**"Understanding the Digestive System: Anatomy and Physiology"**

1. Digestive System • Anatomy • Alimentary canal or gastrointestinal tract • Mouth (Oral cavity) with tongue and teeth • Pharnyx • Esophagus (gullet) • Four layers • Mucosa-innermost, moistened layer • Submucosa-contains blood vessels, nerve endings • Muscularis Externa-muscle layer • Serosa-contains serous fluid and the peritoneum

2. Stomach-can hold up to 1 gallon • Rugae-folds in stomach, used to increases size. • Small Intestine-major digestive organ • Pancreatic and Bile duct supply enzymes for food breakdown • Large surface area • Circular folds (plicae circulares) • Villi fingerlike folds on the deep folds • Microvilli-Tiny projections on the villi • Large Intestine • Cecum, appendix, colon, rectum, anal canal

4. Accessory Organs • Salivary Glands • Empty into mouth • Helps moisten and bind food together • Contains salivary amylase • Begins starch digestion • Has antibodies to kill bacteria • Pancreas-produces enzymes in alkaline solution to be secreted into the small intestine

5. Liver • produces bile, solution containing salts that aid in digestion of fats • Detoxifies blood from alcohol and drugs • Breaks down hormones • Synthesizes cholesterol and some blood proteins • Maintains blood glucose levels • Glycogenesis-formation of glycogen from glucose • Glygogenolysis-formation of glucose from glycogen • Gluconeogenesis-making of glucose from non-carbohydrate (fats and proteins) • Gallbladder-stores bile

7. Physiology • Ingestion-food placed in mouth, eating • Propulsion-food moved along digestive system. • Food Breakdown • Mechanical • Mixing by tongue and teeth (chewing) • Churning of food in stomach • Segmentation in small intestine • Back and forth movement along intestine wall • Chemical

8. Chemical • Breaking down of large molecules into their building blocks by enzymes (hydrolysis) • Carbohydrates to monosaccharides (glucose) • Proteins to amino acids • Lipids (fat) to glycerol and fatty acids • Absorption-transport of nutrients from digestive tract to blood or lymph • Can be done by active or passive transport • Defecation-Elimination of indigestible food (feces)

9. Digestion of food • Mouth (Oral cavity) and Esophagus • Food Ingestion and Breakdown • Mechanically broken into smaller parts • Teeth to masticate (chew) • Salivary amylase (from salivary glands) breaks down starch chemically into sugar. • Saliva is always produced, but production increases when something is placed in mouth (mechanical stimulus) • Thought of food can also start saliva production (psychological stimulus)

10. Food Propulsion-swallowing (Deglutition) • Buccal phase • Voluntary phase • Food is forced into pharynx by tongue • Pharyngeal-esophageal phase • Involuntary • Transports food from pharynx to esophagus by peristalsis • Peristalsis-rhythmic muscle contractions • By autonomic nervous system • Uvula rise to block Nasal passageway • Larnyx rises to push epiglottis to block airway • Hits cardioesophageal sphincter (valve) causing it to open and food enters the stomach

12. Stomach • Food breakdown • Churning-mechanical breakdown • Produces gastric juice • Pepsinogens to Pepsin-digest protein • Rennin-breaks down milk (infants) • Hydrochloric acid-activates enzymes Ulcers-stomach acid eating away at stomach which is usually protected by mucus Heartburn-stomach acid that gets into the esophagus • Produces chyme-heavy cream-like substance • Gastrin-hormone that tells stomach to produce more gastric juice (hydrochloric acid) • 4 hours for stomach to digest meal, 6 if high in fat

13. Absorption • Alcohol and aspirin are only things absorbed in stomach • Food propulsion • Cardioesophageal sphincter-food enters stomach • Pyloric sphincter lets liquids and small particles enter small intestine • Larger particles continue to be broken down by churning • Enterogastric reflex-pyloric sphincter shuts when small intestine is full

14. Vomiting • Reverse peristalsis occurring in stomach • Emetic center in brain stimulated by bacterial infection and disturbance of equilibrium

15. Small Intestine-3-6 hours • Food breakdown • Movement by peristalsis and segmentation • Brush border enzymes-break down double sugars into simple sugars and complete protein digestion • On microvilli • Intestinal juice-enzyme poor, but has protective mucous • Bile-nonenzyme, causes fat to be broken down further, produced by liver

16. Pancreatic juice-enzyme rich from pancreas • Pancreatic amylase-complete digestion of starch • Trypsin, chymotrypsin, carboxypeptidase-some more protein digestion • Lipases-complete fat digestion (only place) • Nucleases-complete nucleic acid digestion • Bicarbonate-makes pH of 8 (alkaline) • Mucus cells-release hormones • Secretin-causes liver to produce more bile and stimulate pancreas • Cholecystokinin-causes gallbladder to release bile and stimulate pancreas

17. Absorption • Water is absorbed the entire length • Most nutrients absorbed by active transport • Fats are absorbed passively by diffusion • Cellulose (plants) is not broken down yet

18. Large Intestine-12 to 24 hours • Food breakdown and absorption • Bacteria that live in lumen metabolize remaining nutrients which produces gas • Bacteria make vitamins (K and B) • Absorption is limited to vitamins, ions, and water • Not absorbed=feces

19. Propulsion • Mass Movement • Long and slow moving • Happens three to four times a day, usually around eating • Defecation reflex-stretching of large intestine wall, can be delayed • Diarrhea-rushes food through large intestine too fast to absorb water • Result in dehydration and electrolyte imbalance

20. Nutrition and Metabolism • ATP=energy • Kilocalories (Calories)-unit of measure of energy in food • Nutrient-substance of food used by the body • Anabolism-large molecules built from small ones • Catabolism-large substances are broken down • Carbohydrates

21. Carbohydrates • Most derived from plants • Preferred fuel for body • Glucose (monosaccharide) major breakdown product • Bonds are broken, combined with Oxygen in Cellular respiration • Glycolysis, Krebs cycle, and electron transport chain • If you have high blood sugar levels, Glucose gets stored as glycogen. If it is still high, glucose gets converted to fat.

22. Lipids • Saturated fats-Found mostly in meats and dairy food • Unsaturated fats-seeds, nuts, and vegetable oil • Broken down to synthesize cholesterol, hormones, build myelin sheath, and protect organs • Excess gets stored in fat deposits • Cholesterol-egg yolk and milk products • Makes hormones and Vitamin D • Only fat not used as energy source • Only 15% of cholesterol is from diet, 85% is made by liver • Low-density lipoproteins (LDLs)-transport cholesterol and fat to body cells • High-density lipoproteins (HDLs)-transport cholesterol and fat from body cells

23. Proteins • Found in animal products • Break down to amino acids • Produce hormones, antibodies, structural material, etc. • Vitamins • Work as coenzymes • Need well balanced diet • Minerals • Most are found in vegetables, legumes, milk, and meat

24. Body Energy • Energy intake-energy taken during food breakdown • calories-energy required to increase 1 ml of water 1 degree Celsius • Carbs and proteins-4kcal/gram • fat-9kcal/gram • Energy output-energy we lose as heat, do work, store as fat and glycogen • Basal Metabolic Rate-amount of heat produced by the body per unit of time (60-72 kcal/hour) • Total metabolic rate-total calories body must consume fuel ongoing activities • TMR is equal to calories consumed, homeostasis is maintained • TMR is less than calories consumed, gain weight

25. Body temperature • 60% of energy is lost as heat to warm body • Heat promoting • Vasoconstriction • Shivering • Heat loss • Vasodilation • Evaporation (perspiration) • Homeostatic Imbalance • Heat stroke-skin is hot and dry, heat-loss mechanisms have shut down, can be fatal • Heat exhaustion-Skin is cold and clammy, can still sweat, heat-loss mechanisms still work