Human nutrition is a very vast and profound topic that has always been extensively taught and read about in every part of the world. Considering man to be the most developed being on earth, it is logical that each and every organ system is complex, elaborate but at the same time very systematic. So it really makes sense that when we talk of something like human nutrition, an array of many different organs comes to our mind. To make this simple to understand, author David Krough has come up with the fourth edition of his famous book, A Guide to the Natural World in order to explain and enlighten about the various components of human system.

In the chapter Human Nutrition he has elaborated on each and every organ and its functions in the human system. He begins by explaining about the elements of the digestive system; that is, what would be the chief components in it. The central structure of the human digestive system, the digestive tract is defined as a muscular passageway for food and food waste that runs through the human body from the mouth to the anus.

There are four chief functions of the digestive system, namely:

a) To get the foods the body ingests into a form the body can use.

b) To move food in this form out of the digestive tract and into blood circulation.

c) To retain the waste that remains after nutrients from the food have been transferred.

d) To eliminate this waste from the body

The author describes Digestion as a process of breaking down foods-first into small pieces and then into small molecules. These small molecules leave the digestive system for transport through the rest of the body.