The Science Behind Digestion

The Science Behind Digestion

The Science Behind Digestion

The digestive system is made up of the digestive tract and three organs—the pancreas, liver, and gallbladder. The digestive system works to digest food in two unique ways. Digestion happens on a mechanical level through chewing and squeezing, and on a chemical level through enzyme activity. 

The digestive tract is a flexible, muscular tube that is tasked with digesting food and absorbing nutrients. The digestive tract does not act alone in these ways, but instead requires help from organs in the digestive system, including the pancreas and gallbladder. 

Let’s take a deep dive into the digestive tract.

Starting in the Mouth

First, in the mouth, solid food pieces are shredded into smaller particles through chewing. Saliva mixes with the food and softens it so it can be swallowed easily. Besides the chewing and crushing action that happens in the mouth, the saliva contains enzymes that begin breaking down carbohydrate and fat molecules. 

Moving Through the Esophagus to the Stomach

Next, the food moves through the esophagus and into the stomach. In the stomach, food is liquefied and mashed through squeezing actions. The environment of the stomach is incredibly acidic due to secreted hydrochloric acid. In fact, the stomach is even more acidic than lemon juice. The combination of squeezing and mashing, acidity, and digestive enzymes allow your body to begin protein digestion. 

In the stomach, your body breaks down protein molecules into smaller fragments known as amino acids, while carbohydrates and fats only get sloshed around for a few hours. Carbohydrates and fats must wait until they enter the small intestine to continue digestion.

The Science Behind Digestion

Hanging out in the Small Intestine

The next section of the digestive tract that comes into play is the small intestine. The small intestine is quite powerful, and it’s where the vast majority of digestion happens. The small intestine does not work alone; the pancreas and the gallbladder both help the small intestine continue digestion. 

When food enters the small intestine from the stomach, hydrochloric acid tags along. The pancreas plays a role, by sending digestive enzymes and a pancreatic juice known as “bicarbonate” directly to the small intestine. Bicarbonate helps neutralize the acidity. When fat enters the small intestine, the gallbladder sends bile to aid in digestion; bile helps the body digest fat. 

Don’t worry. Even if you don’t have a gallbladder, you can still digest fat. The liver produces bile, the gallbladder only stores it!

Protein digestion continues in the small intestine by way of enzymes secreted by the pancreas and the small intestine. And the enzymes that digest carbohydrates and fats can now get to work. The wall of the small intestine produces enzymes that are vital to carbohydrate digestion. 

Sucrase, the enzyme that breaks down sucrose, is one of those enzymes secreted from the walls of the small intestine. Under normal conditions, sucrase helps split sucrose into the two sugar molecules, fructose and glucose. Once fructose and glucose are unbound from each other, the body can absorb them from the digestive tract and use them for energy. 

Other enzymes found in the small intestine include lactase and maltase, which help the body break down lactose and maltose. Once the enzymes break the bonds of these sugars, the body is also able to absorb and use them for energy.

When all digestive enzymes are present and active, most carbohydrates, fats, and proteins can be broken down efficiently and used by the body. Unfortunately for some, their bodies have a digestive enzyme that does not function—like the disorder Sucrose Intolerance caused by Congenital Sucrase-Isomaltase Deficiency (CSID), where the non-functioning digestive enzyme means the bonded sugar molecules are not able to be split into absorbable units that can be used by the body. The inability of any digestive enzyme to function normally can trigger common symptoms like diarrhea, gas and bloating, or even constipation.

Getting Help from the Colon

Some large carbohydrates are not able to be digested in the small intestine. One of these large carbohydrates is fiber. Fiber is broken down with help from the bacteria that live in the colon, also called the “large intestine” or “large bowel.” 

It is thought that each of you has over 100 trillion bacteria in your digestive tract! The bacteria in the colon ferment fibers by consuming them, helping your body break them down. In addition, these gut bugs breakdown any undigested protein. Any leftover food particles that are not needed by the body are passed out through feces. 

As you can see, digestion is a complex process that requires the coordination of several organs in the digestive system. Due to the digestive tract’s multifaceted nature, many digestive issues can arise and cause unpleasant symptoms. When working correctly, the digestive tract is continuously digesting food, absorbing nutrients, and providing the body with energy.


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Sucrose Intolerance May Be More Common Than You Think