1. Neutralising the acidic environment.
The stomach and bile.
The stomach is very acidic due to cells in the lining producing HCl. This means that the semi digested food is very acidic entering the small intestine. Bile plays two main parts.
Neutralising the acidic environment.
Emulsifying fats to provide a larger surface area for lipase to work on.

2. Problem!
The gastric juices are acidic! There could be a danger of the lining of the small intestine being digested.
Luckily two substances are produced to stop this happening. The first is mucus and we have seen how this works. The second is Bile.
Bile is made in the Liver. It is a yellow/green liquid that is naturally alkaline (pH > 7).

3. + This means that when Bile and the Gastric Juices meet,
…the result is neutralisation of the acid.
This is essential for the lipase (the enzyme that digests fat) to function properly.
pH >7 +
pH <7
Neutralisation

4. Part of the Small Intestine

5. Let’s consider the process of fat digestion.
 This section of the digestive system exemplifies the true idea of an organ system as a group of organs working together for a common function.
The influential organs in the digestion of fat are the:
Liver
Gall bladder,
Pancreas
Small intestine.
Each organ plays its part in turning Fat into fatty acids and glycerol phosphates

6. Fat within the gastric juice
Liver produces Bile
Fat within the gastric juice
It is released from the Gall bladder and passes down through the bile duct
The Bile and the fat meet within the small intestine. The Bile emulsifies the fat. This basically means the fat is physically broken into smaller pieces.
Emulsification
Notice that the fat has not been chemically digested, only physically. The result is a greater surface area over which the enzyme, lipase, can attack the fat.

7. The pancreas and the small intestine now release enzymes
The pancreas and the small intestine now release enzymes. Both organs produce all three enzymes, Carbohydrase, protease and lipase.
pancreas
small intestine
If we just consider fat, the lipase begins to break its chemical bonds.

8. Lipase
Glycerol Phosphate
Fat
Fatty Acids

9. Bile emulsifies the fat. Muscular action of the small intestine
In summary the digestive action of the small intestine and associated organs can be represented in the following diagram.
Fat
Sugar
Protein
Carbohydrates
Amino Acids
Physical Digestion
Chemical Digestion
Bile emulsifies the fat. Muscular action of the small intestine
Lipase enzyme
Protease enzyme
Carbohydrase enzyme
Sugar
Glycerol Phosphate
Amino Acids
Fatty Acids