The Ins and Outs of Digestion

The Ins and Outs of Digestion

When we become hungry it sends sensations to the the brain and hormones that it is time to prepare the body for digestion of macro nutrients fat, carbohydrates, and protein, to keep the body renewing.

To see a 3-D image of how the digestive system works click here.

Once foods enters the mouth the brain begins to send signals the rest of the body that it is time to begin to digest and absorb the food.  The purpose of the digestive tract is to give the body a large surface area to absorb nutrients into the blood stream, and excrete any unusable materials from the body.  The flexibility of the digestive system allows food to travel through the digestive system.  The food begins its journey through the mouth and travels through the throat, esophagus, stomach, small intestine, large intestine, and through the rectum into the anus.  Each of these areas of the digestive tract has a specific purpose for digestion and absorption of nutrients.  There are also organs on the outside of the digestive tract that help with the digestion of food; the liver, the gallbladder, and the pancreas. 

In the mouth the food is prepared for digestion by being chewed into little pieces using the teeth. The tongue and the jaw help to move the food around in the mouth so that it is masticated enough to be digested.   In the mouth there are acids and enzymes called amylase, as well as water, and mucous.  All of these form saliva that helps to break down the starches and start to break down fat.  

Through mashing and squeezing, otherwise known as peristalsis, the masticated food that is now in the form of a ball or bolus is then moved into the pharynx where this peristalsis pushes it into the esophagus.  The esophagus, which is about 25 cm long (The Digestive Tract, 2001), takes the bolus down through the cardiac sphincter into the stomach where the food is mashed into a "fine paste" (Sizer & Whitney, 2014) using the muscle layers of the stomach.  There are digestive juices in the stomach that help to break down the food.  These digestive juices are made up of Hydrochloric Acid, Pepsin, and Mucous.  The Hydrochloric acid breaks down proteins so that they are soft and can be digested easier.  Hydrochloric acid also acts as a way of protecting the stomach from bacteria.  Pepsin protects the stomach from being burned by its own acids and breaks down the proteins into amino acids.  Once the food has been sufficiently mixed and churned it becomes a liquid called Chyme.  

Now that the food is in Chyme form it will be controllably forced a little at a time through the bottom sphincter muscle called the pyloric valve.  This is the entrance of the small intestine known as the duodenum.  The small intestine is where the nutrients are absorbed through millions of little villi and microvilli.  This occurs over several hours before emptying into the large intestine or colon.    Once in the small intestine hormones signal the gallbladder to contract and release an emulsifier or bile.    The pancreas is also alerted that it needs to release its chemicals known as bicarbonate.  These have to be released in just the right amount in order to help reduce the stomach's acid.  The walls of the small intestines also have enzymes that help make the nutrients small enough to absorb carbohydrates, fats and proteins.  Some water, fiber, and minerals stay in the colon and are broken down by bacteria.  This fiber releases fat that is absorbed by the cells in the intestines for energy.

The large intestine is "wider than the small intestine but shorter in length" (The Digestive Tract, 2001).  The job of the large intestine is to eliminate the unused waste and reabsorb water that was freed in the early digestive process and absorb minerals.  There are not any enzymes released in the colon so there is no digestion occurring at this point.  From here the solids travel through the rectum and out through the anus where they leave the body.

       

A healthy body requires a healthy digestive tract.  When eating our body is signaled to begin the digestive process which consists of mechanical and chemical processes working together to break down the food so that nutrients and minerals as well as fats and proteins can be absorbed into the body to help with the constant renewal of the body and to provide energy.   Maintaining a proper diet and being in tune with the normal workings of the digestive tract can help to ensure healthy digestion and therefore a healthy body.

References:

The Digestive System. YouTube.  Retrieved from http://www.youtube.com/watch?v=Z7xKYNz9AS0&feature=related

Cohen, B.G. & Wood D.L. (2000). Digestive System. Memmler's the Human Body in Health and Disease (9th ed.). Philadelphia Lippencott, Williams, & Wilkins.

The digestive tract. (2001). Chemist & Druggist, , 19. Retrieved from http://search.proquest.com/docview/274881530?accountid=32521

Inner Body. (n.d.). Digestive System. Retrieved from http://www.innerbody.com/image/digeov.html

Sizer, F. & Whitney, E. (2013).  Nutrition: Concepts and Controversies (13th ed.).  Mason, OH: Cengage Learning.