1. Human Digestive system

2. Digestive System
Composed of Gastrointestinal (GI) Tract and accessory organs
Breaks down ingested food for use by the body
Digestion occurs by mechanical and chemical mechanisms
Excretes waste products or feces through process of defecation

3. Gastrointestinal (GI) Tract / Alimentary Canal
Continuous tube from mouth to anus
Mouth
Pharynx
Esophagus
Stomach
Small intestine
Large intestine

4. Accessory Digestive Organs
Provide mechanical and chemical mechanisms to aid digestion
Teeth
Tongue
Salivary glands
Liver
Gallbladder
Pancreas

6. Digestion Phases Include Ingestion Movement
Mechanical and Chemical Digestion
Absorption
Elimination

7. Mechanical and Chemical Digestion (1)
Mechanical (physical)
Chew
Tear
Grind
Mash
Mix
Chemical
Enzymatic reactions to improve digestion of
Carbohydrates
Proteins
Lipids

8. Mechanical and Chemical Digestion (2)
Mixing waves caused by peristaltic movement
Chyme released in process of gastric emptying
Proton pumps bring H+ into the lumen
Carbonic anhydrase forms carbonic acid to provide H+ and bicarbonate ions (HCO3-)

9. Mechanical and Chemical Digestion (3)
Chemical digestion stimulated by nervous system
Parasympathetic neurons release acetylcholine
Works with gastrin
HCl released in presence of histamine
Pepsin begins digestion of proteins
Stomach protected by alkaline mucus secretion
Gastric lipase digests triglycerides
Few molecules absorbed by stomach
Water, ions, short-chain fatty acids, alcohol

10. Mouth
Teeth mechanically break down food into small pieces. Tongue mixes food with saliva
Epiglottis is a flap-like structure at the back of the throat, preventing food from entering the trachea

11. Salivary Glands Release saliva to oral cavity
3 pairs of salivary glands
Parotid
Submandibular
Sublingual

12. Composition of Saliva 99.5 % water 0.5% other solutes Ions Mucus
Immunoglobulin A
Enzymes
Salivation controlled by autonomic nervous system
Stimulated by various mechanisms

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14. Table 23.1

15. Pharynx Composed of skeletal muscle Lined by mucous membrane
Nasopharynx
Oropharynx
Laryngopharynx

16. Esophagus Approximately 10” long Functions include: Secrete mucus
Moves food from the throat to the stomach using muscle movement called peristalsis
If acid from the stomach gets in here that’s heartburn.
A good way to describe peristalsis is an ocean wave moving through the muscle.
These diagrams don’t separate the esophagus from the mouth functions, you might want to talk about what happens in the mouth too.

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18. Stomach
J-shaped muscular bag that stores the food, breaks it down into tiny pieces.
Mixes food with digestive juices that contain enzymes to break down proteins and lipids.
Acid in the stomach kills bacteria.
Food found in the stomach is called chyme.
The stomach takes around 4 hours to do it’s job on the food, depending on what kinds of food are digested.

19. Figure 23.10a

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23. Small Intestine Small intestines are roughly 7 meters long
Lining of intestine walls has finger-like projections called villi, to increase surface area.
The villi are covered in microvilli which further increases surface area for absorption.
Duodenum
Jejunum
Ileum

24. Small Intestine
Nutrients from the food pass into the bloodstream through the small intestine walls.
Absorbs:
80% ingested water
Vitamins
Minerals
Carbohydrates
Proteins
Lipids
Secretes digestive enzymes

25. Large Intestine About 5 feet long
Accepts what small intestines don’t absorb
Rectum (short term storage which holds feces before it is expelled).
Depending on the maturity of the group, you can talk about the feces leaving via the anus.
Mention the appendix at the bottom of the ascending colon and that it might have been used long ago but is not today
Mention the portions of the large intestine, ascending, transverse, descending, sigmoid, and rectum (last one if the audience is mature enough)

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27. Large Intestine
It absorbs water and any remaining absorbable nutrients from the food before sending the indigestible matter to the rectum.
Recycling of various nutrients takes place in colon. Examples include fermentation of carbohydrates, short chain fatty acids, and urea cycling
The colon absorbs vitamins that are created by the colonic bacteria.
The standing gradient osmosis is the reabsorption of water against the osmotic gradient in the intestines.

28. Accessory Organs
Not part of the path of food, but play a critical role.
Include: Liver, gall bladder, and pancreas

29. Liver and Gallbladder Liver Largest gland at 1.4 kg (~3 lb)
Closely associated with liver

30. Liver Directly affects digestion by producing bile
Bile helps digest fat
filters out toxins and waste including drugs and alcohol
Livers can regenerate missing pieces if necessary. Is one of the largest organs in the body.

31. Gall Bladder
Stores bile from the liver, releases it into the small intestine.
Fatty diets can cause gallstones
Explain to students that removing the stones typically means removing the gallbladder, but that the body eventually adjusts to not having the bile stored.

32. Pancreas
Produces digestive enzymes to digest fats, carbohydrates and proteins
Regulates blood sugar by producing insulin
Explain the difference between the two types of diabetes. In type 1, the pancreas fails to produce enough insulin. In type 2, the body stops responding properly to the insulin it creates.

33. Pancreas Produces secretions to aid digestion Head Body Tail
Pancreatic duct /duct of Wirsung
Hepatopancreatic ampulla
Sphincter of the heatopancreatic ampulla (sphincter of (Oddi)
Regulates passage of pancreatic juice and bile
Accessory duct (duct of Santorini)

35. Figure 23.13c

36. Histology of Pancreas Glandular epithelial cells
99% exocrine clusters
Secrete pancreatic juice
Fluid and enzymes
Pancreatic islets (islets of Langerhans)
1% endocrine cells
Hormones
Glucagon
Insulin
Somatostatin
Pancreatic polypeptide

37. Pancreatic Juice 1200-1500 mL/day pH 7.1-8.2 Water Salts
Sodium bicarbonate
Enzymes
Pancreatic amylase
Trypsin
Entereokinase
Chymotrypsin
Carboxypeptidase
Elastase
Pancreatic lipase
Ribonuclease and deoxyribonuclease

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