1. Unit 7 – Digestion and Absorption
1

2. Key Terms
2

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

3. Upper Digestive Tract
3

Mouth
- chewing and saliva
- amylase/lipase

Esophagus
- propels food downward to
stomach

Stomach
- churns and mixes
- Pepsin/intrinsic factor/lipase

4. Lower Digestive Tract
4

Small Intestine

Large Intestine

Rectum

Accessory Organs
- Liver
- Gallbladder
- Pancreas

5. Digestion – Begins in the Mouth
5

Chewing
breaks down food
into smaller
particles

Mixing with saliva

Adding digestive
enzymes

6. Digestion – Mouth – Carbohydrates
6

Salivary Amylase:
Starch  glucose molecules

Teeth and saliva soften fiber for swallowing

7. Digestion – Mouth – Protein
7

Teeth soften fibers to swallow

NO CHEMICAL DIGESTION OF PROTEIN
OCCURS IN THE MOUTH!

8. Digestion – Mouth – Fat
8

Lingual Lipase:
Triglyceride  Monoglyceride + fatty acids

VERY MINIMAL

9. Digestion - Stomach
9

Churns and mixes
contents

Hydrochloric acid
secreted

Digestive enzymes
secreted

10. Digestion – Stomach – CHO & Fat
10
Carbohydrates
Fat

Hydrochloric acid
stops amylase

Very small amount of
lipase is secreted

Mixing and churning
aids in digestion

Fat tends to separate
from the mixture

No digestion of fiber

Last to leave the
stomach  delays
gastric emptying

11. Digestion – Stomach - Protein
11

Hydrochloric acid exposes bonds for enzymes

Denaturization:
irreversibly disrupt the structure of a protein, ending
the function of that protein

Pepsin
Protein
Smaller
Polypeptides
AAs

12. Digestion – Small Intestine
12

MOST
DIGESTION &
ABSORPTION
OCCURS IN THE
SMALL
INTESTINE

Pancreas secreted
digestive enzymes

Liver secretes bile

13. CHO Digestion – Small Intestine
13
Produced in
Small
Intestine

Amylase
- Starch → Glucose

Produced in
Pancreas
Maltase
- Maltose → Glucose + Glucose

Sucrase
- Sucrose → Glucose + Fructose

Lactase
- Lactose → Glucose + Galactose

14. Protein Digestion – Small Intestine
14

Proteases secreted
from the pancreas

Break down
proteins and
peptides into AAs

15. Fat Digestion – Small Intestine
15

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

16. Carbohydrate Absorption
16

ONLY Monosaccharides
- glucose, fructose, galactose

Absorbed in small intestine and travel to liver for
processing

All monosaccharides are
converted into glucose in
the liver

17. Carbohydrate Absorption
17

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

18. Protein Absorption
18

AAs and small amounts of
peptide chains absorbed in
small intestine

Need Vitamin B6

AAs Travel to the liver after
absorption

19. Protein Digestion
19
Protein Digestibility

90-99% animal protein

90% soy and legumes

70-90% plant protein

20. Fat Absorption
20

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

21. Fat Absorption
21

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

22. Excretion
22

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

23. Disorders of the Digestive Tract
23







Nausea and Vomiting
Heartburn (Gastric Reflux)
Ulcers
Constipation
Diarrhea
Irritable Bowel Syndrome
Lactose Intolerance

24. Nausea and Vomiting
24

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

25. Nausea and Vomiting
25

Short-term concerns
- fluid and electrolyte balance

Intractable vomiting: vomiting that is difficult to
manage or cure

Long-term concerns
- dehydration
- weight loss

26. Nutrition Therapy for N/V
26









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

27. Gastroesophageal Reflux Disease (GERD)
27




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

28. Nutrition Therapy for GERD
28
Diet modifications





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”
Lifestyle modifications




exercise
weight loss if BMI >25
avoid lying down for 3
hours after meal
elevate head of bed
during sleep

29. Peptic Ulcer Disease
29




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

30. Peptic Ulcer Disease – H. Pylori
30

H. pylori infection – 70-92% of ulcers

secretes enzyme that
depletes gastric mucus

Antibiotics generally cure

Not everyone infected
develops ulcer

31. Nutrition Therapy for Peptic Ulcers
31




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

32. Constipation
32

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

33. Nutrition Therapy for Constipation
33

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

34. Diarrhea
34




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, acidbase imbalance, metabolic acidosis
Chronic → malnutrition
- impaired digestion, absorption, and intake

35. Nutrition Therapy for Diarrhea
35



TREAT THE UNDERLYING CAUSE
Symptoms may be treated with meds that ↓ motility
or thicken consistency of stools
Primary Goal: restore fluid and electrolyte balance

36. Nutrition Therapy for Diarrhea
36

Avoid stimulation of GI motility
- alcohol, caffeine, clear liquids, milk (lactose), highfiber 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

37. Nutrition Therapy for Diarrhea
37

Lactose-free diet often ordered

BRAT diet
- Banana
- Rice
- Applesauce
- Toast

Both short-term until diarrhea resides

38. Lactose Intolerance
38


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

39. Primary Lactose Intolerance
39

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

40. Irritable Bowel Syndrome (IBS)
40

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

41. Nutrition Therapy for IBS
41

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