The Digestive System

Functions

1. Conversion
The digestive system digest food. This process is, at it's essence, converting the physical stuff that you put in your mouth to actually energy. 
2. Waste Removal
Once all of the nutrients and energy have been extracted in the conversion process, the digestive system also takes care of throwing out what's left. 
3. Hydration
In the process of digesting everything that comes in to the body, the digestive system actually moves around water to maintain body hydration. 

The Mouth

The mouth is the only part of the digestive system that is outwardly evident. It takes care of some basic work for the digestive system, physically breaking down food to provide more surface area for digestive enzymes to take effect. It also secretes saliva, which includes a handful of enzymes and wets food to help it down the esophagus, which simply brings it down to the main digestive organs. 

The Small Intestine

Small is an unfortunate name for this organ with a VERY big job - so big that it has to be split into three subsections. The first, the duodenum, takes care of chemically breaking down the food that is injested. After these are finally broken down to their basic sugars, amino acids, and and simple fatty acids, the jujenum and illeum, the second and third parts of the small intestine, take care of the main part of the digestive system - digestion. Along the intestine are many small, finger-like appendages known as villi, which use a high surface area to maximize the absorption of the nutrients. 

Large Intestine

The large intestine takes everything that the small intestine doesn't absorb and pulls out the water to leave behind the final, solid waste. 

Stomach

The famous symbol o' the digestive system, the stomach is actually a very simple organ that does little past momentary storage. It has a handful of digestive enzymes that further breaks down food, as well as the acid HCL, but past that, it does very little in terms of actual digestion. 

Pancreas

The pancreas in an enzyme production center that is meant to send enzymes that will break down food. It has 4 main enzymes: Trypsin, Lipase, and Amylase, which break down proteins, lipids, and carbohydrates, respectively, as well as insulin, which helps regulate blood sugar levels. 

Liver

The liver is meant almost solely to break down lipids by release bile, a set of inorganic salts which helps break down fatty acids.