Chapter 14 Digestive System PDF

Chapter 14 The Digestive System and Body Metabolism Lecture Presentation by Patty Bostwick-Taylor...

Chapter 14 The Digestive System and Body Metabolism Lecture Presentation by Patty Bostwick-Taylor Florence-Darlington Technical College © 2018 Pearson Education, Inc.  The Digestive System Functions  Ingestion—taking in food  Digestion—breaking food into nutrient molecules  Absorption—movement of nutrients into the bloodstream  Defecation—excretes to rid the body of indigestible waste © 2018 Pearson Education, Inc.  Anatomy of the Digestive System  Two main groups of organs  Alimentary canal (gastrointestinal, or GI, tract)— continuous, coiled, hollow tube  These organs ingest, digest, absorb, defecate  Accessory digestive organs  Include teeth, tongue, and several large digestive organs  Assist digestion in various ways © 2018 Pearson Education, Inc. Figure 14.1 The human digestive system: Alimentary canal and accessory organs. Mouth (oral cavity) Parotid gland Tongue Sublingual gland Salivary Submandibular glands gland Esophagus Pharynx Stomach Pancreas (Spleen) Liver Gallbladder Transverse colon Duodenum Descending colon Small Jejunum intestine Ascending colon Ileum Large Cecum intestine Sigmoid colon Rectum Appendix Anus Anal canal © 2018 Pearson Education, Inc.  Organs of the Alimentary Canal  The alimentary canal is a continuous, coiled, hollow tube that runs through the ventral cavity from stomach to anus  Mouth  Pharynx  Esophagus  Stomach  Small intestine  Large intestine  Anus © 2018 Pearson Education, Inc.  Mouth  Anatomy of the mouth  Mouth (oral cavity)—mucous membrane–lined cavity  Lips (labia)—protect the anterior opening  Cheeks—form the lateral walls  Hard palate—forms the anterior roof  Soft palate—forms the posterior roof  Uvula—fleshy projection of the soft palate © 2018 Pearson Education, Inc.  Mouth  Anatomy of the mouth (continued)  Vestibule—space between lips externally and teeth and gums internally  Oral cavity proper—area contained by the teeth  Tongue—attached at hyoid bone and styloid processes of the skull, and by the lingual frenulum to the floor of the mouth © 2018 Pearson Education, Inc.  Mouth  Anatomy of the mouth (continued)  Tonsils  Palatine—located at posterior end of oral cavity  Lingual—located at the base of the tongue © 2018 Pearson Education, Inc. Figure 14.2a Anatomy of the mouth (oral cavity). Nasopharynx Hard palate Soft palate Oral cavity Uvula Lips (labia) Palatine tonsil Vestibule Lingual tonsil Oropharynx Lingual frenulum Epiglottis Tongue Laryngopharynx Hyoid bone Esophagus Trachea (a) © 2018 Pearson Education, Inc. Figure 14.2b Anatomy of the mouth (oral cavity). Upper lip Gingivae Hard palate (gums) Soft palate Uvula Palatine tonsil Oropharynx Tongue (b) © 2018 Pearson Education, Inc.  Mouth  Functions of the mouth  Mastication (chewing) of food  Tongue mixes masticated food with saliva  Tongue initiates swallowing  Taste buds on the tongue allow for taste © 2018 Pearson Education, Inc. © 2015 Pearson Education, Inc.  Pharynx  Serves as a passageway for foods, fluids, and air  Food passes from the mouth posteriorly into the:  Oropharynx—posterior to oral cavity  Laryngopharynx—below the oropharynx and continuous with the esophagus © 2018 Pearson Education, Inc.  Pharynx  Food is propelled to the esophagus by two skeletal muscle layers in the pharynx  Longitudinal outer layer  Circular inner layer  Alternating contractions of the muscle layers (peristalsis) propel the food © 2018 Pearson Education, Inc. Figure 14.2a Anatomy of the mouth (oral cavity). Nasopharynx Hard palate Soft palate Oral cavity Uvula Lips (labia) Palatine tonsil Vestibule Lingual tonsil Oropharynx Lingual frenulum Epiglottis Tongue Laryngopharynx Hyoid bone Esophagus Trachea (a) © 2018 Pearson Education, Inc.  Esophagus  Anatomy  About 10 inches long  Runs from pharynx to stomach through the diaphragm  Physiology  Conducts food by peristalsis (slow rhythmic squeezing) to the stomach  Passageway for food only (respiratory system branches off after the pharynx) © 2018 Pearson Education, Inc.  Layers of Tissue in the Alimentary Canal Organs  Summary of the four layers from innermost to outermost, from esophagus to the large intestine (detailed next) 1. Mucosa 2. Submucosa 3. Muscularis externa 4. Serosa © 2018 Pearson Education, Inc.  Layers of Tissue in the Alimentary Canal Organs 1. Mucosa  Innermost, moist membrane consisting of:  Surface epithelium that is mostly simple columnar epithelium (except for esophagus—stratified squamous epithelium)  Small amount of connective tissue (lamina propria)  Scanty smooth muscle layer  Lines the cavity (known as the lumen) © 2018 Pearson Education, Inc.  Layers of Tissue in the Alimentary Canal Organs 2. Submucosa  Just beneath the mucosa  Soft connective tissue with blood vessels, nerve endings, mucosa-associated lymphoid tissue, and lymphatic vessels © 2018 Pearson Education, Inc.  Layers of Tissue in the Alimentary Canal Organs 3. Muscularis externa—smooth muscle  Inner circular layer  Outer longitudinal layer 4. Serosa—outermost layer of the wall; contains fluid-producing cells  Visceral peritoneum—innermost layer that is continuous with the outermost layer  Parietal peritoneum—outermost layer that lines the abdominopelvic cavity by way of the mesentery © 2018 Pearson Education, Inc. Figure 14.3 Basic structure of the alimentary canal wall. Visceral peritoneum Intrinsic nerve plexuses Myenteric nerve plexus Submucosal nerve plexus Submucosal glands Mucosa Surface epithelium Lamina propria Muscle layer Submucosa Muscularis externa Longitudinal muscle layer Circular muscle layer Serosa (visceral peritoneum) Nerve Gland in Artery Lumen Mesentery mucosa Vein Duct of gland Lymphoid tissue outside alimentary canal © 2018 Pearson Education, Inc. Figure 14.5 Peritoneal attachments of the abdominal organs. Diaphragm Falciform ligament Lesser Liver omentum Spleen Pancreas Gallbladder Stomach Duodenum Visceral peritoneum Transverse colon Greater omentum Mesenteries Parietal peritoneum Small intestine Peritoneal cavity Uterus Large intestine Cecum Rectum Anus Urinary bladder (a) (b) © 2018 Pearson Education, Inc.  Alimentary Canal Nerve Plexuses  Alimentary canal wall contains two intrinsic nerve plexuses that are part of the autonomic nervous system  Submucosal nerve plexus  Myenteric nerve plexus  Regulate mobility and secretory activity of the GI tract organs © 2018 Pearson Education, Inc.  Stomach  C-shaped organ located on the left side of the abdominal cavity  Food enters at the cardioesophageal sphincter from the esophagus  Food empties into the small intestine at the pyloric sphincter (valve) © 2018 Pearson Education, Inc. © 2015 Pearson Education, Inc.  Stomach  Regions  Cardial (cardia)—near the heart and surrounds the cardioesophageal sphincter  Fundus—expanded portion lateral to the cardiac region  Body—midportion  Greater curvature is the convex lateral surface  Lesser curvature is the concave medial surface  Pylorus—funnel-shaped terminal end © 2018 Pearson Education, Inc. Figure 14.4a Anatomy of the stomach. Cardia Fundus Esophagus Muscularis externa Serosa Longitudinal layer Circular layer Oblique layer Body Lesser Rugae curvature of Pylorus mucosa Greater curvature Duodenum Pyloric Pyloric sphincter antrum (a) (valve) © 2018 Pearson Education, Inc. Figure 14.4b Anatomy of the stomach. Fundus Body Rugae of mucosa Pyloric Pyloric (b) sphincter antrum © 2018 Pearson Education, Inc.  Stomach  Stomach can stretch and hold 4 L (1 gallon) of food when full  Rugae—internal folds of the mucosa present when the stomach is empty  Lesser omentum  Double layer of the peritoneum  Extends from liver to the lesser curvature of stomach  Greater omentum  Another extension of the peritoneum  Covers the abdominal organs  Fat insulates, cushions, and protects abdominal organs © 2018 Pearson Education, Inc. Figure 14.5a Peritoneal attachments of the abdominal organs. Diaphragm Falciform ligament Liver Spleen Gallbladder Stomach Greater omentum Small intestine Large intestine Cecum (a) © 2018 Pearson Education, Inc. Figure 14.5b Peritoneal attachments of the abdominal organs. Diaphragm Lesser Liver omentum Pancreas Stomach Duodenum Visceral peritoneum Transverse colon Greater omentum Mesenteries Parietal peritoneum Small intestine Peritoneal cavity Uterus Urinary bladder Rectum Anus (b) © 2018 Pearson Education, Inc.  Stomach  Structure of the stomach mucosa  Simple columnar epithelium composed almost entirely of mucous cells  Mucous cells produce bicarbonate-rich alkaline mucus  Dotted by gastric pits leading to gastric glands that secrete gastric juice, including:  Intrinsic factor, which is needed for vitamin B12 absorption in the small intestine © 2018 Pearson Education, Inc.  Stomach  Structure of the stomach mucosa (continued)  Chief cells—produce protein-digesting enzymes (pepsinogens)  Parietal cells—produce hydrochloric acid that activates enzymes  Mucous neck cells—produce thin acidic mucus (different from the mucus produced by mucous cells of the mucosa)  Enteroendocrine cells—produce local hormones such as gastrin © 2018 Pearson Education, Inc.  Stomach  Functions  Temporary storage tank for food  Site of food breakdown  Chemical breakdown of protein begins  Delivers chyme (processed food) to the small intestine © 2018 Pearson Education, Inc. Figure 14.4c Anatomy of the stomach. Gastric pits Surface Gastric pit epithelium Pyloric sphincter Mucous neck cells Gastric gland Parietal cells Gastric glands Chief cells (c) © 2018 Pearson Education, Inc. Figure 14.4d Anatomy of the stomach. Pepsinogen Pepsin HCl Parietal cells Chief cells Enteroendocrine (d) cell © 2018 Pearson Education, Inc.  Small Intestine  The body’s major digestive organ  Longest portion of the alimentary tube (2–4 m, or 7–13 feet, in a living person)  Site of nutrient absorption into the blood  Muscular tube extending from the pyloric sphincter to the ileocecal valve  Suspended from the posterior abdominal wall by the mesentery © 2018 Pearson Education, Inc. Figure 14.5 Peritoneal attachments of the abdominal organs. Diaphragm Falciform ligament Lesser Liver omentum Spleen Pancreas Gallbladder Stomach Duodenum Visceral peritoneum Transverse colon Greater omentum Mesenteries Parietal peritoneum Small intestine Peritoneal cavity Uterus Large intestine Cecum Rectum Anus Urinary bladder (a) (b) © 2018 Pearson Education, Inc.  Small Intestine  Subdivisions  Duodenum  Jejunum  Ileum © 2018 Pearson Education, Inc.  Small Intestine  Chemical digestion begins in the small intestine  Enzymes produced by intestinal cells and pancreas are carried to the duodenum by pancreatic ducts  Bile, formed by the liver, enters the duodenum via the bile duct  Hepatopancreatic ampulla is the location where the main pancreatic duct and bile ducts join © 2018 Pearson Education, Inc. Figure 14.6 The duodenum of the small intestine and related organs. Right and left hepatic ducts from liver Cystic duct Common hepatic duct Bile duct and sphincter Accessory pancreatic duct Pancreas Gallbladder Jejunum Duodenal papilla Main pancreatic duct and sphincter Hepatopancreatic ampulla and sphincter Duodenum © 2018 Pearson Education, Inc.  Small Intestine  Structural modifications  Increase surface area for food absorption  Decrease in number toward the end of the small intestine 1. Villi—fingerlike projections formed by the mucosa  House a capillary bed and lacteal 2. Microvilli—tiny projections of the plasma membrane (brush border enzymes) 3. Circular folds (plicae circulares)—deep folds of mucosa and submucosa © 2018 Pearson Education, Inc.  Small Intestine  Peyer’s patches  Collections of lymphatic tissue  Located in submucosa  Increase in number toward the end of the small intestine  More are needed there because remaining food residue contains much bacteria © 2018 Pearson Education, Inc. Figure 14.7a Structural modifications of the small intestine. Blood vessels serving the small intestine Lumen Muscle layers Circular folds (plicae circulares) Villi (a) Small intestine © 2018 Pearson Education, Inc. Figure 14.7b Structural modifications of the small intestine. Absorptive cells Lacteal Villus Blood capillaries Lymphoid tissue Intestinal crypt Muscularis Venule mucosae Lymphatic vessel (b) Villi Submucosa © 2018 Pearson Education, Inc. Figure 14.7c Structural modifications of the small intestine. Microvilli (brush border) (c) Absorptive cells © 2018 Pearson Education, Inc.  Large Intestine  Larger in diameter, but shorter in length at 1.5 m, than the small intestine  Extends from the ileocecal valve to the anus  Subdivisions (detailed next)  Cecum  Appendix  Colon  Rectum  Anal canal © 2018 Pearson Education, Inc.  Large Intestine  Cecum—saclike first part of the large intestine  Appendix  Hangs from the cecum  Accumulation of lymphoid tissue that sometimes becomes inflamed (appendicitis) © 2018 Pearson Education, Inc.  Large Intestine  Colon  Ascending—travels up right side of abdomen and makes a turn at the right colic (hepatic) flexure  Transverse—travels across the abdominal cavity and turns at the left colic (splenic) flexure  Descending—travels down the left side  Sigmoid—S-shaped region; enters the pelvis  Sigmoid colon, rectum, and anal canal are located in the pelvis © 2018 Pearson Education, Inc.  Large Intestine  Anal canal ends at the anus  Anus—opening of the large intestine  External anal sphincter—formed by skeletal muscle and is voluntary  Internal anal sphincter—formed by smooth muscle and is involuntary  These sphincters are normally closed except during defecation  The large intestine delivers indigestible food residues to the body’s exterior © 2018 Pearson Education, Inc. Figure 14.8 The large intestine. Left colic (splenic) flexure Transverse Right colic mesocolon (hepatic) flexure Transverse colon Haustrum Descending colon Ascending colon Cut edge of IIeum (cut) mesentery IIeocecal valve Teniae coli Sigmoid colon Cecum Appendix Rectum Anal canal External anal sphincter © 2018 Pearson Education, Inc.  Large Intestine  Goblet cells produce alkaline mucus to lubricate the passage of feces  Muscularis externa layer is reduced to three bands of muscle, called teniae coli  These bands of muscle cause the wall to pucker into haustra (pocketlike sacs) © 2018 Pearson Education, Inc.  Accessory Digestive Organs  Teeth  Salivary glands  Pancreas  Liver  Gallbladder © 2018 Pearson Education, Inc.  Teeth  Teeth masticate (chew) food into smaller fragments  Humans have two sets of teeth during a lifetime 1. Deciduous (baby or milk) teeth  A baby has 20 teeth by age 2  First teeth to appear are the lower central incisors 2. Permanent teeth  Replace deciduous teeth between ages 6 and 12  A full set is 32 teeth (with the wisdom teeth) © 2018 Pearson Education, Inc. Figure 14.9 Deciduous and permanent teeth. Incisors Central (6–8 mo) Lateral (8–10 mo) Canine (eyetooth) (16–20 mo) Molars First molar (10–15 mo) Deciduous Second molar (milk) teeth (about 2 yr) Incisors Central (7 yr) Lateral (8 yr) Canine (eyetooth) (11 yr) Premolars (bicuspids) First premolar (11 yr) Second premolar (12–13 yr) Molars First molar (6–7 yr) Second molar (12–13 yr) Third molar Permanent (wisdom tooth) (17–25 yr) teeth © 2018 Pearson Education, Inc.  Teeth  Teeth are classified according to shape and function  Incisors—cutting  Canines (eyeteeth)—tearing or piercing  Premolars (bicuspids)—grinding  Molars—grinding © 2018 Pearson Education, Inc.  Teeth  Two major regions of a tooth 1. Crown 2. Root © 2018 Pearson Education, Inc.  Teeth 1. Crown—exposed part of tooth above the gingiva (gum)  Enamel—covers the crown  Dentin—found deep to the enamel and forms the bulk of the tooth, surrounds the pulp cavity  Pulp cavity—contains connective tissue, blood vessels, and nerve fibers (pulp)  Root canal—where the pulp cavity extends into the root © 2018 Pearson Education, Inc.  Teeth 2. Root  Cement—covers outer surface and attaches the tooth to the periodontal membrane (ligament)  Periodontal membrane holds tooth in place in the bony jaw Note: The neck is a connector between the crown and root  Region in contact with the gum © 2018 Pearson Education, Inc. Figure 14.10 Longitudinal section of a canine tooth. Enamel Dentin Crown Pulp cavity (contains blood vessels and nerves) Neck Gum (gingiva) Cement Root canal Root Periodontal membrane (ligament) Bone © 2018 Pearson Education, Inc.  Salivary Glands  Three pairs of salivary glands empty secretions into the mouth 1. Parotid glands  Found anterior to the ears  Mumps affect these salivary glands 2. Submandibular glands 3. Sublingual glands  Both submandibular and sublingual glands empty saliva into the floor of the mouth through small ducts © 2018 Pearson Education, Inc. Figure 14.1 The human digestive system: Alimentary canal and accessory organs. Mouth (oral cavity) Parotid gland Tongue Sublingual gland Salivary Submandibular glands gland Esophagus Pharynx Stomach Pancreas (Spleen) Liver Gallbladder Transverse colon Duodenum Descending colon Small Jejunum intestine Ascending colon Ileum Large Cecum intestine Sigmoid colon Rectum Appendix Anus Anal canal © 2018 Pearson Education, Inc.  Salivary Glands  Saliva  Mixture of mucus and serous fluids  Helps to moisten and bind food together into a mass called a bolus  Contains:  Salivary amylase—begins starch digestion  Lysozymes and antibodies—inhibit bacteria  Dissolves chemicals so they can be tasted © 2018 Pearson Education, Inc.  Pancreas  Soft, pink triangular gland  Found posterior to the parietal peritoneum  Mostly retroperitoneal  Extends across the abdomen from spleen to duodenum © 2018 Pearson Education, Inc.  Pancreas  Produces a wide spectrum of digestive enzymes that break down all categories of food  Secretes enzymes into the duodenum  Alkaline fluid introduced with enzymes neutralizes acidic chyme coming from stomach  Hormones produced by the pancreas  Insulin  Glucagon © 2018 Pearson Education, Inc. Figure 14.6 The duodenum of the small intestine and related organs. Right and left hepatic ducts from liver Cystic duct Common hepatic duct Bile duct and sphincter Accessory pancreatic duct Pancreas Gallbladder Jejunum Duodenal papilla Main pancreatic duct and sphincter Hepatopancreatic ampulla and sphincter Duodenum © 2018 Pearson Education, Inc.  Liver  Largest gland in the body  Located on the right side of the body under the diaphragm  Consists of four lobes suspended from the diaphragm and abdominal wall by the falciform ligament © 2018 Pearson Education, Inc. Figure 14.5 Peritoneal attachments of the abdominal organs. Diaphragm Falciform ligament Lesser Liver omentum Spleen Pancreas Gallbladder Stomach Duodenum Visceral peritoneum Transverse colon Greater omentum Mesenteries Parietal peritoneum Small intestine Peritoneal cavity Uterus Large intestine Cecum Rectum Anus Urinary bladder (a) (b) © 2018 Pearson Education, Inc. Figure 14.6 The duodenum of the small intestine and related organs. Right and left hepatic ducts from liver Cystic duct Common hepatic duct Bile duct and sphincter Accessory pancreatic duct Pancreas Gallbladder Jejunum Duodenal papilla Main pancreatic duct and sphincter Hepatopancreatic ampulla and sphincter Duodenum © 2018 Pearson Education, Inc.  Liver  Digestive role is to produce bile  Bile leaves the liver through the common hepatic duct and enters duodenum through the bile duct  Bile is yellow-green, watery solution containing:  Bile salts and bile pigments (mostly bilirubin from the breakdown of hemoglobin)  Cholesterol, phospholipids, and electrolytes  Bile emulsifies (breaks down) fats © 2018 Pearson Education, Inc.  Gallbladder  Green sac found in a shallow fossa in the inferior surface of the liver  When no digestion is occurring, bile backs up the cystic duct for storage in the gallbladder  While in the gallbladder, bile is concentrated by the removal of water  When fatty food enters the duodenum, the gallbladder spurts out stored bile © 2018 Pearson Education, Inc. Figure 14.6 The duodenum of the small intestine and related organs. Right and left hepatic ducts from liver Cystic duct Common hepatic duct Bile duct and sphincter Accessory pancreatic duct Pancreas Gallbladder Jejunum Duodenal papilla Main pancreatic duct and sphincter Hepatopancreatic ampulla and sphincter Duodenum © 2018 Pearson Education, Inc.  Functions of the Digestive System  Overview of gastrointestinal processes and controls  Digestion  Absorption  We will cover six more specific processes next © 2018 Pearson Education, Inc.  Overview of Gastrointestinal Processes and Controls  Essential processes of the GI tract 1. Ingestion—placing of food into the mouth 2. Propulsion—movement of foods from one region of the digestive system to another  Peristalsis—alternating waves of contraction and relaxation that squeeze food along the GI tract  Segmentation—movement of materials back and forth to foster mixing in the small intestine © 2018 Pearson Education, Inc. Figure 14.12a Peristaltic and segmental movements of the digestive tract. (a) © 2018 Pearson Education, Inc.  Functions of the Digestive System  Essential processes of the GI tract (continued) 3. Food breakdown: mechanical breakdown  Examples  Mixing of food in the mouth by the tongue  Churning of food in the stomach  Segmentation in the small intestine  Mechanical digestion prepares food for further degradation by enzymes © 2018 Pearson Education, Inc. Figure 14.12b Peristaltic and segmental movements of the digestive tract. (b) © 2018 Pearson Education, Inc.  Functions of the Digestive System  Essential processes of the GI tract (continued) 4. Food breakdown: digestion  Digestion occurs when enzymes chemically break down large molecules into their building blocks  Each major food group uses different enzymes  Carbohydrates are broken down to monosaccharides (simple sugars)  Proteins are broken down to amino acids  Fats are broken down to fatty acids and glycerol © 2018 Pearson Education, Inc. © 2015 Pearson Education, Inc. Figure 14.13 Flowchart of digestion and absorption of foodstuffs (1 of 3). Foodstuff Enzyme(s) and source Site of action Starch and disaccharides Digestion of Salivary amylase Mouth carbohydrates Pancreatic amylase Small intestine Oligosaccharides* and disaccharides Brush border enzymes Small intestine Lactose Maltose Sucrose in small intestine (dextrinase, glucoamylase, lactase, maltase, Galactose Glucose Fructose and sucrase) Absorption of The monosaccharides glucose, galactose, and fructose carbohydrates enter the capillary blood in the villi and are transported to the liver via the hepatic portal vein. *Oligosaccharides consist of a few linked monosaccharides. © 2018 Pearson Education, Inc. Figure 14.13 Flowchart of digestion and absorption of foodstuffs (2 of 3). Foodstuff Enzyme(s) and source Site of action Protein Digestion of proteins Pepsin (stomach glands) Stomach in the presence of HCl Large polypeptides Pancreatic enzymes Small intestine (trypsin, chymotrypsin, Small polypeptides carboxypeptidase) Brush border enzymes Small intestine (aminopeptidase, Amino acids carboxypeptidase, (some dipeptides and dipeptidase) and tripeptides) Absorption Amino acids enter the capillary blood in the villi and are of proteins transported to the liver via the hepatic portal vein. © 2018 Pearson Education, Inc. Figure 14.13 Flowchart of digestion and absorption of foodstuffs (3 of 3). Foodstuff Enzyme(s) and source Site of action Unemulsified fats Digestion of fats Emulsified by the Small intestine detergent action of bile salts from the liver Pancreatic lipase Small intestine Monoglycerides Glycerol and and fatty acids fatty acids Fatty acids and monoglycerides enter the lacteals of the villi Absorption and are transported to the systemic circulation via the lymph of fats in the thoracic duct. (Glycerol and short-chain fatty acids are absorbed into the capillary blood in the villi and transported to the liver via the hepatic portal vein.) © 2018 Pearson Education, Inc.  Functions of the Digestive System  Essential processes of the GI tract (continued) 5. Absorption  End products of digestion are absorbed in the blood or lymph  Food must enter mucosal cells and then move into blood or lymph capillaries 6. Defecation  Elimination of indigestible substances from the GI tract in the form of feces © 2018 Pearson Education, Inc. Figure 14.11 Schematic summary of gastrointestinal tract activities. Ingestion Food Mechanical breakdown Pharynx Chewing (mouth) Esophagus Churning (stomach) Propulsion Segmentation Swallowing (small intestine) (oropharynx) Peristalsis Digestion (esophagus, stomach, small intestine, large intestine) Stomach Absorption Lymph vessel Small intestine Blood Large vessel intestine Mainly H2O Feces Anus Defecation © 2018 Pearson Education, Inc.  Activities Occurring in the Mouth, Pharynx, and Esophagus  Food ingestion and breakdown  Food is placed into the mouth  Physically broken down by chewing  Mixed with saliva, which is released in response to mechanical pressure and psychic stimuli  Salivary amylase begins starch digestion  Essentially, no food absorption occurs in the mouth © 2018 Pearson Education, Inc.  Activities Occurring in the Mouth, Pharynx, and Esophagus  Food propulsion—swallowing and peristalsis  Pharynx and esophagus have no digestive function  Serve as passageways to the stomach  Pharynx functions in swallowing (deglutition)  Two phases of swallowing 1. Buccal phase 2. Pharyngeal-esophageal phase © 2018 Pearson Education, Inc.  Activities Occurring in the Mouth, Pharynx, and Esophagus  Food propulsion—swallowing and peristalsis (continued) 1. Buccal phase  Voluntary  Occurs in the mouth  Food is formed into a bolus  The bolus is forced into the pharynx by the tongue © 2018 Pearson Education, Inc.  Activities Occurring in the Mouth, Pharynx, and Esophagus  Food propulsion—swallowing and peristalsis (continued) 2. Pharyngeal-esophageal phase  Involuntary transport of the bolus by peristalsis  Nasal and respiratory passageways are blocked © 2018 Pearson Education, Inc.  Activities Occurring in the Mouth, Pharynx, and Esophagus  Food propulsion—swallowing and peristalsis (continued) 2. Pharyngeal-esophogeal phase (continued)  Peristalsis moves the bolus toward the stomach  The cardioesophageal sphincter is opened when food presses against it © 2018 Pearson Education, Inc. Figure 14.14 Swallowing (1 of 4). Bolus of food Tongue Pharynx Epiglottis up Upper esophageal Glottis (lumen) sphincter of larynx Trachea Esophagus 1 Upper esophageal sphincter contracted © 2018 Pearson Education, Inc. Figure 14.14 Swallowing (2 of 4). Uvula Bolus Epiglottis down Larynx up Esophagus 2 Upper esophageal sphincter relaxed © 2018 Pearson Education, Inc. Figure 14.14 Swallowing (3 of 4). Bolus 3 Upper esophageal sphincter contracted © 2018 Pearson Education, Inc. Figure 14.14 Swallowing (4 of 4). Relaxed muscles Cardioesophageal sphincter open 4 Cardioesophageal sphincter relaxed © 2018 Pearson Education, Inc.  Activities in the Stomach  Food breakdown  Gastric juice is regulated by neural and hormonal factors  Presence of food or rising pH causes the release of the hormone gastrin  Gastrin causes stomach glands to produce:  Protein-digesting enzymes  Mucus  Hydrochloric acid © 2018 Pearson Education, Inc.  Activities in the Stomach  Food breakdown (continued)  Hydrochloric acid makes the stomach contents very acidic  Acidic pH  Activates pepsinogen to pepsin for protein digestion  Provides a hostile environment for microorganisms © 2018 Pearson Education, Inc.  Activities in the Stomach  Food breakdown (continued)  Protein-digestion enzymes  Pepsin—an active protein-digesting enzyme  Rennin—works on digesting milk protein in infants; not produced in adults  Alcohol and aspirin are virtually the only items absorbed in the stomach © 2018 Pearson Education, Inc.  Activities in the Stomach  Food propulsion 1. Peristalsis: waves of peristalsis occur from the fundus to the pylorus, forcing food past the pyloric sphincter 2. Grinding: the pylorus meters out chyme into the small intestine (3 ml at a time) 3. Retropulsion: peristaltic waves close the pyloric sphincter, forcing contents back into the stomach; the stomach empties in 4–6 hours © 2018 Pearson Education, Inc. Figure 14.15 Peristaltic waves in the stomach. Pyloric Pyloric Pyloric valve valve valve closed slightly closed opened 1 Propulsion: Peristaltic 2 Grinding: The most 3 Retropulsion: The waves move from the fundus vigorous peristalsis and peristaltic wave closes the toward the pylorus. mixing action occur close pyloric valve, forcing most of to the pylorus. The pyloric the contents of the pylorus end of the stomach acts as backward into the stomach. a pump that delivers small amounts of chyme into the duodenum. © 2018 Pearson Education, Inc.  Activities of the Small Intestine  Chyme breakdown and absorption  Intestinal enzymes from the brush border function to:  Break double sugars into simple sugars  Complete some protein digestion  Intestinal enzymes and pancreatic enzymes help to complete digestion of all food groups © 2018 Pearson Education, Inc.  Activities of the Small Intestine  Chyme breakdown and absorption (continued)  Pancreatic enzymes play the major role in the digestion of fats, proteins, and carbohydrates  Alkaline content neutralizes acidic chyme and provides the proper environment for the pancreatic enzymes to operate © 2018 Pearson Education, Inc.  Activities of the Small Intestine  Chyme breakdown and absorption (continued)  Release of pancreatic juice from the pancreas into the duodenum is stimulated by:  Vagus nerves  Local hormones that travel via the blood to influence the release of pancreatic juice (and bile)  Secretin  Cholecystokinin (CCK) © 2018 Pearson Education, Inc.  Activities of the Small Intestine  Chyme breakdown and absorption (continued)  Hormones (secretin and CCK) also target the liver and gallbladder to release bile  Bile  Acts as a fat emulsifier  Needed for fat absorption and absorption of fat-soluble vitamins (K, D, E, and A) © 2018 Pearson Education, Inc. Figure 14.16 Regulation of pancreatic juice and bile secretion and release. 4 Secretin causes the liver to secrete more bile; CCK stimulates the gallbladder 1 Chyme entering to release stored duodenum causes bile and the duodenalent hepatopancreatic eroendocrine cells to sphincter to relax release cholecystokinin (allows bile from (CCK) and secretin. both sources to enter the duodenum). 2 CCK (red dots) and secretin (blue dots) 5 Stimulation enter the bloodstream. by vagal nerve fibers causes 3 Upon reaching the release of pancreas, CCK induces pancreatic juice secretion of enzyme- and weak rich pancreatic juice; contractions of secretin causes the gallbladder. secretion of bicarbonate- rich pancreatic juice. © 2018 Pearson Education, Inc.  Activities of the Small Intestine  Chyme breakdown and absorption (continued)  A summary table of hormones is presented next © 2018 Pearson Education, Inc. Table 14.1 Hormones and Hormonelike Products That Act in Digestion (1 of 2) © 2018 Pearson Education, Inc. Table 14.1 Hormones and Hormonelike Products That Act in Digestion (2 of 2) © 2018 Pearson Education, Inc.  Activities of the Small Intestine  Chyme breakdown and absorption (continued)  Water is absorbed along the length of the small intestine  End products of digestion  Most substances are absorbed by active transport through cell membranes  Lipids are absorbed by diffusion  Substances are transported to the liver by the hepatic portal vein or lymph © 2018 Pearson Education, Inc.  Activities of the Small Intestine  Chyme propulsion  Peristalsis is the major means of moving food  Segmental movements  Mix chyme with digestive juices  Aid in propelling food © 2018 Pearson Education, Inc. Figure 14.12 Peristaltic and segmental movements of the digestive tract. (a) (b) © 2018 Pearson Education, Inc.  Activities of the Large Intestine  Nutrient breakdown and absorption  No digestive enzymes are produced  Resident bacteria digest remaining nutrients  Produce some vitamin K and some B vitamins  Release gases  Water, vitamins, ions, and remaining water are absorbed  Remaining materials are eliminated via feces © 2018 Pearson Education, Inc.  Activities of the Large Intestine  Nutrient breakdown and absorption (continued)  Feces contains:  Undigested food residues  Mucus  Bacteria  Water © 2018 Pearson Education, Inc.  Activities of the Large Intestine  Propulsion of food residue and defecation  Sluggish peristalsis begins when food residue arrives  Haustral contractions are the movements occurring most frequently in the large intestine  Mass movements are slow, powerful movements that occur three to four times per day © 2018 Pearson Education, Inc.  Activities of the Large Intestine  Propulsion of food residue and defecation (continued)  Presence of feces in the rectum causes a defecation reflex  Internal anal sphincter is relaxed  Defecation occurs with relaxation of the voluntary (external) anal sphincter © 2018 Pearson Education, Inc.  Part II: Nutrition and Metabolism  Most foods are used as metabolic fuel  Foods are oxidized and transformed into adenosine triphosphate (ATP)  ATP is chemical energy that drives cellular activities  Energy value of food is measured in kilocalories (kcal) or Calories (C) © 2018 Pearson Education, Inc.  Nutrition  Nutrient—substance used by the body for growth, maintenance, and repair  Major nutrients  Carbohydrates  Lipids  Proteins  Water  Minor nutrients  Vitamins  Minerals © 2018 Pearson Education, Inc.  Nutrition  A diet consisting of foods from the five food groups normally guarantees adequate amounts of all the needed nutrients  The five food groups are summarized next in Table 14.2 © 2018 Pearson Education, Inc. Table 14.2 Five Basic Food Groups and Some of Their Major Nutrients (1 of 2) © 2018 Pearson Education, Inc. Table 14.2 Five Basic Food Groups and Some of Their Major Nutrients (2 of 2) © 2018 Pearson Education, Inc.  Dietary Recommendations  Healthy Eating Pyramid  Issued in 1992  Six major food groups arranged horizontally  MyPlate  Issued in 2011 by the USDA  Five food groups are arranged by a round plate © 2018 Pearson Education, Inc. Figure 14.17 Two visual food guides. Red meat, butter: White rice, white bread, use sparingly potatoes, pasta, sweets: use sparingly Dairy or calcium supplement: 1–2 servings Fish, poultry, eggs: 0–2 servings Nuts, legumes: 1–3 servings Vegetables Fruits: in abundance 2–3 servings Whole-grain Plant oils foods at at most most meals Daily excercise and weight control meals (a) Healthy Eating Pyramid (b) USDA’s MyPlate © 2018 Pearson Education, Inc.  Dietary Sources of the Major Nutrients  Carbohydrates  Dietary carbohydrates are sugars and starches  Most are derived from plants such as fruits and vegetables  Exceptions: lactose from milk and small amounts of glycogens from meats © 2018 Pearson Education, Inc.  Dietary Sources of the Major Nutrients  Lipids  Saturated fats from animal products (meats)  Unsaturated fats from nuts, seeds, and vegetable oils  Cholesterol from egg yolk, meats, and milk products (dairy products) © 2018 Pearson Education, Inc.  Dietary Sources of the Major Nutrients  Proteins  Complete proteins—contain all essential amino acids  Most are from animal products (eggs, milk, meat, poultry, and fish)  Essential amino acids: those that the body cannot make and must be obtained through diet  Legumes and beans also have proteins, but the proteins are incomplete © 2018 Pearson Education, Inc. Figure 14.18 The eight essential amino acids. Tryptophan Beans and other Methionine legumes Valine Threonine Phenylalanine Leucine Corn and Isoleucine other grains Lysine © 2018 Pearson Education, Inc.  Dietary Sources of the Major Nutrients  Vitamins  Most vitamins function as coenzymes  Found mainly in fruits and vegetables © 2018 Pearson Education, Inc.  Dietary Sources of the Major Nutrients  Minerals  Mainly important for enzyme activity  Foods richest in minerals: vegetables, legumes, milk, and some meats © 2018 Pearson Education, Inc.  Metabolism  Metabolism is all of the chemical reactions necessary to maintain life  Catabolism—substances are broken down to simpler substances; energy is released and captured to make adenosine triphosphate (ATP)  Anabolism—larger molecules are built from smaller ones © 2018 Pearson Education, Inc.  Carbohydrate Metabolism  Carbohydrates are the body’s preferred source to produce cellular energy (ATP)  Glucose (blood sugar)  Major breakdown product of carbohydrate digestion  Fuel used to make ATP © 2018 Pearson Education, Inc.  Carbohydrate Metabolism  Cellular respiration  As glucose is oxidized, carbon dioxide, water, and ATP are formed © 2018 Pearson Education, Inc. Figure 14.19 Summary equation for cellular respiration. C6H12O6 6 O2 6 CO2 6 H2O ATP Glucose Oxygen Carbon Water Energy gas dioxide © 2018 Pearson Education, Inc.  Carbohydrate Metabolism  Events of three main metabolic pathways of cellular respiration 1. Glycolysis  Occurs in the cytosol  Energizes a glucose molecule so it can be split into two pyruvic acid molecules and yield ATP © 2018 Pearson Education, Inc.  Carbohydrate Metabolism  Events of three main metabolic pathways of cellular respiration (continued) 2. Citric acid cycle (Krebs cycle)  Occurs in the mitochondrion  Produces virtually all the carbon dioxide and water resulting from cellular respiration  Yields a small amount of ATP © 2018 Pearson Education, Inc.  Carbohydrate Metabolism  Events of three main metabolic pathways of cellular respiration (continued) 3. Electron transport chain  Hydrogen atoms removed during glycolysis and the citric acid cycle are delivered to protein carriers  Hydrogen atoms are split into hydrogen ions and electrons in the mitochondria  Electrons give off energy in a series of steps to enable the production of ATP © 2018 Pearson Education, Inc. Figure 14.20 The formation of ATP in the cytosol and the mitochondria during cellular respiration. Chemical energy (high-energy electrons) CO2 Chemical energy CO2 Electron transport Glycolysis chain and oxidative Citric phosphorylation Glucose Pyruvic acid H2 O acid cycle Cytosol Mitochondrion Mitochondrial of cell Via oxidative cristae phosphorylation Via substrate-level phosphorylation 2 2 28 ATP ATP ATP 1 During glycolysis, each 2 The pyruvic acid enters 3 Energy-rich electrons picked up by glucose molecule is broken the mitochondrion, where coenzymes are transferred to the electron down into two molecules of citric acid cycle enzymes transport chain, built into the cristae pyruvic acid as hydrogen remove more hydrogen membrane. The electron transport chain atoms containing high- atoms and decompose it to carries out oxidative phosphorylation, which energy electrons are CO2. During glycolysis and accounts for most of the ATP generated by removed. the citric acid cycle, small cellular respiration, and finally unites the amounts of ATP are formed. removed hydrogen with oxygen to form water. © 2018 Pearson Education, Inc. Figure 14.21 Energy release in the electron transport chain versus one-step reduction of oxygen. NADH NAD+ + H+ Energy released as heat and light 2e– e– Electron flow O2 (a) (b) © 2018 Pearson Education, Inc.  Carbohydrate Metabolism  Hyperglycemia—excessively high levels of glucose in the blood  Excess glucose is stored in body cells as glycogen or converted to fat  Hypoglycemia—low levels of glucose in the blood  Glycogenolysis, gluconeogenesis, and fat breakdown occur to restore normal blood glucose levels © 2018 Pearson Education, Inc. Figure 14.22a Metabolism by body cells. (a) Carbohydrates: polysaccharides, disaccharides; composed of simple sugars (monosaccharides) ATP Glycogen and fat Polysaccharides broken down for Cellular uses ATP formation GI digestion to simple sugars To Excess stored as capillary glycogen or fat Broken down to glucose Monosaccharides and released to blood © 2018 Pearson Education, Inc.  Fat Metabolism  Fats  Insulate the body  Protect organs  Build some cell structures (membranes and myelin sheaths)  Provide reserve energy  Excess dietary fat is stored in subcutaneous tissue and other fat depots © 2018 Pearson Education, Inc.  Fat Metabolism  When carbohydrates are in limited supply, more fats are oxidized to produce ATP  Excessive fat breakdown causes blood to become acidic (acidosis or ketoacidosis)  Breath has a fruity odor  Common with:  ―No carbohydrate‖ diets  Uncontrolled diabetes mellitus  Starvation © 2018 Pearson Education, Inc. Figure 14.22b Metabolism by body cells. (b) Fats: composed of 1 glycerol molecule and 3 fatty acids; triglycerides Cellular ATP Fats are the Metabolized uses primary fuels Lipid (fat) Fatty by liver to in many cells acids GI digestion acetic acid, etc. to fatty acids and glycerol Insulation and fat Fats build myelin cushions to protect sheaths and cell body organs membranes Glycerol © 2018 Pearson Education, Inc.  Protein Metabolism  Proteins form the bulk of cell structure and most functional molecules  Proteins are carefully conserved by body cells  Amino acids are actively taken up from blood by body cells © 2018 Pearson Education, Inc.  Protein Metabolism  Amino acids are oxidized to form ATP mainly when other fuel sources are not available  Ammonia, released as amino acids are catabolized, is detoxified by liver cells that combine it with carbon dioxide to form urea © 2018 Pearson Education, Inc. Figure 14.22c Metabolism by body cells. (c) Proteins: polymers of amino acids ATP formation if inadequate ATP glucose and fats or if essential Protein Normally amino acids are lacking infrequent Functional proteins GI digestion to (enzymes, antibodies, amino acids Cellular hemoglobin, etc.) uses Structural proteins Amino (connective tissue fibers, acids muscle proteins, etc.) © 2018 Pearson Education, Inc. Figure 14.22d Metabolism by body cells. (d) ATP formation (fueling the metabolic furnace): all categories of food can be oxidized to provide energy molecules (ATP) Carbon dioxide Cellular Monosaccharides metabolic “furnace”: Water Citric acid cycle Fatty acids and electron transport Amino acids chain (amine first removed ATP and combined with CO2 by the liver to form urea) © 2018 Pearson Education, Inc.  The Central Role of the Liver in Metabolism  Liver is the body’s key metabolic organ  Roles in digestion  Manufactures bile  Detoxifies drugs and alcohol  Degrades hormones  Produces cholesterol, blood proteins (albumin and clotting proteins)  Plays a central role in metabolism  Liver can regenerate if part of it is damaged or removed © 2018 Pearson Education, Inc.  The Central Role of the Liver in Metabolism  To maintain homeostasis of blood glucose levels, the liver performs:  Glycogenesis—―glycogen formation‖  Glucose molecules are converted to glycogen and stored in the liver  Glycogenolysis—―glycogen splitting‖  Glucose is released from the liver after conversion from glycogen  Gluconeogenesis—―formation of new sugar‖  Glucose is produced from fats and proteins © 2018 Pearson Education, Inc. Figure 14.23 Metabolic events occurring in the liver as the blood glucose level rises and falls. Glycogenesis: Glucose converted to glycogen and stored Stimulus: Rising blood glucose level HOMEOSTATIC BLOOD SUGAR Stimulus: Falling blood glucose level Glycogenolysis: Stored glycogen converted to glucose Gluconeogenesis: Amino acids and fats converted to glucose © 2018 Pearson Education, Inc.  The Central Role of the Liver in Metabolism  Fats and fatty acids are picked up by the liver  Some are oxidized to provide energy for liver cells  The rest are either stored or broken down into simpler compounds and released into the blood © 2018 Pearson Education, Inc.  The Central Role of the Liver in Metabolism  Blood proteins made by the liver are assembled from amino acids  Albumin is the most abundant protein in blood  Clotting proteins  Liver cells detoxify ammonia  Ammonia is combined with carbon dioxide to form urea, which is flushed from the body in urine © 2018 Pearson Education, Inc.  The Central Role of the Liver in Metabolism  Cholesterol metabolism and transport  Cholesterol is not used to make ATP  Functions of cholesterol:  Structural basis of steroid hormones and vitamin D  Building block of plasma membranes  Most cholesterol (85%) is produced in the liver; only 15% is from the diet © 2018 Pearson Education, Inc.  The Central Role of the Liver in Metabolism  Cholesterol metabolism and transport (continued)  Cholesterol and fatty acids cannot freely circulate in the bloodstream  They are transported by lipoproteins (lipid-protein complexes) known as LDLs and HDLs © 2018 Pearson Education, Inc.  The Central Role of the Liver in Metabolism  Cholesterol metabolism and transport (continued)  Low-density lipoproteins (LDLs) transport cholesterol to body cells  Rated ―bad lipoproteins‖ since they can lead to atherosclerosis  High-density lipoproteins (HDLs) transport cholesterol from body cells to the liver  Rated ―good lipoproteins‖ since cholesterol is destined for breakdown and elimination © 2018 Pearson Education, Inc.  Body Energy Balance  Energy intake = Total energy output (heat + work + energy storage)  Energy intake is the energy liberated during food oxidation  Energy produced during glycolysis, citric acid cycle, and the electron transport chain  Energy output  Energy we lose as heat (60%)  Energy stored as fat or glycogen © 2018 Pearson Education, Inc.  Body Energy Balance  Interference with the body’s energy balance leads to:  Obesity  Malnutrition (leading to body wasting) © 2018 Pearson Education, Inc.  Body Energy Balance  Regulation of food intake  Body weight is usually relatively stable  Energy intake and output remain about equal  Mechanisms that may regulate food intake  Levels of nutrients in the blood  Hormones  Body temperature  Psychological factors © 2018 Pearson Education, Inc.  Body Energy Balance  Metabolic rate and body heat production  Nutrients yield different amounts of energy  Energy value is measured in kilocalories (kcal)  Carbohydrates and proteins yield 4 kcal/gram  Fats yield 9 kcal/gram © 2018 Pearson Education, Inc.  Body Energy Balance  Basic metabolic rate (BMR)—amount of heat produced by the body per unit of time at rest  Average BMR is about 60 to 72 kcal/hour for an average 70-kg (154-lb) adult © 2018 Pearson Education, Inc.  Body Energy Balance  Factors that influence BMR  Surface area—a small body usually has a higher BMR  Gender—males tend to have higher BMRs  Age—children and adolescents have higher BMRs  The amount of thyroxine produced is the most important control factor  More thyroxine means a higher metabolic rate © 2018 Pearson Education, Inc. Table 14.3 Factors Determining the Basal Metabolic Rate (BMR) © 2018 Pearson Education, Inc.  Body Energy Balance  Total metabolic rate (TMR)—total amount of kilocalories the body must consume to fuel ongoing activities  TMR increases dramatically with an increase in muscle activity  TMR must equal calories consumed to maintain homeostasis and maintain a constant weight © 2018 Pearson Education, Inc.  Body Energy Balance  Body temperature regulation  When foods are oxidized, more than 60% of energy escapes as heat, warming the body  The body has a narrow range of homeostatic temperature  Must remain between 35.6ºC and 37.8ºC  (96ºF and 100ºF) © 2018 Pearson Education, Inc.  Body Energy Balance  Body temperature regulation  The body’s thermostat is in the hypothalamus  Hypothalamus initiates mechanisms to maintain body temperature  Heat loss mechanisms involve radiation of heat from skin and evaporation of sweat  Heat-promoting mechanisms involve vasoconstriction of skin blood vessels and shivering © 2018 Pearson Education, Inc. Figure 14.24 Mechanisms of body temperature regulation. Skin blood vessels dilate: Capillaries become flushed with warm blood; heat radiates from skin surface Activates heat loss center in hypothalamus Sweat glands are activated: Body temperature Secrete perspiration, which decreases: Blood Blood warmer is vaporized by body heat, temperature than hypothalamic helping to cool the body declines, and set point hypothalamus heat-loss center “shuts off” Stimulus: Increased body temperature (e.g., when exercising or the HOMEOSTASIS = NORMAL BODY climate is hot) TEMPERATURE (35.6ºC–37.8ºC) Stimulus: Decreased body temperature (e.g., due to cold environmental temperatures) Skin blood vessels constrict: Blood cooler than Blood is diverted from skin capillaries and withdrawn to hypothalamic set Body temperature deeper tissues; minimizes point increases: Blood overall heat loss from temperature rises, skin surface and hypothalamus heat-promoting center “shuts off” Activates heat- promoting center in hypothalamus Skeletal muscles are activated when more