Unit 7: The Digestive Tract

fluid containing water, electrolytes and a battery of organic molecules including bile acids, cholesterol, phospholipids and bilirubin : contains bile acids, which are critical for digestion and absorption of fats and fat-soluble vitamins in the small intestine. Many waste products are eliminated from the body by secretion into bile and elimination in feces. From the Liver: Bile

From the pancreas: Bicarbonate is released to quickly neutralize acid from the stomach Many enzymes are released to break down proteins, fats and starches.

Macromolecules are broken down

Polysaccharides: Starch, cellulose & glycogen consist of linked glucose molecules

Triglycerides most abundant storage form of fat in animals or plants most important lipid composed of a molecule of glycerol linked to three fatty acid molecules must be broken down by digestion to be absorbed

Cross-section of Digestive Tract

Blood & Lymph Blood Vessels Arteries and veins infiltrate villi. Arteries pick up nutrients Veins take away wastes. Lymphatic System Vessels infiltrate villi. Lymphatic fluid has substances to bind fat and carry it to blood stream.

Blood from the Small Intestine goes to the Liver first

Stomach Transit Time Varies

Digestive Transit Time

How long does it take?

Digestion and Absorption Over 90% of the protein, fat, & carbohydrate we consume is digested and absorbed. Dietary fiber leaves digestive system in same form as it entered. Humans have no enzymes to break down fiber. Some fiber is digested in the large intestine by bacteria.

Digestive Disorders: common problems Heartburn, hemorrhoids, irritable bowel syndrome, and duodenal and stomach ulcers are leading causes of hospitalization among U.S. and Canadian adults aged years. Digestive disorders are common in children as well as adults. At least one-third of U.S. adults experience heartburn About 30% of school children experience constipation.

Lactose Maldigestion Caused by genetically determined low production of enzyme that digests lactose. After consuming milk  free lactose in large intestine Symptoms: bloated feeling diarrhea due to fluid accumulation, gas and abdominal cramping

Low Lactose and Calcium Rich Foods Dairy Ease Milk and Lactaid Milk Buttermilk, Yogurt, Kefir Cheeses, ice cream (lower than sherbet) Fortified soy milk Orange juice fortified with calcium Often chocolate milk or small amounts of milk with solid food is tolerated well. Lactaid pills or drops. Calcium pills with Vit D