There are identified two types of actions of digestive system, such as: muscular action, enzyme action.
Muscular action is mechanical and it helps for food to be broken down into smaller pieces, having a larger area of a surface that facilitates the enzymatic action.
Enzymatic action is chemical, enzymes acting like catalysts to break down the big molecules, such as proteins and fats, into small molecules, such as amino acids fatty acids, glucose, facilitating their diffusion into the blood.
Digestion process begins when the food is introduced into mouth and it is masticated in order for the food to be broken down in smaller pieces and the nutrients from food to be released into the body. When the food is broken dow is smaller pieces, the chemical components of the food are identified and appropriate enzymes are released. The enzyme from saliva contains amylase, that breaks down the bonds between glucose molecules.
When the chewed food reaches in stomach, the enzymes in the stomach, such as pepsin, continue the food digestion. Pepsin enzyme is the active form of pepsinogen and it helps in digestion process, by breaking down the polypeptides into dipeptides or peptides. Usually, pepsin only acts on proteins, such as collagen.
Then, the partially digested food reaches the small intestine, where it combines with substances secreted by pancreas and liver, such as pancreatic juice and bile. These substances help in fat and carbohydrates digestion. For example, pancreatic juice contains lipase enzyme, which breaks down the fatty molecules into glycerol and fatty acids. Amylase enzyme, also found in pancreatic juice, breaks down carbohydrates into disaccharides, and then in monosaccharides.
After digestion, the resulted glucose, fatty acids, glycerol, and amino acids, can be used by the body.
The digestive system is based on two things. First, the gut uses its muscles to squeeze and break down food into small pieces allowing for a large surface area. Next, various digestive juices break down the molecules and the food is moved to another area for chemical digestion. The second part of the digestive system are the enzymes. Enzymes act as a catalyst, causing the reactions to happen faster and allowing the food to break down faster.