The Digestive System and Body Metabolism Chapter 14

The Digestive System and Body Metabolism Chapter 14 1

Outline • • The Functions of the Digestive Tract The Digestive Tract – Mouth – Pharynx – Esophagus – Stomach – Small Intestine – Large Intestine – Accessory Organs Metabolism Homeostatic Considerations 2

Functions of the Digestive Tract • • • Ingest food. Digest food into nutrients that can cross plasma membranes. Absorb nutrients. Eliminate indigestible remains. Critically involved in homeostasis. 3

Figure 14. 1 The human digestive system: Alimentary canal and accessory organs. The Digestive Tract 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

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

The Digestive Tract: Mouth • Mouth – Ceiling: anterior-hard palate (bone); posteriorsoft palate (cartilage). – Floor: tongue; contains taste buds; composed of skeletal muscle; mixes chewed food with saliva and forms a bolus in preparation for swallowing. – Tonsils help protect against infection. – Teeth used to chew food into pieces small enough to swallow. – Three pairs of salivary glands send juices through ducts to the mouth. v Saliva contains bicarbonate and salivary amylase (some carbohydrate breakdown). 6

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

The Digestive Tract: Mouth and Teeth (Gingiva) 8

The Digestive Tract: The Pharynx • Pharynx – Receives air from the nasal cavities and food from the mouth. Paths of air and food cross. – Swallowing v A reflex action that occurs in the pharynx. v Soft palate moves to close off nasopharynx, and the trachea moves under the epiglottis to cover the glottis. 9

The Digestive Tract: The Pharynx; Swallowing 10

Wall of the Digestive Tract 11

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) Mesentery © 2015 Pearson Education, Inc. Nerve Artery Vein Gland in mucosa Lumen Duct of gland outside alimentary canal Lymphoid tissue

The Digestive Tract: The Esophagus • Esophagus – A muscular tube that conducts food bolus from the pharynx through the thoracic cavity and diaphragm into the stomach in the abdominal cavity. – Motility of GI Tract Peristalsis: Rhythmic smooth muscle movements push food along the digestive tract. v Segmentation: Smooth muscle contractions result in back-and-forth mixing of lumen contents. v – Sphincters encircle tubes and act as valves. 13

Motility of the Gastrointestinal Tract Esophagus Bolus of food Stomach a) Peristalsis. b) Segmentation. © 2012 Pearson Education, Inc. Figure 14. 3

The Digestive Tract: The Stomach • Stomach – Stores food and aids in digestion. – Columnar epithelial lining contains gastric pits leading into gastric glands. v Produce gastric juice containing enzyme pepsin (some protein breakdown), hydrochloric acid (HCl), mucus. v p. H in stomach from HCl is 1 -2; kills bacteria. – Walls of stomach have folds which help churn and mix food and gastric juices. v Chyme leaves the stomach and enters the small intestine. – A bacterium, Helicobacter pylori, lives in the mucus and is the cause of gastric ulcers. 15

Anatomy of the Stomach Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. esophagus lower gastroesophageal sphincter pyloric sphincter muscularis layer has three layers of muscle. mucosa layer has rugae. c. Gastric pits in mucosa gastric pit SEM 3, 260 x lower gastroesophageal sphincter a. Stomach gastric pit gastric gland cells that secrete gastric juice b. Gastric glands pyloric sphincter d. How the stomach empties c: © Dr. Fred Hossler/Visuals Unlimited 16

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.

The Digestive Tract: The Small Intestine • The Small Intestine: Duodenum, Jejunum, Ileum – The primary site for digestion. (duodenum, jejunum) Receives digestive enzymes from pancreas; pancreatic amylase, trypsin, lipase; also sodium bicarbonate to neutralize stomach acid. v Produces peptidases and maltase. v Receives bile from liver to emulsify fat. v – The primary site for nutrient absorption. (jejunum, ileum) Walls contain villi which increase surface area and thus absorptive capability. v Nutrients (amino acids, glucose) move into blood capillaries and fats move into the lacteals headed for the lymphatic system. v 18

Figure 14. 1 The human digestive system: Alimentary canal and accessory organs. The Digestive Tract 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

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

Digestion and Absorption of Nutrients 21

Figure 14. 7 Structural modifications of the small intestine. Blood vessels serving the small intestine Muscle layers Villi Small Intestine Anatomy Microvilli (brush border) Lumen Circular folds (plicae circulares) Absorptive cells Lacteal (a) Small intestine (c) Absorptive cells Villus Blood capillaries Lymphoid tissue Intestinal crypt Muscularis mucosae Venule Lymphatic vessel Submucosa (b) Villi © 2015 Pearson Education, Inc.

Left subclavian vein Villus (greatly enlarged) Chylomicron Heart Liver Hepatic portal vein Thoracic duct Small shortchain fatty acid Blood capillary Amino acid Lacteal Monosaccharide Arteriole Venule Blood Lymphatic vessel Lymph (b) Movement of absorbed nutrients into blood and lymph

Inferior vena cava Accessory Organs: Liver. Hepatic Portal System Hepatic veins Liver Spleen Hepatic portal vein Stomach Pancreas Small intestine Large intestine © 2012 Pearson Education, Inc. Figure 14. 11

Accessory Organs: Liver (Con’t) 25

Accessory Organs: Liver (Cont. ) • Liver: Acts as gate keeper for blood – Hepatic portal system All blood from digestive tract goes to liver first before entering the body v Fats entering lacteals do not go to liver first v – Main biochemical processing plant for body. v v v v Detoxifies blood; excretes drugs and chemically alters them. Stores iron & copper and fat-soluble vitamins (A, B 12, D, E, K). Makes plasma proteins (albumins, fibrinogen, prothrombin) Stores glucose as glycogen, breaks down glycogen to glucose to maintain blood glucose levels. Converts amino acids & lactic acid to glucose or fats Phagocytizes old red & white blood cells, put waste into bile; phagocytizes some bacteria Produces & regulates cholesterol levels, converts some to bile salts 26

Accessory Organs: Liver (Cont. ) • Liver: Acts as gate keeper for blood (Cont. ) – Main biochemical processing plant for body (Cont. ) Stores some triglycerides v Produces lipoproteins that transport fatty acids, triglycerides & cholesterol throughout the body v Involved in activation of vitamin D with skin & kidneys v Protein metabolism- deamination of amino acids so they can be converted to glucose or fats- ammonia converted to urea v 27

• Accessory Organs: Pancreas – Endocrine Function: Secretes insulin and glucagon that regulate blood glucose levels. – Exocrine Function: Secretes digestive enzymes (pancreatic amylase, trypsin, lipase) and sodium bicarbonate. 28

The Digestive Tract: The Large Intestine • • The large intestine absorbs water, salts, and some vitamins, and stores fecal material. Contains bacteria that produce Vitamin K (symbiosis) – Cecum is blind end of large intestine. – Colon. v Ascending. v Transverse. v Descending. v Sigmoid. – Rectum. – Anus. 29

Figure 14. 1 The human digestive system: Alimentary canal and accessory organs. The Digestive Tract 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

Figure 14. 8 The large intestine. The Digestive Tract: 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

The Digestive Tract: Regulation of Digestive Secretions • Secretion of digestive juices is promoted by the nervous system and by hormones. – Hormones are produced by one set of cells and affect a different set of cells. Gastrin: from stomach; increases gastric glands secretion. v Gastric inhibitory peptide (GIP): from duodenum; decrease gastric gland secretion. v Secretin: from duodenum; increase pancreatic and liver secretions. v Cholecystokinin (CCK): from duodenum; increase pancreatic secretions & gallbladder contraction (bile delivery increased). v 32

Hormonal Control of Digestive Secretions 33

Basic Chemical Reactions Underlying Metabolism • Metabolism – Collection of all the controlled biochemical reactions that take place within the body – Enzymes are responsible for controlling all of the reactions – Two types of processes involved: v Catabolism v Anabolism

Basic Chemical Reactions Underlying Metabolism • Catabolism and Anabolism – Two major classes of metabolic reactions – Catabolic pathways v Break larger molecules into smaller products Ø – Exergonic (release energy) Anabolic pathways v Synthesize large molecules from the smaller products of catabolism Ø Endergonic (require more energy than they release)

Exergonic & Endergonic: Differences 36

Potential energy Activation Energy Activation energy Energy absorbed to start reaction Energy released as new bonds form Energy of reactants Energy of products Progress of the reaction

Activation Energy: Effect of Catalyst Activation energy needed without catalyst Potential energy Activation energy needed with catalyst Energy of reactants Energy of products Progress of the reaction

The effect of enzymes on chemical reactions Figure 5. 4

Metabolism composed of catabolic and anabolic reactions Figure 5. 1

ATP as “Energy Currency” of cell Heat released Catabolic reactions transfer energy from complex molecules to ATP Simple molecules such as glucose, amino acids, glycerol, and fatty acids ATP ADP + P Complex molecules such as glycogen, proteins, and triglycerides Anabolic reactions transfer energy from ATP to complex molecules Heat released

• • Glucose Metabolism Glucose breakdown requires three subpathways. – Glycolysis. – Citric Acid Cycle (Krebs cycle). – Electron Transport System. Altogether, the breakdown of one glucose molecule results in 36 ATP molecules. 42

Glucose Metabolism (Cont. ) 43

Figure 14. 20 During cellular respiration, ATP is formed in the cytosol and in the mitochondria. Chemical energy (high-energy electrons) Chemical energy CO 2 Glycolysis Cytosol of cell Krebs cycle Pyruvic acid Glucose 1 During glycolysis, each glucose molecule is broken down into two molecules of pyruvic acid as hydrogen atoms containing high-energy electrons are removed. © 2015 Pearson Education, Inc. H 2 O Mitochondrion Mitochondrial cristae Via substrate-level phosphorylation 2 ATP Electron transport chain and oxidative phosphorylation Via oxidative phosphorylation 2 ATP 2 The pyruvic acid enters the mitochondrion, where Krebs cycle enzymes remove more hydrogen atoms and decompose it to CO 2. During glycolysis and the Krebs cycle, small amounts of ATP are formed. 28 ATP 3 Energy-rich electrons picked up by coenzymes are transferred to the electron transport chain, built into the cristae membrane. The electron transport chain carries out oxidative phosphorylation, which accounts for most of the ATP generated by cellular respiration, and finally unites the removed hydrogen with oxygen to form water.

Summary of Glucose Metabolism 1 Glucose 1 2 GLYCOLYSIS ATP + 2 NADH + 2 H 2 Pyruvic acid 2 FORMATION OF ACETYL COENZYME A 2 CO 2 4 2 NADH + 2 H+ 2 Acetyl coenzyme A ELECTRON TRANSPORT CHAIN 32 or 34 3 KREBS CYCLE 2 ATP 4 CO 2 6 NADH + 6 H+ 2 FADH 2 Electrons ATP e– e– e– 6 O 2 6 H 2 O

Summary of Electron Transport Chain Outer membrane Matrix Inner membrane H+ channel High H+ concentration between inner and outer mitochondrial membranes 2 H+ H+ Electron transport chain (includes proton pumps) Inner mitochondrial membrane 1 3 Energy from NADH + H+ Low H+ concentration in matrix of mitochondrion ADP + P ATP synthase ATP

Summary of Electron Transport Chain Space between outer and inner mitochondrial H+ membranes H+ channel H+ Cyt c e– Inner mitochondrial membrane e– e– Q e– e– Mitochondrial matrix NADH + H+ NAD+ H+ 3 2 H+ + 1/2 O 2 ADP + P H 2 O 1 NADH dehydrogenase complex: FMN and five Fe-S centers 2 H+ Cytochrome b–c 1 complex: cyt b, –cyt c 1, and an Fe-S center 3 ATP synthase Cytochrome oxidase complex: cyt a, cyt a 3, and two Cu ATP

Possible arrangement of an electron transport chain Copyright © 2011 Pearson Education Inc. Figure 5. 18

Lipid Metabolism • Transport of Lipids – Very insoluble in water – Liver and intestine make proteins to make lipids water-soluble v Lipoproteins- spherical combinations of proteins, phospholipids & cholesterol Ø Proteins are called apoproteinsdesignated A, B, C, D & E- each have different function in uptake Ø Four classes of lipoproteins 1. Chylomicrons 2. Very-low-density lipoprotein 3. Low-density lipoprotein 4. High-density lipoprotein

Apo C-2 Nonpolar lipids: Cholesterol ester Triglyceride Apo E Amphipathic lipids: Phospholipid Cholesterol Apo B 100

Lipid Metabolism • Transport of Lipids (Cont. ) 1. 2. 3. Chylomicrons (85% triglycerides) v Made by intestinal cells- transport of dietary lipids to adipose tissue- in plasma only a few minutes; liver takes up chylomicron remnants after adipose passage Very-low-density lipoprotein (VLDL) (50% triglycerides) v Made by hepatocytes- endogenous lipids from liver to adipose tissue for storage- converted to LDL Low-density lipoprotein (LDL) (50% cholesterol) v Made by hepatocytes- deliver cholesterol to all body cells for cell membrane repair, making steroid hormones, bile salts- involved with fatty plaque build up in atherosclerosis

Lipid Metabolism • • Transport of Lipids (Cont. ) 4. High-density lipoprotein (HDL) (40 -45% protein) – Made by hepatocytes- remove excess cholesterol from body cells for transport to liver for elimination; prevent accumulation of cholesterol in blood- help prevent fatty plaque build up & thus atherosclerosis Essential Fatty Acids – Two essential fatty acids the body can’t synthesizemust be ingested 1. Linoleic acid 2. Linolenic acid

Lipid Catabolism: Lipolysis catalyzed by lipases Up to 129 ATP from 16 carbon FA Figure 5. 23

1 Glucose 1 2 GLYCOLYSIS ATP + 2 NADH + 2 H 2 Pyruvic acid 2 FORMATION OF ACETYL COENZYME A 2 CO 2 4 2 NADH + 2 H+ 2 Acetyl coenzyme A ELECTRON TRANSPORT CHAIN 32 or 34 3 KREBS CYCLE 2 ATP 4 CO 2 6 NADH + 6 H+ 2 FADH 2 Electrons ATP e– e– e– 6 O 2 6 H 2 O

Protein Metabolism • No Storage of Protein – Amino acids (dietary) v Oxidized to produce ATP v Used to synthesis new proteins v Excess amino acids converted to glucose (gluconeogenesis) or triglycerides (lipogenesis) v Uptake into cells stimulated by: Insulin

Protein Catabolism • Certain amount of protein catabolism each day – Stimulated by cortisol v Proteins from worn-out cells; amino acids transformed to other amino acids, recycled for use in other proteins Ø Transamination- exchange of amino groups between molecules v Small amount of amino acids oxidized to produce ATP by all cells of the body Ø Deamination- amino group needs to be removed before molecule can enter Krebs cycle § Occurs in liver, produces ammonia (NH 3)- highly toxic, converted to urea by liver

Amination and Transamination Figure 5. 31

Protein catabolism NH 3 Figure 5. 24

Alanine Cysteine Glycine Serine Threonine Phenylalanine Pyruvic acid Tyrosine Leucine Lysine Tryptophan Aspartic acid Asparagine Phenylalanine Tyrosine Acetoacetyl Co. A Acetyl Co. A Oxaloacetic acid Isoleucine Leucine Tryptophan Citric acid Malic acid Isocitric acid Fumaric acid Alpha-ketoglutaric acid Succinyl Co. A Isoleucine Methionine Valine Glutamic acid Arginine Histidine Glutamine Proline

1 Glucose 1 2 GLYCOLYSIS ATP + 2 NADH + 2 H 2 Pyruvic acid 2 FORMATION OF ACETYL COENZYME A 2 CO 2 4 2 NADH + 2 H+ 2 Acetyl coenzyme A ELECTRON TRANSPORT CHAIN 32 or 34 3 KREBS CYCLE 2 ATP 4 CO 2 6 NADH + 6 H+ 2 FADH 2 Electrons ATP e– e– e– 6 O 2 6 H 2 O

Protein Anabolism • • Protein synthesized on ribosomes Stimulated by insulin-like growth factor, thyroid hormones, insulin, estrogen, testosterone Adequate intake of protein is critical to life Essential Amino Acids – Of the 20 amino acids, 10 are essential- 10 essential amino acids can’t be made by the body, 10 nonessential can be made

Essential Amino Acids 62

Homeostatic Considerations • • The digestive system brings in nutrients so that all the cells of the body can survive. Digestive system is part of the endocrine system as it produces hormones to help regulate itself. The pancreas is part of the digestive and endocrine systems as it produces the main digestive enzymes and secretes the main glucose regulatory hormones insulin and glucagon. The liver is part of the digestive system, the endocrine system, the defense system, and regulates all aspects of the blood. As the main biochemical processing plant, it can be considered the most important organ in the body. 63

Need to Know 1. Small Intestine A. Most digestion occurs here B. Most absorption occurs here C. Digestive enzymes come from pancreas such as pancreatic amylase, trypsin, and lipase D. Liver provides bile to help digest fats E. Absorption surface high due to villi and microvilli F. Amino acids and glucose go into capillaries while fat goes into the lacteals G. Digestion under nervous and significant local hormonal control H. Sodium bicarbonate from pancreas neutralizes all of the acid from the stomach 64

Need to Know (Cont. ) 2. Liver A. Main biochemical processing plant B. Hepatic portal system: all blood from digestive tract must flow through the liver first before going to the rest of the body C. Regulates the composition of the blood 65

Need to Know (Cont. ) 3. 4. Stomach A. Low p. H for killing bacteria not for digestion B. Very little digestion occurs in the stomach C. It’s function is to help break up the food so that it can move down the rest of the tube easily Large Intestine A. Principal area where water, salt, and vitamins are absorbed B. Indigestible waste is eliminated 66

Need to Know (Cont. ) 5. 6. Mouth A. Teeth mash food for passage down esophagus B. Salivary glands produce juices to add to the food to make it into a swallowable material C. Tongue: area of taste buds; forms food bolus for swallowing Pancreas A. Besides producing digestive enzymes, the organ produces insulin and glucagon for glucose regulation 67