The six major processes of the human digestive system

Digestive System

Digestion Overview

Without the digestive system, the human body (or the body of any organism, for that matter) would not be able to access the nutrients that exists in the form of various food substances produced by nature and increasingly by man. There are six major processes that occur in the digestive system that allow for the necessary nutrients from food to be delivered to the places in the body where it is needed: ingestion, secretion, propulsion or movement, digestion, absorption, and excretion or defecation (MNSU 2010; Advameg 2010). These are carried out by organs that can be categorized into two major divisions, the alimentary canal and the accessory organs (Smith & Morton 2001). The alimentary canal consists of the pathway of organs that take the food substances from ingestion to defecation, with the absorption of nutrients and the influence of accessory organs occurring along the way.

Accessories Are Key

The basic path of digestion, as can be seen above, follows along the alimentary canal. The organs of this canal could not properly perform their functions without the work of the accessory organs, however, particularly the liver and the pancreas. The blood and lymph systems are also vital to digestion's efficacy, transporting nutrients to the cells of the body where they are needed (Smith & Morton 2001). Again, most of the "action" of the accessory organs and their products takes place in the small intestine where the major work of both breaking down and absorbing nutrients takes place (SUNY 2010). It is here that the enzymes secreted by the pancreas and liver arrive to do their work, and it is through the small intestine -- and primarily through the duodenum -- that carbohydrates, proteins, and lipids (fats) as well as other vitamins and mineral nutrients reach the lymph and circulatory systems that carry them throughout the body where they are useful (MNSU 2010).

Pancreatic amylase, one of the enzymes secreted by the pancreas, continues the breakdown of starches that begins in the mouth, converting these carbohydrates into maltose (SUNY 2010). Trypsin and chymotrypsin both continue the breakdown of proteins that began in the stomach, converting specific amino acids into peptides, while lipase breaks fat down into glycerol and fatty acids; all of these are enzymes secreted by the pancreas into the small intestine (SUNY 2010; Smith & Morton 2001). Bile produced in the liver emulsifies fats, and the liver also regulates the absorption and creation of certain nutrients (SUNY 2010).

After the various components of a food item are broken down, they can be absorbed. Active transport mechanisms, which involve complex networks of channel cells creating a flow through the cell walls of intestinal cells, takes the maltose and glucose broken down by the pancreatic amylase and pass it through the wall of the intestine to the bloodstream (Gillson 2005). Similar processes are used to move the amino acids that result from the breakdown of proteins through the wall and into the bloodstream as well, and from thence to the rest of the body (Gillson 2005; SUNY 2010). The fatty acids and glycerol that are produced by liver enzymes are absorbed into the villi of the small intestine, where they are actually reassembled into fats or lipids before being transported to various parts of the body via the lymph system for storage (Gillson 2005). In this way, many different organs and systems that are not a part of the alimentary canal and thus do not actually come into direct contact with food materials still play an essential role in digestion.

Conclusion

The end result of a properly functioning digestive system is that the necessary nutrients are drawn out of food items with a maximum efficiency, utilizing the body's resources without unnecessary waste and taking full advantage of the available nutrients in foods that are eaten. This requires the organs and functions of the alimentary canal as well as the accessory organs to be fully accomplished. Through the complex interplay of enzymes and transport mechanisms, however, nutrients are delivered properly.