1. ABSORPTION

2. 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

3. 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

4. Seven Functions of Digestive System 1.Receipt, maceration and transport of ingested substances and waste products 2.Secretion of acid, mucus, digestive enzymes, bile and other materials 3.Digestion of ingested foodstuffs 4.Absorption of materials 5.Storage of waste products 6.Excretion 7.Ancillary functions

5. Percent Digestibility of Nutrients FoodProtein Percent Lipid Percent CHO Percent Animal979598 Cereals859098 Legumes789097 Sugars, Starch98 Vegetables839095 Fruits8590 Vege foods849097 Total food929597

6. Digestive System Mouth Esophagus Stomach Small Intestines Large Intestines and Rectum Anus Pancreas Liver and biliary Tract See Overhead

7. Digestion in the Mouth Teeth Saliva secreted by 3 pairs of glands –Parotid, submillary, sublingul –1.5 liters of saliva/d –2 types of saliva Watery - dissolve food Mucus- makes food stick together Salivary amylase - begins starch digestion in mouth

8. Overview of Absorption Absorptive mechanisms –Passive diffusion Facilitated diffusion Active transport

9. Digestion in the Stomach In the process of gastric digestion the food becomes semi-liquid and contains about 50% water –Food remains in stomach about 0.5-2 h –Gastric juices (mucus, HCL) = 2000-2500 mL/d Foodstuff leaves the stomach in the following order: –CHO; protein; lipid (takes the longest) Stomach is normally emptied in 1-4 h –Exercise may delay gastric emptying by decreasing blood flow –Lipid and protein delay gastric emptying

10. Digestion in Small Intestines (duodenum, jujunum, ileum) The well liquefied mass (chyme) slowly moves through the exit valve (pylorus) at the junction of the stomach Valves (sphincters) prevent backflow (influenced by nervous system) When exit pyloric valve tighten or goes into spasm = pain Mild exercise enhances digestive process Violent exercise inhibits digestion Fluid speeds digestion Average meal reaches duodunum 2-3 h after eating

11. 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 in Small Intestines

12. Absorption from Small Intestines Tremendous absorption area (mucosa, convoluted villi; microvilli Mechanism of Absorption –Pores; carriers; pumps; pinocytosis (“drinking in”) Not just a process of diffusion Active “shuttle” transport Pores are selective Carriers are specific –Takes energy (kCal) for digestion Dietary induced thermogenesis See Overhead

13. 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, non- absorbed remains of digestion

14. Absorption from Large Intestines Helpful bacteria in the large intestine feed on the “leftovers” and make vitamins like vitamin K and B

15. Regulation of GI Activity Nervous system –Regulates GI activity Local system of nerves Central nervous system Hormonal system –Increases or decreases GI activity

16. 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

17. 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

18. Digestive Problems and Nutritional Consequences Dry mouth Dental pain and loss of teeth Heartburn Ulcers Vomiting Pancreatic disease Gallstones

19. Heimlich Maneuver - series of under- the-diaphragm abdominal thrusts for helping a person who's choking on a foreign object (foreign-body airway obstruction).

24. Summary: Digestion (general) Digestion breaks down complex molecules into simpler substances for absorption. Self- regulating 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

25. 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.

26. 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).