Nutrition in Animals
Science Class Seven
Oesophagus or Food Pipe
Oesophagus is a muscular flexible long pipe which connects mouth and stomach. Oesophagus is known as Food Pipe also. The length of oesophagus is about 30 cm in an adult person.
Oesophagus (Ref: NCERT Book Science Class seven page number 15)
After chewing and mixing with saliva, food enters from mouth to oesophagus. Food is then pushed down through the wall of food pipe (oesophagus) by a special type of wave like movement. This movement is called peristalsis. Peristalsis takes place throughout the alimentary canal and pushes the food forward. Food reaches to the stomach through the food-pipe. There is no digestion takes place in esophagus. If our stomach does not accept the food because of any reason, it is vomited out through the food pipe.
Stomach
Stomach is a J–shaped thick walled muscular bag. Stomach is the widest part of alimentary canal. Stomach receives food from esophagus from one end and opens into small intestine at the other end. Stomach of an adult person can hold about two litres of food at a time.
The inner lining of stomach secretes mucous, hydrochloric acid and digestive juices. The mucous protects the lining of stomach. Hydrochloric acid kills the bacteria, if any present in food. Here food is converted into acidic medium because of hydrochloric acid. The digestive juices break down the proteins into simple substances. Stomach wall gently churn the food and mix with secreted acid, and digestive juices. In stomach food converted into semi solid. This semi solid state of food is called chime. Food gets partly digested into stomach.
Small Intestine
Chyme reaches into small intestine after stomach. Small intestine is the longest part of alimentary canal. The length of small intestine is about 7.5 meters in an adult person. Small intestine has a highly coiled structure. In the upper part of small intestine, semi-solid food gets bile juice secreted from liver and pancreatic juice secreted from pancreas. Besides these juices, the wall of small intestine secretes digestive juices also.
The partly digest food reaches to the lower part of small intestine. In lower part of small intestine intestinal juice completes the digestion of all components of food. These juices acts upon carbohydrates and break them into simple sugar and glucose. Here fats get broken into fatty acids and glycerol and proteins get broken into amino acids.
Liver
The liver is a reddish brown gland. Liver is situated in the right side of upper part of the abdomen. The liver is the largest gland in human body. Liver secretes bile juice. The bile juice plays very important role in digestion especially in the digestion of fats.
Gall bladder
Gall bladder is situated just below the liver. In gall bladder bile juice, which is secreted from liver, is stored.
Pancreas
The pancreas is a large crème coloured gland. Pancreas is located just below the stomach. Pancreas secretes pancreatic juice. The pancreatic juice converts carbohydrates and proteins into simpler forms.
Absorption in the small intestine
Absorption of digested food takes place in small intestine. The process of passing of digested food into blood vessels is called Absorption. Absorption of food occurs through wall of the intestine. There are thousands of finger-like projections on the inner wall of small intestine. These projections are called villi. The singular of villi is villus. These villi have network of fine blood capillaries closes to their surface. Villi increase the surface area for absorption of digested food. After absorption, the digested food mixed with blood vessels. The absorbed food is then transported to the different parts of body.
Assimilation
In the different parts of body the digested food is used to build complex substances such as proteins which are required by body. In the cells, glucose breaks down with the help of oxygen into carbon dioxide and water, and releases energy. The process of utilization of digested food by different parts of body to release energy is called Assimilation.
Large intestine
All food we eat is not digested and absorbed completely. Portion of foods; left undigested in the small intestine reaches to the large intestine.
The large intestine is wider than small intestine. The length of large intestine is about 1.5 meter in an adult person. In large intestine water and some salts are absorbed from undigested food. The remaining waste in the form of semisolid residue is stored in the last part of large intestine. The last part of large intestine is called rectum.
Egestion
This residue (faeces) which is stored in rectum is finally thrown out of the body through the anus time to time. The process of removal of faeces from anus is called egestion.
Digestion in grass eating animals:
Some of the grass eating animals such as cows, buffaloes, goat, sheep, etc. chewing continuously even when they are not eating anything. Such animals have a separate part in their stomach called rumen. They quickly swallow the grass and store it in rumen. In rumen food is digested partly. This partly digested food is called cud. Later in small lump cud return to the mouth and animal chews it. This process of chewing cud is called rumination. Such animals are called ruminants.
Cellulose is a type of carbohydrate. The grass is rich in cellulose. Human and other many animals cannot digest cellulose. Ruminants have special type of large sac-like structure between their small and large intestine. In this rumen cellulose is digested by the action of certain bacteria. Such type of bacteria are not present in human.
Feeding and digestion in Amoeba:
Human and other animals have digestive system that digest the food. But there are many small organism that do not have even mouth and digestive system; inspite of that they feed. Amoeba is an example of such animals. Amoeba does not have either mouth or digestive system.
Amoeba is a microscopic organism. Amoeba is a single celled organism. Hence, amoeba is called unicellular animals. Amoeba is generally found in pond water. It has a cell membrane and a nucleus rounded in shape. There are many small bubbles like vacuoles found in its cytoplasm. An amoeba has finger like projects, which is used for movement and capturing of food. These projections are called pseudopodia or false feet.
Amoeba takes some microscopic organism as food. When an amoeba sense food, it pushes out its finger like projections or false feet around the food particles and engulfs it. In this way food is trapped in a food vacuole. After engulfing food digestive juices are secreted into the food vacuole. These digestives juices act on food and food is broken down into simpler substances. The digested food is absorbed gradually. The absorbed food is used for growth and maintenance of body. The undigested and unabsorbed food is expelled out by vacuoles.
Although digestive system is different in different animals but the basic process of digestion of food and release of energy is same in all animals.
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