What’s the point of eating food if your body can’t use it? The importance of the small intestine can sometimes be forgotten, but this body organ is essential to living a healthy life. It is responsible for the process of absorption. Without it, all the energy from the food that we eat would pass unused through the digestive system, causing the body to starve and eventually shut down.
It should not be a surprise that serious health problems can arise when there are absorption issues. For example, malabsorption is the main feature of celiac disease and Whipple’s disease. When these illnesses are left untreated, the body is unable to use nutrients properly and it becomes malnourished.
Clearly, the absorption of food can make the difference between health and serious illness. In order to better understand this process, it is helpful to examine the digestive system and the way in which all the organs work together.
The mouth, esophagus, and stomach break down food particles. The gallbladder and pancreas assist with the digestive process by releasing digestive substances into the upper portion of the small intestine. The large intestine prepares the waste to be discarded as feces. And, of course, the actual process of absorption takes place in the ileum, which is the lowest portion of the small intestine.
Together, the digestive organs break food into smaller molecules, extract the useful nutrients, and distribute the energy through the bloodstream to keep the body alive and running.
There are three main stages that make up the digestive process: pre-absorption, absorption, and waste removal.
Food needs to be broken into smaller parts in order to be properly absorbed. The mouth, esophagus, and stomach take care of the larger pieces of food by chewing it, swallowing it, and breaking it down with stomach acids. The resulting substance is called chyme.
The chyme travels from the stomach to the duodenum , which is the upper portion of the small intestine. If there is fat in the chyme, this is where it is broken down. It must be processed differently than other nutrients due to its chemical structure. Bile from the gallbladder and pancreatic juices from the pancreas flows into the duodenum to break apart fat globules.
The jejunum, or middle portion of the small intestine, is where the chyme travels next in order to be further broken apart by more digestive enzymes. Afterwards, it is ready for the absorption stage.
The chyme moves into the final portion of the small intestine, the ileum. The ileum wall is not flat but instead has mucosal folds. Covering the mucosal folds are hundreds of finger-like projections called villi. Each villus is covered in absorptive enterocytes which are in turn covered in hair like structures called microvilli.
The absorptive enterocytes do as their name suggests by taking in food molecules with the help of microvilli. Together, these structures create a large surface area that allows for a highly efficient process of absorption.
When the chyme reaches this part of the small intestine, it has been fully digested and the nutrient molecules are small enough to be absorbed. The nutrients diffuse through the microvilli and absorptive enterocytes to reach the villi.
At this point, the nutrients can go directly to the bloodstream or travel to the lymphatic system for further processing. Each villus is lined with one bed of capillaries that leads to the bloodstream and one lacteal that connects with the lymphatic system.
Fat molecules will enter the lacteal. All other nutrients such as vitamins and minerals are ready to be used immediately; they are delivered directly to the bloodstream via the bed of capillaries.
Digestion in the small intestine is now complete, and the nutrient-depleted chyme moves into the large intestine to be processed and discarded as feces. Although the small intestine has completed most of the absorption process, the large intestine finishes it by reabsorbing excess water through the intestinal walls. This helps to maintain the body’s fluid balance. The remaining waste is of no more use and it exits the body through the anus.
The small intestine is responsible for absorbing nutrients from the food we eat. The other digestive organs play important roles by digesting the food and removing it after it has served its purpose. Without a properly functioning small intestine, people can become sick and malnourished. Thankfully, we can choose to take care of our digestive system and our bodies will return the favor by taking good care of us.