The digestive system includes the organ concerned with the intake of food, its digestion and absorption. In our body this work is done by a long tube called the alimentary canal. The digestive system consists of:
- Small Intestine
- Large Intestine
- Gall Bladder and
Of these organs liver, pancreas and gall bladder are not a part of the alimentary canal but help in the digestion of food by pouring their digestive juices into the digestive system.
Just as a car requires petrol as fuel which is burnt in air to drive it, an animal also requires food as fuel which is burnt inside its body to provide energy for its various activities. In addition to providing energy, food also keeps our body healthy and helps it to grow. But our body cannot use the food in the form in which it is taken in. It must be broken down into simpler substances before it is utilized by the body. The process of breaking down of complex food into simpler soluble substances is called digestion. This breaking down of complex food is mainly done by certain chemicals produced by our body. These chemical are called enzymes. There are many kinds of enzymes in our body- each one acting on different kinds of food. Let us study the organs of digestion in detail.
The mouth contains teeth, tongue and salivary glands. Digestion of food starts as soon as the food enters the mouth. The teeth cut and chew the food and grind it. The salivary glands produce saliva which starts the digestion of food in the mouth.
Saliva contains an enzyme that breaks down the starch present in the food of simple sugars. Saliva moistens the food and helps in the swallowing of food.
You were not born with teeth in your mouth. As a little child, you first grew a set of temporary or milk teeth. The milk teeth are generally twenty in number – ten in each jaw. These teeth fall off and are replaced by permanent teeth. The first permanent tooth appears when the child is six. Between the age of 6 and 12 years all the milk teeth fall off and replaced by permanent teeth. Most adults have 32 permanent teeth – 16 in each jaw.
Let us study the different types of teeth in detail
- Incisors: they are chisel-shaped teeth in front of the jaw. They are used to biting the food.
- Canines: On each side of the incisors are sharp and pointed canines. They are meant for cutting and tearing down the food.
- Premolars: They are flat-topped and thick teeth. They are present on either side of the canines and are meant for crushing and grinding the food.
- Molars: Molars are the biggest teeth.
All teeth are covered by a white shiny substance called enamel. It is the hardest substance in our body.
The types of teeth present in animals depend upon their feeding habits. Herbivores have sharp incisors to cut plants. They also have broad molars to grind their food. On the contrary, carnivores have sharp-pointed canines to tear and shear meat.
The tongue has many functions. The various functions of the tongue are:
- It mixes the food with saliva so that the enzyme present in saliva can act on food.
- It helps in swallowing the food.
- It gives us the taste of food.
- It helps us to speak.
The tongue is able to recognize four different tastes: sweet, salty, bitter and sour due to the presence of tiny structures called taste buds on its surface.
Three pairs of salivary glands are present in the mouth cavity. They produce saliva which contains a digestive enzyme that converts starch into sugar.
Oesophagus is the passage that connects mouth to stomach. The movements of the muscular wall of oesophagus gently push the food into stomach.
The stomach is a ‘J’- shaped muscular bag. It produces a digestive juice called gastric juice which helps to digest food, especially proteins. The muscles of the stomach wall churn and mix the food with the gastric juice. Food stays in the stomach for few hours to get digested. Stomach turns all that you eat into a thick, soupy liquid which is passed on the small intestine for further digestion and absorption
4. Small Intestine:
It is a long narrow, highly coiled tube about six meters long and 2.5cm thick. It produces a digestive juice to completely digest the food it receives from the stomach. Digestive juices produced by liver and pancreas are also poured into the small intestine. Liver is the largest gland in the body and produces bile juice which helps to digest fats. Pancreas is a long yellow-colored gland present beneath the stomach. It produces pancreatic juice. The digestion of food is completed in the small intestine by the combined action o intestinal juice, bile juice and pancreatic juice. The digested food is then absorbed by the small intestine and sent to all the cells of the body through blood. A large part of the food you eat cannot be digested. This undigested food is pushed into the large intestine.
5. Large Intestine:
The large intestine is much shorter and wider than the small intestine. Since all the nutrients present the foods have already been absorbed in the small intestine, what enters the large intestine is waste and must be thrown out. This waste, however, contains a lot of water which is absorbed by the walls of the large intestine. This concentrates the waste, now called feces which are stored in the last part of the intestine called rectum. The feces then leave the body through an opening called anus.