1. The Digestive System

2. Introduction
The digestive system is used for breaking down food into nutrients which then pass into the circulatory system and are taken to where they are needed in the body.

3. Nutrients
Body cells need a constant supply of nutrients for energy and building blocks.
Nutrients include:
Carbohydrates
Fats
Proteins
Vitamins
Minerals

4. Accessory Organs Digestive Tract
(Helps with digesion, but is not in direct contact with the food.
Digestive Tract
(Long tube where food moves and is digested)
Mouth
Salivary Glands
Pharynx
Esophagus
Liver
Stomach
Gall Bladder
(Behind liver)
Small Intestine
Pancreas
(Behind Stomach)
Large Intestine
Rectum
Anus

5. There are 4 Stages to Food Processing
DESCRIPTION
LOCATION(S)
1) Ingestion
Food enters the digestive system
Mouth
2) Digestion
Physical
Chemical
Food is physically broken down into smaller pieces
Digestive Enzymes break food pieces into smaller, microscopic molecules.
Mouth, Stomach
Mouth, Stomach,
Small Intestine
3) Absorption
Water and digested food enter the bloodstream from the digestive system
Small intestine (food), large intestine (water)
4) Elimination
Undigested food leaves the system in the form of feces
Anus

6. The Steps of Digestion - #1 The Mouth
Teeth: physically break down food.
Molars: crushing
Premolars: grinding
Canines: tearing
Incisors: biting
Salivary glands: secrete saliva, which contains the enzyme amylase, which starts to break down carbohydrates.
Tongue: mixes food with saliva & pushes food to back of mouth.
Has your mouth ever “watered” when you were thinking about something to eat?
That “water” is saliva - preparing you for a meal!

7. The Steps of Digestion - #2 From Mouth to Stomach
Bolus: ball of food that travels from mouth to stomach.
Uvula: helps keep food from going up into the nasal cavity when swallowing.
Pharynx: top of throat
Larynx: contains the voice box.
Epiglottis: A flap that covers the trachea (windpipe) so food does not enter lungs.

8. The Steps of Digestion - #2 From Mouth to Stomach
Peristalsis: strong waves of muscular contractions.
Esophagus: muscular tube going from mouth to stomach.

9. The Steps of Digestion - #3 The Stomach
Stomach: muscular, bag-like structure that continues physical and chemical digestion.
Rugae: folds in stomach wall allow it to stretch (from sausage-size to 4L!)
Esophageal Sphincter: keeps contents from going up the esophagus.
Pyloric Sphincter: keeps contents from leaving the stomach too early.
Sphincter: circular muscle that can open and close.

10. The Steps of Digestion - #3 The Stomach
Physical Digestion: Stomach churns by peristalsis, breaking food into smaller pieces.
Chemical Digestion: Gastric Juice is produced by cells in stomach lining
Water, mucus, hydrochloric acid (HCl), enzymes
As acidic as a car battery!
HCl activates pepsin, an enzyme which digest proteins.
The Steps of Digestion - #3 The Stomach
Cells in the stomach lining produce mucus. Mucus forms a barrier between the gastric juice and the stomach lining. Why is this important?
Food + Gastric Juices = Chyme

11. The Steps of Digestion - #4 Small Intestine
Two main functions:
Finish digesting nutrient molecules into simple monomer nutrient molecules
Absorb monomer molecules into the bloodstream, so they can go to where they are needed
Three main regions:
Duodenum
Jejunum
Ileum

12. The Steps of Digestion - #4 Small Intestine - Duodenum
First 25 cm of the small intestine
Ducts from accessory organs join forming one duct, attached to duodenum by the
Sphincter of Oddi.
3 Accessory Organs:
Pancreas
Liver
Gall Bladder
The Steps of Digestion - #4 Small Intestine - Duodenum

13. The Steps of Digestion - #4 Small Intestine - Duodenum
Pancreas
Produces pancreatic juice that contains enzymes that break down proteins, carbohydrates, fats, and nucleic acids.
Contains sodium bicarbonate – neutralizes the HCl in the chyme.
The Steps of Digestion - #4 Small Intestine - Duodenum

14. The Steps of Digestion - #4 Small Intestine - Duodenum
Liver
Largest organ in the body, and has more than 200 functions.
Enzymes are hydrophilic, fats are hydrophobic  enzymes cannot get to fats!
Liver produces bile, which is an emulsifier – helps mix enzymes and fats.
Gall Bladder
Stores bile until chyme triggers it to be released

15. The Steps of Digestion - #4 Small Intestine – Duodenum
Absorption in the Duodenum
Villi:
Tiny, finger-like projections inside the duodenum, each contains thousands of microvilli.
Each contain tiny blood vessels called capillaries
Absorb protein and carbohydrate monomers
Each contain tiny lymph capillaries called lacteals
Absorbs fat monomers
The villi increase the amount of SURFACE AREA for absorption to occur.

16. The Steps of Digestion - #4 Small Intestine – After the Duodenum
Jejunum
About 2.5 meters long
Continues to digest & absorb micronutrients
Ileum
About 3 meters long
Only absorption
Pushes undigested material into the large intestine
Peristalsis continues through the whole digestive system.

17. The Steps of Digestion - #5 Large Intestine
Digestion does not take place in the large intestine.
Concentrates and eliminates waste material
Absorption of water & salts
Colon Bacteria: billions of helpful bacteria break down undigested material.
Peristalsis continues through the whole digestive system.

18. The Steps of Digestion - #6 Elimination
Feces: condensed left-overs and bacteria.
Passes to the rectum where it is stored until release.
Anus: 2 sets of sphincters, one of which is controlled by us
When rectum is full, receptor cells trigger a reflex that causes peristalsis.
What is a “fart?”
Mostly made of swallowed air.
Colon Bacteria produce hydrogen sulfide as a by-product
Hydrogen sulphide smells like rotten eggs.

19. The Appendix
Function
If very ill with severe diarrhea, the good Colon Bacteria will be flushed out of the digestive system.
The Appendix acts as “back-up storage” for good bacteria, which can quickly recolonize the colon after a bought of illness.
Appendicitis – swelling of the appendix due to blockage. If bursts, can be fatal. Must be removed.