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Digestion, Absorption and Metabolism
Presented by
Janice Hermann, PhD, RD/LD
OCES Adult and Older Adult Nutrition Specialist
What Is Digestion
 Process whereby the body breaks down food
into absorbable nutrients.
 Digestive tract is a long tube surrounded by
muscles.
 The muscles alternate contracting and
relaxing pushing food along.
Mouth
 Teeth grind food to reduce the size.
 Saliva released to help moisten food.
 Some carbohydrate digestion begins.
 Tongue pushes food to the back of the mouth
to start swallowing reflex.
 Food passes through the esophagus and
enters stomach.
Stomach
 Distended pouch. Strong circular muscles at
each end control food entering and leaving.
 Mixes food by muscular contractions causing
food to break up further.
 Secretes hydrochloric acid:
 Begins protein digestion.
 Kills microorganisms in food.
 Nutrients not absorbed except water and
alcohol.
Small Intestine
 Most digestion and absorption occurs in small
intestine.
 Bile released to emulsify (break up) fat.
 Pancreatic enzymes released to digest
carbohydrates, proteins and fats.
 Final digestive enzymes in intestinal lining
break down carbohydrates, proteins and fats
into absorbable units.
Final Digestion Products
 Final digestion products absorbed by cells
lining small intestine.
 Carbohydrates:
 Monosaccharides
 Proteins:
 Amino acids
 Chains of 2 or 3 amino acids
 Fats:
 Fatty acids
 Glycerol
 Monoglycerides
 Vitamins, minerals, water and some larger fat-like
compounds such as cholesterol are not broken
down before they are absorbed.
Absorption
 Water-soluble nutrients and short fatty acids
released directly into the bloodstream.
 Longer fatty acids, fat-soluble vitamins, and
fat-like compounds such as cholesterol are
not water-soluble.
 Triglycerides reform in intestinal wall.
 Packaged into a chylomicron and released into
lymphatic system.
Indigestible Matter
 After digestion and absorption of nutrients,
indigestible matter, such as fiber moves into
the large intestine.
 Indigestible matter is compacted by removing
water.
 Little nutrient absorption occurs in large
intestine.
Metabolism
 Chemical reactions that occur in the body:
 Building and maintaining body tissues
 Regulating body functions
 Supplying energy
 For metabolism to occur the body needs:
 Water
 Energy
 Oxygen
 Nutrients