This is how the digestive organs work

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Last Medical Review: April 1, 2020
Medically Reviewed by Dr. Elisabeth Vincent Hamelin
Digestive System (April 1, 2020)

The food you eat breaks down as it passes through your body. It is called digestion or digestion. Various organs and glands help with digestion. The food needs to be broken down in order for the body to absorb the nutrients that the food contains.

The digestion takes place in the gastrointestinal tract

The gastrointestinal tract is the duct that runs from the mouth to the rectum opening. As the food passes through the gastrointestinal tract, it is broken down to its smallest constituents.

The gastrointestinal tract includes the following parts:

  • mouth
  • throat
  • esophagus
  • stomach
  • the small intestine
  • colon
  • rectum.

These glands and organs help with digestion:

  • salivary glands
  • liver
  • the gallbladder with the bile ducts
  • pancreas.

It takes so long for the food to go from the mouth to the rectum

The time it takes to digest the food is different for different people. It also depends on what you eat, different types of food take a long time to digest. About three hours after a meal, half of the contents of the stomach have been emptied. After just over four hours, the stomach is empty. Then it takes three to seven hours for the food to pass through the small intestine. Then it takes from three hours and up to just over two days for the food to pass through the large intestine. The entire process from the mouth to the rectum takes an average of 24 hours.


The food and drink you eat and drink first comes to your mouth. The muscles in your lips and cheeks process the food together with your tongue. The food is also mixed with saliva in the mouth.

Teeth crush and grind the food

The most important task of the teeth is to break down the food. The front teeth have sharp edges and are shaped so you can bite off the food. The cheek teeth have large chew surfaces that are great for crushing and grinding the food.

Saliva helps to break down the food

In the mouth, the food is mixed with saliva. The saliva has several important tasks:

  • It breaks down the food and makes it easier to swallow.
  • It prevents the mucous membrane of the mouth from drying out.
  • It protects the oral cavity and teeth from bacteria.

Saliva consists mostly of water. The liquid contains salts and various substances that are responsible for breaking down the food. These substances are called enzymes.

It is formed more saliva when you feel the taste or smell of food, or think of food.

Saliva is formed in the salivary glands

Saliva is formed in the salivary glands. Every day, 1-1.5 liters of saliva are formed. You have three pairs of major salivary glands:

  • parotid gland
  • heavy pot gland.

The salivary gland is the largest and is found near the ear. The lower jaw jaw is located in the lower jaw, and the tongue jaw in the bottom of the oral cavity. There are also many small salivary glands in the mucous membrane of the mouth.

The pharynx

The pharynx is a cavity located behind the oral cavity and nasal cavity. It continues down to the esophagus and larynx. Here the paths for the esophagus and trachea are crossed. The pharynx is covered by mucosa. In the lower part of the throat, the mucous membrane is more resistant to wear from food and drink.

A reflex causes you to swallow

It is a reflex that makes you swallow the food. The reflex starts when you have chewed and the food reaches the rear pharynx.

The larynx folds over the trachea as you swallow. This prevents the food from entering the trachea instead of the esophagus. Only infants can swallow and breathe at the same time.

Here you can read more about the trachea and the larynx.


The food you eat is transported to the stomach through the esophagus. The esophagus is shaped like a 25 cm long tube. On the inside, the tube is covered with a pleated mucosa. The esophagus lies between the lungs and behind the heart.

The food is pressed down using the muscles of the esophagus

The task of the esophagus is to transport the food from the mouth to the stomach. The enzymes from the saliva continue to decompose the food all the way down to the stomach.

The food is transported by the muscles of the esophagus pushing the food downwards with wave movements. Such wave movements are found throughout the gastrointestinal tract.

From swallowing, it takes almost ten seconds for solid food to reach the stomach, but only a few seconds for drinking.

The stomach

The stomach is a container where the food and drink stops before being transported through the rest of the gastrointestinal tract. The stomach holds about one and a half liters. It is usually emptied of food about four hours after a meal. Drink passes fastest and fatty foods remain at the far end of the stomach.

Upper and lower stomach

The stomach lies high in the abdomen, just below the middle nerve on the left side. It is shaped much like a sack with two openings. The upper opening is from the esophagus. The lower opening extends to the duodenum. Both openings are called upper and lower mouth.

The stomach kneads the food

The stomach is made up of smooth muscles. It is constantly moving because the muscles are constantly alternating and relaxing. The food is kneaded and mixed with stomach juice in the stomach. This causes the food to decompose further. The food that leaves the stomach is a viscous liquid.

Gastric mucosa forms gastric juice

On the inside, the stomach is covered by a very durable mucosa. The mucosa contains glands that form gastric juice. Stomach juice consists of hydrochloric acid which is corrosive and very acidic.

These are the tasks of the gastric juice:

In total, about two liters of gastric juice is formed per day. Already when you see food, the amount of stomach juice begins to increase. This allows the stomach to take care of the food and break it down immediately when it gets into the stomach.

The liver

The liver is the body’s largest gland. It lies high in the abdomen on the right side and is protected by the ribs.

Bile forms in the liver

In the liver, half to one liter of bile is formed every day. The bile contains, among other things, bile acids, bile dyes, hormones, water and salts. The bile is needed to break down the fat in the food. On the back of the liver, the so-called liver passage passes out of the liver. Here, blood vessels also go to and from the liver. The bile is transported in the delivery aisle.

The liver not only forms bile but has many other important functions:

  • The liver produces substances needed for digestion, such as cholesterol and bile.
  • The liver stores sugar, fat, vitamins and iron.
  • The liver helps the pancreas to regulate blood sugar levels.
  • The liver takes care of toxins that have entered the body.
  • The liver stores blood and purifies the blood.

The gallbladder concentrates the bile

The gallbladder lies on the back of the liver. The bile forms in the liver, but it is collected and stored in the gallbladder. The bile stays in the gallbladder until it is needed to break down fat in the duodenum, which is the first part of the small intestine. The bile can only pass out into the gut when there is food to be broken down. A ring muscle at the orifice to the duodenum prevents the bile from passing at other times.

The pancreas forms hormones

The pancreas is located just in front of the spine. The pancreas contains enzymes that help break down the food. The pancreas also contains bicarbonate which helps neutralize the acidic contents of the stomach. The pancreas is guided through a hallway that goes along with the bile duct and then opens into the duodenum.

The pancreas also forms the hormones insulin and glucagon. These hormones are important for keeping the body’s blood sugar at the right level.

The small intestine

The food leaves the stomach through the lower stomach. It will then reach the small intestine.

The small intestine has the following information:

  • The small intestine continues to decompose the food.
  • The small intestine absorbs water and nutrients from the food.

The small intestine is three to five meters long. Contractions in the muscles of the small intestine create wave movements that knead the intestinal contents and move it forward.

The duodenum is the first part of the small intestine

The first part of the small intestine is called the duodenum. There, the food is mixed with various substances from the liver, gallbladder and pancreas. The substances are needed for the breakdown of the food.

The duodenum has its name because it is twelve finger widths, that is about 25 centimeters.

The surface of the small intestine is very large

The inside of the small intestine is covered with mucosa. The mucosa is strongly wrinkled. On the mucous membrane there are small protrusions called intestinal mucosa. On the surface of the intestinal mucosa is a layer of intestinal cells, which take up nutrition. The wrinkled surface, intestinal fluid and intestinal cells make the small intestine surface very large. It is important for the small intestine to be able to absorb enough nutrition from the food.

The small intestine receives fluid and emits fluid

Each day, the small intestine receives six to seven liters of fluid. It is partly food and fluid that we have eaten and drunk, and liquids that have been added to the gastrointestinal tract, ie saliva, gastric juice, bile and pancreas.

The mucous membrane of the small intestine itself releases about two liters of liquid in the form of intestinal juice. The intestinal juice contains digestive enzymes as well as water and mucus that lubricates the intestine and facilitates transport. Of the eight to nine liters of fluid passing through the small intestine, most are absorbed again, the largest part of the small intestine and the large intestine. Barely two deciliters of fluid leave the body each day along with the stool.

The small intestine absorbs important nutrients from the food

In the small intestine, the food has been broken down to its smallest constituents. This allows the small intestine to begin to absorb the parts of the food that the body needs.

The mucous membrane of the small intestine absorbs sugar, fat, vitamins, salts and amino acids. Amino acids are what proteins consist of. These substances are then transported to the liver where they are either used to form different substances or stored.

What remains of the intestinal contents leaves the small intestine after three to seven hours. It is necessary that the passage through the small intestine takes quite a long time as all the important nutrients must be able to absorb.

The colon

The large intestine is a continuation of the small intestine. The large intestine is almost one and a half meters long and twice as thick as the small intestine. The first part of the colon is called the appendix.

Wave movements for the intestinal contents downwards

The colon receives 1-2 liters of intestinal contents from the small intestine every day. This stays in the large intestine for three hours up to over a day. Intestinal contents are transported down the intestine by means of wave movements. A large part of the intestinal contents consists of water, the rest of food that is not broken down, salts and bacteria. Most of the water is absorbed from the intestine into the blood. Therefore, the stool gets a firmer texture. The large intestine also absorbs some salts.

Bacteria are needed for the breakdown of food

The bacteria in the colon have several tasks. They play a part in the body’s immune system and, for example, they form vitamin K that the body needs. The bacteria also break down certain substances that the digestive enzymes have failed to break down when the food has passed through the gastrointestinal tract.

During decomposition, gas is formed, a total of one to two liters per day. Sometimes the gases can cause the intestinal wall to be stretched out and you get stomach or stomach ache. Some types of food can produce more gas than others, such as cabbage, beans and products sweetened with certain sweeteners.

The bacterial colon is prevented from entering the body by means of so-called lymphatic tissue in the intestinal wall. In the large intestine mucosa there are special cells that form mucus that lubricates the stool.

The rectum

In the pelvis, the large intestine passes into the rectum. It is barely 15 centimeters long. The lower part of the rectum is slightly larger than the other part of the rectum. Therefore, some stools can be collected there before the bowel has to be emptied. The very last part is called the rectum or anus. Around the rectum opening are two annular muscles, so-called ring muscles, one of which can be controlled by the will.

The stool consists of water bacteria, food debris that has not broken down, cells that have been pushed away from the intestinal mucosa and mucus.

Reflexes allow the bowel to be emptied

There are special recipients in the rectum that feel when the bowel is stretched by the stool. A reflex causes the large intestine and rectum to contract to push out the stool, while relaxing the muscles around the rectum.

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