2. Nutrition in Animals

Alimentary canal or digestive track

It is a long tube of organs through which the food enters & leaves the body starting from the mouth & ending at the anus.

Features:

1. The food passes through a long continuous canal which begins at the buccal cavity & ends at the anus.
2. It is also called the digestive track.
3. There are various compartments in this canal which gradually digest the various food components.

The alimentary canal is divided into:

Let's understand the function of each organ in detail.

Buccal cavity or mouth

1. Food is taken into the body through the mouth or buccal cavity.
2. The process of taking food into the body is called ingestion.
3. When we chew the food, the teeth break it into small pieces.
4. Saliva secreted by the salivary glands gets mixed with the food.
5. The saliva breaks down the starch into sugars.
6. The process of digestion begins in the mouth.

Teeth

1. Teeth are located in the mouth.
2. We chew the food in the mouth with the help of teeth.
3. Teeth break the food into small pieces in the mouth.

Milk teeth:

1. They are the first set of teeth.
2. They grow during infancy & fall off between the age of six to eight years.
3. There are a set of 20 milk teeth.
4. They are also called baby teeth or primary teeth.

Permanent teeth:

1. The second set that replaces the milk teeth are the permanent teeth.
2. They may last throughout life or fall off during old age or due to some dental disease
3. Most adults have 32 permanent teeth, 16 in the upper jaw & 16 in the lower jaw.
4. They vary in appearance & perform different functions.
5. Each tooth is rooted in a separate socket in the gums.

Types of permanent teeth:

Diagram:

Tooth Decay:

1. If the teeth & mouth are not kept clean after eating food, some harmful bacteria begin to grow.
2. These bacteria break down the sugars present from the leftover food & release acids.
3. The acids gradually damage the teeth leading to tooth decay.
4. Tooth decay can lead to severe toothache & tooth loss in extreme cases.
5. Hence, tooth decay should be treated immediately.
6. Chocolates, sweets, soft drinks & other sugar products lead to tooth decay.
7. To prevent tooth decay we should brush our teeth & dental floss at least twice a day & rinse the mouth after every meal.
8. Also prevent putting dirty fingers or any unwashed object in the mouth.

Tongue 

1. The tongue is a fleshy muscular organ attached at the back to the floor of the buccal cavity.
2. It is free at the front & can be moved in all directions.
3. It is used for talking.
4. It mixes saliva with the food during chewing & helps in swallowing food.
5. It has taste buds that detect different tastes of food. 

Diagram:

Oesophagus:

1. Oesophagus is also called the food pipe.
2. It is a muscular tube that runs along the neck & chest.
3. It carries swallowed food from the mouth to the stomach.
4. Food is pushed down by movement of the wall of the food pipe.
5. Hence it is an important part of the alimentary canal.
6. At times the food is not accepted by our stomach and is vomited out.

Why do we get hiccups?

1. The windpipe or trachea carries air from the nostrils to the lungs.
2. The windpipe runs adjacent to the food pipe.
3. Inside the throat, they both share a common passage.
4. There is a flap-like valve, called the epiglottis that closes the passage of the windpipe when we swallow food or liquids.
5. This ensures that the food enters the food pipe only.
6.  Sometimes when we eat in a hurry, talk or laugh while eating, the food particles enter the windpipe.
7. Hence, we feel choked or get hiccups or cough.

Stomach

1. It is a muscular organ that connects the oesophagus at the top & small intestine at the bottom.
2. It is a thick-walled bag which has a shape like a flattened J.
3. It is the widest part of the alimentary canal.
4. The inner lining of the stomach secretes mucous, hydrochloric acid & digestive juices.
5. In 1822, Doctor William Beaumont, discovered the process of digestion in the stomach.

Functioning:

1. The stomach receives the food from the food pipe.
2. The food that enter the stomach contains many bacteria.
3. The acid in the stomach kills these bacteria & makes the medium in the stomach acidic.
4. The digestive juices break down the proteins into simpler substances.
5. The mucous protects the lining of the stomach from the acid.
6. Stomach holds food & then pushes the partly digested food in the small intestine.

Liver:

1. The liver is a reddish brown gland situated in the upper part of the abdomen on the right side.
2. It is the largest gland in the body.
3. It secretes bile juice that is stored in a sac called as the gall bladder.
4. The bile helps in the digestion of fats.

Pancreas:

1. The pancreas is a large cream coloured gland located just below the stomach.
2. The pancreatic juice acts on carbohydrates, fats & proteins to change them into simpler forms.

3. The pancreas also produces insulin, which helps regulate blood sugar levels.

Thus, the liver, gall bladder & pancreas are secretory glands that help in the process of digestion.

Small Intestine

1. It is the longest part of the alimentary canal.
2. It is highly coiled & about 7.5 metres long.

Digestion:

1. It receives digestive juices from the liver & pancreas.
2. The partly digested food reaches the lower part of the small intestine. 
3. Here the intestinal juice completes the digestion of all components of the food.
4. It converts complex food components into simple substances.

Cabohydrates = Simple sugar (i.e. glucose)

Fats = Fatty acids & Glycerol

Proteins = Amnio acids

Absorption:

1. It is the process in which the digested food is taken in by the blood vessels present in the wall of the intestine.
2. The inner walls of the small intestine have thousands of finger-like outgrowths called as villi.
3. Each villus has a network of thin & small blood vessels close to its surface. 
4. Thus the villi increases the surface area for absorption of the digested food.

Assimilation:

1. The absorbed substances are transported via the blood vessels to different organs of the body.
2. There they are used to build complex substances such as proteins required by the body.
3. This is process is called assimilation.
4. In the cells, glucose breaks down with the help of oxygen into carbon dioxide and water & energy is released.

The food that remains undigested & unabsorbed enters into the large intestine.

Large Intestine

1. It is wider & shorter than small intestine.
2. It is about 1.5 metre in length.

Function:

1. It absorbs water & some salts from the undigested food.
2. The remaining waste is passed into the rectum where it remains as semi-solid faeces.

Anus:

The faecal matter is removed through the anus. 

This process is called egestion.