Most of us are familiar with our stomach and its role in letting us know when it is hungry or full. But what really goes on after we start munching on food? Let’s take a deeper look into our digestive system and how it functions to fuel our body.
Parts of the Digestive System and Their Processes
Our digestive system is responsible for breaking down food and utilizing the nutrients to keep our body up and running efficiently. Our mouth, esophagus, stomach, small intestines, large intestines and rectum are all part of our gastrointestinal tract (GIT). This connection of hollow organs is what carries food from our mouth, through our body to absorb the nutrients it needs and then eliminates the rest through our waste. The gallbladder, pancreas and liver also play important roles in the digestive processes by releasing various enzymes to help breakdown and absorb nutrients [1]. Let’s take a deeper look into each part of the digestive system and what it does during the digestive process.
Mouth
The first step in breaking down foods begins with our mouth. Seeing, smelling and tasting foods sends signals to our GIT to begin preparing for the digestive process.
Before we even start eating our food, glands in our mouth, known as salivary glands, will begin to produce saliva. This is where the term “mouth-watering” comes from [1]. We use saliva to soften food, while chewing helps to break food down into small, easily moved bits to prevent any injury or blockage when traveling through our esophagus.
Esophagus
Once food is broken down enough, it begins its descent into our esophagus. This is a hollow tube-like structure that sits directly behind our trachea, also known as our windpipe. Because our esophagus is located directly next to our airway, there is a special flap, known as the epiglottis, that temporarily covers the opening when we swallow food to prevent choking [1]. The food then travels down the esophagus into the stomach using a wave action by our muscles known as peristalsis.
When a food has traveled the entire length of the esophagus, it then has to pass through the lower esophageal sphincter to be released into the stomach. This sphincter is what helps to control food from going back up the esophagus from the stomach. Once food is detected, the esophageal sphincter will relax and allow food to enter [1]. When this sphincter is disrupted, contents of the stomach can flow back into the esophagus and result in uncomfortable acid reflux symptoms.
Stomach
The stomach acts as a vessel for our food while further breaking it down. After food enters the stomach, our stomach muscles begin to churn the food with various secretions and enzymes produced by the stomach lining, such as stomach acid. This helps to further break down nutrients into their smallest form to prepare them for absorption in the small intestines [2]. Once this process is complete, nutrients are now passed through the pyloric sphincter which connects the lower part of the stomach to the small intestines.
Small Intestines
The small intestines are made up of three different sections, all with different functions- the duodenum, jejunum and ileum. Food is moved through the intestines using the same muscle wave action of peristalsis as with the esophagus. As it moves through the three different segments of the small intestines, enzymes and bile are released from the gallbladder and the pancreas to help with the absorption process [3]. Once these nutrients, now referred to as chyme, begins to travel down the small intestines, the majority of nutrient absorption will occur.
The first section of the small intestines is the duodenum. This is where the last of the remaining nutrient are broken down. While processing the chyme in the duodenum, the pancreas releases enzymes to help with the process.
Our pancreas is located in the upper left part of our abdomen, behind our stomach and it performs two functions – endocrine and exocrine. It’s endocrine function uses hormones to regulate things like our blood sugar levels while it’s exocrine function helps to produce digestive enzymes. These enzymes include trypsin and chymotripsyn which helps to digest proteins, amylase to digest carbohydrates and lipase to break down fats. [4].
Our liver, located right above our stomach, is responsible for creating bile, a substance needed to help breakdown and absorb the fats we eat. Bile is only needed during digestion therefore any bile secreted by the liver when digestion is not in process is stored in the gallbladder which is located right beneath the liver. When chyme reaches the duodenum, the gallbladder will release stored bile [5]. Most absorption is complete within the small intestines before the chyme reaches the ileum, the last section.
The jejunum is where the majority of nutrient absorption occurs. This is the second section of the small intestines that connects the duodenum with the ileum. The muscles of our small intestines will push chyme back and forth to allow it to make contact with the walls of the jejunum where nutrients are then absorbed [3].
The Ileum is the last section of the small intestines and it’s main role is to absorb any nutrients that were left behind by the other two sections. This mainly includes vitamin B12 and bile salts [3]. Once nutrient absorption is complete within the small intestines, the remaining contents, now in liquid form, are sent to the large intestines. It can take anywhere from 6 to 8 hours for food to travel from our mouth to our large intestines.
Large Intestines
Whatever is left over after this process is then passed into the large intestines, also known as the colon. The colon connects the small intestines to the rectum and is where the majority of water absorption occurs. When reaching the colon, leftover waste is typically in a liquid form. As it travels through, water is absorbed forming a solid stool to be removed by the rectum [3]. It can take up to 36-hours for food to move through the colon before evacuation.
Rectum
The rectum is what connects the colon to the anus and is used to detect when the body needs to eliminate waste by sending signals back and forth to the brain. When our brain tells us it is okay to evacuate, it will release the stool into our anus to be removed from our body [3].
The Role of Probiotics
Most well known for their benefit on our gut, probiotics are organisms found in food that improve the balance of microbes in our intestinal tract needed for good digestion [6]. A disruption in the balance of these microbes can result in diarrhea, constipation, irritable bowel syndrome, inflammatory bowel disease, food allergies and even increase your risk for certain cancers [6].
You might have heard the saying “A good immune system begins with the gut.” This is because probiotics function to help prevent bad microbes from penetrating our gut and helping to keep our immune system strong. Probiotics also help with the production of certain nutrients such as vitamins, antioxidants and more [6].
These ‘good bugs’ live mostly within our colon but can also be found in the mouth, lungs, urinary tract and even the skin. Good sources include your fermented foods such as yogurt, kimchi, kefir and sauerkraut to name a few.
The Role of Enzymes
Enzymes are prevalent throughout most of the major parts of the digestive process. You can find enzymes produced within our salivary glands, stomach, pancreas, liver and small intestines [7]. Digestive enzymes act to break down nutrients into their smallest form so our body is able to absorb them. There are no enzymes prevalent within our colon because by this time all nutrients have been absorbed [7].
How Diet Affects Digestion
Our digestive system is responsible for taking nutrients from the foods we eat and utilizing them to maintain our health and body functions. A low-quality diet can affect the absorption and utilization of nutrients leading to deficiencies and increased risk of disease as well as unfavorable gastro-intestinal symptoms.
In order to maintain good digestive health, it is recommended to consume a variety of nutrient dense foods and limit highly processed food items. This means choosing more fruits, vegetables, whole grains, nuts, seeds, and legumes. These are the foods that will contain the most vitamins and minerals needed to support healthy body functions as well as provide adequate fiber to keep our gut working at it’s best.
