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What is Digestive System in Humans? Everything You Need to Know

by Sankalan Baidya
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digestive system

The Digestive System in humans is one of various systems that make up the entire human body. One of those systems known as the Excretory System has been discussed in details and you can find it here. Today we will discuss about the digestive system in details. So, what are we going to cover in this article? Here is what you can expect from the article:

  • What is digestive system? What are its functions?
  • Which organs make up the digestive system?
  • Anatomy of digestive system.
  • Some interesting facts about digestive system.

Before we start with the article, we will like to mention that digestive system and every other system in our body are actually interconnected and they cannot work independently. So, despite the fact that we will focus on digestive system in particular, know that there are other systems that we will ignore as mentioning all of them in conjunction is not possible.

Oh yes, did we tell you?

Pooping is a part of the digestion and not excretion. Pooping is actually elimination and not excretion.

Let’s begin…

What is Digestive System? What Are Its Functions?

It is a system present in our body that helps us to break down the food we consume into small particles (nutrients) and energy that are used by our body to stay alive. A number of organs work together to achieve this incredible feat. It is complex and the process is long. The primary functions of the system include the following:

  • Ingestion: This is intake of food from oral cavity or mouth.
  • Secretion: Release of various fluids like bile, saliva, digestive enzymes, hydrochloric acid, mucus etc.
  • Mixing and movement: It is nothing but mixing of the ingested food with various fluids and moving the same through various segments of the digestive tract. There are basically three ways it happens – swallowing, peristalsis and segmentation.
  • Digestion: This is the method of breaking down of large food pieces into smaller component chemicals. This happens in two ways – mechanical digestion and chemical digestion. Mechanical digestion is chewing of food for breaking it down into smaller pieces. Chemical digestion is breaking down food into smaller particles using chemicals like acids, enzymes etc.
  • Absorption: Absorption of chemical components (created from ingested food). Absorption takes place in stomach, small intestine and large intestine.
  • Elimination (some sources may mention it as Excretion but that is not true): This is removal of solid waste (undigested food particles) through anus. This is known as defecation. It is the last stage of digestive system.

Which Organs Make Up the Digestive System?

The digestive system is made up of two distinct parts. They are:

  • Gastrointestinal Tract or GI Tract. It is also known as the Alimentary Canal. There is another name for it. It is known as Digestive Tract.
  • Accessory Organs.

Gastrointestinal Tract

The Gastrointestinal Tract, which is also known as the Alimentary Canal, is made up of the following:

  • Oral cavity
  • Pharynx
  • Esophagus
  • Stomach
  • Small Intestine
  • Large Intestine

If you notice, the organs that are involved in making up the digestive tract or the alimentary canal are actually hollow and interconnected. They start at the mouth and end at the anus from where we poop out. This whole tract is long and twisted and covers a total distance of 9 meters starting from the mouth all the way down to the anus. The large intestine of the GI tract is the one that includes both the rectum and the anus.

The food that we eat enters through the mouth and passes through the entire digestive tract where it is broken down into small nutrients and energy before the remaining indigestible part of the food is removed from the body in form of poop.

While the food passes through the alimentary canal, a number of accessory organs pitch in and provide the necessary support for breaking down of the food consumed. This brings us to the question: ‘what are the accessory organs that are involved in the process of digestion?’ Let’s find out…

Accessory Organs

There are several accessory organs that come to the aid of digestion. These accessory organs include the following:

  • Teeth
  • Tongue
  • Salivary glands
  • Pancreas
  • Liver
  • Gallbladder

In case you have noticed, the accessory organs of the whole digestive system are actually solid organs unlike the hollow organs that make up the alimentary canal or the gastrointestinal tract or digestive tract.

Anatomy of Digestive System: How the System Works?

The modus operandi (working procedure) of the digestive system is very complex. It starts right at the mouth, which is technically referred to as the oral cavity. This is from where the food enters into our body. So, let us start with the mouth…

Oral Cavity in Digestive System

The oral cavity or the mouth is an interesting place. It has number of accessory organs that perform different function. The accessory organs in the mouth include:

  • Teeth
  • Tongue
  • Salivary Glands

Function of Teeth

When the food enters into our mouth (we place the food in our oral cavity using our hands), the first thing that needs to be done is to grind the food into small pieces. The digestive system cannot work with large food pieces. The food has to be ground down into smaller pieces. This job is performed by our teeth. They cut and grind the food into numerous smaller pieces.

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Function of Tongue

The tongue is a small muscular organ present in the mouth. Its primary function in the process of digestion is that pushing the chewed up food in the posterior part of the mouth. The tongue is blessed with small structures called the taste buds that are connected with the nervous system. These taste buds are known for picking up the taste information of the food we put in mouth and send that information through the nerves to the brain.

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Function of Salivary Glands

There are in total 3 sets of salivary glands present inside our mouth. These glands are known for producing watery secretion that is known as saliva. This saliva has several functions which are mentioned below:

  • Moistening and softening the food.
  • Bolus formation (bolus is a ball-like mixture of saliva and food).
  • Lubrication of the bolus so that it can pass into the esophagus by passing through pharynx.
  • Breaking of carbohydrates in the food using digestive enzyme known as amylase (actually 30% of the starch present in carbohydrate is initially digested by saliva).
  • Breaking down of fat using another digestive enzyme known as lipase.
  • Cleaning mouth and teeth.
  • Providing antibodies that prevent infection of salivary glands.

Pharynx in Digestive System

Generally referred to as the throat, the pharynx is a tube of the shape of a funnel. It is connected to the oral cavity’s posterior end. The pharynx is really important because it has a dual role to play. It’s presence is vital for protection of the respiratory system. The air that enters through our nasal cavity needs to reach the lungs by passing through larynx but before it goes into larynx, it needs to pass through pharynx.

There is a problem. Both food and air passes through the pharynx then how come food doesn’t enter into our lungs? There is something called epiglottis. It is a flap-like structure, an elastic cartilage that sits right at the entrance of the larynx. When food enters pharynx, the epiglottis directs it towards the esophagus and when air enters the pharynx, the epiglottis directs its towards the larynx.

Esophagus in Digestive System

The esophagus is a long muscular tube. It connects our stomach and the pharynx. When the food enters into the esophagus a wave like movement (peristalsis) of the walls of the esophagus sends the food down towards the stomach. Once the food enters into the stomach from the esophagus, the cardiac sphincter closes the entrance and prevents food from passing back into the esophagus from the stomach.

So, what is this cardiac sphincter? It is a small muscular ring that is located at the end of the esophagus where it meets the stomach. This cardiac sphincter is also known as lower esophageal sphincter.

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Stomach in Digestive System

The stomach is one of the most important parts of the digestive systems present in human body. It is a hollow sac-like organ and is blessed with very strong muscular walls. On one end the stomach connects with the esophagus and on the other end it connects with the small intestine. The stomach is where the gastric acid is produced. This gastric acid, also known as the gastric juice, is very important for the process of digestion. The gastric acid is primarily composed of sodium chloride and hydrochloric acid.

The production of the gastric juice or gastric acid is stimulated by a special type of hormone known as gastrin, which produced by special types of cells known as G Cells that are present in gastric glands present inside the stomach.

Once the gastric juice is produced is responsible for activation of digestive enzymes that are present in the stomach. These digestive enzymes, once activated, continue the digestion of the food that actually started at the mouth.

The gastric glands that are present inside the stomach are responsible for producing what is known as mucus. This mucus in turn protects the walls of the stomach from the acid (hydrochloric acid) of the gastric juice as well as other chemicals.

While food continues to be digested in the stomach, something else also happens. Even the stomach performs peristalsis – a mechanical wave-like motion of the inner walls of the stomach. As a result of this peristalsis, the food that enters into the stomach gets mixed with gastric juices and enzymes thoroughly.

Through this process of digestion and peristalsis, the food is converted into chyme. It is a thick semi-liquid thing. The food particles that are actually broken down in the stomach are basically proteins. It takes nearly 2 hours to produce the chyme.

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Small Intestine in Digestive System

Once the chyme has been produced, it will be moved into the small intestine. This small intestine has three major parts, which are:

  • Duodenum
  • Jejunum
  • Ileum

The stomach connects to the small intestine at the duodenum. In the duodenum part, the food (chyme) gets broken down even further. This breaking down of the food is assisted by bile secreted by the liver and the digestive juices that are released by the pancreas.

The bile and the digestive juices that are secreted from the liver and the pancreas are actually more alkaline in nature. They mix with the chyme and neutralize the acid (caused by the gastric juice). This neutralization of acid is necessary because the acidic chyme can damage the walls of the small intestine.

In the duodenum, the chyme is converted into a liquid substance and breaking down of food is further continued. The food then moves very slowly (known as segmentation contraction: helps in mixing and moving chyme) into the jejunum where digested sugars, fatty acids and amino acids are absorbed into the bloodstream. From the jejunum, the food is then passed into the ileum where any residual nutrients and bile acids are absorbed.

By the time the chyme leaves the small intestine, 90% of the nutrients in the food are already absorbed by the body. Things that cannot be digested are converted into semi-solid material known as feces inside the ileum. The feces is then passed on to the large intestine.

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Liver in Digestive System

Liver plays very important roles in our body but when it comes to digestive system, there are two major roles of liver:

  • Production of bile which is responsible for helping with digestion of fat.
  • Processing of blood which picked up the raw nutrients from small intestine and converting them into various chemicals that are required by our body.

The liver filters the blood and purifies it before it is released back for traveling throughout the body.

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Gallbladder in Digestive System

The gallbladder is a unique organ which is basically a storage unit. Shaped like a sac, its main function is storage of bile. When liver produces bile, it travels into small intestine using bile ducts but if the bile is not needed, it travels back into the gallbladder and stored. When food comes in small intestine, the small intestine sends signal to the gallbladder and the bile is released back into the small intestine.

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Pancreas in Digestive System

The job of the pancreas is to produce digestive enzymes that are released into the small intestine. These enzymes help in breaking down carbohydrate, fats and proteins. Pancreas is also responsible for insulin production, which is released straight into our bloodstream. This insulin helps in metabolism of sugar.

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Large Intestine in Digestive System

This is a specialized organ. The undigested feces from the ileum enters the large intestine known as colon. This is where gut flora (bacteria) comes into action. In the colon, the gut flora helps in fermenting and breaking down whatever digestible material is left in the feces. As the food waste passes slowly through the colon, all the water content and little nutrients processed by the bacteria are absorbed to be used by the body. The rest is converted into solid waste that is passed on to the rectum where it is stored until defecated or eliminated from the anus. The passage of stool from the colon to the rectum can take up to 36 hours or more.

The rectum, which is an 8-inch chamber is where the stool gets stored. There are sensors in the rectum which sends message to the brain when stool or gas is received. The brain then tells whether the waste is to be released or not.

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Amazing Digestive System Facts

  • Around 7 liters of fluid are secreted by the digestive system every day.
  • Anywhere between 0.75 liters to 1.5 liters of saliva is produced every day.
  • The digestive system, from mouth to anus is around 30 feet long (9 meters).
  • The small intestine alone is around 22 feet long.
  • The stomach (adult’s) is capable of holding around 1.5 liters of food material.
  • Food takes approximately 7 seconds to travel through esophagus and reach the stomach.
  • Maximum digestion takes place in small intestine and not the stomach.
  • ‘Borborygmi’ is the term for stomach growling.
  • Exactly how the food is digested is dependent on our emotions. Sadness, anxiety, anger etc. can all affect how food gets digested.
  • The digestive system is capable of moving food in the right direction even if someone stands on his or her head. This is because, it is not dependent on gravity but is rather dependent on muscular movements called peristalsis.
  • The gut flora contains around 300 to 1,000 different species of bacteria. There are around 1012 bacterial cells for every 1 gram of intestinal content. This is why, around 60% of the feces or stool is actually bacteria.
  • When food in put in mouth, it is either warmed up or cooled down as required.
  • The colon or the large intestine is around 5 feet to 6 feet long.

That concludes our article on digestive system. In case we missed something or you need to know something in greater details or if we have mentioned something that you feel in incorrect information, feel free to get in touch.

Sources: 1, 2, 3, 4, 5, 6, 7

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