Our digestive system is a formidable machine, as powerful as it is complex. From the mouth to the large intestine, chemical and physical processes take place to extract maximum nutrients from ingested food, while protecting the body from potential dangers.
If you're aiming for long-term health and disease prevention, it's worth understanding the digestive process.
Indeed, problems with the digestive system are often signs of a malfunction somewhere in the process. In this article, we'll take a look at the different stages of digestion and how it all works.
The mouth and salivary glands
The first stage of the digestion process takes place in the mouth. Here, mastication serves to grind up the food. The salivary fluid produced by the glands is a mixture of secretions that help lubricate and break down food.
Mastication also has the effect of sending a signal to the stomach to prepare its own secretions for the arrival of the "food bowl" created in the mouth.
During swallowing, the tongue pushes the food bolus into the esophagus, which then takes over.
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Did you know? We produce up to a liter of saliva a day! Three pairs of salivary glands (in addition to those located under the tongue), enable us to produce it in sufficient quantity. |
The oesophagus
Muscles in the lining of the esophagus create synchronized waves that, one after the other, slowly propel food into the stomach.
In this process, called peristalsis, the muscles behind the food bolus contract, pressing it forward, while the muscles in front relax, allowing it to move forward without resistance.
As a result, it's possible to swallow food, even while doing handstands!
| Good to knowThe esophagus is made up of several layers of muscle fibers, allowing food to pass through. |
When the food bolus reaches the lower end of the esophagus, the pressure exerted by the food signals a muscular valve - the lower esophageal sphincter - to relax and let the food enter the stomach.
The esophagus is hermetically isolated from the stomach, as it has no wall to protect it from stomach acids.
The stomach
The stomach is an organ with strong muscular walls. When food reaches the stomach, it is mixed with acid and powerful enzymes that break it down.
These gastric juices also act to kill any bacteria that may be present in the food.
The enzymes and acids mix with food that has already begun to break down in the mouth and esophagus, and thanks to the muscles in the stomach, are transformed into "chyme", a semi-liquid mass that is expelled from the stomach and sent to the intestines during digestion.
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How does it work? Through muscular contraction, the stomach pushes the resulting mass towards the small intestine. |
At the end of the stomach, the pyloric sphincter, which opens onto the small intestine, only opens a few millimeters. As a result, the larger pieces remain in the stomach to liquefy a little more.
Small intestine
The small intestine is made up of distinct segments: the duodenum, the jejunum and the ileum.
It is in the small intestine that most digestion takes place, and where all remaining nutrients are absorbed.
The duodenum
The duodenum performs much of the chemical digestion, as well as a small part of the absorption of nutrients; the main function of the jejunum and ileum is to complete the chemical digestion and absorb these nutrients as well as water and vitamins.
The secretion of digestive enzymes in the stomach usually triggers the production of chemicals by the pancreas and liver, including the famous bile, which are used in the duodenum.
The jejunum
The jejunum, like other parts of the small intestine, is responsible for absorbing nutrients from food into the bloodstream. The jejunum is able to absorb these nutrients because it is lined with finger-like projections called villi.
The villi absorb nutrients in the form of minerals, electrolytes, carbohydrates, proteins and fats. Nutrients are absorbed into the bloodstream, where they can be used as a source of energy by the whole body.
The ileum
The chyme then passes into the last and longest part of the small intestine, called the ileum. Its main function is to absorb vitamin B12, bile salts and all the products of digestion that have not been absorbed by the jejunum.
As a result, the ileum has an extremely large surface area, both for the adsorption of enzymatic molecules and for the absorption of digestive products.
What remains of the food when it reaches the end of the ileum is a combination of water, electrolytes - such as sodium and chloride - and waste products, such as plant fibers and dead cells detached from the wall of the digestive tract.
The small intestine is also home to some 100 billion bacteria, divided into several hundred species. Lining the walls of the digestive tract, they play a major role in digestion and metabolism. disease prevention.
The large intestine
The large intestine is a wide muscular tube about 7 to 10 cm in diameter, extending from the cecum (the first part, connected to the small intestine) to the rectum. It is about 1.5 m long.
Digested food passes from the small intestine through the ileocecal valve and cecum into the colon, where it mixes with beneficial colonic bacteria.
It's a common misconception that vitamins are nutrients that are only absorbed further up the digestive tract, but the colon plays a very important role in the absorption of vitamins necessary for good health. These vitamins are actually produced by healthy bacteria in the colon via fermentation.
The chyme moves through the four regions of the colon over several hours, thanks to peristalsis. In some cases, this process can become much faster thanks to the stronger waves of peristalsis that follow a hearty meal.
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Did you know? Diseases affecting the large intestine, such as irritable bowel syndrome (IBS) or Crohn's disease can lead to partial removal of this part of the digestive tract. |
As it passes through the large intestine, more water and nutrients are absorbed, and the mixture becomes stool. This stool is then stored in the sigmoid colon until the body evacuates it via the rectum and anus.
Stool consists mainly of food debris and bacteria. When the descending colon is full, it empties its contents into the rectum.
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