How your digestive system works

And why it’s the foundation of good health

Did you know that digestion is a north to south process? It begins in your brain and ends up at your bottom. Digestion requires two basic actions involving the mechanical and chemical breakdown of food: to reduce the food into the smallest possible particles so that the body can easily and efficiently absorb nutrients. These nutrients are critical for every function in your body and used by every cell, organ and system for fuel and energy!

Here’s how your digestive system works from top to bottom:

Diagram showing how the digestive system works

It’s amazing that just the sight and smell of food awakens and ignites our salivary glands so that they can begin producing saliva. Saliva is key to all digestion because it contains water and solutes. Solutes are enzymes, and in this case, amylase that helps to break down carbohydrates. All this is occurring even before we are finished chewing. When we say that something is mouthwatering good, this is why!

The mouth is the entryway to the digestive system and where the ingestion of all nutrients takes place. Along with the physical action of chewing, there is the chemical (enzymatic) breakdown of food here and this creates a bolus (a ball of chewed up food).

As we swallow, the bolus enters the esophagus, getting ready for the passage into the stomach. It makes its way down toward a teeny valve, called a cardiac sphincter. When everything is functioning and happy within the digestive system, that little valve will open (and close when it needs to) to allow the bolus to make its way down into the stomach and prevent it from coming back up.

Once the bolus reaches the stomach, it mixes with gastric juices and becomes chyme (from Greek khūmos “juice”). If digestion is working properly, the stomach secretes gastric juice from millions of tiny glands in its mucosal lining. This is where an optimally functioning digestive system will produce HCl (hydrochloric acid) and pepsin. Unfortunately, many of us are out of balance and lacking these critical digestive secretions. Without proper stomach acid levels, chyme cannot break down to the point where it’s released into the small intestines. Food remains in the stomach where it can cause acid reflux, H. pylori, GERD and other digestive issues.*

Once the stomach has completed its task of breaking down the bolus into chyme, it triggers a valve at the bottom of the stomach to open, allowing the chyme to enter a chamber known as the duodenum. The duodenum is the first and shortest segment of the small intestine that receives the chyme from the stomach and plays a vital role in the chemical digestion of chyme in preparation for absorption in the small intestine. It is in the duodenum where the very acidic chyme is “cooled off” and further broken down by the bile and pancreatic juices. This is necessary for the emulsification and absorption of fats.

Note: The liver, gallbladder and pancreas are called the biliary tract. Food particles do not directly pass through the biliary tract. Rather, the bile (produced by the liver and stored in the gallbladder) plus digestive juices, enzymes and bicarbonate (produced by the pancreas) enter the digestive tract through ducts in the duodenum. In other words, while the liver, gallbladder and pancreas do not “digest the food,” they’re critical to all digestion (as are the valves/sphincters (little gates).

The largest organ inside the body, the liver has more than 500 functions that include making bile and filtering toxins. Bile is a liquid that helps break down fats and takes toxins filtered by the liver out of the body. Bile also lubricates the intestines preventing constipation. Without good functioning bile, the body cannot properly absorb fats and fat-soluble vitamins A, D, E and K.

The gallbladder is a gland that stores the bile produced by the liver. When fats are consumed, the gallbladder is triggered to release bile into the duodenum, where it mixes with pancreatic juices to break down food into molecules that can be absorbed in the small intestines.

The pancreas is a gland that produces digestive juices, a mixture that includes bicarbonate and pancreatic enzymes that further digest fats, proteins and carbohydrates. When bile from the gallbladder breaks down fat into certain microscopic particles, the digestive lipase enzymes from the pancreas can further break down the fats for absorption in the small intestines. The pancreas produces insulin that converts sugars to energy and stores excess sugars as fat, too. And, the pancreas helps your digestive system by making hormones. Pancreatic hormones help regulate blood sugar levels and appetite, stimulate stomach acids, and tell your stomach when to empty.

Small intestine
The small intestine is the part of the intestines where 90% of the digestion and absorption of food occurs. (The other 10% takes place in the stomach and large intestine, in addition to the support of the accessory organs like the liver, pancreas and gallbladder). The main function of the small intestine is the absorption of nutrients and minerals from food.

Large intestine
The large intestine recycles water and waste material, which nourishes the colon cells. It captures any lost nutrients that are still available (with the help of the bowel microbes) and converts the nutrients to vitamins K, B1, B2, B12. Then, butyric acid forms and it’s time to go to the bathroom!

Diagram showing how digestion works from north to south