Though biting into a delicious meal is simple, the processing that this ingested food need to go through to become usable energy within the body is rather complicated. The body has an advanced system for taking food, breaking it down into pieces, absorbing key nutrients, and then ridding itself of the waste. There are four stages of digestion: Ingestion and propulsion, digestion, absorption, and egestion.
Here is everything you need to know about the four stages of digestion:
1. Ingestion & Propulsion
When you bite down on a sandwich, you are ingesting that food. Chewing starts to move the food towards the esophagus, shaped this masticated meal into a rounded lump called a bolus. The bolus is then swallowed into the esophagus, where it is moved along by an involuntary muscular contraction called peristalsis. Eventually, the bolus hits the stomach.
The stomach does two things: store food and digest it. The churning action of the stomach will break down food. Glands in the stomach will also secrete acid and an enzyme called pepsin. Other enzymes that aid in digestion will come from the small intestine, pancreas, and gallbladder. Eventually, everything is broken down to macronutrients and vitamins.
Though food begins to get digested almost immediately, absorption can only happen once everything has been broken down to small enough pieces to be assimilated into the body. This happens in the small intestine, where the cells that line this organ absorb the nutrients from a substance called chyme. The villi that line the small intestine work to help draw in things like proteins, carbohydrates, fats, and vitamins. The bloodstream will absorb water and alcohol.
Defined as the “discharge or expulsion of undigested material (food) from the digestive tract via the anus,” egestion is exactly what you think it is. Other words to describe what happens would be excretion, elimination, and defecation. Once the nutrients have been taken from the food, what remains that cannot be digested, such as insoluble fiber, is passed through the large intestine and into the rectum for egestion.
Every stage in digestion has to be completed before the next step can begin. Should one of the four stages of digestion be interrupted or skipped over, the body may wind up feeling ill or get poisoned. Understanding the four functions in the digestive system is important, because when you have an idea of what’s happening inside normally, when something starts to go wrong, you can adequately describe what you think is wrong.