hlt 138 unit 7
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Unit 7 – Digestion and Absorption 1
Key Terms
Digestion:
Processes that convert ingested food
into substances that can be absorbed by
the intestinal tract & used by the body
Absorption:
Processes that transfer nutrients from
the digestive system into body fluids
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Upper Digestive Tract
Mouth
- chewing and saliva
- amylase/lipase
Esophagus
- propels food downward to
stomach
Stomach
- churns and mixes
- Pepsin/intrinsic factor/lipase
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Lower Digestive Tract
Small Intestine
Large Intestine
Rectum
Accessory Organs
- Liver
- Gallbladder
- Pancreas
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Digestion – Begins in the Mouth
Chewing
breaks down food
into smaller
particles
Mixing with saliva
Adding digestive
enzymes
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Digestion – Mouth – Carbohydrates
Salivary Amylase:
Starch glucose molecules
Teeth and saliva soften fiber for swallowing
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Digestion – Mouth – Protein
Teeth soften fibers to swallow
NO CHEMICAL DIGESTION OF PROTEIN
OCCURS IN THE MOUTH!
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Digestion – Mouth – Fat
Lingual Lipase:
Triglyceride Monoglyceride + fatty acids
VERY MINIMAL
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Digestion - Stomach
Churns and mixes
contents
Hydrochloric acid
secreted
Digestive enzymes
secreted
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Digestion – Stomach – CHO & Fat
Hydrochloric acid
stops amylase
Mixing and churning
aids in digestion
No digestion of fiber
Very small amount of
lipase is secreted
Fat tends to separate
from the mixture
Last to leave the
stomach delays
gastric emptying
Carbohydrates
Fat
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Digestion – Stomach - Protein
Hydrochloric acid exposes bonds for enzymes
Denaturization:
irreversibly disrupt the structure of a protein, ending
the function of that protein
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Pepsin
Protein
Smaller AAs
Polypeptides
Digestion – Small Intestine
MOST
DIGESTION &
ABSORPTION
OCCURS IN THE
SMALL
INTESTINE
Pancreas secreted
digestive enzymes
Liver secretes bile
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CHO Digestion – Small Intestine
Amylase
- Starch → Glucose
Maltase
- Maltose → Glucose + Glucose
Sucrase
- Sucrose → Glucose + Fructose
Lactase
- Lactose → Glucose + Galactose
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Produced in
Small
Intestine
Produced in
Pancreas
Protein Digestion – Small Intestine
Proteases secreted
from the pancreas
Break down
proteins and
peptides into AAs
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Fat Digestion – Small Intestine
Need BILE made by liver
Gallbladder stores Bile and
releases into small intestine
Bile emulsifies fat in the
watery intestinal fluid
Makes more surface area
for pancreatic lipase to work
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Carbohydrate Absorption
ONLY Monosaccharides
- glucose, fructose, galactose
Absorbed in small intestine and travel to liver for
processing
All monosaccharides are
converted into glucose in
the liver
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Carbohydrate Absorption
Body is not 100% efficient (≈ 99% efficient)
Small amounts of CHO do not get fully digested and
absorbed by small intestine
Indigestible CHO (Fiber) does not get broken down
and absorbed
Undigested CHO travels to large intestine
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Protein Absorption
AAs and small amounts of
peptide chains absorbed in
small intestine
Need Vitamin B6
AAs Travel to the liver after
absorption
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Protein Digestion
Protein Digestibility
90-99% animal protein
90% soy and legumes
70-90% plant protein
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Fat Absorption
Micelles – fat particles encircled by bile salts to
facilitate absorption
≈ 95% ingested fat is absorbed
Short and medium-chain fatty acids and glycerol
transported to the liver
Monoglycerides and long-chain fatty acids are
insoluble in the bloodstream
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Fat Absorption
Inside intestinal wall – combine
to reform triglycerides
Reformed triglycerides and
cholesterol are encased with
proteins – chylomicron
Chylomicrons travel through
lymphatic system before
entering bloodstream
Chylomicrons – distribute
dietary lipids throughout body
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Excretion
Undigested CHO provide
small amount of energy for
microbes in the colon
(large intestine)
All undigested food travels
through large intestine
Then excreted in stool
through the rectum
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Disorders of the Digestive Tract
Nausea and Vomiting
Heartburn (Gastric Reflux)
Ulcers
Constipation
Diarrhea
Irritable Bowel Syndrome
Lactose Intolerance
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Nausea and Vomiting
May be related to:
- in HCl secretion
- digestive enzyme activity
- gastric irritation
- bacterial/viral infection
- intracranial pressure
- equilibrium imbalance
- liver, pancreatic, and gallbladder disorders
- obstruction
- drugs and certain medical treatments
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Nausea and Vomiting
Short-term concerns
- fluid and electrolyte balance
Intractable vomiting: vomiting that is difficult to
manage or cure
Long-term concerns
- dehydration
- weight loss
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Nutrition Therapy for N/V
Food is withheld until nausea subsides
Progress from clear liquids to regular DAT
Small, frequent meals of low fat, readily digested CHO
Slow eating
Promote good oral hygiene
Limit liquids with meals – may cause fullness/bloating
Liberal fluids in between meals
Serve foods at room temp
Avoid foods that contribute i.e. high-fat and spicy
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Gastroesophageal Reflux Disease (GERD)
Backflow of gastric acid into the esophagus
Abnormal relaxation of lower esophageal sphincter
Symptoms:
- lump in throat
- heartburn
- regurgitation
GERD when symptoms
occur ≥2 times/week
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Nutrition Therapy for GERD
avoid large and/or fatty meals
eat slowly
avoid alcohol, caffeinated
bevs, coffee, soft drinks
avoid spicy foods, chocolate,
citrus foods,
PEPPERMENT
Often called “BLAND
DIET”
exercise
weight loss if BMI >25
avoid lying down for 3
hours after meal
elevate head of bed
during sleep
Diet modifications Lifestyle modifications
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Peptic Ulcer Disease
Erosion of the mucosal layer of the stomach (gastric
ulcer) or duodenum (duodenal ulcer)
Excessive secretion of, or decreased mucosal
resistance to, HCl
15% - stomach
85% - duodenum
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H. pylori infection – 70-92% of ulcers
secretes enzyme that
depletes gastric mucus
Antibiotics generally cure
Not everyone infected
develops ulcer
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Peptic Ulcer Disease – H. Pylori
Nutrition Therapy for Peptic Ulcers
Avoid foods that stimulate HCl secretion/irritate
- coffee, alcohol, chocolate, pepper, garlic
Avoid eating 2 hours before bed
Avoid individual intolerances
High-fiber diet may reduce risk of duodenal ulcers
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Constipation
Difficult/infrequent passage of stools that are hard & dry
Usually less than 3 bowel movements per week
Secondary to irregular bowel habits, psychogenic
factors, lack of activity, chronic laxative use, inadequate
of fiber, metabolic/endocrine disorders, bowel
abnormalities (tumors, hernias, strictures)
Medications such as codeine, aluminum hydroxide,
iron supplements, morphine
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Nutrition Therapy for Constipation
TREAT THE UNDERLYING CAUSE
Fiber and water usually works
Insoluble fiber
– wheat bran, fruit/veggie skins
- increases stool bulk and stimulates peristalsis
Soluble fiber
– oats, barley, nuts, seeds
- absorbs water to produce softer, bulkier stools
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Diarrhea
More than 3 bowel movements per day of large amounts of liquid of semiliquid stool
Shortened transit time → ↓ time for water, Na, and K absorption
→ dehydration, hyponatremia, hypokalemia, acid-base imbalance, metabolic acidosis
Chronic → malnutrition - impaired digestion, absorption, and intake
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Nutrition Therapy for Diarrhea
TREAT THE UNDERLYING CAUSE
Symptoms may be treated with meds that ↓ motility or thicken consistency of stools
Primary Goal: restore fluid and electrolyte balance
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Nutrition Therapy for Diarrhea
Avoid stimulation of GI motility - alcohol, caffeine, clear liquids, milk (lactose), high-fiber and gas-producing foods, sugar alcohols
Mild diarrhea (24-48 hours) requires no intervention other than hydration
Diet ↓ in fat, fiber, lactose diet may ↓GI stimulation
Intractable diarrhea may require complete bowel rest
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Nutrition Therapy for Diarrhea
Lactose-free diet often ordered
BRAT diet
- Banana
- Rice
- Applesauce
- Toast
Both short-term until diarrhea resides
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Lactose Intolerance
Lactase is absent or deficient
Particles of undigested lactose ↑ osmolality of intestinal contents
osmotic diarrhea
Lactose fermented in colon
bloating, cramping, flatulence
Symptoms occur within 15 min – 2 hours after ingestion
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Primary Lactose Intolerance
Occurs in “well” people who do not secrete adequate lactase
Asians, Native Americans, and Africans
Tolerations vary between individuals
Treatment: avoid lactose-containing foods (permanent)
Lactase enzymes
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Irritable Bowel Syndrome (IBS)
Most frequently diagnosed digestive disorder in the US
Affections as many as 20% of American Adults
Symptoms: lower abdominal pain, constipation,
diarrhea, alternating periods of constipation and
diarrhea, bloating, mucus in stool
Can significantly impair quality of life
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Nutrition Therapy for IBS
No conclusive causes/cures/relief of symptoms
Associated with anxiety and depression
Elimination diet: systematically eliminate foods to identify potential food intolerances or allergies
No single therapy is entirely effective
Treatments address symptoms of abdominal pain,
bloating, diarrhea, and constipation
Add soluble fiber, probiotics
Controlled with diet, stress management, and medications
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