Everybody enjoys a good meal. It is one of the few pleasures in life that we all can share. But, once we get past the experience of the taste, the feel, the satisfaction involved in satisfying our hunger, do we really ever consider just what happens in our bodies as we convert that meal into the energy we need to sustain us. I’m willing to bet that not many of us give much thought to what happens after that final mouthful. Maybe an impolite burp and a muttered excuse me gives us pause to consider just what is happening as that once delicious morsel makes its deliberate journey to its inevitable outcome. “Outcome” being the polite term for what happens to all waste products. Maybe we can shed a bit of light on this magical mystery tour, describing what happens at each step of the way, and how and why it does happen.
The gastrointestinal system, also known as the digestive tract, is a collection of organs within humans and other animals dedicated to the intake, digestion, and eventual expulsion of nutrients. It is therefore responsible for turning that candy bar into a needed energy spike or that second baked potato into an unwanted bit of pudge around the midsection. The systems consist of the mouth, the esophagus, the stomach, and the intestines, which are aided along the way by other important organs such as the liver, pancreas, and gallbladder.
The first stop in the gastrointestinal tract, the port of entry, as it were, is the mouth. It is here where the nutrients you take in, be they in the form of chocolate cake or a well-done steak, are first broken down into parts small enough for your body to use for energy, growth, and cell repair. Carbohydrates, fats, vitamins, minerals, proteins, and water are all nutrients contained in the food we eat, but they cannot be used until they are converted by our digestive system. The process begins in the mouth, where chewing breaks down our food into smaller, more manageable pieces and saliva moistens it, making it softer. Saliva also contains an enzyme which begins the breakdown of starches. The tongue then moves the food into your esophagus to continue its journey southward.
Once the food has moved into the esophagus the process becomes automatic. Nerves sense the arrival of food, and signal the brain to begin peristalsis, the alternating contracting and relaxing of muscles in the lining of the esophagus, which moves the food along to its next destination, which is, of course, the stomach. It is in the stomach where the true process of digestion begins. The stomach manufactures digestive juices, and glands produce various stomach acids and enzymes to expedite the breakdown of nutrients into usable elements. Muscles in the stomach churn the mixture, blending it into a semi-liquid mass called chyme, which is then fed into the small intestine, where the really heavy duty work is accomplished.
The small intestine processes chyme with the help of three nearby organs. The pancreas produces an enzyme, insulin, to break down carbohydrates, fats, and proteins. This enzyme is fed into the small intestine through a series of ducts. Ducts also bring bile from the liver to help in the digestion of fats and some vitamins. The liver produces bile constantly, and when it is not needed immediately, it is stored in the gallbladder until required. The small intestine also manufactures its own digestive juice, which mixes with insulin and bile to complete the breakdown of food. Proteins are ultimately broken down into amino acids, the building blocks used to repair damaged cells and build new ones, fats are broken down into fatty acids and glycerol, which provide the body with energy and aid in the use of vitamins A, D, E, and K. Carbohydrates are eventually broken down into simple sugars which provide us with energy. It is important to note that a veritable jungle of living organisms thrives within our small intestine. These bacteria, known as gut flora or our microbiome, produce enzymes which aid greatly in the breakdown of carbohydrates. It is important to maintain a healthy balance of these bacteria. The right number and type of these microorganisms is beneficial to our health and well-being. The wrong type can cause discomfort and disease.
The small intestine is definitely the workhorse of the digestive systems. While peristalsis moves the food along, water is transported from the bloodstream into this organ to aid in the digestive process. But water containing digested nutrients is also absorbed by small cells in the lining to be returned to the bloodstream to be carried by the circulatory systems to wherever they are required. Some vitamins and salts are transported to the liver to be processed and delivered as needed.
Finally, what once was food is delivered into the large intestine, where water is once again removed, turning the soft, liquid morass into something more solid. The large intestine also contains a large amount of bacteria, which aid in the final breakdown of the nutrients and the production of vitamin K. These final products are absorbed into the bloodstream and transported throughout the circulatory system. Finally, with all the good stuff removed, the waste which is left, called stool, is removed from the body through the anus.
The whole journey from top to bottom takes an average of 53 hours, according to the Mayo Clinic, not that long for so important a job. Most of this time seems to be spent in the large intestine as the finishing touches are added. Food tends to linger here for at least a day or more while every last particle of nutritional value is scavenged. Food tends to pass through the stomach and small intestine within 6 to 8 hours of consumption. These figures may vary, of course, depending on the individual and the type of food consumed, so there is no reason to worry unless you experience pain or difficulty in swallowing, stomach pain, or problems with elimination. Men tend to digest their food more quickly than women, but it’s not a race, after all, so don’t be concerned.