1. The Digestive System

2. DIGESTION (di-'jes-chen): the process of making food absorbable by changing it and breaking it down into simpler chemical compounds

3. all the usable parts of food (called nutrients) can't be used by your body until they are absorbed into the cells & tissues of your body.
They can't be absorbed unless they are small & soluble --- soluble means that they can be dissolved.  So the proteins, carbohydrates, & fats in a turkey sub have to be digested, i.e. changed into a form that can be absorbed and used by the body.
Digestion involves the chemical process of HYDROLYSIS
And the main nutrients in food exist as large proteins, fats, & carbohydrates; which are converted into small amino acids, simple sugars (monosaccharides), and fatty acids. 

4. A turkey sub… FOOD ITEM Chemical Nutrient Building Block
Function of nutrient
Roll
Complex carbohydrate
Simple sugar (monosaccharides)
ENERGY
Slices of TURKEY
Protein
Amino acids
Growth and repair
Cheese and oil dressing
Lipids (FATS)
Fatty acids and glycerol
Structure, stored energy

5. Organs of the Digestive System
anus appendix esophagus gall bladder large intestine (colon) liver mouth (teeth) pancreas pharynx (throat) rectum salivary glands small intestine stomach tongue

6. Organs of the Digestive System - Their Functions
You can think of the digestive system as two sets of structures.
The first set, called the alimentary canal, consists of the organs that food passes through directly. It is a one-way tube with two openings; the mouth (entrance) and anus (exit). Because scientists LOVE to name the same thing more than once, the alimentary canal is also referred to as the gastrointestinal (GI) tract.
The second set of structures are called the accessory organs. These organs are outside of, but connected to, the alimentary canal. For the most part these organs produce chemicals (digestive enzymes) that are used during the process of digestion.  Food that is being digested DOES NOT directly enter any of the accessory organs.  Instead, the accessory organs/glands produce their chemicals & then the chemicals are released into the alimentary canal where they do their job.  

7. Organs of the alimentary canal
Enzymes present
What happens here
MOUTH
Amylase (in saliva)
Mechanical digestion of all food – grinding and chewing, chemical digestion of carbs begins
Esophagus
None
Passageway from mouth to stomach
STOMACH
Pepsin, gastric juice and HCL (hydrochloric acid)
Mechanical digestion of food (churning of stomach walls) chemical digestion of proteins begins
SMALL INTESTINE
Pancreatic juice, intestinal juice, bile
Chemical digestion of carbs, proteins and lipids continues and is completed, small soluble nutrients (sugars, amino acids, fatty acids) are absorbed
LARGE INTESTINE
NONE
Water is absorbed from unusable, indigestable wastes (feces)
RECTUM
Feces are temporarily stored and eliminated through the anus

8. As you can see from the chart, there are two types of digestion, chemical & mechanical.
When you read "mechanical digestion", think chewing, churning or grinding. These are physical processes that break food into smaller pieces, but DO NOT change them chemically. The importance of mechanical digestion is that by breaking food into smaller pieces it increases the surface area on which digestive enzymes can react during chemical digestion.
Chemical digestion is straight forward: it involves chemicals (digestive enzymes) and the process of hydrolysis. Large chemical nutrients are chemically converted to their smaller subunits.
·  The chemicals marked with are technically NOT enzymes, but they are chemicals that help to break down food.  HCl is hydrochloric acid, which is a fairly strong acid (pH of 3). Bile is a liquid that assists in the digestion of lipids (fats). In fancy terms we say that "bile emulsifies fats", which translates as: bile breaks big globs of fat into smaller globs of fat. Enzymes in the small intestine have an easier time digesting small globs of fat.
·Notice that digestion only occurs in three organs: the mouth, stomach, and small intestine.

9. The inside of the small intestine is well-adapted for absorbing nutrients.  Hanging from the walls of the small intestine (which is 6.5 meters long!) are thousands of projections called VILLI.
Inside the villi are two types of vessels, capillaries & lacteals. (The capillaries look like a "web" around the lacteal.) The end products of protein & carbohydrate digestion (namely amino acids & simple sugars) are absorbed into the capillaries. The end products of lipid digestion (fatty acids & glycerol) are absorbed into the lacteals, which are part of the lymph system. The nutrients are then circulated to body cells where they are used for growth, energy, etc.

10. The organs of the alimentary canal are made of smooth muscles, which contract & keep food moving through the long digestive tube. These "waves of contraction" are called peristalsis.

11. Accessory organs of the digestive system
WHAT IT DOES
TONGUE
Helps mix food with saliva, assists in swallowing
SALIVARY GLANDS
Produce saliva, which contain amylase which chemically digests carbs
LIVER
Produces bile, which breaks down fat
GALL BLADDER
Stores bile then releases it into the small intestine
PANCREAS
Produces pancreatic juice which is a mixture of digestive enzymes, aids in digestion of proteins, fats and carbs in the small intestine

12. Epiglottis- little flap of flesh at the top of your esophagus that covers your windpipe when you swallow, so food goes down the esophagus to the stomach rather than getting lodged in your windpipe & causing you to choke.
There is one more flap of flesh to mention.  The appendix is a little deflated-balloon-looking thing that hangs from the large intestine, right around the spot where the small & large intestines meet. It has no function, but scientists think it used to. It's an example of a "vestigial organ", the remains of a once functioning organ from our evolutionary past. You will never pay attention to your appendix unless it becomes infected (appendicitis), in which case you better pay attention to it or it could rupture inside you & cause lots of trouble (even kill you).