Chapter 4

1. Chapter 4 Digestion, Absorption, and Metabolism in Health and Disease

2. The Digestive System

3. Ingestion Genetic and environmental factors affecting taste preferences Children with heightened preference for sweet flavor and greater rejection of bitter flavors May be a supertaster, taster, or nontaster Ability to smell is needed to recognize flavors Evidence in animal studies that taste preference is related to relevant mineral deficiency; may have implications for humans Lambs choose feed high in calcium and phosphorus with deficient state (Villalba et al., 2008) Rats prefer potassium foods when deficient (Guenthner et al., 2007)

4. Ingestion (continued) Hormonal impact on hunger and satiety affects quantities of food consumed Insulin promotes hunger Cholecystokinin and leptin promote satiety Chewing ability affects food choices Poor dental status or cleft lip affects ability to ingest foods Ability to swallow Neurologic problems due to impaired neuromuscular strength/coordination affects ability to swallow various consistencies of foods/drinks—referred to as dysphagia Achalasia (esophagus cannot relax to allow food into the stomach)

5. Dysphagia Inability to swallow efficiently (generally the result of neurologic damage, as with premature birth, stroke, head injury, or neurodegeneration Speech-language pathologist (SLP) evaluates swallowing ability; videofluoroscopy may be used with a barium swallow to observe transit of food through the esophagus and stomach Thickened liquids are easier to swallow than thin liquids because of added control

6. Altered Consistencies Solids: Mechanical soft (ground meats, soft foods) Puree (all foods with solid consistency blenderized) Liquids: Nectar thick (fluids need to be thickness of fruit nectars) Honey thick (all fluids are the thickness of honey) Pudding thick (all fluids are the thickness of pudding)

7. Process of Digestion Digestion is the ingestion and breakdown of food matter through mechanical and chemical means to allow for intestinal absorption and cellular metabolism of energy Digestion occurs with the macronutrients carbohydrate (CHO), protein (PRO), and fat (FAT)

8. Two Forms of Digestion Mechanical: involves chewing of food into small particles to allow surface area for digestive enzymes and peristalsis, i.e., squeezing process of gastrointestinal tract that propels food through GI Peristalsis can be impaired with neurologic damage Gastroparesis: the condition when the stomach cannot mechanically move food into the intestines Chemical: “hydrolysis” involves addition of water and use of digestive enzymes to chemically break down food particles

9. Enzymes Sources of enzymes—names usually end in “ase” Salivary amylase, or ptyalin (digests CHO) Gastric pepsin (digests PRO) and lipase (digests fats) Intestinal & pancreatic: sucrase, lactase, maltase, trypsin (digests PRO), lipase (digests fats) Bile is a substance that helps fat digestion through emulsification; acts like soap detergent No digestion occurs in large intestines

10. Absorption Occurs mainly in small intestines through the villi (microscopic hair-like projections) Minerals are mainly absorbed in the duodenum Glucose and water-soluble vitamins are mainly absorbed in the jejunum Protein, fats, and fat-soluble vitamins are primarily absorbed in the ileum Water & electrolytes are chiefly absorbed in the colon only, or large intestine

11. Wall of the Small Intestine Wall of the small intestine. (From Applegate EJ: The anatomy and physiology learning system, ed 3, Philadelphia, 2006, Saunders.)

12. Carbohydrate Digestion Monosaccharides do not require digestion (glucose and fructose) Digestion starts in the mouth with amylase Disaccharides and starches continue to be broken down by pancreatic enzymes sucrase, lactase and maltase Fiber is mainly indigestible by humans; intestinal bacteria allow some digestion, with the bacteria giving off hydrogen and methane gases in the process, referred to as flatus

13. Lactose Intolerance Lactase deficiency is the most common digestive problem; inadequate lactase prevents the digestion of the disaccharide lactose into monosaccharides Can be a temporary situation accompanying GI irritation, as with the “stomach flu”

14. Protein Digestion Chemical digestion starts with HCL as well as protease digestive enzymes (AKA pepsin) in the stomach Trypsin: digestive enzyme in the small intestine Digested into peptides and then amino acids

15. Fat Digestion Digested into glycerol and fatty acids Only finely emulsified fats begin digestion in the stomach via gastric lipase Other fats require bile, as produced in the liver and stored in the gallbladder, for digestion Continue to be broken down by lipase in the small intestine

16. Role of Water in Digestion and Metabolism Needed for saliva and gastric secretions, helps with swallowing (avoidance of dehydration), used for body temperature control (fever increases need for kilocalories); needed for cellular metabolism with electrical conduction and other processes, allows loss of waste material, toxins Found inside and outside of body cells, in blood and other body fluids Need to ingest about 2 L daily (minimum 6 cups for adults); calculated needs generally 30 mL/kg body weight for adults—includes all substances liquid at room temperature

17. Altered Hydration Status Dehydration leads to hypernatremia (high blood sodium) that alters electrolyte balance and causes stress on the heart, affects sense of balance with increased risk of falls; severe dehydration causes renal failure Electrolytes are compounds that when dissolved in water allow for electric current to occur Excess intake of water can leach minerals out of the system and lead to hyponatremia (low blood sodium level), with potential death from “water intoxication” resulting from cerebral edema

18. Digestion Review

19. The Digestive System - REVIEW • Trace the digestion of a meal composed of a ham sandwich on whole-wheat bread, a glass of low-fat milk, and a fresh apple. Describe the mechanical and chemical processes that occur, and name the enzymes involved.

20. Metabolism Cellular nutrition Krebs cycle occurs in the mitochondria of cells Uses O2 “oxidation” Releases CO2, H2O, energy (ATP) Specific dynamic action of food The energy required to ingest (chew and transport), digest, and metabolize food nutrients Hormones are required for metabolic processes Insulin is the only hormone that allows blood glucose to be used by the body cells Thyroxine: produced from the amino acid tyrosine; contains iodine and has a major effect on the rate of metabolism

21. Other Hormones Involved in Cellular Metabolism Glucagon: primary hormone that works opposite of insulin to raise blood glucose levels via glycogenolysis (breakdown of glycogen stores of the liver and muscle) Epinephrine (adrenalin): another counter-regulatory hormone (works counter to insulin); released in response to hypoglycemia (low blood glucose); increases metabolic rate Cortisol: generally released along with epinephrine to correct hypoglycemia; also released with any form of stress (physical or emotional) Growth hormone: released, along with cortisol, at the time of waking and results in a natural rise in blood glucose at dawn; increases metabolic rate

22. Basal Metabolic Rate Amount of energy (kcal) required for basic processes of life Approximately 1200-1400 kcal for women Approximately 1600-1800 kcal for men Harris Benedict equation for BMR: Women: BMR = 655 + ( 4.35 x weight in pounds ) + ( 4.7 x height in inches ) - ( 4.7 x age in years ) Men: BMR = 66 + ( 6.23 x weight in pounds ) + ( 12.7 x height in inches ) - ( 6.8 x age in year )

23. Common Stomach Problems Dyspepsia: indigestion Gastritis: inflammatory condition Peptic ulcer: erosion of stomach lining; may be due to infection by Helicobacter pylori, and treated with antibiotics Gastroesophageal reflux disease (GERD): simply known as heartburn Dumping syndrome: when food suddenly leaves the stomach rapidly before stomach digestion is complete Hiatal hernia: opening of the diaphragm allows the stomach to move up through it

24. Hiatal Hernia Sketch of hiatal hernia. (From Damjanov I: Pathology for the health professions, ed 3, St Louis, 2006, Saunders.)

25. Common Intestinal Problems Malabsorption causing diarrhea; may be related to impaired digestion (e.g., antibiotic use destroys harmful and beneficial bacteria needed for digestion); replace beneficial bacteria with yogurt containing live bacterial cultures or buttermilk; lacking enzymes may be replaced (lactase and pancreatic tablets) Bariatric surgery that removes portions of the small intestinal tract will lead to malabsorption of nutrients Irritable bowel syndrome (IBS): treated with increased soluble fiber as in psyllium seed (Metamucil™) or low fermentable CHO diet

26. Common Intestinal Problems (continued) Constipation: corrected with increased fiber, fluids, and exercise Crohn’s disease (regional enteritis): an inflammatory bowel disease; may benefit from bowel rest with provision of an elemental diet Ulcerative colitis: another inflammatory condition of the large intestine; may benefit from consumption of fatty fish (omega-3 fats)

27. Diverticulosis Increased fiber helps prevent diverticulosis Soluble fiber helps prevent worsening without adverse effects (tolerated with diverticulitis) Mechanism by which low-fiber, low-bulk diets might generate diverticula. Where colon contents are bulky (top), muscular contractions exert pressure longitudinally. If lumen is smaller (bottom), contractions can produce occlusion and exert pressure against colon wall, which may produce diverticular ballooning.

28. Food Intolerances Versus Food Allergies Food intolerances are not life threatening Food intolerances cause discomfort but not anaphylactic shock Food allergies are potentially life threatening with ingestion of the food item Example: Lactose intolerance: low-lactose milk products are fineto try and are often tolerated (e.g., yogurt, cheese,lactose-reduced milk) Milk protein allergy: No milk products (including cheese, yogurt, cream sauce, ice cream) because allcontain protein and could lead to anaphylactic shock

29. Immune-Mediated Food Allergies An immune response to protein with release of antibodies and histamine Immediate onset: most severe form; anaphylactic shock with risk of death due to suffocation Delayed onset: disrupts quality of life; generally not life threatening Common food allergens: milk, fish, shellfish, nuts, berries, egg white, chocolate, corn, wheat, pork, legumes and soy, citrus fruit Testing: radioallergosorbent test (RAST blood test), skin pricks, elimination diet: no testing method infallible, but help to predict

30. Celiac Disease Genetic autoimmune condition, not a true allergy Individuals with celiac need to avoid all traces of Wheat Oats (gluten free oats okay) Barley Rye

31. Medical Implications of Celiac Now recognized as one of the most common food intolerances in the world due to newer blood testing Most common among persons with European heritage Found with other autoimmune diseases (type 1 diabetes, Addison’s disease) Villi of the small intestinal atrophy with ingestion of foods containing gluten (wheat/rye/barley), but regenerate with exclusion of all traces of gluten and the protein gliadin Multiple nutrient deficiency can exist due to malabsorption from villi atrophy

32. Signs and Symptoms of Celiac Conditions related to deficiencies of minerals, water-soluble vitamins, and protein due to damage to the duodenum and jejunum areas Poor growth and delayed puberty of children Iron-deficiency and other forms of anemia Recurrent miscarriage and infertility Osteoporosis Irritable bowel syndrome may actually be celiac Elevated liver enzymes (transaminases)

33. Tests to Confirm Celiac Disease Blood tests IgA TTG (antihuman tissue transglutaminase)and/or Intestinal biopsy Needed to confirm diagnosis with evidence of villous atrophy; if only antibodies are confirmed, may be due to early development of celiac

34. Effects of Excess Alcohol on Digestion, Absorption, and Metabolism Erosions of GI tract leading to impaired digestion and malabsorption Altered appetite with reduced food intake, leading to malnutrition Liver damage with impaired protein metabolism Pancreatic damage causing reduced insulin production (a form of diabetes) and reduced ability to digest dietary fat Wernicke-Korsakoff syndrome with deficiency of vitamin B3 causing neurologic damage, psychosis, and dementia

35. Effects of Moderate Alcohol Intake: 2 Drinks/Day for Men; 1 Drink for Women Increases cellular use of insulin Raises HDL cholesterol (the “good” cholesterol) Decreases tendency to form clots Cautions with moderate alcohol intake: May lead to hypoglycemia for a person on insulin Possible genetic link to alcoholism, preventing health care professionals from advising a person to start drinking alcohol in moderation

36. Study Guide • Vocabulary • Dysphagia • Digestion • Absorption • Peristalsis • Gastroparesis • Intestinal microvilli • Lactose intolerance • Hyper/hyponatremia • Specific dynamic action of food • Dyspepsia • Gastritis • Peptic ulcer • Gastroesophageal reflux disease (GERD) • Dumping syndrome • Hiatal hernia • Ulcerative colitis • Crohn’s disease • Diverticulitis

37. Study Guide (continued) • Factors affecting ingestion • Two forms of digestion • Know the basics of digestion/absorption for CHO, protein, and fat (slide 18 – i.e. where does digestion start? What is the end product of digestion? Where does absorption take place? What enzymes are involved? In addition to enzyme what is needed to help break fats down?) • Is fiber digested by humans? • Why is water important in digestion/absorption? • Where are water and electrolytes absorbed? • What is the relationship of hydration and sodium status? • What is the Krebs Cycle? • How do the following hormones affect blood sugar? Insulin, glucagon, cortisol • What grains need to be avoided in celiac disease?