The Human Digestive System

Chemical Digestion of Food• Use the following words

to label the diagram (in boxes):– Triglyceride– Monosaccharides– Amino Acids– Fatty Acids– Polypeptide– Polysaccharide– Disaccharide– Glycerol

Form when eaten Form after digestion

• What is the name of the process represented by the arrows? __________________

Polypeptide

TriglycerideHydrolysis

• Carbohydrates (2 places) ______________________

• Proteins (2 places) ________________________

• Lipids ____________________________

• Which enzyme(s) digest these molecules in each location? Add to answers above:– pepsin, amylase, lipase, trypsin, sucrase, lactase, peptidase

Where does the chemical digestion of each of the following occur? Try to follow this during lecture/discussion and your reading. Return to & answer these questions after reading or lecture… We will not answer these just yet!

The Fours Stages of Food Processing

(Eating) (Breaking down food MECHANICALLY & CHEMICALLY)

(Nutrients & water go from digestive system into BLOOD, to CELLS)

(Undigested food/solid waste leaves body as poop)

Your Digestive System is like the hole in a

doughnut…

The Digestive system is like a tube that runs through the middle of your body.Food goes in one end, and food waste comes out the other.

http://thumbs.ifood.tv/files/dood.jpg

The Human Digestive System

How it begins…Mouth to Stomach

• Mouth: Food is chewed (mechanical digestion) & moistened with saliva. Salivary amylase begins chemical digestion of starches (carbohydrates).

• A slimy food ball (the bolus) leaves mouth, slides past epiglottis (covering opening to trachea) to the esophagus.

What happens if the epiglottis does not do it’s job??

http://bio1903.nicerweb.com/Locked/media/ch41/41_16SwallowPeristalsis_1.jpghttp://bio1152.nicerweb.com/Locked/media/ch41/pharynx_swallow.html

Digestive Problem: ChokingWhen you try to talk & eat at the same time…

http://thehealthybear.com/wp-content/uploads/2012/08/choking-first-aid.jpg

How it begins…Mouth to Stomach

• Esophagus: The bolus moves down this muscular tube by peristalsis (waves of muscle contractions), to the stomach.

http://images.tutorvista.com/content/nutrition/peristalsis.jpeg

Esophagus

PERISTALSISWhat happens when you do a handstand and try to eat a Gummi Bear, while upside-down?

In the Stomach

• Stomach: Muscular sac that releases hydrochloric acid (HCl) & the enzyme Pepsin to begin digestion of proteins. Stomach lining is protected from acid by continually secreting protective mucus.

• Digesting food kept in stomach by the lower esophageal sphincter (at entrance) and the pyloric sphincter (at exit).

• Pyloric sphincter squirts partially digested mix of nutrients, water, & acid into the duodenum of the small intestine over 2-6 hours. This liquid is called chyme.

http://www.drhirani.com/wp-content/uploads/2012/07/Stomach-Plain.jpg

Digestive Problem: Acid Reflux & GERD• What happens when acid escapes the stomach into the

esophagus? This is called Acid Reflux or “heartburn”.

http://img.webmd.com/dtmcms/live/webmd/consumer_assets/site_images/tools/heartburn-tool/understanding_heartburn.jpg

Digestive Problem: Ulcers• Mucus can be eroded by several causes: H. pylori bacterium

infection or stomach exposure to NSAIDs, asprin, alcohol, gastric hyper-acidity, cigarettes, etc.

• Result: damage to cells lining stomach gastric ulcer

http://images.wisegeek.com/peptic-ulcer-diagram.jpg

Ulcers can also occur in the esophagus or the duodenum.

Completion of Digestion in Small Intestine

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Small Intestine (duodenum)• Digestion of carbs, fats & proteins is completed using bile from

liver & enzyme-filled pancreatic juice & intestinal juice.• Sodium bicarbonate from the pancreas neutralizes acidic chyme in

duodenum. (not shown in picture)

Digestion is necessary

for Absorption

http://www.skinmed.co.uk/images/skinsideout/enzyme%20function.jpg

Chemical Digestion SummaryNutrient Mouth Stomach Small Intestine

Carbohydrates (Starch)

Hydrolysis of starch into disaccharides begins (by salivary amylase).

Starch into disaccharides continues (by pancreatic amylase).Disaccharides into monosaccharides (by maltase, sucrase, lactase, etc.)Monosacchrides like glucose can now be absorbed.

Proteins Large polypeptides into smaller polypeptides (by the enzyme pepsin).

Large polypeptides into smaller polypeptides (by trypsin, chymotrypsin).Smaller polypeptides into amino acids (by peptidases).Amino acids can now be absorbed.

Fats Fat globules into fat droplets (by bile salts – emulsifiers, not enzymes…more like detergent).Fats (triglycerides) into Fatty acids and glycerol (by lipase).Fatty acids and glycerol can now be absorbed.

Note: Mechanical digestion of all nutrients occurs in all locations listed above.

Absorption of Nutrients in Small IntestineSmall Intestine (jejunum & ileum)• Absorption: Nutrient monomers are transported from lumen of small

intestine into bloodstream, and from there to body’s cells.• Absorption helped by large surface area of small intestine, due to projections

called villi, and their projections called microvilli.

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Villi of Small Intestine

http://video.ecb.org/badger/download/vlc/images/VLC181_Villi_in_small_intestine.jpg

Where next?

Large Intestine: Absorption of Water & More!Large Intestine: Colon• Remaining water is absorbed & undigested solids are compacted

into feces (poop). • Home to mutualistic bacteria, like E. coli, which produce

important vitamins (B vitamins, vitamin K)

Large Intestine: Rectum• Stores waste until

elimination.

http://img.webmd.com/dtmcms/live/webmd/consumer_assets/site_images/media/medical/hw/h9991263_001.jpg

Problems/Diseases of Digestive System• Heartburn / Acid Reflux: HCl escapes stomach & “burns” lining of esophagus• Ulcer: “hole” in mucus & cells lining stomach, caused by HCl and H.Pylori bacterium• Lactose Intolerance: Inability to digest milk sugar, bloating & gas when dairy is consumed• Diarrhea: too much water in feces, frequent watery elimination• Constipation: not enough fiber in diet, infrequent elimination & compacted feces• Appendicitis: infection & inflammation of appendix• Gallstones: “stones” of bile salts in gall bladder, can be eliminated through narrow bile

duct into digestive system (painful)• Celiac disease: cannot process gluten (a protein found in wheat), destroys villi &

negatively affects nutrient absorption• Inflammatory Bowl Disease (IBD): chronic inflammation of all or part of your digestive

tract. IBD primarily includes ulcerative colitis and Crohn's disease. Both usually involve severe diarrhea, pain, fatigue and weight loss. IBD can be debilitating and sometimes leads to life-threatening complications.*

• Cancers of the digestive system, esp. colon or rectum (most common)

* From http://www.mayoclinic.org/diseases-conditions/inflammatory-bowel-disease/basics/definition/con-20034908