Chapter 14 The Digestive System and Body Metabolism

The Digestive System Functions § Ingestion—taking in food § Digestion—breaking food into nutrient molecules § Absorption—movement of nutrients into the bloodstream § Defecation—elimination of indigestible waste © 2015 Pearson Education, Inc.

Organs 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 § Includes teeth, tongue, and other large digestive organs © 2015 Pearson Education, Inc.

Figure 14. 1 The human digestive system: Alimentary canal and accessory organs. Mouth (oral cavity) Tongue Parotid gland Sublingual gland Submandibular gland Salivary glands Pharynx Esophagus Stomach Pancreas (Spleen) Liver Gallbladder Small intestine Duodenum Jejunum Ileum Anus © 2015 Pearson Education, Inc. Transverse colon Descending colon Ascending colon Cecum Sigmoid colon Rectum Appendix Anal canal Large intestine

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 © 2015 Pearson Education, Inc.

Mouth (Oral Cavity) § Anatomy of the mouth § The 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 © 2015 Pearson Education, Inc.

Mouth (Oral Cavity) § 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 © 2015 Pearson Education, Inc.

Mouth (Oral Cavity) § Anatomy of the mouth (continued) § Tonsils § Palatine—located at

Figure 14. 2 a Anatomy of the mouth (oral cavity). Nasopharynx Hard palate Oral cavity Soft palate Uvula Lips (labia) Palatine tonsil Vestibule Lingual tonsil Lingual frenulum Tongue Hyoid bone Trachea (a) © 2015 Pearson Education, Inc. Oropharynx Epiglottis Laryngopharynx Esophagus

Figure 14. 2 b Anatomy of the mouth (oral cavity). Upper lip Gingivae (gums)

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 © 2015 Pearson Education, Inc.

Pharynx § Food passes from the mouth posteriorly into the: § Oropharynx—posterior to oral

Figure 14. 2 a Anatomy of the mouth (oral cavity). Nasopharynx Hard palate Oral cavity Soft palate Uvula Lips (labia) Palatine tonsil Vestibule Lingual tonsil Lingual frenulum Tongue Hyoid bone Trachea (a) © 2015 Pearson Education, Inc. Oropharynx Epiglottis Laryngopharynx Esophagus

Pharynx § The pharynx serves as a passageway for food, fluids, and air § Food is propelled to the esophagus by two skeletal muscle layers in the pharynx § Longitudinal inner layer § Circular outer layer § Alternating contractions of the muscle layers (peristalsis) propel the food © 2015 Pearson Education, Inc.

Esophagus (Gullet) § 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) © 2015 Pearson Education, Inc.

Figure 14. 5 Peritoneal attachments of the abdominal organs. Diaphragm Falciform ligament Liver Spleen Gallbladder Stomach Visceral peritoneum Greater omentum Lesser omentum Pancreas Duodenum Transverse colon Mesenteries Parietal peritoneum Small intestine Peritoneal cavity Uterus Large intestine Cecum Rectum Anus Urinary bladder (a) © 2015 Pearson Education, Inc. (b)

Alimentary Canal Nerve Plexuses § Two important nerve plexuses serve the alimentary canal § Both are part of the autonomic nervous system § Submucosal nerve plexus § Myenteric nerve plexus § Function is to regulate mobility and secretory activity of the GI tract organs © 2015 Pearson Education, Inc.

Stomach § The stomach is a 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) © 2015 Pearson Education, Inc.

Stomach § Regions of the stomach § Cardial part (cardia)—near the heart § Fundus—expanded portion lateral to the cardiac region § Body—midportion § Pylorus—funnel-shaped terminal end © 2015 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 § External regions § Lesser curvature—concave medial surface § Greater curvature—convex lateral surface © 2015 Pearson Education, Inc.

Figure 14. 4 a Anatomy of the stomach. Cardia Fundus Esophagus Muscularis externa • Longitudinal layer • Circular layer • Oblique layer Pylorus Serosa Body Lesser curvature Rugae of mucosa Greater curvature Duodenum (a) © 2015 Pearson Education, Inc. Pyloric sphincter (valve) Pyloric antrum

Figure 14. 4 b Anatomy of the stomach. Fundus Body Rugae of mucosa (b)

Figure 14. 5 a Peritoneal attachments of the abdominal organs. Diaphragm Falciform ligament Liver Spleen Gallbladder Stomach Greater omentum Small intestine Large intestine Cecum (a) © 2015 Pearson Education, Inc.

Figure 14. 5 b Peritoneal attachments of the abdominal organs. Diaphragm Liver Lesser omentum Pancreas Stomach Visceral peritoneum Greater omentum Duodenum Transverse colon Mesenteries Parietal peritoneum Small intestine Uterus Peritoneal cavity Rectum Urinary bladder (b) © 2015 Pearson Education, Inc. Anus

Stomach § Functions of the stomach § Temporary storage tank for food § Site of food breakdown § Chemical breakdown of protein begins § Delivers chyme (processed food) to the small intestine © 2015 Pearson Education, Inc.

Stomach § Structure of the stomach mucosa: § Simple columnar epithelium dotted by gastric pits that lead to gastric glands § Mucous cells produce bicarbonate-rich alkaline mucus § Gastric glands—situated in gastric pits and secrete gastric juice, including: § Intrinsic factor, which is needed for vitamin B 12 absorption in the small intestine © 2015 Pearson Education, Inc.

Stomach § Structure of the stomach mucosa (continued) § Chief cells—produce protein-digesting enzymes (pepsinogens) § Parietal cells—produce hydrochloric acid § Mucous neck cells—produce thin acidic mucus (different from the mucus produced by cells of the mucosa) § Enteroendocrine cells—produce a hormone called gastrin © 2015 Pearson Education, Inc.

Figure 14. 4 c Anatomy of the stomach. Pyloric sphincter Gastric pits Surface epithelium

Figure 14. 4 d Anatomy of the stomach. Pepsinogen HCI Pepsin Parietal cells Chief

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 © 2015 Pearson Education, Inc.

Small Intestine § Subdivisions § Duodenum § Attached to the stomach § Curves around the head of the pancreas § Jejunum § Attaches anteriorly to the duodenum § Ileum § Extends from jejunum to large intestine § Meets the large intestine at the ileocecal valve © 2015 Pearson Education, Inc.

Small Intestine § Chemical digestion begins in the small intestine § Enzymes are produced by: § Intestinal cells § Pancreatic ducts carry enzymes to the duodenum § Bile, formed by the liver, enters the duodenum via the bile duct © 2015 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 Hepatopancreatic ampulla and sphincter © 2015 Pearson Education, Inc. Main pancreatic duct and sphincter Duodenum

Small Intestine § Three structural modifications that increase surface area for food absorption 1. Microvilli—tiny projections of the plasma membrane (create a brush border appearance) 2. Villi—fingerlike projections formed by the mucosa § House a capillary bed and lacteal 3. Circular folds (plicae circulares)—deep folds of mucosa and submucosa © 2015 Pearson Education, Inc.

Figure 14. 7 a Structural modifications of the small intestine. Blood vessels serving the small intestine Muscle layers Villi (a) Small intestine © 2015 Pearson Education, Inc. Lumen Circular folds (plicae circulares)

Figure 14. 7 b Structural modifications of the small intestine. Absorptive cells Lacteal Villus Blood capillaries Lymphoid tissue Intestinal crypt Muscularis mucosae Venule Lymphatic vessel Submucosa (b) Villi © 2015 Pearson Education, Inc.

Figure 14. 7 c Structural modifications of the small intestine. Microvilli (brush border) (c)

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: § Cecum § Appendix § Colon § Rectum § Anal canal © 2015 Pearson Education, Inc.

Large Intestine Anatomy § Cecum—saclike first part of the large intestine § Appendix § Accumulation of lymphoid tissue that sometimes becomes inflamed (appendicitis) § Hangs from the cecum © 2015 Pearson Education, Inc.

Large Intestine Anatomy § Colon § Ascending—travels up right side of abdomen § Transverse—travels across the abdominal cavity § Descending—travels down the left side § Sigmoid—S-shaped region; enters the pelvis § Sigmoid colon, rectum, and anal canal are located in the pelvis © 2015 Pearson Education, Inc.

Large Intestine Anatomy § Anal canal ends at the anus § Anus—opening of the large intestine § External anal sphincter—formed by skeletal muscle and under voluntary control § Internal anal sphincter—formed by smooth muscle and involuntarily controlled § These sphincters are normally closed except during defecation § The large intestine delivers undigestible food residues to the body’s exterior © 2015 Pearson Education, Inc.

Figure 14. 8 The large intestine. Left colic (splenic) flexure Transverse mesocolon Right colic (hepatic) flexure Transverse colon Haustrum Descending colon Ascending colon Cut edge of mesentery Ileum (cut) Ileocecal valve Teniae coli Sigmoid colon Cecum Appendix Rectum Anal canal © 2015 Pearson Education, Inc. External anal sphincter

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) © 2015 Pearson Education, Inc.

Accessory Digestive Organs § Teeth § Salivary glands § Pancreas § Liver § Gallbladder

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 © 2015 Pearson Education, Inc.

Teeth 2. Permanent teeth § Replace deciduous teeth between the ages of 6 and 12 § A full set is 32 teeth, but some people do not have wisdom teeth (third molars) § If they do emerge, the wisdom teeth appear between ages of 17 and 25 © 2015 Pearson Education, Inc.

Classification of Teeth § Incisors—cutting § Canines (eyeteeth)—tearing or piercing § Premolars (bicuspids)—grinding §

Regions of a Tooth § Two major regions of a tooth 1. Crown 2.

Regions of a Tooth 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 © 2015 Pearson Education, Inc.

Regions of a Tooth § Note: The neck is a connector between the crown and root. § Region in contact with the gum § Connects crown to root 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 © 2015 Pearson Education, Inc.

Salivary Glands § Three pairs of salivary glands empty secretions into the mouth 1. Parotid glands § Found anterior to the ears 2. Submandibular glands 3. Sublingual glands § Both submandibular and sublingual glands empty saliva into the floor of the mouth through small ducts © 2015 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 to begin starch digestion § Dissolves chemicals so they can be tasted © 2015 Pearson Education, Inc.

Pancreas § Found posterior to the parietal peritoneum § Mostly retroperitoneal § Extends across

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 © 2015 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 § Connected to the gallbladder via the common hepatic duct © 2015 Pearson Education, Inc.

Liver § Bile is produced by cells in the liver § Bile leaves the liver through the common hepatic duct and enters duodenum through the bile duct § Bile is a yellow-green, watery solution containing: § Bile salts and bile pigments (mostly bilirubin from the breakdown of hemoglobin) § Cholesterol, phospholipids, and electrolytes © 2015 Pearson Education, Inc.

Liver § Function of bile § Emulsify fats by physically breaking large fat globules

Gallbladder § Sac found in shallow fossa of liver § When no digestion is occurring, bile backs up the cystic duct for storage in the gallbladder § During digestion of fatty food, bile is introduced into the duodenum from the gallbladder § Gallstones are crystallized cholesterol, which can cause blockages © 2015 Pearson Education, Inc.

Functions of the Digestive System § Major functions of the digestive system are summarized

Functions of the Digestive System 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 squeezes food along the GI tract § Segmentation—movement of materials back and forth to foster mixing in the small intestine © 2015 Pearson Education, Inc.

Figure 14. 12 Peristaltic and segmental movements of the digestive tract. (a) (b) ©

Functions of the Digestive System 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 © 2015 Pearson Education, Inc.

Functions of the Digestive System 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 to monosaccharides (simple sugars) § Proteins are broken to amino acids § Fats are broken to fatty acids and glycerol © 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 carbohydrates Salivary amylase Mouth Pancreatic amylase Small intestine Brush border enzymes in small intestine (dextrinase, glucoamylase, lactase, maltase, and sucrase) Small intestine Oligosaccharides* and disaccharides Lactose Maltose Sucrose Galactose Glucose Fructose The monosaccharides glucose, galactose, and Absorption of carbohydrates fructose 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. © 2015 Pearson Education, Inc.

Figure 14. 13 Flowchart of digestion and absorption of foodstuffs. (2 of 3) Foodstuff Digestion of proteins Protein Enzyme(s) and source Pepsin (stomach glands) in the presence of HCI Site of action Stomach Large polypeptides Small polypeptides, small peptides Amino acids (some dipeptides and tripeptides) Absorption of proteins © 2015 Pearson Education, Inc. Pancreatic enzymes (trypsin, chymotrypsin, carboxypeptidase) Small intestine Brush border enzymes (aminopeptidase, carboxypeptidase, and dipeptidase) Small intestine Amino acids enter the capillary blood in the villi and are transported to the liver via the hepatic portal vein.

Figure 14. 13 Flowchart of digestion and absorption of foodstuffs. (3 of 3) Foodstuff Digestion of fats © 2015 Pearson Education, Inc. Site of action Emulsified by the detergent action of bile salts from the liver Small intestine Pancreatic lipase Small intestine Unemulsified fats Monoglycerides and fatty acids Absorption of fats Enzyme(s) and source Glycerol and fatty acids Fatty acids and monoglycerides enter the lacteals of the villi and are transported to the systemic circulation via the lymph 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. )

Functions of the Digestive System 5. Absorption § End products of digestion are absorbed in the blood or lymph § Food must enter mucosal cells and then into blood or lymph capillaries 6. Defecation § Elimination of indigestible substances from the GI tract in the form of feces © 2015 Pearson Education, Inc.

Figure 14. 11 Schematic summary of gastrointestinal tract activities. Ingestion Mechanical breakdown • Chewing (mouth) • Churning (stomach) • Segmentation (small intestine) Digestion Food Pharynx Esophagus Propulsion • Swallowing (oropharynx) • Peristalsis (esophagus, stomach, small intestine, large intestine) Stomach Absorption Lymph vessel Small intestine Blood vessel Large intestine Mainly H 2 O Feces Defecation © 2015 Pearson Education, Inc. Anus

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 © 2015 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-esophgeal phase © 2015 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 © 2015 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 © 2015 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 © 2015 Pearson Education, Inc.

Figure 14. 14 a Swallowing. Bolus of food Tongue Pharynx Upper Epiglottis esophageal up sphincter Glottis (lumen) of larynx Esophagus Trachea (a) Upper esophageal sphincter contracted © 2015 Pearson Education, Inc.

Figure 14. 14 b Swallowing. Uvula Bolus Epiglottis down Larynx up Esophagus (b) Upper

Figure 14. 14 c Swallowing. Bolus (c) Upper esophageal sphincter contracted © 2015 Pearson

Figure 14. 14 d Swallowing. Relaxed muscles Cardioesophageal sphincter open (d) Cardioesophageal sphincter relaxed

Activities in the Stomach § Food breakdown § Gastric juice is regulated by neural and hormonal factors § Presence of food or rising p. H causes the release of the hormone gastrin § Gastrin causes stomach glands to produce: § Protein-digesting enzymes § Mucus § Hydrochloric acid © 2015 Pearson Education, Inc.

Activities in the Stomach § Food breakdown (continued) § Hydrochloric acid makes the stomach contents very acidic § Acidic p. H § Activates pepsinogen to pepsin for protein digestion § Provides a hostile environment for microorganisms © 2015 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 adults § Alcohol and aspirin are virtually the only items absorbed in the stomach © 2015 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 content back into the stomach. The stomach empties in 4– 6 hours © 2015 Pearson Education, Inc.

Figure 14. 15 Peristaltic waves in the stomach. Pyloric valve closed Pyloric valve slightly opened 1 Propulsion: Peristaltic waves move from the fundus toward the pylorus. 2 Grinding: The most vigorous peristalsis and mixing action occur close to the pylorus. The pyloric end of the stomach acts as a pump that delivers small amounts of chyme into the duodenum. © 2015 Pearson Education, Inc. Pyloric valve closed 3 Retropulsion: The peristaltic wave closes the pyloric valve, forcing most of the contents of the pylorus backward into the stomach.

Activities of the Small Intestine § Food 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 © 2015 Pearson Education, Inc.

Activities of the Small Intestine § Food 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 © 2015 Pearson Education, Inc.

Activities of the Small Intestine § Food 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) © 2015 Pearson Education, Inc.

Activities of the Small Intestine § Food 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) © 2015 Pearson Education, Inc.

Figure 14. 16 Regulation of pancreatic juice and bile secretion and release. 1 Chyme entering duodenum causes duodenal enteroendocrine cells to release cholecytokinin (CCK) and secretin. 2 CCK (red dots) and secretin (blue dots) enter the bloodstream. 3 Upon reaching the pancreas, CCK induces secretion of enzyme-rich pancreatic juice; secretin causes secretion of bicarbonate-rich pancreatic juice. © 2015 Pearson Education, Inc. 4 Secretin causes the liver to secrete more bile; CCK stimulates the gallbladder to release stored bile and the hepatopancreatic sphincter to relax (allows bile from both sources to enter the duodenum). 5 Stimulation by vagal nerve fibers cause release of pancreatic juice and weak contractions of the gallbladder.

Activities of the Small Intestine § Food breakdown and absorption (continued) § A summary

Table 14. 1 Hormones and Hormonelike Products That Act in Digestion (1 of 2).

Table 14. 1 Hormones and Hormonelike Products That Act in Digestion (2 of 2).

Activities of the Small Intestine § Food 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 © 2015 Pearson Education, Inc.

Activities of the Small Intestine § Food breakdown and absorption § Peristalsis is the major means of moving food § Segmental movements § Mix chyme with digestive juices § Aid in propelling food © 2015 Pearson Education, Inc.

Figure 14. 12 b Peristaltic and segmental movements of the digestive tract. (b) ©

Activities of the Large Intestine § Food breakdown and absorption § No digestive enzymes are produced § Resident bacteria digest remaining nutrients § Produce some vitamin K and B § Release gases § Water and vitamins K and B are absorbed § Remaining materials are eliminated via feces © 2015 Pearson Education, Inc.

Activities of the Large Intestine § Food breakdown and absorption (continued) § Feces contains:

Activities of the Large Intestine § Propulsion of the residue and defecation § Sluggish peristalsis begins when food residue arrives § Haustral contractions are most seen in the large intestine § Mass movements are slow, powerful movements that occur 3 to 4 times per day © 2015 Pearson Education, Inc.

Activities of the Large Intestine § Propulsion of the 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 © 2015 Pearson Education, Inc.

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) © 2015 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 © 2015 Pearson Education, Inc.

Table 14. 2 Five Basic Food Groups and Some of Their Major Nutrients (1

Table 14. 2 Five Basic Food Groups and Some of Their Major Nutrients (2

Dietary Sources of 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 © 2015 Pearson Education, Inc.

Dietary Sources of 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) © 2015 Pearson Education, Inc.

Dietary Sources of 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 © 2015 Pearson Education, Inc.

Dietary Sources of Major Nutrients § Vitamins § Most vitamins are used as coenzymes

Dietary Sources of Major Nutrients § Minerals § Mainly important for enzyme activity § Foods richest in minerals: vegetables, legumes, milk, and some meats § Iron is important for making hemoglobin § Calcium is important for building bone, blood clotting, and secretory activities © 2015 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 § Anabolism—larger molecules are built from smaller ones © 2015 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 © 2015 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 © 2015 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 © 2015 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 © 2015 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 © 2015 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 © 2015 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 © 2015 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, Krebs cycle, and the electron transport chain § Energy output § Energy we lose as heat (60%) § Energy stored as fat or glycogen © 2015 Pearson Education, Inc.

Body Energy Balance § Interference with the body’s energy balance leads to: § Obesity

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 © 2015 Pearson Education, Inc.

Metabolic Rate and Body Heat Production § Nutrients yield different amounts of energy § Energy value is measured in kilocalorie (kcal) § Carbohydrates and proteins yield 4 kcal/gram § Fats yield 9 kcal/gram © 2015 Pearson Education, Inc.

Basal Metabolic Rate § 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 © 2015 Pearson Education, Inc.

Basal Metabolic Rate § 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 © 2015 Pearson Education, Inc.

Total Metabolic Rate (TMR) § 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 © 2015 Pearson Education, Inc.

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. 6°C and 37. 8°C (96°F and 100°F) © 2015 Pearson Education, Inc.

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 © 2015 Pearson Education, Inc.

Body Temperature Regulation § Fever—controlled hyperthermia § Results from infection, cancer, allergic reactions, CNS injuries § If the body thermostat is set too high, body proteins may be denatured, and permanent brain damage may occur © 2015 Pearson Education, Inc.

Developmental Aspects of the Digestive System and Metabolism § The alimentary canal is a continuous, hollow tube present by the fifth week of development § Digestive glands bud from the mucosa of the alimentary tube § The developing fetus receives all nutrients through the placenta § In newborns, feeding must be frequent, peristalsis is inefficient, and vomiting is common © 2015 Pearson Education, Inc.

Developmental Aspects of the Digestive System and Metabolism § Common congenital defects that interfere with normal nutrition: § Cleft palate § Cleft lip § Tracheoesophageal fistula § Common inborn errors of metabolism: § Phenylketonuria (PKU) § Cystic fibrosis (CF) © 2015 Pearson Education, Inc.

Developmental Aspects of the Digestive System and Metabolism § Newborn reflexes § Rooting reflex helps the infant find the nipple § Sucking reflex helps the infant hold on to the nipple and swallow § Teething begins around age 6 months © 2015 Pearson Education, Inc.

Developmental Aspects of the Digestive System and Metabolism § Problems of the digestive system: § Gastroenteritis—inflammation of the gastrointestinal tract; can occur at any time § Appendicitis—inflammation of the appendix; common in adolescents § Metabolism decreases with old age § Middle-age digestive problems § Ulcers § Gallbladder problems © 2015 Pearson Education, Inc.

Developmental Aspects of the Digestive System and Metabolism § Later middle-age problems § Obesity § Diabetes mellitus § Activity of the digestive tract in old age § Fewer digestive juices § Peristalsis slows § Diverticulosis and gastrointestinal cancers are more common © 2015 Pearson Education, Inc.