Transcript No Slide Title

Chapter 4
Digestion, Absorption, and
Metabolism in Health and
Disease
The Digestive System
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Ingestion
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(Includes internal factors affecting intake of
food)
Genetic and environmental factors affecting
taste preferences
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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)
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Ingestion (continued)
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Hormonal impact on hunger and satiety affects
quantities of food consumed
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Chewing ability affects food choices
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Insulin promotes hunger
Cholecystokinin and leptin promote satiety
Poor dental status or cleft lip affects ability to ingest
foods
Ability to swallow
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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)
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The Stages of Swallowing
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Dysphagia
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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
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Altered Consistencies
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Solids:
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Mechanical soft (ground meats, soft foods)
Puree (all foods with solid consistency
blenderized)
Liquids:
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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)
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Process of Digestion
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Digestion is the ingestion and breakdown
of food matter through mechanical and
physical means to allow for intestinal
absorption and cellular metabolism of
energy
Digestion occurs with the macronutrients
carbohydrate (CHO), protein (PRO), and
fat (FAT)
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Two Forms of Digestion
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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
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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
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Enzymes
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Sources of enzymes—names usually end in
“ase”
Salivary amylase, or ptyalin (digests CHO)
Gastric amylase, pepsin (digests PRO), lipase
(digests fats)
Intestinal pancreas (digests fats), sucrase,
lactase, maltase, trypsin (digests PRO), lipase
Bile is a substance that helps fat digestion
through emulsification; acts like soap detergent
No digestion occurs in large intestines
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Absorption
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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 is chiefly absorbed in the colon only,
or large intestine
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Wall of the Small Intestine
Wall of the small intestine. (From Applegate EJ: The anatomy and physiology learning
system, ed 3, Philadelphia, 2006, Saunders.)
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Metabolism
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Cellular nutrition
Krebs cycle occurs in the mitochondria of cells
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Specific dynamic action of food
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Uses O2 “oxidation”
Releases CO2, H2O, energy (ATP)
The energy required to ingest (chew and transport),
digest, and metabolize food nutrients
Hormones are required for metabolic processes
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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
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Other Hormones Involved
in Cellular Metabolism
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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
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Basal Metabolic Rate
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Amount of energy (kcal) required for basic
processes of life
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Approximately 1200-1400 kcal for women
Approximately 1600-1800 kcal for men
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See handout for how to calculate IBW,
BMR/BEE and TEE (activity level)
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Metabolic Pathways
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Role of Water in
Digestion and Metabolism
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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
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Altered Hydration Status
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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
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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
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Anabolic Processes
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The building process
Examples:
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Liver reassembles amino acids to PRO
DNA directs PRO building
Glycogen from CHO or glucose
Lipogenesis from excess kilocalories
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Catabolic Processes
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The breakdown process
Examples:
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Glycogenolysis
Gluconeogenesis (the creation of sugar is an
anabolic process, but use of muscle or protein
as the substrate is a catabolic process
resulting in muscle loss)
Lipolysis
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Carbohydrate Digestion
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Monosaccharides do not require digestion
(glucose and fructose)
The chemical bonds that connect double sugars
and starches break apart through digestion into
monosaccharides in a similar time frame
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
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Prebiotics (bifidobacteria, lactobacilli) are the beneficial
bacteria needed for digestion
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Lactose Intolerance
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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”
Challenging the gut with 4 oz milk may be
tolerated and encourages increased
lactase production
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Protein Digestion
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Digested into peptides and then amino
acids
Protease digestive enzymes, or pepsin, in
the stomach
Trypsin: digestive enzyme in the small
intestine
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Fat Digestion
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Digested into glycerol and fatty acids
Only finely emulsified fats begin digestion
in the stomach (butter, cream, egg yolks)
Other fats require bile, as produced in the
liver and stored in the gallbladder, for
digestion
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Common Stomach Problems
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Dyspepsia: indigestion
Gastritis: inflammatory condition
Peptic ulcer: erosion of stomach lining; may be
due to infection by Helicobacter pylori, and treated
with antibiotic
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
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Common Intestinal Problems
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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)
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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™)
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Common Intestinal
Problems (continued)
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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)
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Diverticulosis
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Increased fiber helps
prevent diverticulosis
Soluble fiber helps prevent
worsening without adverse
effects (tolerated with
diverticulitis)
Low fat diet is also advised
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.
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Food Intolerances
Versus Food Allergies
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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:
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Lactose intolerance: low-lactose milk products are fine
to 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 all
contain protein and could lead to anaphylactic shock
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Immune-Mediated Food Allergies
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An immune response to protein with release of
antibodies and histamine
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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
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Celiac Disease
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A form of food intolerance due to a genetic
autoimmune condition, not a true allergy
Individuals with celiac need to avoid all
traces of
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Wheat
American oats (Irish/Scottish oats okay)
Barley
Rye
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Medical Implications of Celiac
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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
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Effects of Excess Alcohol on
Digestion, Absorption, and Metabolism
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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
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Effects of Moderate Alcohol Intake: 2
Drinks/Day for Men; 1 Drink for Women
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Increases cellular use of insulin
Raises HDL cholesterol (the “good”
cholesterol)
Decreases tendency to form clots
Cautions with moderate alcohol intake:
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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
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