chapter 4 digestion, absorption, and metabolism in health and disease

Chapter 4Chapter 4

Digestion, Absorption, and Digestion, Absorption, and Metabolism in Health and Metabolism in Health and

DiseaseDisease

2Elsevier items and derived items © 2010, 2007 by Saunders, an imprint of Elsevier Inc.

The Digestive SystemThe Digestive System


IngestionIngestion

Genetic and environmental factors affecting Genetic and environmental factors affecting taste preferencestaste preferences Children with heightened preference for sweet flavor and greater Children with heightened preference for sweet flavor and greater

rejection of bitter flavorsrejection of bitter flavors May be a supertaster, taster, or nontasterMay be a supertaster, taster, or nontaster Ability to smell is needed to recognize flavorsAbility to smell is needed to recognize flavors Evidence in animal studies that taste preference is related to relevant Evidence in animal studies that taste preference is related to relevant

mineral deficiency; may have implications for humans mineral deficiency; may have implications for humans • Lambs choose feed high in calcium and phosphorus with deficient Lambs choose feed high in calcium and phosphorus with deficient

state (Villalba et al., 2008)state (Villalba et al., 2008)• Rats prefer potassium foods when deficient (Guenthner et al., Rats prefer potassium foods when deficient (Guenthner et al.,

2007)2007)


Ingestion (continued)Ingestion (continued)

Hormonal impact on hunger and satiety affects Hormonal impact on hunger and satiety affects quantities of food consumedquantities of food consumed Insulin promotes hungerInsulin promotes hunger Cholecystokinin and leptin promote satietyCholecystokinin and leptin promote satiety

Chewing ability affects food choicesChewing ability affects food choices Poor dental status or cleft lip affects ability to ingest Poor dental status or cleft lip affects ability to ingest

foodsfoods Ability to swallowAbility to swallow

Neurologic problems due to impaired neuromuscular Neurologic problems due to impaired neuromuscular strength/coordination affects ability to swallow various strength/coordination affects ability to swallow various consistencies of foods/drinks—referred to as consistencies of foods/drinks—referred to as dysphagiadysphagia

Achalasia (esophagus cannot relax to allow food into the Achalasia (esophagus cannot relax to allow food into the stomach)stomach)


DysphagiaDysphagia

Inability to swallow efficiently (generally Inability to swallow efficiently (generally the result of neurologic damage, as with the result of neurologic damage, as with premature birth, stroke, head injury, or premature birth, stroke, head injury, or neurodegenerationneurodegeneration

Speech-language pathologist (SLP) Speech-language pathologist (SLP) evaluates swallowing ability; evaluates swallowing ability; videofluoroscopy may be used with a videofluoroscopy may be used with a barium swallow to observe transit of food barium swallow to observe transit of food through the esophagus and stomachthrough the esophagus and stomach

Thickened liquids are easier to swallow Thickened liquids are easier to swallow than thin liquids because of added control than thin liquids because of added control


Altered ConsistenciesAltered Consistencies

Solids:Solids: Mechanical soft (ground meats, soft foods)Mechanical soft (ground meats, soft foods) Puree (all foods with solid consistency Puree (all foods with solid consistency

blenderized)blenderized) Liquids:Liquids:

Nectar thick (fluids need to be thickness of fruit Nectar thick (fluids need to be thickness of fruit nectars)nectars)

Honey thick (all fluids are the thickness of Honey thick (all fluids are the thickness of honey)honey)

Pudding thick (all fluids are the thickness of Pudding thick (all fluids are the thickness of pudding)pudding)


Process of DigestionProcess of Digestion

Digestion is the ingestion and breakdown Digestion is the ingestion and breakdown of food matter through mechanical and of food matter through mechanical and chemical means to allow for intestinal chemical means to allow for intestinal absorption and cellular metabolism of absorption and cellular metabolism of energyenergy

Digestion occurs with the macronutrients Digestion occurs with the macronutrients carbohydrate (CHO), protein (PRO), and carbohydrate (CHO), protein (PRO), and fat (FAT)fat (FAT)


Two Forms of DigestionTwo Forms of Digestion

Mechanical: involves chewing of food into small Mechanical: involves chewing of food into small particles to allow surface area for digestive particles to allow surface area for digestive enzymes and peristalsis, i.e., squeezing process enzymes and peristalsis, i.e., squeezing process of gastrointestinal tract that propels food through of gastrointestinal tract that propels food through GIGI PeristalsisPeristalsis can be impaired with neurologic damage can be impaired with neurologic damage GastroparesisGastroparesis: the condition when the stomach cannot : the condition when the stomach cannot

mechanically move food into the intestinesmechanically move food into the intestines Chemical: “hydrolysis” involves addition of water Chemical: “hydrolysis” involves addition of water

and use of digestive enzymes to chemically break and use of digestive enzymes to chemically break down food particlesdown food particles


EnzymesEnzymes

Sources of enzymesSources of enzymes——names usually end in names usually end in “ase”“ase”

Salivary amylase, or ptyalin (digests CHO)Salivary amylase, or ptyalin (digests CHO) Gastric pepsin (digests PRO) and lipase Gastric pepsin (digests PRO) and lipase

(digests fats)(digests fats) Intestinal & pancreatic: sucrase, lactase, Intestinal & pancreatic: sucrase, lactase,

maltase, trypsin (digests PRO), lipase (digests maltase, trypsin (digests PRO), lipase (digests fats)fats)

Bile is a substance that helps fat digestion Bile is a substance that helps fat digestion through emulsification; acts like soap detergentthrough emulsification; acts like soap detergent

No digestion occurs in large intestinesNo digestion occurs in large intestines


AbsorptionAbsorption

Occurs mainly in small intestines through Occurs mainly in small intestines through the villi (microscopic hair-like projections)the villi (microscopic hair-like projections)

Minerals are mainly absorbed in the Minerals are mainly absorbed in the duodenumduodenum

Glucose and water-soluble vitamins are Glucose and water-soluble vitamins are mainly absorbed in the jejunummainly absorbed in the jejunum

Protein, fats, and fat-soluble vitamins are Protein, fats, and fat-soluble vitamins are primarily absorbed in the ileumprimarily absorbed in the ileum

Water & electrolytes are chiefly absorbed Water & electrolytes are chiefly absorbed in the colon only, or large intestinein the colon only, or large intestine


Wall of the Small IntestineWall of the Small Intestine

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


Carbohydrate DigestionCarbohydrate Digestion

Monosaccharides do not require digestion Monosaccharides do not require digestion (glucose and fructose)(glucose and fructose)

Digestion starts in the mouth with amylaseDigestion starts in the mouth with amylase Disaccharides and starches continue to be broken Disaccharides and starches continue to be broken

down by pancreatic enzymes sucrase, lactase down by pancreatic enzymes sucrase, lactase and maltaseand maltase

Fiber is mainly indigestible by humans; intestinal Fiber is mainly indigestible by humans; intestinal bacteria allow some digestion, with the bacteria bacteria allow some digestion, with the bacteria giving off hydrogen and methane gases in the giving off hydrogen and methane gases in the process, referred to as process, referred to as flatusflatus


Lactose IntoleranceLactose Intolerance

Lactase deficiency is the most common Lactase deficiency is the most common digestive problem; inadequate lactase digestive problem; inadequate lactase prevents the digestion of the disaccharide prevents the digestion of the disaccharide lactose into monosaccharideslactose into monosaccharides

Can be a temporary situation Can be a temporary situation accompanying GI irritation, as with the accompanying GI irritation, as with the “stomach flu”“stomach flu”


Protein DigestionProtein Digestion

Chemical digestion starts with HCL as well Chemical digestion starts with HCL as well as protease digestive enzymes (AKA as protease digestive enzymes (AKA pepsin) in the stomachpepsin) in the stomach

Trypsin: digestive enzyme in the small Trypsin: digestive enzyme in the small intestineintestine

Digested into peptides and then amino Digested into peptides and then amino acidsacids


Fat DigestionFat Digestion

Digested into glycerol and fatty acidsDigested into glycerol and fatty acids Only finely emulsified fats begin digestion Only finely emulsified fats begin digestion

in the stomach via gastric lipasein the stomach via gastric lipase Other fats require bile, as produced in the Other fats require bile, as produced in the

liver and stored in the gallbladder, for liver and stored in the gallbladder, for digestiondigestion

Continue to be broken down by lipase in Continue to be broken down by lipase in the small intestinethe small intestine


Role of Water in Role of Water in Digestion and MetabolismDigestion and Metabolism

Needed for saliva and gastric secretions, helps with Needed for saliva and gastric secretions, helps with swallowing (avoidance of dehydration), used for body swallowing (avoidance of dehydration), used for body temperature control (fever increases need for temperature control (fever increases need for kilocalories); needed for cellular metabolism with kilocalories); needed for cellular metabolism with electrical conduction and other processes, allows electrical conduction and other processes, allows loss of waste material, toxinsloss of waste material, toxins

Found inside and outside of body cells, in blood and Found inside and outside of body cells, in blood and other body fluidsother body fluids

Need to ingest about 2 L daily (minimum 6 cups for Need to ingest about 2 L daily (minimum 6 cups for adults); calculated needs generally 30 mL/kg body adults); calculated needs generally 30 mL/kg body weight for adults—includes all substances liquid at weight for adults—includes all substances liquid at room temperatureroom temperature


Altered Hydration StatusAltered Hydration Status

Dehydration leads to hypernatremia (high blood Dehydration leads to hypernatremia (high blood sodium) that alters electrolyte balance and causes sodium) that alters electrolyte balance and causes stress on the heart, affects sense of balance with stress on the heart, affects sense of balance with increased risk of falls; severe dehydration causes increased risk of falls; severe dehydration causes renal failurerenal failure Electrolytes are compounds that when dissolved in Electrolytes are compounds that when dissolved in

water allow for electric current to occurwater allow for electric current to occur Excess intake of water can leach minerals out of Excess intake of water can leach minerals out of

the system and lead to hyponatremia (low blood the system and lead to hyponatremia (low blood sodium level), with potential death from “water sodium level), with potential death from “water intoxication” resulting from cerebral edemaintoxication” resulting from cerebral edema


Digestion ReviewDigestion Review


The Digestive System - REVIEWThe 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.


MetabolismMetabolism

Cellular nutritionCellular nutrition Krebs cycle occurs in the mitochondria of cellsKrebs cycle occurs in the mitochondria of cells

Uses OUses O22 “oxidation” “oxidation” Releases COReleases CO22, H, H22O, energy (ATP)O, energy (ATP)

Specific dynamic action of foodSpecific dynamic action of food The energy required to ingest (chew and transport), The energy required to ingest (chew and transport),

digest, and metabolize food nutrientsdigest, and metabolize food nutrients Hormones are required for metabolic processesHormones are required for metabolic processes

Insulin is the only hormone that allows blood glucose to Insulin is the only hormone that allows blood glucose to be used by the body cellsbe used by the body cells

Thyroxine: produced from the amino acid tyrosine; Thyroxine: produced from the amino acid tyrosine; contains iodine and has a major effect on the rate of contains iodine and has a major effect on the rate of metabolismmetabolism


Other Hormones Involved Other Hormones Involved in Cellular Metabolismin Cellular Metabolism

Glucagon: primary hormone that works opposite of insulin to Glucagon: primary hormone that works opposite of insulin to raise blood glucose levels via glycogenolysis (breakdown of raise blood glucose levels via glycogenolysis (breakdown of glycogen stores of the liver and muscle)glycogen stores of the liver and muscle)

Epinephrine (adrenalin): another counter-regulatory Epinephrine (adrenalin): another counter-regulatory hormone (works counter to insulin); released in response to hormone (works counter to insulin); released in response to hypoglycemia (low blood glucose); increases metabolic ratehypoglycemia (low blood glucose); increases metabolic rate

Cortisol: generally released along with epinephrine to Cortisol: generally released along with epinephrine to correct hypoglycemia; also released with any form of stress correct hypoglycemia; also released with any form of stress (physical or emotional) (physical or emotional)

Growth hormone: released, along with cortisol, at the time of Growth hormone: released, along with cortisol, at the time of waking and results in a natural rise in blood glucose at waking and results in a natural rise in blood glucose at dawn; increases metabolic ratedawn; increases metabolic rate


Basal Metabolic RateBasal Metabolic Rate

Amount of energy (kcal) required for basic Amount of energy (kcal) required for basic processes of lifeprocesses of life Approximately 1200-1400 kcal for womenApproximately 1200-1400 kcal for women Approximately 1600-1800 kcal for menApproximately 1600-1800 kcal for men

Harris Benedict equation for BMR:Harris Benedict equation for BMR: Women: BMR = 655 + ( 4.35 x weight in pounds ) + ( 4.7 x Women: BMR = 655 + ( 4.35 x weight in pounds ) + ( 4.7 x

height in inches ) - ( 4.7 x age in years )height in inches ) - ( 4.7 x age in years ) Men: BMR = 66 + ( 6.23 x weight in pounds ) + ( 12.7 x height Men: BMR = 66 + ( 6.23 x weight in pounds ) + ( 12.7 x height

in inches ) - ( 6.8 x age in year )in inches ) - ( 6.8 x age in year )


Common Stomach ProblemsCommon Stomach Problems

Dyspepsia: indigestionDyspepsia: indigestion Gastritis: inflammatory conditionGastritis: inflammatory condition Peptic ulcer: erosion of stomach lining; may be Peptic ulcer: erosion of stomach lining; may be

due to infection by due to infection by Helicobacter pylori,Helicobacter pylori, and treated and treated with antibioticswith antibiotics

Gastroesophageal reflux disease (GERD): simply Gastroesophageal reflux disease (GERD): simply known as heartburnknown as heartburn

Dumping syndrome: when food suddenly leaves Dumping syndrome: when food suddenly leaves the stomach rapidly before stomach digestion is the stomach rapidly before stomach digestion is completecomplete

Hiatal hernia: opening of the diaphragm allows the Hiatal hernia: opening of the diaphragm allows the stomach to move up through itstomach to move up through it


Hiatal HerniaHiatal Hernia

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


Common Intestinal ProblemsCommon Intestinal Problems

Malabsorption causing diarrhea; may be related to Malabsorption causing diarrhea; may be related to impaired digestion (e.g., antibiotic use destroys impaired digestion (e.g., antibiotic use destroys harmful and beneficial bacteria needed for harmful and beneficial bacteria needed for digestion); replace beneficial bacteria with yogurt digestion); replace beneficial bacteria with yogurt containing live bacterial cultures or buttermilk; containing live bacterial cultures or buttermilk; lacking enzymes may be replaced (lactase and lacking enzymes may be replaced (lactase and pancreatic tablets)pancreatic tablets) Bariatric surgery that removes portions of the small Bariatric surgery that removes portions of the small

intestinal tract will lead to malabsorption of nutrientsintestinal tract will lead to malabsorption of nutrients Irritable bowel syndrome (IBS): treated with Irritable bowel syndrome (IBS): treated with

increased soluble fiber as in psyllium seed increased soluble fiber as in psyllium seed (Metamucil(Metamucil™) or low fermentable CHO diet™) or low fermentable CHO diet


Common Intestinal Common Intestinal Problems Problems (continue(continued)d)

Constipation: corrected with increased Constipation: corrected with increased fiber, fluids, and exercisefiber, fluids, and exercise

Crohn’s disease (regional enteritis): an Crohn’s disease (regional enteritis): an inflammatory bowel disease; may benefit inflammatory bowel disease; may benefit from bowel rest with provision of an from bowel rest with provision of an elemental dietelemental diet

Ulcerative colitis: another inflammatory Ulcerative colitis: another inflammatory condition of the large intestine; may benefit condition of the large intestine; may benefit from consumption of fatty fish (omega-3 from consumption of fatty fish (omega-3 fats)fats)


DiverticulosisDiverticulosis

Increased fiber helps Increased fiber helps prevent diverticulosisprevent diverticulosis

Soluble fiber helps prevent Soluble fiber helps prevent worsening without adverse worsening without adverse effects (tolerated with effects (tolerated with diverticulitis)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.


Food Intolerances Food Intolerances Versus Food AllergiesVersus Food Allergies

Food intolerances are Food intolerances are notnot life threatening life threatening Food intolerances cause discomfort but not Food intolerances cause discomfort but not

anaphylactic shockanaphylactic shock Food allergies are potentially life threatening Food allergies are potentially life threatening

with ingestion of the food itemwith ingestion of the food item Example:Example:

Lactose intolerance: low-lactose milk products are fineLactose intolerance: low-lactose milk products are fineto try and are often tolerated (e.g., yogurt, cheese,to try and are often tolerated (e.g., yogurt, cheese,lactose-reduced milk)lactose-reduced milk)

Milk protein allergy: Milk protein allergy: No milk productsNo milk products (including (including cheese, yogurt, cream sauce, ice cream) because allcheese, yogurt, cream sauce, ice cream) because allcontain protein and could lead to anaphylactic shock contain protein and could lead to anaphylactic shock

29Elsevier items and derived items © 2010, 2007 by Saunders, an imprint of Elsevier Inc.29

Immune-Mediated Food AllergiesImmune-Mediated Food Allergies

An immune response to protein with release of An immune response to protein with release of antibodies and histamineantibodies and histamine Immediate onset: most severe form; anaphylactic shock Immediate onset: most severe form; anaphylactic shock

with risk of death due to suffocationwith risk of death due to suffocation Delayed onset: disrupts quality of life; generally not life Delayed onset: disrupts quality of life; generally not life

threateningthreatening Common food allergens: milk, fish, shellfish, nuts, Common food allergens: milk, fish, shellfish, nuts,

berries, egg white, chocolate, corn, wheat, pork, berries, egg white, chocolate, corn, wheat, pork, legumes and soy, citrus fruitlegumes and soy, citrus fruit

Testing: radioallergosorbent test (RAST blood Testing: radioallergosorbent test (RAST blood test), skin pricks, elimination diet: no testing test), skin pricks, elimination diet: no testing method infallible, but help to predictmethod infallible, but help to predict


Celiac DiseaseCeliac Disease

Genetic autoimmune condition, not a true Genetic autoimmune condition, not a true allergyallergy

Individuals with celiac need to avoid all Individuals with celiac need to avoid all traces oftraces of WheatWheat Oats (gluten free oats okay)Oats (gluten free oats okay) BarleyBarley RyeRye


Medical Implications of CeliacMedical Implications of Celiac

Now recognized as one of the most common food Now recognized as one of the most common food intolerances in the world due to newer blood testingintolerances in the world due to newer blood testing

Most common among persons with European Most common among persons with European heritageheritage

Found with other autoimmune diseases (type 1 Found with other autoimmune diseases (type 1 diabetes, Addison’s disease)diabetes, Addison’s disease)

Villi of the small intestinal atrophy with ingestion of Villi of the small intestinal atrophy with ingestion of foods containing gluten (wheat/rye/barley), but foods containing gluten (wheat/rye/barley), but regenerate with exclusion of all traces of gluten and regenerate with exclusion of all traces of gluten and the protein gliadinthe protein gliadin

Multiple nutrient deficiency can exist due to Multiple nutrient deficiency can exist due to malabsorption from villi atrophymalabsorption from villi atrophy


Signs and Symptoms of CeliacSigns and Symptoms of Celiac

Conditions related to deficiencies of Conditions related to deficiencies of minerals, water-soluble vitamins, and minerals, water-soluble vitamins, and protein due to damage to the duodenum protein due to damage to the duodenum and jejunum areasand jejunum areas Poor growth and delayed puberty of childrenPoor growth and delayed puberty of children Iron-deficiency and other forms of anemiaIron-deficiency and other forms of anemia Recurrent miscarriage and infertilityRecurrent miscarriage and infertility OsteoporosisOsteoporosis

Irritable bowel syndrome may actually be Irritable bowel syndrome may actually be celiacceliac

Elevated liver enzymes (transaminases)Elevated liver enzymes (transaminases)


Tests to Confirm Celiac DiseaseTests to Confirm Celiac Disease

Blood testsBlood tests IgA TTG (antihuman tissue transglutaminase)IgA TTG (antihuman tissue transglutaminase)

and/orand/or

Intestinal biopsyIntestinal biopsy Needed to confirm diagnosis with evidence of Needed to confirm diagnosis with evidence of

villous atrophy; if only antibodies are villous atrophy; if only antibodies are confirmed, may be due to early development of confirmed, may be due to early development of celiacceliac


Effects of Excess Alcohol on Effects of Excess Alcohol on Digestion, Absorption, and MetabolismDigestion, Absorption, and Metabolism

Erosions of GI tract leading to impaired digestion Erosions of GI tract leading to impaired digestion and malabsorptionand malabsorption

Altered appetite with reduced food intake, leading Altered appetite with reduced food intake, leading to malnutritionto malnutrition

Liver damage with impaired protein metabolismLiver damage with impaired protein metabolism Pancreatic damage causing reduced insulin Pancreatic damage causing reduced insulin

production (a form of diabetes) and reduced production (a form of diabetes) and reduced ability to digest dietary fat ability to digest dietary fat

Wernicke-Korsakoff syndrome with deficiency of Wernicke-Korsakoff syndrome with deficiency of vitamin Bvitamin B33 causing neurologic damage, psychosis, causing neurologic damage, psychosis,

and dementiaand dementia


Effects of Moderate Alcohol Intake: Effects of Moderate Alcohol Intake: 2 2 Drinks/Day for Men; Drinks/Day for Men; 1 Drink for Women 1 Drink for Women

Increases cellular use of insulinIncreases cellular use of insulin Raises HDL cholesterol (the “good” Raises HDL cholesterol (the “good”

cholesterol)cholesterol) Decreases tendency to form clotsDecreases tendency to form clots Cautions with moderate alcohol intake:Cautions with moderate alcohol intake:

May lead to hypoglycemia for a person on May lead to hypoglycemia for a person on insulininsulin

Possible genetic link to alcoholism, preventing Possible genetic link to alcoholism, preventing health care professionals from advising a health care professionals from advising a person to start drinking alcohol in moderationperson to start drinking alcohol in moderation


Study GuideStudy Guide


Study Guide (continued)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?

chapter 4 digestion, absorption, and metabolism in health and disease

Documents