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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