The food we eat must be broken down into other substances that our bodies can use, and any waste must be removed. It is called digestion. If we didn’t digest our food, we couldn’t use it and turn it into energy.

In short, the digestive system moves food and drink from the mouth, through the throat, into the stomach, the small intestine, and finally into the large intestine. At each stage, nutrients are pulled from the body to be used by the body.

The digestive system is the system for digestion in the human body; it describes how we break down our food. The digestive system is the name given to all the apparatus which enables our bodies to do this.

How Does the Digestive System Work?

There are seven parts to the digestive system, each vital in transporting our food through the human body, absorbing important nutrients, and removing waste. Digestion in the human body involves the following body parts, organs, and muscles:

  • mouth;
  • esophagus;
  • stomach;
  • small intestine;
  • liver;
  • gall bladder;
  • large intestine.

How does the Human Body control Digestion?

Hormones and nerves work together to control the digestive system. Hormones tell the parts of the body, like the stomach, to make digestive liquids like stomach acid.

Nerves connect the brain to the digestive system. The brain sends signals to the different parts of the process, causing them to begin working. For example, the brain triggers the salivary glands to produce saliva once the food is smelt. Spit allows us to break down food and prepare it for its journey through the digestive system.

What is the journey of food through the digestive system?

The 7 Stages of the Digestive System

The human digestive system comprises seven distinct stages; food or water we ingest will go through these seven stages (the journey of food through the digestive system). Each stage has a unique function: to make the food safe to travel through our body and pull out any nutrients our body needs.

Children are expected to understand the digestive system at KS2. To know how digestion works, you’ll need to understand the seven stages of the digestive system.


The first stage of the journey of food through the digestive system is the mouth. It is where the food begins its digestive process.

In the mouth, food is chewed to make it softer and smaller, so it can be swallowed and will not get stuck in the intestines. To do this, the mouth needs assistance:

  • The tongue is a muscle in the mouth, covered with thousands of taste buds. It helps to push food into the throat.
  • Your teeth allow us to break down food so that it is smaller and easier to digest.
  • The salivary gland produces saliva, which softens our food and helps us swallow it.


The second stage of digestion in the human body is the esophagus. From here, the digestive process becomes automatic, which means you don’t need to think about doing it; your brain will automatically send messages to the muscles in your body to continue the process.

The esophagus is a tube that connects the mouth to the stomach. The esophagus has muscles that work in waves to move food safely down to the stomach and stop anything from getting stuck. This process is called peristalsis.

What is Peristalsis?

  • The esophagus has a layer of muscle that creates a wave-like motion to squeeze food down it.
  • This muscle layer means that food would get to your stomach even if you were standing on your head!
  • The esophagus also creates a slimy mucus that oozes out to help the food make its way down.
  • The esophagus is about 25 cm long.


The stomach is a very important organ in the food journey through the digestive system. First, the stomach will fill up with the food that has traveled down the esophagus and cover it in special enzymes and liquids. These enzymes kill many harmful microorganisms that might have been swallowed along with the food. When the stomach eventually breaks down food, it becomes a porridge-like substance called chyme.

The stomach is a very strong organ; it is not affected by the strong acid it produces (which can break down most substances).

After the chyme comes out of the stomach, it goes into the duodenum. Here, it continues to be broken down. The duodenum also connects to other organs in the journey, such as the liver, the gall bladder, and the pancreas.


The liver is a factory for your body; it uses chemicals to change food into substances that your body can use for energy. It also removes the things that are useless or toxic to your body. For example, the liver produces a liquid called bile, which aids digestion and helps to absorb fats.

Gall Bladder

The gall bladder is a small pouch that sits just under your liver. It is where the bile that the liver produces is stored.

The Small Intestine

Only after the food has been properly broken down and the liver has absorbed all the useful nutrients is it ready to go into the small intestine. This part of the journey comprises a long, stretchy tube that processes the remaining food and allows any remaining vitamins and minerals to be absorbed through its walls.

What Does the Large Intestine do?

Now that we have followed food through the digestive system, we can answer the question of what does the large intestine do?

The large intestine is the last step in the food journey through the digestive system. At this point, all the nutrients, vitamins, and minerals have been extracted from the food, toxic bacteria have been destroyed, and all that is left is the waste material that needs to be removed from our bodies.

What does the large intestine do now? First, it removes all of the water content of the waste material, which will then be pushed through the intestine until it reaches the rectum (at the end of the large intestine). Then, finally, the waste material is removed from the body through a bowel movement.

How Does the Digestive System Break Food Down?

Each part of the digestive system works to break down food using the following:

  • chewing
  • squeezing
  • stomach acid
  • bile
  • enzymes

A mixture of physical motion, chewing and squeezing, and chemical processes in the liver, stomach, gall bladder, and intestines play a role in breaking down food. This breakdown allows the body to extract and absorb nutrients that provide us with energy and support cell growth.

What are the 2 Types of Digestion?

There are two different types of digestion that happen within the body. These are known as chemical digestion and mechanical digestion.

What is Chemical Digestion?

Chemical digestion is how digestive enzymes break down food as it travels from the mouth into the digestive system. It is through chemical digestion that food is transformed into smaller nutrients that can be absorbed easily by the body. Without chemical digestion, our bodies can’t absorb nutrients from our food.

What is Mechanical Digestion?

While chemical digestion is, as the name suggests, the chemical aspect of digestion, Mechanical digestion is the physical aspect of the process. During mechanical digestion, the food’s chemical nature is not altered. Instead, the food is made physically smaller through chewing and tongue movements. Mechanical digestion breaks food down into smaller bits and mixes it with saliva.

The Difference Between Chemical Digestion and Mechanical Digestion?

Mechanical digestion begins in the mouth, with chewing and tongue movements that break the food into smaller pieces. Then, it moves to churn in the stomach and segmentation in the small intestine. Peristalsis also plays a huge role in mechanical digestion. Peristalsis is the name for involuntary contractions and relaxations of the muscles of the body’s esophagus, stomach, and intestines. These contractions help break down food and move it through the digestive system.

Chemical digestion also begins in the mouth. As you chew, your salivary glands release saliva into your mouth, which contains a range of digestive enzymes that start the process of chemical digestion. The majority of chemical digestion, however, occurs in the small intestine and involves the secretions of enzymes throughout the digestive tract. The enzymes are designed to break the chemical bonds that hold food particles together. Once these bonds are broken, the food can be broken down into small, digestible pieces.

How Do These Processes Work Together?

Once the food particles have reached the small intestine, the intestines continue to move. It helps the food particles to continue moving along, thus exposing more of them to digestive enzymes. These movements are also beneficial in moving the digested food toward the large intestine for excretion.

What is the Purpose of Chemical Digestion?

Essentially, both digestion processes are necessary; we would not be able to digest food successfully with just one of them. For instance, chewing and peristalsis in mechanical digestion are good for physically breaking down large pieces of food into smaller ones so that cells can absorb them. However, chemical digestion is required to make these food particles small enough to be fully digested.

Chemical digestion breaks down nutrients into smaller parts. For instance:

  • Fats are broken down into fatty acids and monoglycerides.
  • Nucleic acids are broken down into nucleotides.
  • Polysaccharides, or carbohydrate sugars, are broken down into monosaccharides.
  • Proteins are broken down into amino acids.

Without chemical digestion, the body wouldn’t be able to absorb nutrients from food, leading to many deficiencies and diseases.

Digestive Enzymes In the Mouth:

As previously mentioned, chemical digestion begins in the mouth with various enzymes found in saliva. These enzymes include lingual lipase, which is responsible for breaking down triglycerides and fat. In addition, salivary amylase is also found in the mouth, which is responsible for breaking down ​​polysaccharides, a complex sugar that is a carbohydrate.

The Path of Chemical Digestion

While chemical digestion begins in the mouth, it doesn’t end there. It is a whistle-stop tour of the path of chemical digestion throughout the body:

  • Stomach

In the stomach, chief cells secrete a range of digestive enzymes.l One of these enzymes is called pepsin, whose role is to break down proteins. Then there is gastric lipase, the enzyme responsible for breaking down triglycerides. Fat-soluble substances, such as alcohol, are also absorbed in the stomach.

  • Small intestine

The small intestine is where the majority of chemical digestion takes place. It is here that the main components of food, such as amino acids, peptides, and glucose for energy, are absorbed. In addition, there are a large number of enzymes that are released in the small intestine and the pancreas, all for digestion. These enzymes include lactase to digest lactose and sucrase to digest sugar.

  • Large intestine

There are no digestive enzymes released in the large intestine. However, it does contain a range of bacteria that helps to break down nutrients further. The large intestine also absorbs vitamins, minerals, and water.

Why is Digestion in the Human Body Important?

Through the digestive system journey, the human body receives the important nutrients from food and drink needed to function properly. These nutrients are called macronutrients and are vital for a healthy body. The digestive system involves different stages, and in each stage, the nutrients are broken down so that we can absorb them, using them for energy, growth, and repair.

The body breaks down nutrients from food and drinks into carbohydrates, protein, fats, and vitamins.


Sugars, starches, and fiber are carbohydrates found in many foods. Simple carbohydrates include natural sugars in foods such as fruits, vegetables, and milk. Complex carbohydrates contain vitamins, minerals, and fiber that your body needs and are found in food like wholegrain bread, cereal, starchy vegetables, and legumes.


Proteins are made up of amino acids, which our body needs to grow and maintain its cells and tissues. The body absorbs amino acids through the small intestine into the blood and transports them around the body. Proteins are found in foods such as meat, eggs, and beans.


Fat supplies the body with energy and helps it absorb vitamin A, vitamin D, and vitamin E. Healthy fats (known as unsaturated fats) are found in sunflower, soybean, and olive oil. Unhealthy fats (saturated fats) are found in food like butter, candy, cheese, and fatty cuts of meat. The body breaks down fat molecules into fatty acids and glycerol during digestion.


Vitamins are organic substances that are found in small amounts in certain foods. Each vitamin plays a different role in the body’s growth and health. For example, the body stores fat-soluble vitamins in the liver and fatty tissues but does not easily store water-soluble vitamins and flushes out any excess vitamins in the urine.

What are Some Common Conditions that Affect the Digestive System?

The digestive system is home to many different organs and is affected by several temporary and long-term diseases. Some of these diseases or disorders are more common than others; for instance, around 1 in every seven adults and 1 in every three children in the UK has constipation at any time. While digestive issues like this are common, they can still be painful and cause great discomfort. More minor digestive problems can also lead to more serious conditions requiring medical treatment.

Here are some temporary issues or disorders that affect the digestive system:

  • Constipation: Constipation happens when you cannot have a bowel movement (i.e., you can’t poo) as frequently as you typically do. Bowel movements can also often be painful when you are constipated.
  • Diarrhea: Diarrhoea is pretty much the exact opposite of constipation. You have bowel movements much more frequently than normal when you have diarrhea. Without getting too graphic, these bowel movements are also not always ‘solid.’ There is a range of things that can cause diarrhea, including bacteria.
  • Heartburn: Judging by its name, it would be fair to assume that heartburn affects the heart. However, heartburn is an issue that affects the digestive system. When you have heartburn, you will feel an uncomfortable, burning sensation in your chest, which sometimes migrates to the neck and throat. The cause of heartburn is acidic digestive juices traveling from the stomach to the esophagus.
  • Stomach Flu: Stomach flu, also known as gastroenteritis, is an infection of the stomach and the upper section of the small intestine that is typically caused by a virus. Millions of people get the stomach flu yearly, lasting around a week.
  • Ulcers: An ulcer is a sore that grows on the esophagus, stomach, or small intestine lining. Ulcers are commonly caused by infection with bacteria called Helicobacter pylori. However, they can also be caused by the long-term use of anti-inflammatory drugs like ibuprofen.
  • Gallstones: Gallstones are tiny pieces of solid material that have formed from digestive fluid in the gallbladder. The gallbladder is a small organ located below your liver.

Here are some diseases, also known as gastrointestinal diseases, and disorders that affect the digestive system:

  • Chronic Acid Reflux: Chronic acid reflux is also called GERD, standing for gastro-oesophageal reflux disease. GERD is a condition where acid-rich contents in the stomach leak back up to the esophagus frequently.
  • Irritable Bowel System: Irritable bowel system, or IBS, is a condition in which the colon contracts either more or less often than normal. It can cause increased gassiness, stomach pain, cramps, bloating, and irregular bowel movements.
  • Lactose Intolerance: Lactose Intolerance is the inability to digest lactose. Lactose is the sugar found primarily in milk and dairy products. Therefore, people who are lactose intolerant have to stay away from eating any dairy products.
  • Diverticulosis and Diverticulitis: Diverticulosis and diverticulitis are two different conditions that affect the colon. In both situations, bulges, known as diverticula, form in the colon’s wall.
  • Cancer: Cancer is a disease that can affect a wide range of areas in the body. One of these areas is the digestive system. Cancers that affect the digestive system are called gastrointestinal (GI) cancers. There are many GI cancers, the most common of which are oesophageal, gastric (stomach), colon and rectal (colorectal), pancreatic, and liver.
  • Crohn’s Disease: Crohn’s disease is a chronic illness that lasts a lifetime. Crohn’s is an inflammatory bowel disease that irritates the digestive tract. The side effects of Crohn’s disease include irregular bowel movements, stomach pain, weight loss, and extreme tiredness.
  • Celiac Disease: Celiac disease is an autoimmune disorder that affects the small intestine. If a person has celiac disease, they are intolerant to gluten, a protein found in wheat, barley, and rye. Therefore, when a person with celiac disease consumes gluten, it can damage their small intestine.

How Can I Keep My Digestive System Healthy?

As you can see above, various conditions and diseases can impact your digestive system’s health. Thankfully, there are also lots of small, everyday things that you can do to keep your gut in good health and, thus, prevent some of these conditions from occurring.

Here are some easy ways to maintain your gut health:

  • Water! Water! Water! Drinking lots of water is a key part of maintaining good gut health. When you drink water, it helps food flow more easily through your digestive system. Dehydration, caused by a lack of water in the body, can lead to digestive issues like constipation.
  • Eat Plenty of Fibre: Fibre is a chemical compound found in foods like wholegrain cereals, oats, and other carbs, in addition to a range of fruits, vegetables, nuts, and legumes. Fiber is extremely beneficial to the digestive system, as it helps the body have regular bowel movements. There are two types of fiber: soluble and insoluble, both of which should be included in your diet for good gut health.
  • A Balanced Diet: Eating a balanced diet is one of the simplest ways to maintain a healthy gut. A balanced diet should include every macronutrient group, i.e., protein, carbs, fat, and micronutrients.
  • Opt for Wholegrains: It is always best to opt for wholegrains over processed grains, as they are easier for the body to digest. A good rule to have is to try to avoid processed foods in general.
  • Cut Down on Red Meat: Red meat is okay in moderation, but too much of it can cause unwanted stress on the digestive system. In addition, red meat is hard for the body to digest and can lead to bloating and stomach pain. Therefore, it is best to opt for poultry and fish instead of red meat.
  • Probiotics are good bacteria that help fight off bad bacteria in the gut. They also created healthy substances that nourish the gut. Probiotics can be found in various foods, such as yogurt, sauerkraut, tempeh, kimchi, pickles, and a bunch of fruits. Alternatively, probiotics can be taken in the form of supplements.
  • Eat Slowly: Eating slowly allows your body the time it needs to digest food properly. Eating slowly also gives your body time to signal to your brain to let you know when you are full. It helps you avoid overeating, which can negatively affect the digestive system.
  • Take Time to Chew: While we might not give it a second thought, chewing is integral to maintaining good gut health. When you take time to chew your food, it helps ensure your body has produced enough saliva (spit) for digestion. What’s more, chewing your food thoroughly makes it easier for your digestive system to absorb the nutrients in the food.
  • Exercise Regularly: Exercise and physical activity are vital for helping food move through the digestive system. This exercise doesn’t have to be anything crazy. Going for a walk, especially after a meal, is a great way to help your digestive system process food.
  • Avoid Alcohol: Alcohol can greatly increase the amount of acid in the stomach, leading to various issues like heartburn, acid reflux, and stomach ulcers. It is not necessary to avoid alcohol in general, but it is important to watch how much you consume.
  • Say No to Smoking: Studies have shown that smoking can almost double your risk of experiencing acid reflux. It has also been proven that people who suffer from digestive issues and frequently smoke see their problems improve after they quit smoking.
  • Keep Stress to a Minimum: Stress is the root of many body issues. In all honesty, nothing good comes from stress. However, the digestive system is particularly affected by it, and increased stress can lead to problems like constipation, diarrhea, and IBS. Therefore, it is important to take steps to ensure that your stress is at a minimum.

Fast Facts about the Digestive System for KS2

  • The average person produces 2 pints (1.14 liters) of saliva daily.
  • The second part of your small intestine is called the jejunum.
  • Enzymes in your digestive system separate food into the different nutrients your body needs.
  • A close bond exists between your brain and your digestive system. It is called ‘the gut-brain axis.’ It explains why emotions and brain disorders affect how your body digests food.
  • The whole digestive system is disconnected from gravity. But because it works with muscles, you can digest food whether standing up, upside down, or lying on your side.
  • Some enzymes in clothes-washing detergents are the same as those in your digestive system.
  • The large intestine is only about 5 feet (1.52 meters) long, making it smaller than the small intestine, which is about 22-23 feet long.
  • The gas in your body is produced by fermented bacteria and then mixed with air, which is why it doesn’t smell good.
  • Platypuses don’t have stomachs!
  • Stomach growling happens all the time, but you can hear it much more when your stomach is empty because there’s no food to silence it.
  • When the stomach is fully stretched, it can simultaneously hold up to 4 pounds (1.81 kilograms) of food.
  • The best exercise you can do to keep a healthy digestive system is aerobic exercise — like walking and running.
  • Babies aren’t born with the healthy bacteria your system needs to digest food.
  • Hiccups can be caused by a change in temperature that happens suddenly. For example, the longest attack of constant hiccups lasted 68 years!
  • You might have noticed your mouth has more saliva when you are about to be sick. It is to protect your teeth from the acids in your stomach that will come up.

The digestive system journey (simplified)

  • The mouth: food is chewed and swallowed.
  • Esophagus: your chewed-up food is transported from the mouth to the stomach via the esophagus.
  • Stomach: a large amount of food can be quickly stored here and digested over a long time.
  • Liver: a liquid called bile is made here, which aids digestion and helps absorb fats.
  • Gall bladder: the bile is stored here.
  • Small intestine: the small intestine plays a BIG role in the digestive process. And in actuality, it’s not that small! Measuring seven meters long, it’s the small intestine’s job to absorb nutrients from the food.
  • Large intestine: here, any undigested material, excess fluid, and mucus all combine to form a stool.
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