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Digestion in Humans
The food that we eat passes through a Canal inside our body.
The food is processed and utilized in the body and unused food is collected inside the canal only.
This Canal is often called as the Alimentary Canal or the Digestive Tract.
The canal is divided into different parts:
- The Mouth or Buccal Cavity
- Food Pipe or Oesophagus
- Stomach
- Small Intestine
- Large Intestine
- Anus
Figure 2: Digestive Tract in Humans
There are three glands associated with the alimentary canal that secrete digestive juices that are used to convert the complex food substances into simpler substances.
- liver
- pancreas
- salivary glands
The Digestive System – The alimentary canal and the digestive glands together form a system in the human body which is responsible for the digestion of food in the body. This system is called the Digestive System.
The Mouth or Buccal Cavity
The Mouth or Buccal Cavity
Ingestion refers to the process of taking in the food through the mouth. The food is chewed with the help of teeth, saliva and the tongue present in the mouth.
The salivary glands present in our mouth secrete saliva which mixes with the food, moist it and breaks the starch present in the food into sugar.
The tongue present in the mouth helps in mixing the food with the saliva and helps in swallowing it inside the mouth. It also has taste buds which help in identifying the taste of anything that we eat. Besides this, the tongue also helps in talking.
The Teeth. Teeth pay an important role in digestion , they help in cutting , tearing ,chewing and grinding of food into finer particles that can be digested by enzymes. There are two sets of teeth.
Milk Teeth – In the early childhood a set of teeth growth in children that then fall off after certain age 6 to 8 years. These teeth are called Milk Teeth.
Permanent Teeth – The teeth that grow after milk teeth fall off are called Permanent Teeth. They generally remain during the lifetime of a person or at least until old age.
Teeth can also be classified into four major sets as shown in the diagram below.
Different Types of Teeth
Tooth Decay
Tooth decay refers to the gradual damage of teeth caused due to presence of bacteria in the mouth that grow if we do not keep our mouth and teeth clean. Tooth decay is caused mainly because of eating food with high sugar content, soft drinks and chocolates. Any leftover food present inside our teeth is broken down by such bacteria. As a result, an acid is released which damages the teeth slowly. Tooth decay can cause severe pain and even toothless.
How can we prevent tooth decay?
- Clean your teeth with a brush or dental floss at least twice a day
- Rinse your mouth after every meal you eat
- Do not put a dirty finger or any unwashed food items in your mouth
Food Pipe or Oesophagus
The food pipe starts from the neck region and runs until the chest area in animals.
The food, when the chewed, moves through the food pipe and reach the stomach through this path.
The food moves in download direction in the food pipe.
The Stomach
The stomach is the widest part of the alimentary canal. It’s a bag like structure in a flat U shape.
The stomach is connected with the food pipe and the small intestine. The stomach’s inner lining produces three things:
- Mucous:It protects the stomach lining
- Hydrochloric Acid: It kills the bacteria present inside the stomach and activates the digestive juices
- Digestive Juices: They help in digestion of the food by breaking down the proteins present in the food into simple substances (olympiads)
Small Intestine
The small intestines is a highly coiled structure. With a length of approximately 7.5m. The small intestine breaks the carbohydrates into glucose, fats into fatty acids and proteins into amino acids.
The inner lining of the intestine also secretes some digestive juices on its own. It is also connected to the liver and pancreas release digestive juices into the small intestine.
.The Liver
Liver is the known largest gland of the human body. It is usually reddish brown in colour . It secretes a digestive juice called bile juice. The bile juice is stored in the gallbladder. The bile juice makes it possible for the body to digest the fats.
The Pancreas
Pancreas is a cream coloured gland present in the human body. Which secretes pancreatic juice that helps in digestion of fats, carbohydrates and proteins.
Absorption of Nutrients in the small intestines
Absorption is a process by which the digested food enters the blood vessels of the small intestine.
The small intestine contains small finger-like structures called Villi. They increase the surface area of the intestine thereby increasing the amount of absorption. The digested food gets into the blood vessels through villi and then reaches the whole body.
Villi in Small Intestine
The process by which the organs of the body utilize the digested food and form complex substances which the body needs such as proteins are called Assimilation.
Parts of Small Intestine
The small intestine has been divided into three parts:
- Duodenum
It is the first part of the small intestine whose main function is to initiate the digestive process. In this process, the food that enters the small intestine from the stomach is mixed with the digestive juices (bile and pancreatic juice) and is further broken down into simpler substances.
- Jejunum
It is the middle part of the small intestine that contains the villi and hence undergoes absorption and assimilation.
- Ileum
It is the third and last part of the small intestine that contains villi-like structures. The ileum absorbs vitamin B12, bile acids and any other nutrients present in the food.
The Large Intestine
Any food that is left undigested passes through the small intestine and enters the large intestine.
It is a wide tube-like structure.
It is only 1.5 m long.
The main function of the large intestine is to absorb water and salts from the undigested food.
The rest of the waste, undigested food passes through the rectum.
Egestion: The process by which the waste, undigested food (the faecal matter) get out of the body through the anus.
The food that we eat passes through a Canal inside our body.
The food is processed and utilized in the body and unused food is collected inside the canal only.