The human digestive system is complex, and has multiple parts that work in cohesion to break down, process and distribute nutrients to the body. There is a mechanical and chemical process involved, which makes the system efficient in those areas. A properly functioning digestive system is imperative for the nutrients we receive from our food to be used to fuel our bodies effectively.

The purpose of the digestive system is to first break down the food we eat, which means to reduce it from its whole form, and then absorb the nutrients and some non-nutrients while passing the left over substances through excretion. The digestion and absorption process is composed of multiple individual levels and functions, performed by several different organs during the overall process. “The digestive tract and alimentary canal are names for the tubular organs that extend from the mouth to the anus. The whole system, which includes the pancreas, liver and gallbladder, is sometimes called the gastrointestinal or GI system” (Sizer & Whitney, p. 79). After the digestion process, the nutrients from the food are then absorbed by the body and used as energy for the body’s organs and tissue. During absorption, nutrients are dispersed to cells after they are digested.

The digestive process begins with the mechanical aspect. The mechanical digestion process begins in the mouth, through chewing. When a piece of food is put in the mouth, it is first torn into smaller pieces in order to prevent choking. During the chewing process, saliva coats the food to help is slide easily down the esophagus. After a bite has been swallowed, it passes to the stomach. This is when the stomach and intestines liquefy the food through “mashing and squeezing actions” (Sizer & Whitney, p. 79). The first of these actions is called peristalsis. Peristalsis is a squeezing motion that starts with the tongue’s movement and continues as the food slides down the esophagus. The stomach also holds solid food and purees it into a paste form while adding moisture to help it move more easily through the digestive tract. The food would then be squeezed slowly from the stomach’s upper portion into its lower portion. The food paste is kept in the stomach by the sphincter muscle at the base of the esophagus, which prevents the substance from being pushed back up through the esophagus when the stomach contracts (Sizer & Whitney, p. 81). In the stomach, the food would be ground and mixed with digestive chemicals turning it into chyme, an even more liquefied form. When the food takes the form of chyme, it no longer has any physical resemblance to the original source. “The starches have been partially split, proteins have been uncoiled and clipped, and the fat has separated from the mass” (Sizer & Whitney, p. 81). The pyloric valve then forcefully releases the chyme a little at a time into the small intestine. The small intestine then moves the contents along to the large intestine. By the time the intestinal contents arrive at the large intestine, (also known as the colon), the digestion and absorption of the food source and its nutrients are nearly finished. The colon then reabsorbs the water contributed by digestive organs, and absorbs minerals. After these substances have been absorbed, the remainder is excreted in the form of feces.             

While the mechanical and chemical processes of absorption work concurrently, they are their own separate aspects. Both involve using organs to fulfill their procedure, but in different ways. During the chemical feature, “several organs of the digestive system secrete special digestive juices that contain enzymes that break down nutrients into their component parts” (Sizer & Whitney, p. 82). This is the main difference between the mechanical and chemical processes; the mechanical process is specific to physically breaking down the food, allowing it to travel more easily through the digestive tract, while the chemical aspect deals with the breakdown of the nutrients the food contains.

Chemical digestion also begins in the mouth. Enzymes in saliva start by breaking down starch and beginning to digest small amounts of fat. Once the food reaches the stomach, protein digestion begins. “Cells in the stomach release gastric juice, a mixture of water, enzymes and hydrochloric acid to initiate digestion of protein” (Sizer & Whitney, p. 83). Mucus coats the digestive tract lining, preventing it from also being digested in the process. In the small intestine, the liver and gallbladder contribute bile that blends fat, and the pancreas and small intestine donate enzymes that make absorption possible. After the nutrients are absorbed, the colon then uses bacteria to break down certain fibers before excretion.

This digestion and absorption process ensures that only the necessary nutrients from the food source are used to fuel the body, while rest is excreted in what should be a timely manner if a person is healthy. This is where the importance of fiber comes in to the process. Fiber helps regulate bowel movements, and regular bowel movements are a sign of good health. Bowel movements prevent non-essential food properties from sitting in our stomach longer than necessary, which can cause excess weight gain as well as other negative health effects. Excess fat and protein should be excreted from the body as quickly as possible. These are several different areas where nutritional aspects of food are used to help the body operate properly.  While these areas are separated in ways, digestion and absorption helps promote healthy function through the combination of procedures, ultimately making it a process with a singular goal.

While fats are digested and absorbed in the same fashion, not all fats benefit the body in similar ways. The only thing all fats have in common is there calorie content, with each gram of fat containing 9 calories. This is where the similarity stops. The good types of fat are unsaturated fats; polyunsaturated and monounsaturated. The bad types are saturated fat and trans fat. “Bad fats (saturated and trans) raise the levels of bad cholesterol. Moreover, bad fat-containing foods also tend to be high in cholesterol. Trans fats also lower good cholesterol. Good fats (mono and poly-unsaturated) don’t raise bad cholesterol and, when eaten in moderation, actually are beneficial” (Zimney MD, 2007). Saturated fat is generally found in meat and dairy products. “Trans fats are almost always man-made” (Zimney MD, 2007). Trans fat is generally found in sweets that use hydrogenated oils and added sugar.

                Conversely, while saturated and trans fat have negative health benefits, especially on the heart, unsaturated fats actually produce positive health benefits. Monounsaturated and polyunsaturated fats have benefits that range from heart health, to muscle and organ health to tissue health. These fatty acids are considered essential fatty acids. Healthy unsaturated fats such as Omega-6 and Omega-3 fats help improve heart health by reducing LDL cholesterol levels. These fats have also been shown to improve brain function and vision, as well as reduce inflammation, reduce blood clotting, lower blood pressure and provide antioxidants (Sizer & Whitney, p. 185). These fats are highly prevalent in many types of fish and fish oil, most types of nuts, as well as flaxseed and olive oils. Unsaturated fat should be eaten instead of saturated fat, not in addition to it. It should also still be eaten in moderation, because too much of any kind of fat can have negative health effects.

Resources

Sizer, F. & Whitney, E. (2011). Nutrition: Concepts and Controversies of Nutrition (12th ed).  Mason, OH: Cenage Learning

Zimney, E., MD. (2007). Good vs. Bad Fats - How to Tell Them Apart. Retrieved from http://www.everydayhealth.com/blog/zimney-health-and-medical-news-you-can-use/good-vs-bad-fats-how-to-tell-them-apart/