Human Digestive System

Question 1 What is meant by digestion? 

Question 2 Name the various organs of the human digestive system? 

Question 3 What is the function of various glands associated with human digestive system? 

Question 4 Draw a labelled diagram of human digestive system? 

Question 5 What is the function of large intestine? 

Question 6 What is the function of small intestine? 

Question 7 What is the role of mucus in stomach? 

Question 8 What is the role of hydrochloric acid in stomach? 

Question 9 What is an alimentary canal? 

Question 10 What is the action of saliva on food? 

Question 11 Which organ of the body secretes bile? Where is bile stored? 

Question 12 What is the function of bile in the digestion of food? 

Question 13 What are vili? Where are vili located? What is the function of vili? 

Question 14 What is meant by egestion? 

Question 15 Define the term assimilation? 

Question 16 How digestion of food takes place in human being?

☛ Also Read NCERT Solutions for Chapter 2 Nutrition In Animals

Animal Nutrition

 

Animals cannot make their own food by photosynthesis. Since animals cannot make their own food, they need readymade food. This ready made food comes from plants or from other animals.

Animals obtain their food from plants or from other animals. Some animals eat both plant food as well as animal food.

All animals require food for obtaining energy, growth and repair of damaged body parts. The process of taking in food by an animal and its utilisation in the body is called Animal Nutrition.

Every animal has some special structures (or organs) for taking food inside its body.

The methods used by some of the animals to take in food (or eat food) are described below:

(1) Frog is an animal which eats flying insects as food. The frog uses its long and cleft tongue (forked tongue) to catch its prey like insects.

(2) All wall lizard and a chameleon also catch their prey with the help of their fairly long tongue.

(3) The food of butterfly is nectar (Nectar is a sugary liquid present inside the flowers). The butterfly uses its long feeding tube to suck nectar from flowers.

(4) Bees and hummingbirds also suck the nectar from flowers in plants.

(5) Both male and female mosquitoes feed by sucking nectar from flowers. The female mosquitoes also suck blood from other animals (including human beings).

(6) Infants (small babies) of humans and many other animals,(such as cows, dogs, etc.) feed on mother’s milk by sucking.

(7) Lice are wingless insects which live on hair. Lice feed by sucking blood from the skin of scalp.

(8) Houseflies feed on filth and refuse. They take in only liquid food by sucking. Houseflies spit out saliva on solid food to convert it into a liquid and then suck this liquid.

(9) Ants feed on plant material and other animals by biting and chewing.

(10) Snakes are flesh eaters. They eat animals like rats etc.

(11) Eagle feeds on the flesh of its prey by tearing its flesh with powerful hooked beak.

(12) Amoeba is a tiny aquatic animal which ingests its food with the help of its pseudopodia (or false feet) and then suck this liquid.

(13) Snails feed on algae by scraping it from rocks.

(14) We (human beings) use our hands to put food into our mouth.

(15) Hydra is an animal which uses its tentacles with sting cells to kill the prey and put it into the mouth.

(16) A spider weaves a web to catch its prey.

Digestion

The process in which the food containing large, insoluble substances is broken down into small, water soluble substances which can be absorbed by our body, is called digestion.

Digestion makes the food soluble so that it can be absorbed and utilised by the body.

We use both physical and chemical methods for digesting (breaking up) the large substances present in food.

Physical methods include chewing and grinding the food in mouth.

Chemical methods include the addition of digestive juices to food by the body itself.

During the process of digestion, the complex starch carbohydrate present in our food is broken down into a simple sugar called glucose. Fats are broken into simpler substances called fatty acids and glycerol and proteins are broken down into simple substances called amino acids.

Now, glucose, fatty acids, glycerol and amino acids are all water soluble, simple substances which can pass through the wall of our small intestine into the blood and hence get absorbed in the body. The process of digestion takes place inside our body.

 

Alimentary Canal

(1) A long tube running from mouth to anus of a human being (or other animals) in which digestion and absorption of food takes place is called alimentary canal. It is also known as gut or digestive tract.

(2) It is about 8 to 9 metres long in humans.

(3) The alimentary canal is a continuous canal which has many parts such as mouth (buccal cavity), oesophagus (food pipe), stomach, small intestine, large intestine, rectum and anus.

(4) Three glands are also associated with alimentary canal. These are salivary glands, liver and pancreas.

(5) The food enters the alimentary canal at the mouth (or buccal cavity). As the food travels through the various parts of alimentary canal, it gradually gets digested. During the passage of food through alimentary canal, the various glands (salivary glands, liver, pancreas) and inner walls of stomach and small intestine, secrete digestive juices. These digestive juices convert the complex substances of food into simpler substances which can be absorbed by the body.

(6) The undigested part of food is defecated (thrown out) through the last part of alimentary canal called anus.

HUMAN DIGESTIVE SYSTEM

When we eat food, it gets broken down into smaller and soluble substances during digestion. The digested food is absorbed and utilised by our body. The undigested and unabsorbed portion of food removed from the body in the form of waste material called faeces.

The human digestive system consists of the alimentary canal and its associated glands. The various organs of the human digestive system in sequence are : Mouth (Buccal cavity), Oesophagus (or Food pipe), Stomach, Small intestine, Large intestine, Rectum and Anus.

The glands which are associated with human digestive system and form a part of human digestive system are: Salivary glands, Liver and Pancreas.

Salivary glands are located in our mouth (os buccal cavity). Liver is a reddish-brown gland situated in the upper part of abdomen on the right side. Liver is the largest gland in the body. Pancreas is a large, cream coloured gland located just below the stomach.

The ducts (or pipes) of various gland open into the alimentary canal and pour the secretions of their digestive juices into the alimentary canal.

(1) In the Mouth (or Buccal Cavity)

Food is taken into the body (or ingested) through the mouth. The mouth (or buccal cavity) contains teeth, tongue and salivary glands. The teeth cut the food into small pieces, chew and grind it. The salivary glands secrete a watery liquid called saliva. The tongue helps in mixing saliva with food. Saliva is a digestive juice which helps to digest the starch present in the food partially. The slightly digested food is swallowed by the tongue and goes down into oesophagus (or food pipe) 

(2) In the Oesophagus (or Food Pipe)

The oesophagus is a tube (or pipe) which connects the mouth (or buccal cavity) to stomach.

Oesophagus is commonly known as food pipe. It runs along the neck and chest. Oesophagus carries the slightly digested food from the mouth to the stomach . The food coming from mouth moves down through oesophagus by peristalsis.

When the food enters oesophagus at the top end, the muscles in the walls of oesophagus start alternate contractions and relaxations producing a wave-like movement which pushes the food downwards towards the stomach. During vomiting, however, the food moves in the opposite direction, from stomach to mouth, by the process of anti-peristalsis in the food pipe.

 

(3) In the Stomach

The stomach is a thick walled bag present on the left side of the abdomen. It is the widest part of the alimentary canal. Oesophagus (or food pipe) brings the slightly digested food

from the mouth into stomach, The food is further digested in the stomach. The food is churned in the stomach for about three hours. During this time, the food breaks down into still smaller pieces and makes a semi-solid paste. The inner lining of stomach secretes mucus, hydrochloric acid and  digestive juices.

Mucus protects the lining of stomach from its own secretions of hydrochloric acid.

Hydrochloric acid kills any bacteria which may enter the stomach with food.It also makes the medium in the stomach acidic (which is necessary for the proper action of digestive juices on proteins).

The digestive juices secreted by the stomach lining break down the proteins present in our

food into simpler substances. The partially digested food then goes from the stomach into the small intestine.

(4) In the Small Intestine

The small intestine is a very long tube. It is about 7.5 metres long. Though small intestine is very long it is called small intestine because it is quite narrow tube. The small intestine is arranged in the form of a coil in our belly . The small intestine in human beings is the site of complete digestion of food. The small intestine is also the main region for the absorption of digested food.

(a) Complete Digestion of Food in Small Intestine

The partially digested food from stomach comes into small intestine. The small intestine receives secretions of digestive juices from the liver, pancreas and its own walls. All these digestive juices carry out the complete digestion of food.

Liver secretes a liquid called bile (which is stored temporarily in the sac called gall bladder).

The bile plays an important part in the digestion of fats. Actually, bile converts fats into tiny droplets so that their further breakdown becomes easy.

Pancreas secretes pancreatic juice. Pancreatic juice breaks down fats completely into fatty acids and glycerol. Pancreatic juice also breaks down starch carbohydrate and proteins into simpler forms.

The walls of small intestine secrete a digestive juice called intestinal juice. Intestinal juice breaks down the starch carbohydrate completely into the simplest sugar called glucose, and the proteins into amino acids. Our food breaks down completely into very small, water soluble substances like glucose, fatty acids, glycerol and amino acids. This is called digested food.

(b) Absorption of Digested Food in Small Intestine

The digested food can now pass into the blood vessels in the walls of the small intestine. This process is called absorption.

The inner surface of the small intestine has millions of tiny, finger-like outgrowths called villi. The presence of villi gives the inner walls of the small intestine a very large surface area (which helps in the rapid absorption of food). Thus, the role of villi in the small intestine is to increase the surface area for the rapid absorption of digested food. Each villus has a network of thin and small blood vessels (called blood capillaries) close to its surface. The surface of villi absorbs the digested food materials into blood flowing through them.

Blood carries the absorbed food materials to the cells in all the parts of the body. In the cells, food is used for energy, growth and repair. This is called assimilation. Glucose breaks down in the cells with the help of oxygen to form carbon dioxide and water, and releases energy. Fatty acids and glycerol build components of cells and form fats to be stored in the body as food reserves. Amino acids are used to make proteins required for the growth and repair of the body.

The food that remains undigested and unabsorbed passes from the small intestine into large intestine

(5) In the Large Intestine

The large intestine is about 1.5.metres long. It is called large intestine because it is a quite wide tube. The undigested and unabsorbed food from the small intestine enters into large intestine. The large intestine absorbs most of the water from the undigested food material. Due to the removal of water, the undigested food becomes semi-solid. This undigested food (or waste material) is stored in the last part of large intestine called rectum for some time. The undigested , semi-solid waste is passed out from our body through anus in the form of faeces. This is called egestion.