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ABSORPTION Digestion and Absorption of Food Nutrients Digestion •Proteins break down to amino acids •Carbohydrates break down to simple sugars •Fats break down to fatty acids and glycerol Absorption • Digestion and absorption do not take place one step at a time as isolated functions – 92-97% of food is digested – Most substances must be broken down to simple form • When contents pass too slowly (and too much water is removed) = constipation Absorption in Small Intestines Absorption Villi-expand absorptive surface Most nutrients absorbed here Nutrients move from the villi to the blood to be transported all over the body Absorption from Large Intestines • Site of water, salt, vitamin absorption (leaving a mass in a semi-solid state) • Almost everything of nutritional value has been utilized by time it reaches the large intestines -leaving only waste • Feces contains some water, dead intestinal cells, bacteria, nonabsorbed remains of digestion Absorption from Large Intestines • Helpful bacteria in the large intestine feed on the “leftovers” and make vitamins like vitamin K and B Nutrition and GI Disorders • Acid Reflux – Reduced by smaller meals, less fat • Ulcers – Caused by bacteria • Constipation – When too much water is removed in the large intestine Nutrition and GI Disorders • Constipation – Hard, dry, infrequent stools – Reduced by high fiber, fluid intake, exercise • Diarrhea – Loose, watery, frequent stools – Symptom of diseases/infections – Can cause dehydration • Diverticulosis – Pouches along colon – High fiber diet reduces formation Gastric emptying research tells us: Maximal rates of 1-1.2 L /hr with gastric volumes of 100 - 200 mL. Effects of Solution Characteristics on the Rate of Gastric Emptying Solution characteristic Rate of emptying Volume of the solution Increases with larger volumes Caloric content density Decreases as the caloric increases Osmolarity Decreases with hyperosmolar solutions Temperature Faster for cooler fluids than warm solutions pH Decreases with more acidic solutions Summary: Digestion (general) • Digestion breaks down complex molecules into simpler substances for absorption. Selfregulating processes control the liquidity, mixing and transit time of the digestive mixture • Physically altering food in the mouth makes it easier to swallow, and increases access to enzymes and other digestive substances. Swallowing transfers the food to the esophagus where peristalsis propels it into the stomach Summary (cont.) • In the stomach, food contents mix as hydrochloric acid and enzymes continue the breakdown process. Little absorption takes place in the stomach except for some water and alcohol. • About 90% of digestion occurs along the first half of the 3-m long small intestines. Highly specific intestinal enzymes act on more complex CHO, lipid and protein structures, splitting them into simpler subunits. Bile, produced in the liver and secreted by the gallbladder emulsifies lipid droplets, thus facilitating digestive enzyme action. Summary (cont.) • The villi of the small intestine provide a tremendous surface area to absorb digested nutrients. • The large intestine serves and the final path for absorption of water and electrolytes, and storage of undigested food residue (feces).