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 IntestineMost 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 ProductsFinal digestion products absorbed by cells lining small

intestine.Carbohydrates:

MonosaccharidesProteins:

Amino acidsChains of 2 or 3 amino acids

Fats: Fatty acidsGlycerolMonoglycerides

Vitamins, minerals, water and some larger fat-like compounds such as cholesterol are not broken down before they are absorbed.

AbsorptionWater-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.

MetabolismChemical reactions that occur in the body:

Building and maintaining body tissuesRegulating body functionsSupplying energy

For metabolism to occur the body needs:WaterEnergyOxygenNutrients