What Happens Inside Your Body When You Eat?

This is the first post in a two part series on the GI tract. Read Part 2 (Digestive Tract Problems and Tests: They Want to Put a Tube Up Where?).

Nutrition and the type of food we choose to consume is such a hot topic, and rightfully so. Having the right nutrition supports every function that our body needs to do. But how does our body actually process the food we eat?

Chew

The process of digestion begins as soon as you place a bite of food into your mouth. Your body starts to break down that bite as your teeth begin to chew with the help of your tongue. As you are chewing your food, your salivary glands are hard at work. They are releasing saliva. Saliva coats your mouth and throat to enable your food to be swallowed. It also contains an enzyme called amylase. Amylase helps our body to begin to break down starches (those carbs we eat). Amylase will coat the food as we chew and continue to work on breaking down the carbohydrates when that food enters the stomach.

Swallow

Your tongue then moves the food to the back of your mouth so that it can be swallowed. Your food passes through your pharynx (the area in the back of your throat that both the air you breathe and your food passes through. You know that dangly thing that hangs in the back of your mouth? That is your uvula and when you swallow that helps to keep food and liquid from going up into your nose. It has a counterpart below that, called your epiglottis. Your epiglottis is a small piece of tissue just behind your tongue and it has the important job of closing the opening to your trachea (airway) when you swallow. We do not want any food or liquid to enter your airway or lungs as this would lead to either choking or infection. Every time you swallow, your epiglottis moves into place to cover your larynx (voice box) to direct your food down your esophagus. When you swallow, 30 different nerves and muscles are working together to transfer food or liquid to your esophagus, all while protecting your airway.

Esophagus

Your esophagus is a round muscular tube that transports food and liquid into your stomach. The muscled wall of your esophagus moves food through a process called peristalsis. This is an automatic process performed by your body (meaning we don’t have to think “esophagus please move my food down into my stomach”). The muscles of the esophagus wall gradually contract in a wave like motion to push food in the right direction down your digestive tract. At the end of your esophagus is your esophageal sphincter. Food easily passes through this into your stomach as it’s main purpose is to prevent anything from traveling the wrong direction in your gastrointestinal system (like back up your throat). People who have GERD (gastro-esophageal reflux disease) have a sphincter that isn’t closed correctly and allows the contents of the stomach to go into the throat.

Stomach

The stomach is the next stop for that bite of food you ate. Here is where the large process of breaking down your food occurs. Before your body can absorb any of the nutrients from the food you eat, it must be completely broken down. This process begins in earnest as soon as the stomach starts contracting because it recognizes that food has arrived. The contracting stimulates the release of different enzymes and acids. The most common enzymes break down carbohydrates, fats, and protein. Gastric acid and the contraction of the stomach itself also assist in breaking down food to a consistency that it can enter the small intestine. The stomach has it’s own protective systems as well, to include mucous production that helps by coating the lining of the stomach to protect it from the acidic environment it needs to create to break down our food.

Small Intestine

Once the stomach has processed the food, it passes into the small intestine. While it may be considered the “smaller” of our two intestines due to it’s diameter it can be 25 feet long! Food travels through the small intestine through peristalsis. This is where some of the most important work happens. This is where the nutrients and water from the food you eat get absorbed by the bloodstream. In order to do this the small intestine continues the work of breaking down your food. It does this through the help of secretions from your pancreas, liver and gall bladder. The pancreas secretes enzymes, the liver secretes bile, the gallbladder stores the bile that the liver produces. The liver is also the main place where the nutrients that the small intestine absorbs into the body are processed. The pancreas also secretes that important little hormone called insulin that allows sugar to be used by your cells. The small intestine has the absolutely amazing system in it’s walls called villi. These villi are fingerlike projections that increase the surface area of your intestines so that more nutrients and fat can be absorbed into the blood stream.

Colon

Once the small intestine has absorbed the nutrients and most of the water from the food, it passes into the large intestine. This is also known as your colon. At the start of your colon is that sometimes pesky little pocket of tissue called the appendix. Amazingly, we still aren’t completely sure what it’s purpose is. There is a theory that it is part of the immune system and acts as a reserve of healthy bacteria. For instance, if you lost the healthy bacteria in your gut, it could be replaced utilizing the bacteria that was safely stored in your appendix. The colon’s main job is to make your poop. When it receives what is left of the food you ate from your small intestine, it is liquid and most of the nutrients and water have been absorbed into your blood stream. The colon’s job is to now take this waste, absorb the rest of the water and electrolytes, and turn it into stool. The bacteria in your colon continues to break down the waste. It completes the break down of carbohydrates and allows for the absorption of some vitamins. As the waste becomes firmer it is coated in mucus to help it travel through the rest of the colon on it’s way to the rectum. When the waste enters the rectum you receive the “I need to poop” signal. The sphincter between your rectum and anus automatically open but thankfully you are able to control the sphincter on the far end of your anus to allow you time to find a toilet.

Part of Your Body’s Defense

Did you ever consider that your digestive tract is actually part of your body’s defense system? The entire digestive system is a large tube that starts with your mouth and ends with your anus. Even if you eat something it hasn’t technically “entered” your body until it has been absorbed. The link between “gut health” and a healthy immune system is still being studied. It has been found that the largest amount of your body’s immune cells are located in your digestive tract. These cells have an important job of distinguishing between what is “good and normal” bacteria of the digestive tract and what is a food-borne pathogen that can cause illness.