the oral cavity

56 24-2 The Oral Cavity Tongue Four primary functionsMechanical digestion by compression, abrasion, and distortion Manipulation to assist in chewing and to prepare food for swallowing Sensory analysis by touch, temperature, and taste receptors Secretion of mucins and lingual lipase

57 24-2 The Oral Cavity Tongue Anterior body Posterior rootFrenulum of tongue Along inferior midline Extrinsic tongue muscles Perform all gross movements Intrinsic tongue muscles Smaller Perform precise movements

58 24-2 The Oral Cavity Teeth Assisted by tongue while chewing DentinA mineralized matrix in teeth similar to that of bone Does not contain cells Pulp cavity Interior chamber of tooth that receives blood vessels and nerves through the root canal Apical foramen—opening through which blood vessels and nerves enter root canal

59 24-2 The Oral Cavity Root of toothSits in a bony socket (tooth alveolus) A layer of cement covers dentin of root Protects and anchors periodontal ligament Periodontal ligament extends from dentin of root to alveolar bone Creating a gomphosis (strong articulation)

60 24-2 The Oral Cavity Crown Exposed portion of toothProjects beyond soft tissue of gingiva Separated from root by neck of tooth Gingival sulcus surrounds the neck Enamel Covers dentin Forms occlusal surface (biting surface) Cusps—elevations or projections of occlusal surface

61 a A diagrammatic section through a typical adult tooth. Cusp EnamelFigure 24–7a The Teeth. Cusp Enamel Crown Dentin Pulp cavity Gingiva Gingival sulcus Neck Cement Periodontal ligament Root Root canal Alveolar process Apical foramen Branches of alveolar vessels and nerve a A diagrammatic section through a typical adult tooth.

62 24-2 The Oral Cavity Alveolar processes of maxillae and alveolar part of mandible Form maxillary dental arcade and mandibular dental arcade Types of teeth Incisor teeth Canine teeth Premolar teeth Molar teeth

63 Upper jaw Lower jaw b The adult teeth from the right side of the upperFigure 24–7b The Teeth. Incisors Canines (cuspids) Premolars (bicuspids) Molars Upper jaw Lower jaw b The adult teeth from the right side of the upper and lower jaws. Figure 24–8a,b shows a view of the occlusal surfaces.

64 24-2 The Oral Cavity Incisor teeth Blade-shapedLocated at front of mouth Used for clipping or cutting Have a single root Canine teeth (cuspids) Conical with single, pointed cusp Used for tearing or slashing

65 24-2 The Oral Cavity Premolar teeth (bicuspids) Flattened crownsTwo prominent, rounded cusps Used to crush, mash, and grind Have one or two roots Molar teeth Very large, flattened crowns Four to five prominent, rounded cusps Used for crushing and grinding Have two to three roots

66 24-2 The Oral Cavity Sets of teethDuring development, two sets of teeth form Deciduous teeth Permanent teeth Also called primary teeth, milk teeth, or baby teeth 20 temporary teeth Five on each side of upper and lower jaws 2 incisors, 1 canine, and 2 deciduous molars

67 Figure 24–8a Deciduous and Permanent Dentitions.Central incisors (7.5 mo) Lateral incisor (9 mo) Canine (18 mo) Deciduous 1st molar (14 mo) Deciduous 2nd molar (24 mo) Deciduous 2nd molar (20 mo) Deciduous 1st molar (12 mo) Canine (16 mo) Lateral incisor (7 mo) Central incisors (6 mo) a The deciduous teeth, with the age at eruption given in months

68 24-2 The Oral Cavity Permanent teethReplace deciduous teeth by eruption 32 permanent teeth 8 on each side of upper and lower jaws 2 incisors, 1 canine, 2 premolars, and 3 molars

69 Figure 24–8b Deciduous and Permanent Dentitions.Maxilla exposed to show developing permanent teeth Erupted deciduous teeth First and second molars Mandible exposed to show developing permanent teeth b Maxilla and mandible with unerupted teeth exposed

70 Figure 24–8c Deciduous and Permanent Dentitions (Part 1 of 2).Central incisors (7–8 yr) Lateral incisor (8–9 yr) Canine (11–12 yr) 1st Premolar (10–11 yr) Maxillary dental arcade Maxillary dental arcade 2nd Premolar (10–12 yr) 1st Molar (6–7 yr) 2nd Molar (12–13 yr) Hard palate Hard palate 3rd Molar (17–21 yr)

71 Figure 24–8c Deciduous and Permanent Dentitions (Part 2 of 2).3rd Molar (17–21 yr) 2nd Molar (11–13 yr) 1st Molar (6–7 yr) 2nd Premolar (11–12 yr) Mandibular dental arcade Mandibular dental arcade 1st Premolar (10–12 yr) Canine (9–10 yr) Lateral incisor (7–8 yr) Central incisors (6–7 yr) c The permanent teeth, with the age at eruption given in years

72 24-2 The Oral Cavity Salivary glandsThree major pairs secrete into oral cavity Parotid glands Sublingual glands Submandibular glands Each pair has distinctive cellular organization And produces saliva with slightly different properties

73 24-2 The Oral Cavity Parotid glands Inferior to zygomatic archProduce serous secretion Containing salivary amylase to break down starches Each is drained by parotid duct Empties into vestibule at second upper molar

74 24-2 The Oral Cavity Sublingual glandsCovered by mucous membrane of floor of mouth Produce mucus Acts as a buffer and lubricant Numerous sublingual ducts Open along either side of lingual frenulum

75 24-2 The Oral Cavity Submandibular glands Lie within mandibular grooveSecrete buffers, glycoproteins (mucins), and salivary amylase Submandibular ducts Open on each side of frenulum of tongue immediately posterior to teeth

76 Figure 24–9a Anatomy of the Salivary Glands.Parotid duct Openings of sublingual ducts Major Salivary Glands Parotid gland Frenulum of tongue Sublingual gland Opening of left submandibular duct Submandibular gland Submandibular duct a A lateral view, showing the relative positions of the major salivary glands and ducts on the left side of the head. For clarity, the left ramus and body of the mandible have been removed. For the positions of the parotid and submandibular ducts in the oral cavity, see Figure 24–6.

77 Figure 24–9b Anatomy of the Salivary Glands.Mucous cells Serous cells Duct Submandibular gland LM × 300 a The submandibular gland secretes a mixture of mucins, produced by mucous cells, and enzymes, produced by serous cells.

78 24-2 The Oral Cavity SalivaSalivary glands produce 1.0–1.5 liters each day 70 percent from submandibular glands 25 percent from parotids 5 percent from sublingual glands 99.4 percent water Remaining 0.6 percent Electrolytes, buffers, glycoproteins, antibodies, enzymes, and wastes

79 24-2 The Oral Cavity Functions of saliva Cleaning oral surfacesMoistening and lubricating food Keeping pH of mouth near 7.0 Controlling populations of bacteria and limiting acids that they produce Dissolving chemicals that stimulate taste buds Initiating digestion of complex carbohydrates with salivary amylase

80 24-2 The Oral Cavity Regulation of salivary secretionsSalivary glands have parasympathetic and sympathetic innervation Parasympathetic efferents Originate in superior salivatory nucleus and inferior salivatory nucleus of medulla oblongata Stimulated by any object in mouth, other brainstem nuclei, and activities of higher centers Parasympathetic stimulation accelerates secretion by all salivary glands

81 24-2 The Oral Cavity Mastication (chewing)Food is forced from oral cavity to vestibule and back across occlusal surfaces of teeth Muscles of mastication Close jaws Slide lower jaw from side to side Tongue compacts chewed food into a bolus Moist, rounded ball Fairly easy to swallow

82 24-3 The Pharynx and EsophagusPharynx (throat) Common passageway for food, liquid, and air Regions of the pharynx Nasopharynx Oropharynx Laryngopharynx Food passes through parts of pharynx on its way to esophagus

83 24-3 The Pharynx and EsophagusA hollow muscular tube Conveys food and liquids to stomach About 25 cm long and 2 cm wide Begins posterior to cricoid cartilage Enters abdominopelvic cavity through the esophageal hiatus Innervated by parasympathetic and sympathetic fibers from esophageal plexus

84 24-3 The Pharynx and EsophagusResting muscle tone in circular muscle layer Prevents air from entering esophagus Prevents backflow of materials from stomach Histology of esophagus Wall of esophagus has three layers Mucosa Submucosa Muscular layer

85 24-3 The Pharynx and EsophagusHistology of esophagus Mucosa contains nonkeratinized stratified squamous epithelium Mucosa and submucosa form large folds Muscularis mucosae consists of smooth muscle Submucosa contains esophageal glands that produce mucus Muscular layer has inner circular and outer longitudinal layers Adventitia anchors esophagus to body wall

86 Figure 24–10a Anatomy of the Esophagus.Muscularis mucosae Mucosa Submucosa Muscular layer Adventitia a A transverse section through an empty esophagus (LM × 5).

87 Figure 24–10b Anatomy of the Esophagus.Stratified squamous epithelium Lamina propria Muscularis mucosae Esophageal mucosa LM × 275 b This light micrograph illustrates the extreme thickness of the epithelial portion of the esophageal mucosal layer.

88 24-3 The Pharynx and EsophagusDeglutition (swallowing) Can be initiated voluntarily, but proceeds automatically Swallowing reflex Begins when tactile receptors on palatal arches and uvula are stimulated by bolus Information is relayed to swallowing center of medulla oblongata Buccal, pharyngeal, and esophageal phases

89 Figure 24–11 The Process of Deglutition (Swallowing) (Part 1 of 4).Buccal Phase The buccal phase begins with the compression of the bolus against the hard palate. Retraction of the tongue then forces the bolus into the oropharynx and assists in elevating the soft palate, thereby sealing off the nasopharynx. Once the bolus enters the oropharynx, reflex responses begin and the bolus is moved toward the stomach. Hard palate Soft palate Bolus Tongue Oropharynx Epiglottis Trachea

90 Figure 24–11 The Process of Deglutition (Swallowing) (Part 2 of 4).Pharyngeal Phase The pharyngeal phase begins as the bolus comes into contact with the palatal arches and the posterior pharyngeal wall. Elevation of the larynx and folding of the epiglottis direct the bolus past the closed glottis. At the same time, the uvula and soft palate block passage back to the nasopharynx. Uvula Tongue Bolus Epiglottis Larynx

91 Figure 24–11 The Process of Deglutition (Swallowing) (Part 3 of 4).Esophageal Phase The esophogeal phase begins as the contraction of pharyngeal muscles forces the bolus through the entrance to the esophagus. Once in the esophagus, the bolus is pushed toward the stomach by a peristaltic wave. Peristalsis Trachea Esophagus

92 Figure 24–11 The Process of Deglutition (Swallowing) (Part 4 of 4).Bolus Enters Stomach The approach of the bolus triggers the opening of the lower esophageal sphincter. The bolus then continues into the stomach. Thoracic cavity Lower esophageal sphincter Stomach

93 24-4 The Stomach Major functions of stomachTemporary storage of ingested food Mechanical digestion with muscular contractions Chemical digestion of food with acid and enzymes Chyme Partially digested food mixed with acidic secretions of stomach

94 24-4 The Stomach Gross anatomy of stomach Shaped like an expanded JShort lesser curvature forms medial surface Long greater curvature forms lateral surface Anterior and posterior surfaces are rounded Shape and size vary from person to person and from one meal to the next Typically extends between levels of vertebrae T7 and L3

95 24-4 The Stomach Regions of stomach Cardia Fundus Body Pyloric part

96 24-4 The Stomach Cardia Superior, medial portion of stomachAbundant mucous glands Fundus Superior to junction of stomach and esophagus Contacts diaphragm Body Between fundus and curve of the J Largest region of stomach Mixing tank for ingested food and secretions

97 24-4 The Stomach Pyloric part Between body and duodenumShape changes often during digestion Pyloric antrum connects to body Pyloric canal empties into duodenum Pylorus Muscular tissue surrounding pyloric orifice (stomach outlet) Pyloric sphincter Thick circular layer of muscle within pylorus

98 Figure 24–12a Gross Anatomy of the Stomach.Esophagus Diaphragm Left gastric artery Liver, right lobe Liver, left lobe Vagus nerve (X) Lesser curvature Common hepatic artery Fundus Gallbladder Cardia Spleen Body of stomach Bile duct Greater curvature with greater omentum attached Pyloric sphincter Pyloric part Greater omentum a The position and external appearance of the stomach, showing superficial landmarks

99 Figure 24–12b Gross Anatomy of the Stomach.Esophagus Fundus Anterior surface Cardia Longitudinal muscle layer Left gastro-epiploic vessels Circular muscle layer Body Lesser curvature (medial surface) Pyloric sphincter Oblique muscle layer overlying mucosa Duodenum Rugae Pyloric orifice Greater curvature (lateral surface) Pyloric part Pylorus Pyloric canal Pyloric antrum b The structure of the stomach wall

100 24-4 The Stomach Rugae Prominent folds in mucosa of empty stomachFlatten out as stomach fills Allow for expansion of gastric lumen Up to 50 times its empty size Muscularis mucosae and muscular layer Contain extra layers of smooth muscle cells Oblique layer in addition to circular and longitudinal layers

101 24-4 The Stomach Histology of stomachSimple columnar epithelium lines all portions Epithelium is a secretory sheet Produces mucus that covers interior surface Gastric pits Shallow depressions that open onto gastric surface Mucous cells at base (neck) of each gastric pit Actively divide, replacing superficial cells

102 24-4 The Stomach Gastric glands In fundus and body of stomachExtend deep into underlying lamina propria Each gastric pit communicates with several gastric glands Parietal cells Chief cells Secrete about 1500 mL of gastric juice each day

103 Figure 24–13a Histology of the Stomach Lining.Esophagus Diaphragm Stomach Greater omentum Layers of the Stomach Wall Mucosa Gastric pit (opening to gastric gland) Mucous epithelium Lamina propria Muscularis mucosae Submucosa Artery and vein Muscular layer Oblique muscle Circular muscle Lymphatic vessel Longitudinal muscle Myenteric plexus Serosa a Stomach wall

104 Figure 24–13b Histology of the Stomach Lining.Lamina propria Gastric pit Mucous cells Neck Cells of Gastric Glands Parietal cells Gastric gland G cell Chief cells Smooth muscle cell b Gastric gland

105 24-4 The Stomach Parietal cellsCommon along proximal portions of gastric glands Secrete intrinsic factor Glycoprotein that helps absorb vitamin B12 Also indirectly secrete hydrochloric acid (HCl) Chief cells Most abundant near base of gastric glands Secrete pepsinogen (an inactive proenzyme) Pepsinogen is converted to pepsin (an active proteolytic enzyme) by HCl in gastric lumen

106 Figure 24–14 The Secretion of Hydrochloric Acid Ions.Hydrogen ions (H+) are generated inside a parietal cell as the enzyme carbonic anhydrase converts CO2 and H2O to carbonic acid (H2CO3), which then dissociates. KEY Parietal cell Diffusion CO2 + H2O Carbonic anhydrase Carrier-mediated transport 2 4 Active transport An anion countertransport mechanism ejects the bicarbonate ions into the interstitial fluid and imports chloride ions into the cell. The hydrogen ions are actively transported into the lumen of the gastric gland. H2CO3 Countertransport Dissociation HCO3– HCO3– + H+ H+ Interstitial fluid Cl– Cl– Cl– 3 Alkaline tide The chloride ions then diffuse across the cell and exit through open chloride channels into the lumen of the gastric gland. Lumen of gastric gland Enters bloodstream

107 24-4 The Stomach Stomachs of newborn infantsProduce enzymes important for digestion of milk Rennin (chymosin) Gastric lipase

108 24-4 The Stomach Pyloric glands Located in pyloric part of stomachProduce mucous secretions Enteroendocrine cells Produce at least seven hormones G cells produce gastrin Stimulates secretion by parietal and chief cells Stimulates contractions of gastric wall D cells release somatostatin Inhibits release of gastrin

109 24-4 The Stomach Chemical digestion in stomachSome digestion of carbohydrates (by salivary amylase) and lipids (by lingual lipase) As stomach contents become more fluid, pH approaches 2.0 Preliminary digestion of proteins by pepsin increases Nutrients are not absorbed in stomach

110 24-4 The Stomach Regulation of gastric activityProduction of acid and enzymes by gastric mucosa can be controlled by CNS Short reflexes of ENS Hormones of digestive tract Three overlapping phases of gastric control Cephalic phase Gastric phase Intestinal phase

111 Figure 24–15 The Regulation of Gastric Activity (Part 1 of 4).CEPHALIC PHASE Food Sight, smell, taste, or thoughts of food Central nervous system Vagus nerve (X) Submucosal plexus Mucous cells Mucus Chief cells Pepsinogen Parietal cells HCl Gastrin KEY Neural stimulation G cells Secretion

112 Figure 24–15 The Regulation of Gastric Activity (Part 2 of 4).GASTRIC PHASE Neural Response Distension Stretch receptors Submucosal and myenteric plexuses Elevated pH Chemoreceptors carried by bloodstream Mucous cells Mucus Chief cells Pepsinogen Mixing waves Parietal cells Gastrin HCI G cells Partly digested peptides KEY Neural stimulation Hormonal stimulation

113 Figure 24–15 The Regulation of Gastric Activity (Part 3 of 4).INTESTINAL PHASE Neural Responses Enterogastric reflex Myenteric plexus carried by bloodstream Chief cells Parietal cells Duodenal stretch and chemoreceptors Peristalsis CCK Presence of lipids and carbohydrates KEY GIP Neural inhibition Secretin Decreased pH Hormonal inhibition

114 24-5 Accessory Digestive OrgansPancreas Lies posterior to stomach Extends from duodenum toward spleen Retroperitoneal Bound to posterior wall of abdominal cavity Wrapped in thin, connective tissue capsule

115 24-5 Accessory Digestive OrgansGross anatomy of pancreas Head Broad; in loop formed by duodenum Body Slender; extends toward spleen Tail Short and rounded Pancreatic duct Delivers secretions of pancreas to duodenum

116 24-5 Accessory Digestive OrgansHistology of pancreas Lobules separated by connective tissue partitions Ducts in lobules branch repeatedly and end in blind pockets (pancreatic acini) Acini are lined with simple cuboidal epithelium Pancreatic islets Endocrine tissues of pancreas Scattered among pancreatic acini Account for about 1 percent of pancreatic cells

117 Figure 24–16a Anatomy of the Pancreas.Accessory pancreatic duct Bile duct Pancreatic duct Lobules Tail of pancreas Body of pancreas Body of pancreas Head of pancreas Head of pancreas Duodenal papilla Duodenum Duodenum a The gross anatomy of the pancreas. The head of the pancreas is tucked into a C-shaped curve of the duodenum that begins at the pylorus of the stomach.

118 Figure 24–16b Anatomy of the Pancreas.Pancreatic duct Connective tissue septum Exocrine cells in pancreatic acini Endocrine cells in pancreatic islet Diagram of the cellular organization of the pancreas. b

119 Figure 24–16c Anatomy of the Pancreas.Duct Pancreatic islet (endocrine) Pancreatic acini (exocrine) Pancreas LM × 75 Light micrograph of the cellular organization of the pancreas. c

120 24-5 Accessory Digestive OrgansEndocrine cells of pancreatic islets Secrete insulin and glucagon into bloodstream Exocrine cells Acinar cells and epithelial cells of duct system Secrete alkaline pancreatic juice into small intestine About 1000 mL per day Contains digestive enzymes, water, and ions Controlled by hormones from duodenum

121 24-5 Accessory Digestive OrgansPancreatic enzymes Pancreatic alpha-amylase Pancreatic lipase Nucleases Proteolytic enzymes

122 24-5 Accessory Digestive OrgansPancreatic alpha-amylase A carbohydrase Breaks down certain starches Almost identical to salivary amylase Pancreatic lipase Breaks down certain complex lipids Releases products (e.g., fatty acids) that are easily absorbed

123 24-5 Accessory Digestive OrgansNucleases Break down RNA or DNA Proteolytic enzymes Break apart proteins Proteases break apart large protein complexes Peptidases break small peptide chains into individual amino acids 70 percent of all pancreatic enzyme production Secreted as inactive proenzymes Activated after reaching small intestine

124 24-5 Accessory Digestive OrgansProenzymes secreted by pancreas Trypsinogen Converted to active trypsin in duodenum Chymotrypsinogen Converted to active chymotrypsin by trypsin Procarboxypeptidase Converted to active carboxypeptidase by trypsin Proelastase Converted to active elastase by trypsin

125 24-5 Accessory Digestive OrgansLiver Largest visceral organ (1.5 kg) Lies in right hypochondriac and epigastric regions May extend into left hypochondriac and umbilical regions Performs essential metabolic and synthetic functions

126 24-5 Accessory Digestive OrgansGross anatomy of liver Wrapped in tough, fibrous capsule Covered with visceral peritoneum Divided into Left and right lobes Caudate lobe Quadrate lobe Falciform ligament Marks division between left and right lobes Thickening in posterior margin is round ligament

127 24-5 Accessory Digestive OrgansGross anatomy of liver Blood vessels converge at porta hepatis Nearly one-third of blood supply is arterial blood from hepatic artery proper Remaining two-thirds is venous blood from hepatic portal vein Hepatocytes Liver cells Adjust circulating levels of nutrients through selective absorption and secretion

128 Figure 24–17a Gross Anatomy of the Liver.Sternum Falciform ligament Left lobe of liver Porta hepatis Stomach Right lobe of liver Lesser omentum Caudate lobe of liver Inferior vena cava Aorta Pleural cavity Spleen Cut edge of diaphragm Peritoneal cavity a A transverse section through the superior abdomen (diagrammatic view)

129 Figure 24–17b Gross Anatomy of the Liver.Coronary ligament Right lobe Right lobe Left lobe Left lobe Falciform ligament Round ligament Gallbladder The anterior surface of the liver b

130 Figure 24–17c Gross Anatomy of the Liver.Left hepatic vein Inferior vena cava Coronary ligament Lobes of Liver Porta Hepatis Left lobe Bile duct Caudate lobe Hepatic portal vein Right lobe Hepatic artery proper Quadrate lobe Gallbladder c The posterior surface of the liver

131 24-5 Accessory Digestive OrgansHistology of liver Each lobe is divided by connective tissue Into approximately 100,000 lobules Lobules are basic functional units of liver Roughly 1 mm in diameter Hepatocytes form a series of irregular plates arranged like wheel spokes Sinusoids between plates empty into central vein Many stellate macrophages (Kupffer cells) in lining of sinusoids

132 Figure 24–18a Histology of the Liver.1 mm Interlobular septum Interlobular bile duct Interlobular vein Bile ductules Portal triad a A diagram of liver structure, showing relationships among lobules

133 Figure 24–18b Histology of the Liver.Central vein Hepatocytes Sinusoids Stellate macrophages Bile canaliculi Portal Triad Interlobular bile duct Interlobular vein Interlobular artery A single liver lobule and its cellular components b

134 Figure 24–18c Histology of the Liver.Portal Triad Interlobular bile duct Interlobular vein (containing blood) Interlobular artery Hepatocytes Sinusoids Portal area LM × 320 A micrograph showing the vessels and ducts within a portal triad c

135 24-5 Accessory Digestive OrgansHepatic portal system Liver lobules are hexagonal in cross section Each of six corners has a portal triad containing Interlobular vein Interlobular artery Interlobular bile duct

136 24-5 Accessory Digestive OrgansBile duct system Liver secretes bile Into a network of narrow channels (bile canaliculi) between adjacent liver cells Right and left hepatic ducts Collect bile from all bile ducts of liver lobes Unite to form common hepatic duct From common hepatic duct, bile enters either Bile duct, which empties into duodenal ampulla Cystic duct, which leads to gallbladder

137 24-5 Accessory Digestive OrgansBile duct Formed by union of Cystic duct Common hepatic duct Passes within lesser omentum toward stomach Penetrates wall of duodenum Meets pancreatic duct at duodenal ampulla

138 A portion of the lesser omentum has been cut away.Figure 24–19a Anatomy and Physiology of the Gallbladder and Bile Ducts. Round ligament Left hepatic duct Right hepatic duct Left hepatic artery Cystic duct Common hepatic duct Gallbladder Fundus Cut edge of lesser omentum Body Bile duct Neck Hepatic portal vein Common hepatic artery Liver Liver Duodenum Duodenum Right gastric artery Stomach Stomach Pancreas Pancreas a A view of the inferior surface of the liver, showing the position of the gallbladder and ducts that transport bile from the liver to the gallbladder and duodenum. A portion of the lesser omentum has been cut away.

139 Pancreatic duct Bile ductFigure 24–19b Anatomy and Physiology of the Gallbladder and Bile Ducts. Pancreatic duct Bile duct Hepatopancreatic sphincter Duodenal ampulla Duodenal papilla Pancreas Pancreas Intestinal lumen A sectional view through a portion of the duodenal wall, showing the duodenal ampulla and related structures. b

140 A radiograph (cholangiogram, anterior-posterior view) Figure 24–19c Anatomy and Physiology of the Gallbladder and Bile Ducts. Left hepatic duct Right hepatic duct Common hepatic duct Gallbladder Neck Body Fundus Duodenum Bile duct A radiograph (cholangiogram, anterior-posterior view) of the hepatic ducts, gallbladder, and bile duct. c

141 d 1 The liver secretes bile continuously— about 1liter per day. 2Figure 24–19d Anatomy and Physiology of the Gallbladder and Bile Ducts. 1 The liver secretes bile continuously— about 1liter per day. 2 Bile becomes more concentrated the longer it remains in the gallbladder. Liver Duodenum 3 CCK The release of CCK by the duodenum triggers dilation of the hepatopancreatic sphincter and contraction of the gallbladder. This ejects bile into the duodenum through the duodenal ampulla. 4 In the lumen of the digestive tract, bile salts break the lipid droplets apart by emulsification. Lipid droplet Physiology of the gallbladder. d

142 24-5 Accessory Digestive OrgansPhysiology of liver Liver has over 200 functions in three categories Metabolic regulation Hematological regulation Bile production

143 24-5 Accessory Digestive OrgansAll blood leaving absorptive surfaces of digestive tract enters hepatic portal system Flows into liver Liver cells extract nutrients or toxins from blood Before blood reaches systemic circulation through hepatic veins Liver removes and stores excess nutrients Corrects nutrient deficiencies by mobilizing stored reserves or performing synthetic activities

144 24-5 Accessory Digestive OrgansRegulatory activities of liver affect Carbohydrate metabolism Lipid metabolism Amino acid metabolism Waste removal Vitamin storage Mineral storage Drug inactivation

145 24-5 Accessory Digestive OrgansLiver receives about 25 percent of cardiac output Largest blood reservoir in body Hematological regulation by liver involves Phagocytosis and antigen presentation Synthesis of plasma proteins Removal of circulating hormones Removal of antibodies Removal or storage of toxins

146 24-5 Accessory Digestive OrgansProduction and functions of bile Bile salts in bile break lipid droplets apart (emulsification) in duodenum Creates tiny emulsion droplets coated with bile salts Increases surface area exposed to enzymes Necessary because mechanical digestion in stomach creates large droplets of lipids Pancreatic lipase can interact only at surface Enterohepatic circulation Cycling of bile salts between liver and small intestine

147 24-5 Accessory Digestive OrgansGallbladder Hollow, pear-shaped muscular sac Stores and concentrates bile prior to secretion into small intestine Located in fossa in posterior surface of liver’s right lobe

148 24-5 Accessory Digestive OrgansRegions of gallbladder Fundus Body Neck Cystic duct Extends from gallbladder Unites with common hepatic duct to form bile duct Bile duct joins pancreatic duct before emptying into duodenal ampulla Opens into duodenum at duodenal papilla

149 24-5 Accessory Digestive OrgansGallbladder releases bile into duodenum Only when stimulated by cholecystokinin (CCK) Without CCK Hepatopancreatic sphincter encircling lumen of bile duct remains closed Bile exiting liver in common hepatic duct enters cystic duct and is stored in gallbladder When chyme enters duodenum, CCK is released Hepatopancreatic sphincter relaxes Gallbladder contracts

150 24-5 Accessory Digestive OrgansPhysiology of gallbladder Full gallbladder contains 40–70 mL bile Bile composition gradually changes in gallbladder Water is absorbed Bile salts and other components become increasingly concentrated

151 24-6 The Small Intestine Small intestine Long, muscular tube whereChemical digestion is completed 90 percent of nutrient absorption occurs Consists of three segments Duodenum Jejunum Ileum

152 24-6 The Small Intestine DuodenumSegment of small intestine closest to stomach 25 cm long “Mixing bowl” that receives chyme from stomach and digestive secretions from pancreas and liver Jejunum Middle segment of small intestine 2.5 meters long Site of most chemical digestion and nutrient absorption

153 24-6 The Small Intestine Ileum Final segment of small intestine3.5 meters long Ends at ileocecal valve Sphincter that controls flow of material from ileum into cecum of large intestine

154 Figure 24–20a Gross Anatomy and Segments of the Intestine.Small Intestine Duodenum Jejunum Ileum Large intestine Rectum a The positions of the duodenum, jejunum, and ileum in the abdominopelvic cavity

155 Figure 24–24b Anatomy of the Large Intestine.Ileocecal valve Cecum (cut open) Appendix The cecum and appendix b

156 24-6 The Small Intestine Histology of small intestine Circular foldsTransverse folds in intestinal lining Permanent features that do not disappear when small intestine fills Intestinal villi Fingerlike projections in mucosa of small intestine Covered by simple columnar epithelium Carpeted with microvilli that form brush border

157 Figure 24–20b Gross Anatomy and Segments of the Intestine.Circular folds Gross anatomy of the jejunum A representative view of the jejunum b

158 24-6 The Small Intestine Histology of small intestine LactealLymphatic vessel in each villus Transports chylomicrons that are too large to enter blood capillaries Intestinal glands (intestinal crypts) Extend deep into lamina propria Stem cells near base produce new epithelial cells Paneth cells at base function in innate immunity Contain enteroendocrine cells

159 Figure 24–21a Histology of the Intestinal Wall.Segment of the small intestine a

160 Figure 24–21b Histology of the Intestinal Wall.Villi Intestinal gland Lymphoid nodule Lamina propria Lacteal Layers of the Small Intestine Mucosa Muscularis mucosae Lymphatic vessel Submucosal plexus Submucosa Circular layer of smooth muscle Muscular layer Myenteric plexus Serosa Longitudinal layer of smooth muscle Submucosal artery and vein b The organization of the intestinal wall

161 Figure 24–21c Histology of the Intestinal Wall.Epithelial cell Stem cell Paneth cell Cellular components of an intestinal gland c

162 Figure 24–21d Histology of the Intestinal Wall.Columnar epithelial cell Goblet cell Lacteal Nerve Capillary network Lamina propria Lymphatic vessel Smooth muscle cell Arteriole Venule d Internal structures in a single villus, showing the capillary and lymphatic supplies

163 Figure 24–21e Histology of the Intestinal Wall.Capillaries Goblet cells Lacteal Brush border Tip of villus LM × 250 A villus in sectional view e

164 24-6 The Small Intestine Duodenal submucosal glandsProduce copious quantities of mucus When chyme arrives from stomach Mucus protects epithelium from acidity of chyme Contains bicarbonate ions that raise pH

165 24-6 The Small Intestine Physiology of small intestine1.8 liters of intestinal juice enters intestinal lumen each day Intestinal juice Moistens chyme Assists in buffering acids Keeps digestive enzymes and products of digestion in solution

166 24-6 The Small Intestine Mucosa of small intestine produces few enzymes involved in chemical digestion Brush border enzymes Integral membrane proteins on intestinal microvilli Break down materials in contact with brush border Enteropeptidase A brush border enzyme Activates pancreatic trypsinogen

167 24-6 The Small Intestine Intestinal motilityAfter chyme arrives in duodenum Weak peristaltic contractions move it slowly toward jejunum Contractions are myenteric reflexes Not under CNS control Parasympathetic stimulation accelerates local peristalsis and segmentation

168 24-6 The Small Intestine Reflexes of small intestineGastroenteric reflex Stimulates motility and secretion along entire small intestine Gastroileal reflex Triggers opening of ileocecal valve Allows materials to pass from small intestine into large intestine Opposite effect from that of enterogastric reflex Which causes constriction of pyloric sphincter

169 Figure 24–15 The Regulation of Gastric Activity (Part 4 of 4).CENTRAL REFLEXES Central Gastric Reflexes The gastroenteric reflex stimulates motility and secretion along the entire small intestine. The gastroileal (gas-tro-IL-e-al) reflex triggers the opening of the ileocecal valve, allowing materials to pass from the small intestine into the large intestine. The ileocecal valve controls the passage of materials into the large intestine.

170 24-6 The Small Intestine Neural and hormonal mechanismsCoordinate activities of digestive glands Centered on duodenum Where acids are neutralized and enzymes are added

171 24-6 The Small Intestine Neural mechanisms involving CNSPrepare digestive tract for activity Through parasympathetic innervation Inhibit gastrointestinal activity Through sympathetic innervation Coordinate movement of materials along digestive tract Through reflexes Motor neuron synapses in digestive tract release neurotransmitters

172 24-6 The Small Intestine Intestinal hormonesIntestinal tract secretes peptide hormones with multiple effects In several regions of digestive tract In accessory glandular organs

173 24-6 The Small Intestine Major hormones of duodenum Gastrin SecretinGastric inhibitory peptide (GIP) Cholecystokinin (CCK) Vasoactive intestinal peptide (VIP) Enterocrinin

174 24-6 The Small Intestine Gastrin Secreted by G cells in duodenumWhen exposed to incompletely digested proteins Promotes increased stomach motility Stimulates production of acids and enzymes Secretin Released when chyme arrives in duodenum Increases secretion of buffers by pancreas and bile by liver Reduces gastric motility and secretory rates

175 24-6 The Small Intestine Gastric inhibitory peptide (GIP)Secreted when fats and carbohydrates enter small intestine Cholecystokinin (CCK) Secreted when chyme arrives in duodenum Accelerates pancreatic production and secretion of digestive enzymes Relaxes hepatopancreatic sphincter and contracts gallbladder Ejecting bile and pancreatic juice into duodenum

176 24-6 The Small Intestine Vasoactive intestinal peptide (VIP)Stimulates secretion of intestinal glands Dilates regional capillaries Inhibits acid production in stomach Enterocrinin Released when chyme enters duodenum Stimulates alkaline mucus production by submucosal glands

177 Figure 24–23 The Secretion and Effects of Major Digestive Tract Hormones.Ingested food Hormone Action Food in stomach Acid production by parietal cells KEY Stimulates Inhibits Gastrin Stimulation of gastric motility; mixing waves increase in intensity Release of insulin from pancreas GIP Pancreas Release of pancreatic enzymes and buffers Chyme in duodenum Secretin and CCK Bile secretion and ejection of bile from gallbladder Dilation of intestinal capillaries VIP facilitates facilitates facilitates NUTRIENT UTILIZATION BY ALL TISSUES Material arrives in jejunum Nutrient absorption

178 24-6 The Small Intestine Absorption in small intestineMovements of mucosa increase absorptive effectiveness Stir and mix intestinal contents Quickly eliminate local differences in nutrient concentration

179 24-7 The Large Intestine Large intestine (large bowel)Horseshoe shaped Extends from end of ileum to anus Lies inferior to stomach and liver Frames the small intestine About 1.5 meters long and 7.5 cm wide

180 24-7 The Large Intestine Parts of large intestine CecumPouchlike first portion Colon Largest portion Rectum The last 15 cm and end of digestive tract

181 24-7 The Large Intestine Cecum Expanded pouchReceives and stores materials arriving from ileum Begins compaction Appendix (vermiform appendix) Slender, hollow structure about 9 cm long Attached to posteromedial surface of cecum Dominated by lymphoid nodules Meso-appendix (small mesentery) connects appendix to ileum and cecum

182 24-7 The Large Intestine ColonLarger diameter and thinner wall than small intestine Haustra Pouches in wall of colon Permit expansion and elongation

183 24-7 The Large Intestine Teniae coliThree longitudinal bands of smooth muscle Run along outer surfaces of colon, deep to serosa Similar to outer layer of muscular layer Muscle tone in teniae coli creates haustra Omental appendices Numerous teardrop-shaped sacs of fat in serosa of colon

184 24-7 The Large Intestine Four regions of colon Ascending colonTransverse colon Descending colon Sigmoid colon

185 24-7 The Large Intestine Ascending colonBegins at superior border of cecum Ascends along right lateral and posterior wall of peritoneal cavity To inferior surface of liver Bends sharply to the left at right colic flexure (hepatic flexure)

186 24-7 The Large Intestine Transverse colonCrosses abdomen from right to left Turns at left colic flexure (splenic flexure) Supported by transverse mesocolon Separated from anterior abdominal wall by greater omentum Descending colon Proceeds inferiorly along left side to iliac fossa (inner surface of left ilium) Retroperitoneal, firmly attached to abdominal wall

187 24-7 The Large Intestine Sigmoid colonS-shaped segment, about 15 cm long Lies posterior to urinary bladder Suspended from sigmoid mesocolon Empties into rectum

188 24-7 The Large Intestine Large intestineReceives blood from branches of superior mesenteric and inferior mesenteric arteries Venous blood is collected by superior mesenteric and inferior mesenteric veins

189 Figure 24–24a Anatomy of the Large Intestine (Part 2 of 3).Splenic vein Superior mesenteric artery Inferior mesenteric vein Left colic (splenic) flexure Greater omentum (cut) Descending colon Left colic vein Inferior mesenteric artery Left colic artery Haustra The gross anatomy and regions of the large intestine a

190 24-7 The Large Intestine Rectum Forms last 15 cm of digestive tractExpandable organ for temporary storage of feces Anal canal Last portion of rectum Contains small longitudinal folds (anal columns) Anus Exit of anal canal Keratinized epidermis like skin

191 24-7 The Large Intestine Internal anal sphincter Circular muscle layerSmooth muscle cells Not under voluntary control External anal sphincter Encircles distal portion of anal canal Skeletal muscle fibers Under voluntary control

192 Figure 24–24c Anatomy of the Large Intestine.Rectum Rectum Anal canal Anal columns Internal anal sphincter External anal sphincter Anus The rectum and anus c

193 24-7 The Large Intestine Histology of large intestine Lacks villiAbundance of goblet cells Distinctive intestinal glands Deeper than glands of small intestine Dominated by goblet cells Mucus provides lubrication for fecal material Large lymphoid nodules scattered throughout lamina propria and submucosa

194 Figure 24–25a Histology of the Colon.Teniae coli Omental appendices Haustrum Simple columnar epithelium Aggregated lymphoid nodule Layers of the Large Intestine Goblet cells Mucosa Intestinal gland Muscularis mucosae Muscularis mucosae Submucosa Submucosa Muscular layer Circular layer Longitudinal layer (teniae coli) Serosa a Diagrammatic view of the colon wall

195 Figure 24–25b Histology of the Colon.Simple columnar epithelium Goblet cells Intestinal gland Muscularis mucosae Submucosa The colon LM × 110 b Colon histology showing detail of mucosal layer

196 24-7 The Large Intestine Functions of large intestineAbsorption or reabsorption of Water Nutrients (less than 10 percent) Bile salts Organic wastes Vitamins and toxins produced by bacteria Compaction of intestinal contents into feces Storage of fecal material prior to defecation

197 24-7 The Large Intestine MicrobiomeMicrobes (bacteria, fungi, and viruses) that live in and on human body Including those that inhabit large intestine Vitamins Organic molecules Important as cofactors or coenzymes in metabolism Normal bacteria in colon make three vitamins that supplement diet

198 24-7 The Large Intestine Vitamins produced by bacteria in colonVitamin K (fat soluble) Required by liver for synthesizing four clotting factors, including prothrombin Biotin (water soluble) Important in glucose metabolism Vitamin B5 (pantothenic acid; water soluble) Required in manufacture of steroid hormones and some neurotransmitters

199 24-7 The Large Intestine Organic wastesBacteria convert bilirubin to urobilinogens and stercobilinogens Some urobilinogens are absorbed into bloodstream and excreted in urine Urobilinogens and stercobilinogens remaining in colon are converted to urobilins and stercobilins By exposure to oxygen

200 24-7 The Large Intestine Organic wastesBacteria break down peptides in feces and generate Ammonia, as soluble ammonium ions Indole and skatole (nitrogen-containing compounds responsible for odor of feces) Hydrogen sulfide gas that produces “rotten egg” odor Bacteria feed on indigestible carbohydrates Produce flatus (intestinal gas) in large intestine

201 24-7 The Large Intestine Motility of large intestineGastroileal and gastroenteric reflexes Move materials into cecum while you eat Movement from cecum to transverse colon is very slow, allowing hours for water absorption Peristaltic waves move material along length of colon Segmentation movements (haustral churning) mix contents of adjacent haustra

202 24-7 The Large Intestine Motility of large intestineMovement from transverse colon through rest of large intestine Results from powerful peristaltic contractions (mass movements) Stimulus is distension of stomach and duodenum Relayed over intestinal nerve plexuses Distension of rectal wall initiates defecation reflex Involves two positive feedback loops Both triggered by stretch receptors in rectum

203 24-7 The Large Intestine Positive feedback loopsIntrinsic myenteric defecation reflex Short reflex Triggers peristaltic contractions in sigmoid colon and rectum Parasympathetic defecation reflex Long reflex Coordinated by sacral parasympathetic neurons Stimulates mass movements

204 24-7 The Large Intestine Elimination of fecesRequires relaxation of internal and external anal sphincters Reflexes open internal sphincter Somatic nervous system must be activated to consciously open external sphincter Pudendal nerves carry somatic motor commands

205 Figure 24–26 The Defecation Reflex.Voluntary relaxation of the external anal sphincter allows defecation to occur at a convenient time. Spinal cord 3 The long reflex is a spinal reflex coordinated by the sacral parasympathetic system. This reflex stimulates mass movements that push feces toward the rectum from the descending colon and sigmoid colon. It also further relaxes the internal anal sphincter. 1 Feces move into rectum causing distension, stimulating stretch receptors 2 The first loop is a short reflex that triggers a series of peristaltic contractions in the rectum that move feces toward the anus. This reflex is mediated by the myenteric plexus in the sigmid colon and rectum. The internal anal sphincter relaxes. DISTENSION OF RECTUM Stretch receptors Internal anal sphincter External anal sphincter

206 24-8 Chemical Digestion Nutrients A balanced diet containsCarbohydrates Lipids Proteins Vitamins Minerals Water

207 24-8 Chemical Digestion Processing and absorption of nutrientsDigestive system breaks down physical structure of food Then disassembles component molecules Molecules released into bloodstream are absorbed by cells and either Broken down to provide energy for ATP synthesis Used to synthesize carbohydrates, proteins, and lipids

208 24-8 Chemical Digestion Digestive enzymesBreak molecular bonds in large organic molecules Carbohydrates, proteins, lipids, and nucleic acids In a process called hydrolysis Divided into classes by their specific substrates Carbohydrases break bonds between simple sugars Proteases break bonds between amino acids Lipases separate fatty acids from glycerides

209 24-8 Chemical Digestion Digestive enzymes Secreted by Salivary glandsTongue Stomach Pancreas Brush border enzymes Break down digestive fragments further

210 24-8 Chemical Digestion Carbohydrate digestion and absorptionComplex carbohydrates are digested in two steps Salivary amylase and pancreatic alpha-amylase Carbohydrases from salivary glands and pancreas Brush border enzymes of intestinal microvilli Maltase splits bonds between maltose Sucrase breaks apart sucrose Lactase hydrolyzes lactose Insufficient lactase leads to lactose intolerance

211 24-8 Chemical Digestion Absorption of monosaccharidesVia facilitated diffusion and cotransport, which differ in Number of transported substances Concentration gradients ATP requirement

212 Figure 24–27 The Chemical Events of Digestion (Part 1 of 3).REGION and Hormonal Controls CARBOHYDRATES Salivary amylase ORAL CAVITY ESOPHAGUS STOMACH Stimulus: Anticipation or arrival of food Hormone: Gastrin Source: G cells of stomach Disaccharides Trisaccharides Proenzyme released: Pepsinogen by chief cells, activated to pepsin by HCl SMALL INTESTINE Stimulus: Arrival of chyme in duodenum Pancreatic alpha-amylase Hormone: CCK Proenzymes released: Chymotrypsinogen, procar- boxypeptidase, proelastase, trypsinogen. Enteropeptidase activates trypsin, which activates other enzymes. Disaccharides Trisaccharides Enzymes released: Pancreatic amylase, pancreatic lipase, nuclease, enteropeptidase. INTESTINAL MUCOSA Lactase Maltase, sucrase Brush border FACILITATED DIFFUSION AND COTRANSPORT Monosaccharides Cell body FACILITATED DIFFUSION ROUTE TO BLOODSTREAM Capillary Carbohydrates and amino acids are absorbed and transported by intestinal capillaries. Lipids form chylomicrons that diffuse into lacteals and are delivered to the left subclavian vein by the thoracic duct. Monosaccharides

213 24-8 Chemical Digestion Lipid digestion and absorptionInvolves lingual lipase and pancreatic lipase Pancreatic lipase breaks triglycerides into monoglycerides and fatty acids Interact with bile salts to form micelles (lipid–bile salt complexes) New triglycerides are assembled by intestinal cells Join with steroids, phospholipids, vitamins, and proteins to form chylomicrons Most chylomicrons diffuse into intestinal lacteals

214 Figure 24–27 The Chemical Events of Digestion (Part 2 of 3).REGION and Hormonal Controls LIPIDS ORAL CAVITY Lingual lipase ESOPHAGUS STOMACH Stimulus: Anticipation or arrival of food Hormone: Gastrin Source: G cells of stomach Proenzyme released: Pepsinogen by chief cells, activated to pepsin by HCl SMALL INTESTINE Bile salts and pancreatic lipase Stimulus: Arrival of chyme in duodenum Hormone: CCK Proenzymes released: Chymotrypsinogen, procar- boxypeptidase, proelastase, trypsinogen. Enteropeptidase activates trypsin, which activates other enzymes. Monoglycerides, fatty acids in micelles Enzymes released: Pancreatic amylase, pancreatic lipase, nuclease, enteropeptidase. INTESTINAL MUCOSA DIFFUSION Brush border Monoglycerides, fatty acids Cell body Triglycerides Chylomicrons EXOCYTOSIS ROUTE TO BLOODSTREAM Lacteal Carbohydrates and amino acids are absorbed and transported by intestinal capillaries. Lipids form chylomicrons that diffuse into lacteals and are delivered to the left subclavian vein by the thoracic duct. Chylomicrons

215 24-8 Chemical Digestion Protein digestion and absorptionComplex and time consuming Involves mechanical digestion, hydrochloric acid, and proteases Dipeptidases in epithelial surfaces of small intestine Break short peptide chains into individual amino acids

216 Figure 24–27 The Chemical Events of Digestion (Part 3 of 3).REGION and Hormonal Controls PROTEINS ORAL CAVITY ESOPHAGUS STOMACH Pepsin Stimulus: Anticipation or arrival of food Hormone: Gastrin Source: G cells of stomach Polypeptides Proenzyme released: Pepsinogen by chief cells, activated to pepsin by HCl SMALL INTESTINE Trypsin Chymotrypsin Elastase Carboxypeptidase Stimulus: Arrival of chyme in duodenum Hormone: CCK Proenzymes released: Chymotrypsinogen, procar- boxypeptidase, proelastase, trypsinogen. Enteropeptidase activates trypsin, which activates other enzymes. Short peptides, amino acids Enzymes released: Pancreatic amylase, pancreatic lipase, nuclease, enteropeptidase. INTESTINAL MUCOSA Dipeptidases Brush border FACILITATED DIFFUSION AND COTRANSPORT Cell body Amino acids FACILITATED DIFFUSION AND COTRANSPORT ROUTE TO BLOODSTREAM Capillary Carbohydrates and amino acids are absorbed and transported by intestinal capillaries. Lipids form chylomicrons that diffuse into lacteals and are delivered to the left subclavian vein by the thoracic duct. Amino acids

217 24-8 Chemical Digestion Nucleic acid digestion and absorptionNucleic acids are broken down into nucleotides Brush border enzymes digest nucleotides into sugars, phosphates, and nitrogenous bases Absorbed by active transport Water absorption Cells cannot actively absorb or secrete water Movement of water across digestive tract involves passive water flow down osmotic gradients

218 Figure 24–28 Digestive Secretion and Water Reabsorption in the Digestive Tract.Secretions Dietary Input Food and drink 2200 mL Saliva 1500 mL Gastric secretions 1500 mL 5200 mL Liver (bile) 1000 mL Pancreas (pancreatic juice) 1000 mL Water Reabsorption Intestinal secretions 2000 mL 9200 mL Small intestine reabsorbs 8000 mL 1200 mL Colonic mucous secretions 200 mL Colon reabsorbs 1250 mL 1400 mL 150 mL lost in feces

219 24-8 Chemical Digestion Ion absorptionOsmosis does not distinguish among solutes Determined by total concentration of solutes To maintain homeostasis Concentrations of specific ions must be regulated Rate of sodium ion uptake Generally proportional to concentration of Na+ in intestinal contents Increased by aldosterone

220 24-8 Chemical Digestion Ion absorption Calcium ion absorptionInvolves active transport at epithelial surface Rate is increased by calcitriol Potassium ions Increase in concentration as other solutes move out of lumen Diffuse into epithelial cells along concentration gradient

221 24-8 Chemical Digestion Ion absorptionAbsorption of magnesium, iron, and other cations Involves specific carrier proteins Cell must use ATP to transport ions to interstitial fluid Anions (chloride, iodide, bicarbonate, and nitrate) Absorbed by diffusion or carrier-mediated transport Phosphate and sulfate ions Enter epithelial cells only by active transport

222 24-8 Chemical Digestion VitaminsOrganic compounds required in very small quantities Water-soluble vitamins Include B vitamins and vitamin C Fat-soluble vitamins Vitamins A, D, E, and K

223 24-9 Effects of Aging on Digestive SystemAge-related changes Division rate of epithelial stem cells declines Smooth muscle tone decreases Effects of cumulative damage become apparent Cancer rates increase Dehydration is common among the elderly Changes in other systems have direct or indirect effects on the digestive system

224 24-10 Digestive System IntegrationExtensive anatomical and physiological connections to several other systems Nervous Cardiovascular Endocrine Lymphatic Digestive tract is an endocrine organ Produces a variety of hormones Produces neurotransmitters

225 Cardiovascular SystemFigure 24–29 Integration of the DIGESTIVE system with the other body systems presented so far. Integumentary System Nervous System • The Integumentary System provides vitamin D3 needed for the absorption of calcium and phosphorus • The Nervous System regulates movement and secretion with the ANS and ENS; reflexes coordinate passage of materials along tract; control over skeletal muscles regulates ingestion and defecation; hypothalamic centers control hunger, satiation, and feeding • The digestive system provides lipids for storage by adipocytes in hypodermis Skeletal System • The digestive system provides compounds essential for neurotransmitter synthesis • The Skeletal System (axial division and pelvic girdle) supports and protects parts of digestive tract; teeth are used in mechanical processing of food Endocrine System • The Endocrine System produces epinephrine and norepinephrine that stimulate constriction of sphincters and depress digestive activity; hormones coordinate activity along digestive tract • The digestive system absorbs calcium and phosphate ions for use in bone matrix; provides lipids for storage in yellow marrow • The digestive system provides nutrients and substrates to endocrine cells; endocrine cells of pancreas secrete insulin and glucagon; liver produces angiotensinogen Cardiovascular System • The Cardiovascular System distributes hormones of the digestive tract; carries nutrients, water, and ions from sites of absorption; delivers nutrients and toxins to liver Lymphatic System • The Lymphatic System defends against infection and toxins absorbed from the digestive tract; lymphatic vessels carry absorbed lipids to the general circulation • The digestive system absorbs fluid to maintain normal blood volume; absorbs vitamin K; liver excretes heme (as bilirubin), synthe- sizes blood clotting proteins • The digestive system secretes acids and enzymes that provide innate (nonspecific) immunity against pathogens Respiratory System • The Respiratory System can assist in defecation by producing increased thoracic and abdominal pressure through contraction of respiratory muscles Digestive System The digestive system provides organic substrates, vitamins, minerals, electrolytes (inorganic ions), and water required by all cells. It: • The digestive system produces pressure with digestive organs against the diaphragm that can assist in exhalation and limit inhalation • ingests solid and liquid materials into the oral cavity of the digestive tract • mechanically digests solid materials to ease their movement and propels them down the digestive tract Muscular System • chemically digests food into smaller molecules in the digestive tract • The Muscular System protects and supports digestive organs in abdominal cavity; controls entrances and exits of digestive tract • secretes water, acids, enzymes, and buffers into the digestive tract • absorbs small organic molecules (organic substrates), ions, vitamins, and water across the digestive epithelium • The digestive system regulates blood glucose and fatty acid levels and metabolizes lactate from active muscles with the liver • eliminates wastes and indigestible materials from the body by defecation