The gut technically is the gastrointestinal tract or digestive system, a pathway from your mouth to your rear. The gut processes food from the time it is first eaten until it is either absorbed by the body or passes out as stool (feces).

When we eat our food, we chew it or masticate it. Then the food goes down to oesophagus then to the stomach. Once the food gets broken down in the stomach, it moves to the small intestine. During this time, the food, which is now called chyme is bathed in digestive enzymes and juices that flow into the small intestine through ducts from the liver and pancreas. The small intestine which is about 6 meters or 20 inches long is where things get assimilated. This has three sections: the the duodenum, the jejunum and the ileum. The digestion of food take place primarily here. In the duodenum, bile and pancreatic juice are added to the mixture. In the jejunum, fat, starch and proteins from the food material are broken down and absorbed by the intestinal lining. The lining is covered with millions of tiny villi, or finger-like projections, that greatly increase the surface area, allowing nutrients to be more efficiently absorbed into the bloodstream. In the ileum, which is the last part of the small intestine, water and nutrients such as vitamin B12 are absorbed.

Bile which is released by the gallbladder into the duodenum in order to help emulsify ingested fats, is absorbed in the ileum to prevent its loss from the body. Once reduced to products the body can manage, the nutrients from digested food are absorbed by the intestine’s thin lining and sent to cells throughout the body by way of the bloodstream and lymphatic system.

When the food mixture or chyme from the small intestine gets to the large intestine, there are hardly any nutrients left. Bacteria in your large intestine help break down remaining nutrients and make vitamin K. The large intestine is around 1.5 meters or 5 feet long and wider than the small intestine. But it does not contain villi unlike the small intestine. However, it still has a very important job to do. That is to take water from the chyme and returns it to the body. Once chyme has been in the large intestine for several hours, it becomes semisolid (or stool) because most of the water has been removed. This digestion process from mouth to rectum takes around 12 hours.

Reference:

Brownstein, D. and Gould, J. (2017). Heal Your Gut. Humanix Books, P.O. Box 20989, West Palm Beach, FL 33416, USA