Human Digestion

1. Human Digestion • This part of the life process of NUTRITION process by which an organism obtains and utilizes food

2. Food processing in four stages • Ingestion: taking in food • Digestion: mechanical and chemical breakdown of food so that it can be absorbed by the cells • Absorption: cells lining the digestive tract take up (absorb) small nutrient molecules • Elimination: undigested material passes out of the digestive tract

3. Human Digestion Digestion ≡ 2 part process that changes food into a form useable by the body cells • Mechanical digestion – physical breakdown of large pieces of food into smaller ones • Chemical digestion – hydrolysis – the splitting of large insoluble molecules into small, soluble molecules with the use of water and enzymes ( in other words; breaking complex molecules into simple ones) • The process of chemical digestion (hydrolysis) is regulated by enzymes

4. Examples of chemical Digestion • Carbohydrates + water  simple sugars ( e.g. glucose) • Proteins + water  amino acids • Lipids + water  3 fatty acids + glycerol

5. HUMAN DIGESTIVE SYSTEM • Human digestive tract = GI (gastrointestinal) Consists of a one-way continuous tube (mouth to anus)

6. Mouth • Functions • mechanical digestion • teeth • break up food • chemical digestion (saliva) • amylase enzyme • digests starch All thatin spit!

7. Mouth • mucus • protects soft lining of digestive system • lubricates food for easier swallowing • buffers • neutralizes acid to prevent tooth decay • anti-bacterial chemicals • kill bacteria that enter mouth with food All thatin spit!

8. HUMAN DIGESTIVE SYSTEM • Mouth: (oral cavity) ingests food • Teeth: function in mechanical breakdown of food, increases surface area of food for enzyme action • Tongue: acts as a plunger to push food back into the throat (pharynx) • Taste buds are located on the surface of the tongue

9. mouth break up food digest starch kill germs moisten food

10. HUMAN DIGESTIVE SYSTEM • Pharynx: food is pushed by tongue to back of throat, initiates swallowing – food is now in the form of a bolus • Epiglottis: flap that prevents choking • Esophagus: muscular tube that moves food from mouth to the stomach by process of peristalsis: • wave of muscular contractions that moves chewed food to stomach

11. Swallowing (& not choking) • Epiglottis≡ flap of cartilage • closes trachea (windpipe) when swallowing • food travels down esophagus • Peristalsis≡ involuntary muscle contractions to move food along

12. Stomach • Structure: muscular, expandable bag • Functions • disinfect food • hydrochloric acid ≈pH 2 • kills bacteria • food storage • can stretch to fit ≈2L food • Digestion: pepsin (enzyme) proteins  A.A. But the stomach is made out of protein! What stops the stomach from digesting itself? mucus secreted by stomach cells protects stomach lining

13. stomach kills germs break up food digest proteins store food mouth break up food digest starch kill germs moisten food Cardiac sphincter Pyloric sphincter

14. Ulcers Free of H. pylori Colonized by H. pylori • Used to think all ulcers were caused by stress • tried to treat with antacids • Now know some ulcers caused by bacterial infection of stomach • H. pylori bacteria • now treat with antibiotics inflammation of stomach inflammation of esophagus H. pylori cell damaging proteins (VacA) inflammatory proteins (CagA) cytokines  helper T cells  neutrophil cells white blood cells

15. Small intestine • Functions • digestion • digest carbohydrates • amylase from pancreas • digest proteins • trypsin & chymotrypsin from pancreas • digest lipids (fats) • bile from liver & lipase from pancreas This iswhere all thework is done!

16. Small intestine • Functions • absorption • nutrients move into body cells by: • diffusion • active transport This iswhere all thework is done!

17. Absorption in Small Intestines • Absorption through villi & microvilli • finger-like projections • increases surface area for absorption SMALL INTESTINE6 meters long,but can stretchto cover a tennis court

18. small intestines breakdown food - proteins - starch - fats absorb nutrients mouth break up food digest starch kill germs moisten food stomach kills germs break up food digest proteins store food

19. Pancreas: accessory organ • Produces digestive enzymes • digest proteins • trypsin, chymotrypsin • digest starch • amylase • digest lipids • lipase • Produces buffers • buffers neutralize stomach acid smallintestine pancreas

20. pancreas produces enzymes to digest all foods mouth break up food digest starch kill germs moisten food stomach kills germs break up food digest proteins store food

21. Liver & Gall Bladder: accessory organs • Liver produces bile • Bile breaks down fats • gallbladder only stores bile • that’s why you can have your gall bladder removed bile contains colors from old red blood cells collected in liver = iron in RBC rusts & makes feces brown

22. liver produces bile - stored in gall bladder break up fats mouth break up food digest starch kill germs moisten food stomach kills germs break up food digest proteins store food pancreas produces enzymes to digest all foods

23. Large Intestines • Functions to re-absorb water • use ≈ 9 liters of water every day in digestive juices • if don’t reabsorb water would die of dehydration

24. Large Intestines • Function • 90% of water re-absorbed • not enough water re-absorbed: • diarrhea • can be fatal! • too much water re-absorbed: • constipation • reabsorb by diffusion

25. You’ve got company! • Living in the large intestine is a community of helpful bacteria • Escherichia coli: E. coli • digest cellulose • digests fruits & vegetables • produce vitamins • vitamin K & B vitamins • BUT generate gaseous (flatus) by-products of bacterial metabolism • Methane (CH4), hydrogen sulfide (H2S) • STINKY! Everyone makes 1L to 2L daily PEE-YOO!

26. large intestines absorb water mouth break up food digest starch kill germs moisten food stomach kills germs break up food digest proteins store food liver produces bile - stored in gall bladder break up fats small intestines breakdown food - proteins - starch - fats absorb nutrients pancreas produces enzymes to digest all foods

27. Rectum • Last section of large intestines • after the colon (s-shaped holding area) • eliminate feces through anus • what’s left over? • undigested materials • mainly cellulose from plants • called roughage or fiber • keeps everything moving & cleans out intestines • masses of bacteria, mucus So don’t forget to wash your hands!

28. Vermiform Appendix • Remnant from ancient grass-eating ruminant ancestor Vestigial organ

29. Digestive Homeostasis Disorders • Constipation– person has uncomfortable or infrequent bowel movements results from sluggish peristalsis that allows excess water to be removed from feces (fecal matter hardens)-may result from insufficient fiber in diet • Diarrhea– opposite of constipation– associated with intestinal disturbances caused by infections or stress– prolonged diarrhea may result in severe dehydration • Gall stones– small hard particles made of cholesterol which form & collect in gall bladder- may block the bile duct and cause pain • Acid reflux -backflow of stomach contents upward into esophagus • Appendicitis- inflammation of vermiform appendix