Fundamentals of Anatomy Physiology Eleventh Edition Chapter 24

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Fundamentals of Anatomy & Physiology Eleventh Edition Chapter 24 The Digestive System Lecture Presentation

Fundamentals of Anatomy & Physiology Eleventh Edition Chapter 24 The Digestive System Lecture Presentation by Deborah A. Hutchinson Seattle University © 2018 Pearson Education, Inc.

An Introduction to the Digestive System § Digestive system – Acquires nutrients from environment

An Introduction to the Digestive System § Digestive system – Acquires nutrients from environment • Used to synthesize essential compounds (anabolism) • Broken down to provide energy to cells (catabolism) 2 © 2018 Pearson Education, Inc.

24 -1 The Digestive System § Digestive system – Digestive tract • Gastrointestinal (GI)

24 -1 The Digestive System § Digestive system – Digestive tract • Gastrointestinal (GI) tract or alimentary canal • Muscular tube • Extends from oral cavity to anus – Accessory organs • Teeth, tongue, and various glandular organs 3 © 2018 Pearson Education, Inc.

Figure 24– 1 Organs of the Digestive System (Part 1 of 2). Major Organs

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 4

Figure 24– 1 Organs of the Digestive System (Part 2 of 2). Accessory Organs

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 5

24 -1 The Digestive System § Integrated processes of digestive system – Ingestion –

24 -1 The Digestive System § Integrated processes of digestive system – Ingestion – Mechanical digestion and propulsion – Chemical digestion – Secretion – Absorption – Defecation 6 © 2018 Pearson Education, Inc.

24 -1 The Digestive System § Ingestion – Occurs when food enters oral cavity

24 -1 The Digestive System § Ingestion – Occurs when food enters oral cavity § Mechanical digestion and propulsion – Crushing and shearing of food – Propelling food along digestive tract 7 © 2018 Pearson Education, Inc.

24 -1 The Digestive System § Chemical digestion – Chemical breakdown of food into

24 -1 The Digestive System § Chemical digestion – Chemical 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 8 © 2018 Pearson Education, Inc.

24 -1 The Digestive System § Absorption – Movement of organic molecules, electrolytes, vitamins,

24 -1 The Digestive System § Absorption – Movement 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 9 © 2018 Pearson Education, Inc.

24 -1 The Digestive System § Lining of digestive tract – Safeguards surrounding tissues

24 -1 The Digestive System § Lining of digestive tract – Safeguards 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 10 © 2018 Pearson Education, Inc.

24 -1 The Digestive System § Peritoneum – Serous membrane lining peritoneal cavity –

24 -1 The Digestive System § Peritoneum – Serous 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 11 © 2018 Pearson Education, Inc.

24 -1 The Digestive System § Peritoneal fluid – Produced by serous membrane lining

24 -1 The Digestive System § Peritoneal fluid – Produced 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 12 © 2018 Pearson Education, Inc.

24 -1 The Digestive System § Mesenteries – Double sheets of peritoneal membrane –

24 -1 The Digestive System § Mesenteries – Double 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 13 © 2018 Pearson Education, Inc.

24 -1 The Digestive System § During embryonic development – Digestive tract and accessory

24 -1 The Digestive System § During embryonic development – Digestive 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 14 © 2018 Pearson Education, Inc.

Figure 24– 2 a The Mesenteries. Neural tube Notochord Mesoderm Coelomic cavity Dorsal mesentery

Figure 24– 2 a The Mesenteries. Neural tube Notochord Mesoderm Coelomic cavity Dorsal mesentery Peritoneal cavity Developing liver Digestive tract 4 weeks Ventral mesentery Parietal peritoneum Digestive tract Visceral peritoneum 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). 15

24 -1 The Digestive System § Lesser omentum – Stabilizes position of stomach –

24 -1 The Digestive System § Lesser omentum – Stabilizes 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 16 © 2018 Pearson Education, Inc.

24 -1 The Digestive System § Dorsal mesentery – Enlarges to form an enormous

24 -1 The Digestive System § Dorsal mesentery – Enlarges 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 17 © 2018 Pearson Education, Inc.

24 -1 The Digestive System § Adipose tissue in greater omentum – Conforms to

24 -1 The Digestive System § Adipose tissue in greater omentum – Conforms 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” 18 © 2018 Pearson Education, Inc.

24 -1 The Digestive System § Mesentery proper – Thick mesenterial sheet – Provides

24 -1 The Digestive System § Mesentery proper – Thick mesenterial sheet – Provides 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 19 © 2018 Pearson Education, Inc.

24 -1 The Digestive System § Mesocolon – Mesentery associated with part of large

24 -1 The Digestive System § Mesocolon – Mesentery 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 20 © 2018 Pearson Education, Inc.

24 -1 The Digestive System § Histology of digestive tract – Major layers of

24 -1 The Digestive System § Histology of digestive tract – Major 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 21 © 2018 Pearson Education, Inc.

24 -1 The Digestive System § Mucosa – Inner lining of digestive tract –

24 -1 The Digestive System § Mucosa – Inner lining of digestive tract – Mucous membrane consisting of • Epithelium, moistened by glandular secretions • Lamina propria of areolar tissue • Muscular muscularis mucosae 22 © 2018 Pearson Education, Inc.

24 -1 The Digestive System § Digestive epithelium – Mucosal epithelium is simple or

24 -1 The Digestive System § Digestive epithelium – Mucosal 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 23 © 2018 Pearson Education, Inc.

24 -1 The Digestive System § Lamina propria – A layer of areolar tissue

24 -1 The Digestive System § Lamina propria – A layer of areolar tissue that contains • Blood vessels • Sensory nerve endings • Lymphatic vessels • Smooth muscle cells • Scattered lymphatic tissue 24 © 2018 Pearson Education, Inc.

24 -1 The Digestive System § Muscularis mucosae – In most areas of digestive

24 -1 The Digestive System § Muscularis mucosae – In 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) 25 © 2018 Pearson Education, Inc.

24 -1 The Digestive System § Submucosa – Layer of dense irregular connective tissue

24 -1 The Digestive System § Submucosa – Layer 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 26 © 2018 Pearson Education, Inc.

24 -1 The Digestive System § Muscular layer – Dominated by smooth muscle cells

24 -1 The Digestive System § Muscular layer – Dominated 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 27 © 2018 Pearson Education, Inc.

24 -1 The Digestive System § Muscular layer – Myenteric plexus • Network of

24 -1 The Digestive System § Muscular layer – Myenteric plexus • Network of parasympathetic ganglia, sensory neurons, interneurons, and sympathetic postganglionic fibers • Between circular and longitudinal muscle layers 28 © 2018 Pearson Education, Inc.

24 -1 The Digestive System § Serosa – Serous membrane covering muscular layer •

24 -1 The Digestive System § Serosa – Serous 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 29 © 2018 Pearson Education, Inc.

24 -1 The Digestive System § Motility of digestive tract – Visceral smooth muscle

24 -1 The Digestive System § Motility of digestive tract – Visceral smooth muscle tissue • Rhythmic cycles of activity • Controlled by pacesetter cells that undergo spontaneous depolarization • Wave of contraction spreads throughout entire muscular sheet 30 © 2018 Pearson Education, Inc.

24 -1 The Digestive System § Peristalsis – Waves of muscular contractions that move

24 -1 The Digestive System § Peristalsis – Waves of muscular contractions that move a bolus along length of digestive tract 1. Circular muscles behind bolus contract • While circular muscles ahead of bolus relax 2. Longitudinal muscles ahead of bolus contract • Shortening adjacent segments 3. Wave of contraction in circular muscle layer • Forces bolus forward 31 © 2018 Pearson Education, Inc.

Figure 24– 4 Peristalsis (Part 4 of 4). 32

Figure 24– 4 Peristalsis (Part 4 of 4). 32

24 -1 The Digestive System § Segmentation – Cycles of contraction that churn and

24 -1 The Digestive System § Segmentation – Cycles 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 33 © 2018 Pearson Education, Inc.

24 -1 The Digestive System § Regulation of digestive functions – Local factors –

24 -1 The Digestive System § Regulation of digestive functions – Local factors – Neural mechanisms – Hormonal mechanisms 34 © 2018 Pearson Education, Inc.

24 -1 The Digestive System § Local factors – p. H, volume, or chemical

24 -1 The Digestive System § Local factors – p. H, 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 35 © 2018 Pearson Education, Inc.

24 -1 The Digestive System § Neural mechanisms – Visceral motor neurons • Control

24 -1 The Digestive System § Neural mechanisms – Visceral motor neurons • Control smooth muscle contraction and glandular secretion • Located in myenteric plexus 36 © 2018 Pearson Education, Inc.

24 -1 The Digestive System § Neural mechanisms – Short reflexes (local reflexes) •

24 -1 The Digestive System § Neural mechanisms – Short 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 37 © 2018 Pearson Education, Inc.

24 -1 The Digestive System § Hormonal mechanisms – Enteroendocrine cells in digestive tract

24 -1 The Digestive System § Hormonal mechanisms – Enteroendocrine 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 38 © 2018 Pearson Education, Inc.

24 -2 The Oral Cavity § Functions of oral cavity – Sensory analysis •

24 -2 The Oral Cavity § Functions of oral cavity – Sensory analysis • Of 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 39 © 2018 Pearson Education, Inc.

24 -2 The Oral Cavity § Oral mucosa – Lining of oral cavity –

24 -2 The Oral Cavity § Oral mucosa – Lining of oral cavity – Stratified 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 40 © 2018 Pearson Education, Inc.

24 -2 The Oral Cavity § Oral vestibule – Space between cheeks (or lips)

24 -2 The Oral Cavity § Oral vestibule – Space between cheeks (or lips) and teeth § Gingivae (gums) – Ridges of oral mucosa – Surround base of each tooth on alveolar processes of maxillae and mandible 41 © 2018 Pearson Education, Inc.

24 -2 The Oral Cavity § Uvula – Dangling process at posterior margin of

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 42 © 2018 Pearson Education, Inc.

Figure 24– 6 a Anatomy of the Oral Cavity. Hard palate Palatoglossal arch Soft

Figure 24– 6 a Anatomy of the Oral Cavity. Hard palate Palatoglossal arch Soft palate Nasal cavity Pharyngeal tonsil Opening of parotid duct Entrance to auditory tube Upper lip Nasopharynx Cheek Uvula Dorsum of tongue Lower lip Palatine tonsil Fauces Palatopharyngeal arch Oropharynx Lingual tonsil Gingiva Oral vestibule Body of tongue Epiglottis Hyoid bone Laryngopharynx Root of tongue Geniohyoid Mylohyoid a A sagittal section of the oral cavity 43

Figure 24– 6 b Anatomy of the Oral Cavity. Frenulum of upper lip Hard

Figure 24– 6 b Anatomy of the Oral Cavity. Frenulum of upper lip Hard palate Soft palate Fauces Uvula Palatoglossal arch Palatopharyngeal arch Palatine tonsil Frenulum of tongue Gingiva Tongue Oral vestibule Frenulum of lower lip Openings of submandibular ducts b An anterior view of the oral cavity 44 44

24 -2 The Oral Cavity § Tongue – Four primary functions • Mechanical digestion

24 -2 The Oral Cavity § Tongue – Four primary functions • Mechanical 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 45 © 2018 Pearson Education, Inc.

24 -2 The Oral Cavity § Tongue – Anterior body – Posterior root –

24 -2 The Oral Cavity § Tongue – Anterior body – Posterior root – Frenulum of tongue • Along inferior midline – Extrinsic tongue muscles • Perform all gross movements – Intrinsic tongue muscles • Smaller • Perform precise movements 46 © 2018 Pearson Education, Inc.

24 -2 The Oral Cavity § Teeth – Assisted by tongue while chewing §

24 -2 The Oral Cavity § Teeth – Assisted by tongue while chewing § Dentin – A 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 47 © 2018 Pearson Education, Inc.

24 -2 The Oral Cavity § Root of tooth – Sits in a bony

24 -2 The Oral Cavity § Root of tooth – Sits 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) 48 © 2018 Pearson Education, Inc.

24 -2 The Oral Cavity § Crown – Exposed portion of tooth – Projects

24 -2 The Oral Cavity § Crown – Exposed portion of tooth – Projects 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 49 © 2018 Pearson Education, Inc.

24 -2 The Oral Cavity § Alveolar processes of maxillae and alveolar part of

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 50 © 2018 Pearson Education, Inc.

Figure 24– 7 b The Teeth. Incisors Canines Premolars (cuspids) (bicuspids) Molars Upper jaw

Figure 24– 7 b The Teeth. Incisors Canines Premolars (cuspids) (bicuspids) Molars Upper jaw Lower jaw b The adult teeth from the right side of the upper and lower jaws. Figure 24– 8 a, b shows a view of the occlusal surfaces. 51

24 -2 The Oral Cavity § Incisor teeth – Blade-shaped – Located at front

24 -2 The Oral Cavity § Incisor teeth – Blade-shaped – Located 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 – Have a single root 52 © 2018 Pearson Education, Inc.

24 -2 The Oral Cavity § Premolar teeth (bicuspids) – Flattened crowns – Two

24 -2 The Oral Cavity § Premolar teeth (bicuspids) – Flattened crowns – Two 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 53 © 2018 Pearson Education, Inc.

24 -2 The Oral Cavity § Sets of teeth – During development, two sets

24 -2 The Oral Cavity § Sets of teeth – During development, two sets of teeth form • Deciduous teeth • Permanent teeth § Deciduous 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 54 © 2018 Pearson Education, Inc.

Figure 24– 8 a Deciduous and Permanent Dentitions. Central incisors (7. 5 mo) Lateral

Figure 24– 8 a Deciduous and Permanent Dentitions. Central incisors (7. 5 mo) Lateral incisor (9 mo) Canine (18 mo) Deciduous 1 st molar (14 mo) Deciduous 2 nd molar (20 mo) Deciduous 1 st 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 55

24 -2 The Oral Cavity § Permanent teeth – Replace deciduous teeth by eruption

24 -2 The Oral Cavity § Permanent teeth – Replace 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 56 © 2018 Pearson Education, Inc.

24 -2 The Oral Cavity § Salivary glands – Three major pairs secrete into

24 -2 The Oral Cavity § Salivary glands – Three 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 57 © 2018 Pearson Education, Inc.

24 -2 The Oral Cavity § Parotid glands – Inferior to zygomatic arch –

24 -2 The Oral Cavity § Parotid glands – Inferior to zygomatic arch – Produce serous secretion • Containing salivary amylase to break down starches – Each is drained by parotid duct • Empties into vestibule at second upper molar 58 © 2018 Pearson Education, Inc.

24 -2 The Oral Cavity § Sublingual glands – Covered by mucous membrane of

24 -2 The Oral Cavity § Sublingual glands – Covered 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 59 © 2018 Pearson Education, Inc.

24 -2 The Oral Cavity § Submandibular glands – Lie within mandibular groove –

24 -2 The Oral Cavity § Submandibular glands – Lie within mandibular groove – Secrete buffers, glycoproteins (mucins), and salivary amylase – Submandibular ducts • Open on each side of frenulum of tongue immediately posterior to teeth 60 © 2018 Pearson Education, Inc.

Figure 24– 9 a Anatomy of the Salivary Glands. Parotid duct Openings of sublingual

Figure 24– 9 a Anatomy of the Salivary Glands. Parotid duct Openings of sublingual ducts Frenulum of tongue Opening of left submandibular duct Major Salivary Glands Parotid gland Sublingual 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. 61

24 -2 The Oral Cavity § Saliva – Salivary glands produce 1. 0– 1.

24 -2 The Oral Cavity § Saliva – Salivary 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 62 © 2018 Pearson Education, Inc.

24 -2 The Oral Cavity § Functions of saliva – Cleaning oral surfaces –

24 -2 The Oral Cavity § Functions of saliva – Cleaning oral surfaces – Moistening and lubricating food – Keeping p. H 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 63 © 2018 Pearson Education, Inc.

24 -2 The Oral Cavity § Regulation of salivary secretions – Salivary glands have

24 -2 The Oral Cavity § Regulation of salivary secretions – Salivary 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 64 © 2018 Pearson Education, Inc.

24 -2 The Oral Cavity § Mastication (chewing) – Food is forced from oral

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 65 © 2018 Pearson Education, Inc.

24 -3 The Pharynx and Esophagus § Pharynx (throat) – Common passageway for food,

24 -3 The Pharynx and Esophagus § Pharynx (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 66 © 2018 Pearson Education, Inc.

24 -3 The Pharynx and Esophagus § Esophagus – A hollow muscular tube –

24 -3 The Pharynx and Esophagus § Esophagus – A 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 67 © 2018 Pearson Education, Inc.

24 -3 The Pharynx and Esophagus § Resting muscle tone in circular muscle layer

24 -3 The Pharynx and Esophagus § Resting 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 68 © 2018 Pearson Education, Inc.

24 -3 The Pharynx and Esophagus § Histology of esophagus – Mucosa contains nonkeratinized

24 -3 The Pharynx and Esophagus § Histology 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 69 © 2018 Pearson Education, Inc.

24 -3 The Pharynx and Esophagus § Deglutition (swallowing) – Can be initiated voluntarily,

24 -3 The Pharynx and Esophagus § Deglutition (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 70 © 2018 Pearson Education, Inc.

Figure 24– 11 The Process of Deglutition (Swallowing) (Part 1 of 4). 1 Buccal

Figure 24– 11 The Process of Deglutition (Swallowing) (Part 1 of 4). 1 Buccal Phase Hard palate Soft palate Bolus Tongue Oropharynx Epiglottis Trachea 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. 71

Figure 24– 11 The Process of Deglutition (Swallowing) (Part 2 of 4). 2 Pharyngeal

Figure 24– 11 The Process of Deglutition (Swallowing) (Part 2 of 4). 2 Pharyngeal Phase Uvula Bolus Epiglottis Larynx Tongue 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. 72

Figure 24– 11 The Process of Deglutition (Swallowing) (Part 3 of 4). 3 Esophageal

Figure 24– 11 The Process of Deglutition (Swallowing) (Part 3 of 4). 3 Esophageal Phase Peristalsis Trachea 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. Esophagus 73

Figure 24– 11 The Process of Deglutition (Swallowing) (Part 4 of 4). 4 Bolus

Figure 24– 11 The Process of Deglutition (Swallowing) (Part 4 of 4). 4 Bolus Enters Stomach Thoracic cavity The approach of the bolus triggers the opening of the lower esophageal sphincter. The bolus then continues into the stomach. Lower esophageal sphincter Stomach 74

24 -4 The Stomach § Major functions of stomach – Temporary storage of ingested

24 -4 The Stomach § Major functions of stomach – Temporary 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 75 © 2018 Pearson Education, Inc.

24 -4 The Stomach § Gross anatomy of stomach – Shaped like an expanded

24 -4 The Stomach § Gross anatomy of stomach – Shaped like an expanded J • Short 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 T 7 and L 3 76 © 2018 Pearson Education, Inc.

24 -4 The Stomach § Regions of stomach – Cardia – Fundus – Body

24 -4 The Stomach § Regions of stomach – Cardia – Fundus – Body – Pyloric part 77 © 2018 Pearson Education, Inc.

24 -4 The Stomach § Cardia – Superior, medial portion of stomach – Abundant

24 -4 The Stomach § Cardia – Superior, medial portion of stomach – Abundant 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 78 © 2018 Pearson Education, Inc.

24 -4 The Stomach § Pyloric part – Between body and duodenum – Shape

24 -4 The Stomach § Pyloric part – Between body and duodenum – Shape 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 79 © 2018 Pearson Education, Inc.

Figure 24– 12 a Gross Anatomy of the Stomach. Esophagus Diaphragm Liver, right lobe

Figure 24– 12 a Gross Anatomy of the Stomach. Esophagus Diaphragm Liver, right lobe Left gastric artery Vagus nerve (X) Liver, left lobe Lesser curvature Common hepatic artery Fundus Cardia Gallbladder Bile duct Body of stomach Spleen Greater curvature with greater omentum attached Pyloric sphincter Pyloric part Greater omentum a The position and external appearance of the stomach, showing superficial landmarks 80 80

Figure 24– 12 b Gross Anatomy of the Stomach. Fundus Esophagus Anterior surface Cardia

Figure 24– 12 b Gross Anatomy of the Stomach. Fundus Esophagus Anterior surface Cardia Longitudinal muscle layer Circular muscle layer Pyloric sphincter Lesser curvature (medial surface) Left gastro-epiploic vessels Body Oblique muscle layer overlying mucosa Duodenum Pyloric orifice Pyloric part Pylorus Rugae Greater curvature (lateral surface) Pyloric canal Pyloric antrum b The structure of the stomach wall 81

24 -4 The Stomach § Rugae – Prominent folds in mucosa of empty stomach

24 -4 The Stomach § Rugae – Prominent folds in mucosa of empty stomach – Flatten 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 82 © 2018 Pearson Education, Inc.

24 -4 The Stomach § Histology of stomach – Simple columnar epithelium lines all

24 -4 The Stomach § Histology of stomach – Simple 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 83 © 2018 Pearson Education, Inc.

24 -4 The Stomach § Gastric glands – In fundus and body of stomach

24 -4 The Stomach § Gastric glands – In fundus and body of stomach • Extend deep into underlying lamina propria – Each gastric pit communicates with several gastric glands • Parietal cells • Chief cells – Secrete about 1500 m. L of gastric juice each day 84 © 2018 Pearson Education, Inc.

Figure 24– 13 a Histology of the Stomach Lining. Esophagus Diaphragm Stomach Greater omentum

Figure 24– 13 a 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 85

24 -4 The Stomach § Parietal cells – Common along proximal portions of gastric

24 -4 The Stomach § Parietal cells – Common along proximal portions of gastric glands – Secrete intrinsic factor • Glycoprotein that helps absorb vitamin B 12 – 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 86 © 2018 Pearson Education, Inc.

24 -4 The Stomach § Stomachs of newborn infants – Produce enzymes important for

24 -4 The Stomach § Stomachs of newborn infants – Produce enzymes important for digestion of milk • Rennin (chymosin) • Gastric lipase 87 © 2018 Pearson Education, Inc.

24 -4 The Stomach § Pyloric glands – Located in pyloric part of stomach

24 -4 The Stomach § Pyloric glands – Located in pyloric part of stomach – Produce 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 88 © 2018 Pearson Education, Inc.

24 -4 The Stomach § Chemical digestion in stomach – Some digestion of carbohydrates

24 -4 The Stomach § Chemical digestion in stomach – Some digestion of carbohydrates (by salivary amylase) and lipids (by lingual lipase) – As stomach contents become more fluid, • p. H approaches 2. 0 • Preliminary digestion of proteins by pepsin increases – Nutrients are not absorbed in stomach 89 © 2018 Pearson Education, Inc.

24 -4 The Stomach § Regulation of gastric activity – Production of acid and

24 -4 The Stomach § Regulation of gastric activity – Production 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 90 © 2018 Pearson Education, Inc.

Figure 24– 15 The Regulation of Gastric Activity (Part 1 of 4). 1 CEPHALIC

Figure 24– 15 The Regulation of Gastric Activity (Part 1 of 4). 1 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 KEY Gastrin G cells Neural stimulation Secretion 91

Figure 24– 15 The Regulation of Gastric Activity (Part 2 of 4). 2 GASTRIC

Figure 24– 15 The Regulation of Gastric Activity (Part 2 of 4). 2 GASTRIC PHASE Neural Response Submucosal and myenteric plexuses Distension Elevated p. H carried by bloodstream Gastrin Mucous cells Chief cells Parietal cells G cells Stretch receptors Chemoreceptors Mucus Pepsinogen HCI Partly digested peptides Mixing waves KEY Neural stimulation Hormonal stimulation 92

Figure 24– 15 The Regulation of Gastric Activity (Part 3 of 4). 3 INTESTINAL

Figure 24– 15 The Regulation of Gastric Activity (Part 3 of 4). 3 INTESTINAL PHASE Neural Responses Enterogastric reflex Myenteric plexus carried by bloodstream Duodenal stretch and chemoreceptors CCK GIP Presence of lipids and carbohydrates Secretin Decreased p. H Chief cells Parietal cells Peristalsis KEY Neural inhibition Hormonal inhibition 93

24 -5 Accessory Digestive Organs § Pancreas – Lies posterior to stomach – Extends

24 -5 Accessory Digestive Organs § Pancreas – Lies posterior to stomach – Extends from duodenum toward spleen – Retroperitoneal • Bound to posterior wall of abdominal cavity – Wrapped in thin, connective tissue capsule 94 © 2018 Pearson Education, Inc.

24 -5 Accessory Digestive Organs § Gross anatomy of pancreas – Head • Broad;

24 -5 Accessory Digestive Organs § Gross 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 95 © 2018 Pearson Education, Inc.

24 -5 Accessory Digestive Organs § Histology of pancreas – Lobules separated by connective

24 -5 Accessory Digestive Organs § Histology 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 96 © 2018 Pearson Education, Inc.

Figure 24– 16 a Anatomy of the Pancreas. Accessory pancreatic duct Bile duct Pancreatic

Figure 24– 16 a Anatomy of the Pancreas. Accessory pancreatic duct Bile duct Pancreatic duct Lobules Tail of pancreas Body of pancreas Head of pancreas Duodenal papilla 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. 97

24 -5 Accessory Digestive Organs § Endocrine cells of pancreatic islets – Secrete insulin

24 -5 Accessory Digestive Organs § Endocrine 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 m. L per day • Contains digestive enzymes, water, and ions – Controlled by hormones from duodenum 98 © 2018 Pearson Education, Inc.

24 -5 Accessory Digestive Organs § Pancreatic enzymes – Pancreatic alpha-amylase – Pancreatic lipase

24 -5 Accessory Digestive Organs § Pancreatic enzymes – Pancreatic alpha-amylase – Pancreatic lipase – Nucleases – Proteolytic enzymes 99 © 2018 Pearson Education, Inc.

24 -5 Accessory Digestive Organs § Pancreatic alpha-amylase – A carbohydrase – Breaks down

24 -5 Accessory Digestive Organs § Pancreatic 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 100 © 2018 Pearson Education, Inc.

24 -5 Accessory Digestive Organs § Nucleases – Break down RNA or DNA §

24 -5 Accessory Digestive Organs § Nucleases – 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 101 © 2018 Pearson Education, Inc.

24 -5 Accessory Digestive Organs § Proenzymes secreted by pancreas – Trypsinogen • Converted

24 -5 Accessory Digestive Organs § Proenzymes 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 102 © 2018 Pearson Education, Inc.

24 -5 Accessory Digestive Organs § Liver – Largest visceral organ (1. 5 kg)

24 -5 Accessory Digestive Organs § Liver – 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 103 © 2018 Pearson Education, Inc.

24 -5 Accessory Digestive Organs § Gross anatomy of liver – Wrapped in tough,

24 -5 Accessory Digestive Organs § Gross 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 104 © 2018 Pearson Education, Inc.

24 -5 Accessory Digestive Organs § Gross anatomy of liver – Blood vessels converge

24 -5 Accessory Digestive Organs § Gross 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 105 © 2018 Pearson Education, Inc.

Figure 24– 17 a Gross Anatomy of the Liver Falciform ligament Sternum Porta hepatis

Figure 24– 17 a Gross Anatomy of the Liver Falciform ligament Sternum Porta hepatis Left lobe of liver Right lobe of liver Stomach Caudate lobe of liver Inferior vena cava Pleural cavity Cut edge of diaphragm Lesser omentum Aorta Spleen Peritoneal cavity a A transverse section through the superior abdomen (diagrammatic view) 106

Figure 24– 17 b Gross Anatomy of the Liver. Coronary ligament Right lobe Left

Figure 24– 17 b Gross Anatomy of the Liver. Coronary ligament Right lobe Left lobe Falciform Round ligament Gallbladder b The anterior surface of the liver 107

24 -5 Accessory Digestive Organs § Histology of liver – Each lobe is divided

24 -5 Accessory Digestive Organs § Histology 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 108 © 2018 Pearson Education, Inc.

24 -5 Accessory Digestive Organs § Hepatic portal system – Liver lobules are hexagonal

24 -5 Accessory Digestive Organs § Hepatic 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 109 © 2018 Pearson Education, Inc.

24 -5 Accessory Digestive Organs § Bile duct system – Liver secretes bile •

24 -5 Accessory Digestive Organs § Bile 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 110 © 2018 Pearson Education, Inc.

24 -5 Accessory Digestive Organs § Bile duct – Formed by union of •

24 -5 Accessory Digestive Organs § Bile 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 111 © 2018 Pearson Education, Inc.

Figure 24– 19 a Anatomy and Physiology of the Gallbladder and Bile Ducts. Round

Figure 24– 19 a 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 Duodenum Right gastric artery Stomach 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. 112

24 -5 Accessory Digestive Organs § Physiology of liver – Liver has over 200

24 -5 Accessory Digestive Organs § Physiology of liver – Liver has over 200 functions in three categories • Metabolic regulation • Hematological regulation • Bile production 113 © 2018 Pearson Education, Inc.

24 -5 Accessory Digestive Organs § All blood leaving absorptive surfaces of digestive tract

24 -5 Accessory Digestive Organs § All 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 114 © 2018 Pearson Education, Inc.

24 -5 Accessory Digestive Organs § Regulatory activities of liver affect – Carbohydrate metabolism

24 -5 Accessory Digestive Organs § Regulatory activities of liver affect – Carbohydrate metabolism – Lipid metabolism – Amino acid metabolism – Waste removal – Vitamin storage – Mineral storage – Drug inactivation 115 © 2018 Pearson Education, Inc.

24 -5 Accessory Digestive Organs § Liver receives about 25 percent of cardiac output

24 -5 Accessory Digestive Organs § Liver 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 116 © 2018 Pearson Education, Inc.

24 -5 Accessory Digestive Organs § Production and functions of bile – Bile salts

24 -5 Accessory Digestive Organs § Production 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 117 © 2018 Pearson Education, Inc.

24 -5 Accessory Digestive Organs § Gallbladder – Hollow, pear-shaped muscular sac – Stores

24 -5 Accessory Digestive Organs § Gallbladder – 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 118 © 2018 Pearson Education, Inc.

24 -5 Accessory Digestive Organs § Regions of gallbladder – Fundus – Body –

24 -5 Accessory Digestive Organs § Regions 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 119 © 2018 Pearson Education, Inc.

24 -5 Accessory Digestive Organs § Gallbladder releases bile into duodenum – Only when

24 -5 Accessory Digestive Organs § Gallbladder 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 120 © 2018 Pearson Education, Inc.

24 -5 Accessory Digestive Organs § Physiology of gallbladder – Full gallbladder contains 40–

24 -5 Accessory Digestive Organs § Physiology of gallbladder – Full gallbladder contains 40– 70 m. L bile – Bile composition gradually changes in gallbladder • Water is absorbed • Bile salts and other components become increasingly concentrated 121 © 2018 Pearson Education, Inc.

24 -6 The Small Intestine § Small intestine – Long, muscular tube where •

24 -6 The Small Intestine § Small intestine – Long, muscular tube where • Chemical digestion is completed • 90 percent of nutrient absorption occurs – Consists of three segments • Duodenum • Jejunum • Ileum 122 © 2018 Pearson Education, Inc.

24 -6 The Small Intestine § Duodenum – Segment of small intestine closest to

24 -6 The Small Intestine § Duodenum – Segment 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 123 © 2018 Pearson Education, Inc.

24 -6 The Small Intestine § Ileum – Final segment of small intestine –

24 -6 The Small Intestine § Ileum – Final segment of small intestine – 3. 5 meters long – Ends at ileocecal valve • Sphincter that controls flow of material from ileum into cecum of large intestine 124 © 2018 Pearson Education, Inc.

Figure 24– 20 a Gross Anatomy and Segments of the Intestine. Segments of the

Figure 24– 20 a Gross Anatomy and Segments of the Intestine. Segments of the Small Intestine Duodenum Jejunum Ileum Large intestine Rectum a The positions of the duodenum, jejunum, and ileum in the abdominopelvic cavity 125

24 -6 The Small Intestine § Histology of small intestine – Circular folds •

24 -6 The Small Intestine § Histology of small intestine – Circular folds • Transverse 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 126 © 2018 Pearson Education, Inc.

Figure 24– 20 b Gross Anatomy and Segments of the Intestine. Circular folds Gross

Figure 24– 20 b Gross Anatomy and Segments of the Intestine. Circular folds Gross anatomy of the jejunum b A representative view of the jejunum 127

24 -6 The Small Intestine § Histology of small intestine – Lacteal • Lymphatic

24 -6 The Small Intestine § Histology of small intestine – Lacteal • Lymphatic 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 128 © 2018 Pearson Education, Inc.

24 -6 The Small Intestine § Duodenal submucosal glands – Produce copious quantities of

24 -6 The Small Intestine § Duodenal submucosal glands – Produce copious quantities of mucus • When chyme arrives from stomach – Mucus protects epithelium from acidity of chyme • Contains bicarbonate ions that raise p. H 129 © 2018 Pearson Education, Inc.

24 -6 The Small Intestine § Physiology of small intestine – 1. 8 liters

24 -6 The Small Intestine § Physiology of small intestine – 1. 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 130 © 2018 Pearson Education, Inc.

24 -6 The Small Intestine § Mucosa of small intestine produces few enzymes involved

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 131 © 2018 Pearson Education, Inc.

24 -6 The Small Intestine § Intestinal motility – After chyme arrives in duodenum

24 -6 The Small Intestine § Intestinal motility – After 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 132 © 2018 Pearson Education, Inc.

24 -6 The Small Intestine § Reflexes of small intestine – Gastroenteric reflex •

24 -6 The Small Intestine § Reflexes of small intestine – Gastroenteric 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 133 © 2018 Pearson Education, Inc.

Figure 24– 15 The Regulation of Gastric Activity (Part 4 of 4). CENTRAL REFLEXES

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. 134

24 -6 The Small Intestine § Neural and hormonal mechanisms – Coordinate activities of

24 -6 The Small Intestine § Neural and hormonal mechanisms – Coordinate activities of digestive glands – Centered on duodenum • Where acids are neutralized and enzymes are added 135 © 2018 Pearson Education, Inc.

24 -6 The Small Intestine § Neural mechanisms involving CNS – Prepare digestive tract

24 -6 The Small Intestine § Neural mechanisms involving CNS – Prepare 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 136 © 2018 Pearson Education, Inc.

24 -6 The Small Intestine § Intestinal hormones – Intestinal tract secretes peptide hormones

24 -6 The Small Intestine § Intestinal hormones – Intestinal tract secretes peptide hormones with multiple effects • In several regions of digestive tract • In accessory glandular organs 137 © 2018 Pearson Education, Inc.

24 -6 The Small Intestine § Major hormones of duodenum – Gastrin – Secretin

24 -6 The Small Intestine § Major hormones of duodenum – Gastrin – Secretin – Gastric inhibitory peptide (GIP) – Cholecystokinin (CCK) – Vasoactive intestinal peptide (VIP) – Enterocrinin 138 © 2018 Pearson Education, Inc.

24 -6 The Small Intestine § Gastrin – Secreted by G cells in duodenum

24 -6 The Small Intestine § Gastrin – Secreted by G cells in duodenum • When 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 139 © 2018 Pearson Education, Inc.

24 -6 The Small Intestine § Gastric inhibitory peptide (GIP) – Secreted when fats

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 140 © 2018 Pearson Education, Inc.

24 -6 The Small Intestine § Vasoactive intestinal peptide (VIP) – Stimulates secretion of

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 141 © 2018 Pearson Education, Inc.

24 -6 The Small Intestine § Absorption in small intestine – Movements of mucosa

24 -6 The Small Intestine § Absorption in small intestine – Movements of mucosa increase absorptive effectiveness • Stir and mix intestinal contents • Quickly eliminate local differences in nutrient concentration 142 © 2018 Pearson Education, Inc.

24 -7 The Large Intestine § Large intestine (large bowel) – Horseshoe shaped –

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 143 © 2018 Pearson Education, Inc.

24 -7 The Large Intestine § Parts of large intestine – Cecum • Pouchlike

24 -7 The Large Intestine § Parts of large intestine – Cecum • Pouchlike first portion – Colon • Largest portion – Rectum • The last 15 cm and end of digestive tract 144 © 2018 Pearson Education, Inc.

24 -7 The Large Intestine § Cecum – Expanded pouch – Receives and stores

24 -7 The Large Intestine § Cecum – Expanded pouch – Receives 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 145 © 2018 Pearson Education, Inc.

24 -7 The Large Intestine § Colon – Larger diameter and thinner wall than

24 -7 The Large Intestine § Colon – Larger diameter and thinner wall than small intestine – Haustra • Pouches in wall of colon • Permit expansion and elongation 146 © 2018 Pearson Education, Inc.

24 -7 The Large Intestine § Teniae coli – Three longitudinal bands of smooth

24 -7 The Large Intestine § Teniae coli – Three 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 147 © 2018 Pearson Education, Inc.

24 -7 The Large Intestine § Four regions of colon – Ascending colon –

24 -7 The Large Intestine § Four regions of colon – Ascending colon – Transverse colon – Descending colon – Sigmoid colon 148 © 2018 Pearson Education, Inc.

24 -7 The Large Intestine § Ascending colon – Begins at superior border of

24 -7 The Large Intestine § Ascending colon – Begins 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) 149 © 2018 Pearson Education, Inc.

24 -7 The Large Intestine § Transverse colon – Crosses abdomen from right to

24 -7 The Large Intestine § Transverse colon – Crosses 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 150 © 2018 Pearson Education, Inc.

24 -7 The Large Intestine § Sigmoid colon – S-shaped segment, about 15 cm

24 -7 The Large Intestine § Sigmoid colon – S-shaped segment, about 15 cm long – Lies posterior to urinary bladder – Suspended from sigmoid mesocolon – Empties into rectum 151 © 2018 Pearson Education, Inc.

24 -7 The Large Intestine § Large intestine – Receives blood from branches of

24 -7 The Large Intestine § Large intestine – Receives blood from branches of superior mesenteric and inferior mesenteric arteries – Venous blood is collected by superior mesenteric and inferior mesenteric veins 152 © 2018 Pearson Education, Inc.

24 -7 The Large Intestine § Rectum – Forms last 15 cm of digestive

24 -7 The Large Intestine § Rectum – Forms last 15 cm of digestive tract – Expandable 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 153 © 2018 Pearson Education, Inc.

24 -7 The Large Intestine § Internal anal sphincter – Circular muscle layer –

24 -7 The Large Intestine § Internal anal sphincter – Circular muscle layer – Smooth muscle cells – Not under voluntary control § External anal sphincter – Encircles distal portion of anal canal – Skeletal muscle fibers – Under voluntary control 154 © 2018 Pearson Education, Inc.

Figure 24– 24 c Anatomy of the Large Intestine. Rectum Anal canal Anal columns

Figure 24– 24 c Anatomy of the Large Intestine. Rectum Anal canal Anal columns Internal anal sphincter External anal sphincter Anus c The rectum and anus 155

24 -7 The Large Intestine § Histology of large intestine – Lacks villi –

24 -7 The Large Intestine § Histology of large intestine – Lacks villi – Abundance 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 156 © 2018 Pearson Education, Inc.

24 -7 The Large Intestine § Functions of large intestine – Absorption or reabsorption

24 -7 The Large Intestine § Functions of large intestine – Absorption 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 157 © 2018 Pearson Education, Inc.

24 -7 The Large Intestine § Microbiome – Microbes (bacteria, fungi, and viruses) that

24 -7 The Large Intestine § Microbiome – Microbes (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 158 © 2018 Pearson Education, Inc.

24 -7 The Large Intestine § Vitamins produced by bacteria in colon – Vitamin

24 -7 The Large Intestine § Vitamins produced by bacteria in colon – Vitamin K (fat soluble) • Required by liver for synthesizing four clotting factors, including prothrombin – Biotin (water soluble) • Important in glucose metabolism – Vitamin B 5 (pantothenic acid; water soluble) • Required in manufacture of steroid hormones and some neurotransmitters 159 © 2018 Pearson Education, Inc.

24 -7 The Large Intestine § Organic wastes – Bacteria convert bilirubin to urobilinogens

24 -7 The Large Intestine § Organic wastes – Bacteria 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 160 © 2018 Pearson Education, Inc.

24 -7 The Large Intestine § Organic wastes – Bacteria break down peptides in

24 -7 The Large Intestine § Organic wastes – Bacteria 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 161 © 2018 Pearson Education, Inc.

24 -7 The Large Intestine § Motility of large intestine – Gastroileal and gastroenteric

24 -7 The Large Intestine § Motility of large intestine – Gastroileal 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 162 © 2018 Pearson Education, Inc.

24 -7 The Large Intestine § Motility of large intestine – Movement from transverse

24 -7 The Large Intestine § Motility of large intestine – Movement 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 163 © 2018 Pearson Education, Inc.

24 -7 The Large Intestine § Positive feedback loops – Intrinsic myenteric defecation reflex

24 -7 The Large Intestine § Positive feedback loops – Intrinsic 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 164 © 2018 Pearson Education, Inc.

24 -7 The Large Intestine § Elimination of feces – Requires relaxation of internal

24 -7 The Large Intestine § Elimination of feces – Requires 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 165 © 2018 Pearson Education, Inc.

24 -8 Chemical Digestion § Nutrients – A balanced diet contains • Carbohydrates •

24 -8 Chemical Digestion § Nutrients – A balanced diet contains • Carbohydrates • Lipids • Proteins • Vitamins • Minerals • Water 166 © 2018 Pearson Education, Inc.

24 -8 Chemical Digestion § Processing and absorption of nutrients – Digestive system breaks

24 -8 Chemical Digestion § Processing and absorption of nutrients – Digestive 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 167 © 2018 Pearson Education, Inc.

24 -8 Chemical Digestion § Digestive enzymes – Break molecular bonds in large organic

24 -8 Chemical Digestion § Digestive enzymes – Break 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 168 © 2018 Pearson Education, Inc.

24 -8 Chemical Digestion § Digestive enzymes – Secreted by • Salivary glands •

24 -8 Chemical Digestion § Digestive enzymes – Secreted by • Salivary glands • Tongue • Stomach • Pancreas – Brush border enzymes • Break down digestive fragments further 169 © 2018 Pearson Education, Inc.

24 -8 Chemical Digestion § Carbohydrate digestion and absorption – Complex carbohydrates are digested

24 -8 Chemical Digestion § Carbohydrate digestion and absorption – Complex carbohydrates are digested in two steps 1. Salivary amylase and pancreatic alpha-amylase • Carbohydrases from salivary glands and pancreas 2. Brush border enzymes of intestinal microvilli • Maltase splits bonds between maltose • Sucrase breaks apart sucrose • Lactase hydrolyzes lactose – Insufficient lactase leads to lactose intolerance 170 © 2018 Pearson Education, Inc.

24 -8 Chemical Digestion § Absorption of monosaccharides – Via facilitated diffusion and cotransport,

24 -8 Chemical Digestion § Absorption of monosaccharides – Via facilitated diffusion and cotransport, which differ in • Number of transported substances • Concentration gradients • ATP requirement 171 © 2018 Pearson Education, Inc.

Figure 24– 27 The Chemical Events of Digestion (Part 1 of 3). REGION and

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 Proenzyme released: Pepsinogen by chief cells, activated to pepsin by HCl SMALL INTESTINE Stimulus: Arrival of chyme in duodenum Hormone: CCK Proenzymes released: Chymotrypsinogen, procarboxypeptidase, proelastase, trypsinogen. Enteropeptidase activates trypsin, which activates other enzymes. Enzymes released: Pancreatic amylase, pancreatic lipase, nuclease, enteropeptidase. INTESTINAL MUCOSA Brush border Disaccharides Trisaccharides Pancreatic alpha-amylase Disaccharides Lactase Trisaccharides Maltase, sucrase FACILITATED DIFFUSION AND COTRANSPORT Cell body Monosaccharides FACILITATED DIFFUSION Capillary ROUTE TO BLOODSTREAM Carbohydrates and amino acids are absorbed and transported by intestinal capillaries. Lipids form Monosaccharides chylomicrons that diffuse into lacteals and are delivered to the left subclavian vein by the thoracic duct. 172

24 -8 Chemical Digestion § Lipid digestion and absorption – Involves lingual lipase and

24 -8 Chemical Digestion § Lipid digestion and absorption – Involves 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 173 © 2018 Pearson Education, Inc.

Figure 24– 27 The Chemical Events of Digestion (Part 2 of 3). REGION and

Figure 24– 27 The Chemical Events of Digestion (Part 2 of 3). REGION and Hormonal Controls LIPIDS Lingual lipase ORAL CAVITY 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 Stimulus: Arrival of chyme in duodenum Hormone: CCK Proenzymes released: Chymotrypsinogen, procarboxypeptidase, proelastase, trypsinogen. Enteropeptidase activates trypsin, which activates other enzymes. Enzymes released: Pancreatic amylase, pancreatic lipase, nuclease, enteropeptidase. INTESTINAL MUCOSA Bile salts and pancreatic lipase Monoglycerides, fatty acids in micelles DIFFUSION Brush border Monoglycerides, fatty acids Cell body Triglycerides Chylomicrons EXOCYTOSIS ROUTE TO BLOODSTREAM 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. Lacteal Chylomicrons 174

24 -8 Chemical Digestion § Protein digestion and absorption – Complex and time consuming

24 -8 Chemical Digestion § Protein digestion and absorption – Complex 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 175 © 2018 Pearson Education, Inc.

Figure 24– 27 The Chemical Events of Digestion (Part 3 of 3). REGION and

Figure 24– 27 The Chemical Events of Digestion (Part 3 of 3). REGION and Hormonal Controls PROTEINS ORAL CAVITY 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 Stimulus: Arrival of chyme in duodenum Hormone: CCK Proenzymes released: Chymotrypsinogen, procarboxypeptidase, proelastase, trypsinogen. Enteropeptidase activates trypsin, which activates other enzymes. Enzymes released: Pancreatic amylase, pancreatic lipase, nuclease, enteropeptidase. INTESTINAL MUCOSA Pepsin Polypeptides Trypsin Chymotrypsin Elastase Carboxypeptidase Short peptides, amino acids Dipeptidases Brush border FACILITATED DIFFUSION AND COTRANSPORT Cell body Amino acids FACILITATED DIFFUSION AND COTRANSPORT ROUTE TO BLOODSTREAM 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. Capillary Amino acids 176

24 -8 Chemical Digestion § Nucleic acid digestion and absorption – Nucleic acids are

24 -8 Chemical Digestion § Nucleic acid digestion and absorption – Nucleic 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 177 © 2018 Pearson Education, Inc.

Figure 24– 28 Digestive Secretion and Water Reabsorption in the Digestive Tract. Digestive Secretions

Figure 24– 28 Digestive Secretion and Water Reabsorption in the Digestive Tract. Digestive Secretions Dietary Input Food and drink 2200 m. L Saliva 1500 m. L Gastric secretions 1500 m. L 5200 m. L Water Reabsorption Small intestine reabsorbs 8000 m. L Liver (bile) 1000 m. L Pancreas (pancreatic juice) 1000 m. L 9200 m. L Intestinal secretions 2000 m. L 1200 m. L Colon reabsorbs 1250 m. L 150 m. L lost in feces 1400 m. L Colonic mucous secretions 200 m. L 178

24 -8 Chemical Digestion § Ion absorption – Osmosis does not distinguish among solutes

24 -8 Chemical Digestion § Ion absorption – Osmosis 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 179 © 2018 Pearson Education, Inc.

24 -8 Chemical Digestion § Ion absorption – Calcium ion absorption • Involves active

24 -8 Chemical Digestion § Ion absorption – Calcium ion absorption • Involves 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 180 © 2018 Pearson Education, Inc.

24 -8 Chemical Digestion § Ion absorption – Absorption of magnesium, iron, and other

24 -8 Chemical Digestion § Ion absorption – Absorption 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 181 © 2018 Pearson Education, Inc.

24 -8 Chemical Digestion § Vitamins – Organic compounds required in very small quantities

24 -8 Chemical Digestion § Vitamins – Organic compounds required in very small quantities – Water-soluble vitamins • Include B vitamins and vitamin C – Fat-soluble vitamins • Vitamins A, D, E, and K 182 © 2018 Pearson Education, Inc.

24 -9 Effects of Aging on Digestive System § Age-related changes – Division rate

24 -9 Effects of Aging on Digestive System § Age-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 183 © 2018 Pearson Education, Inc.

24 -10 Digestive System Integration § Digestive system – Extensive anatomical and physiological connections

24 -10 Digestive System Integration § Digestive system – Extensive 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 184 © 2018 Pearson Education, Inc.