Nutrition in Animals

Plants can prepare their own food by the process of photosynthesis but animals cannot. Animals get their food from plants, either directly by eating plants or indirectly by eating animals that eat plants. Some animals eat both plants and animals.

Animal nutrition includes nutrient requirement, mode of intake of food and its utilization in the body.

The components of food such as carbohydrates are complex substances. These complex substances cannot be utilized as such. So they are broken down into simpler substances. The breakdown of complex components of food into simpler substances is called digestion.

Digestion in Humans:-

When we take in food through the mouth, the food passes through a continuous canal (Fig. 2.2) which begins at the buccal cavity and ends at the anus. The canal can be divided into various compartments:

(1) The buccal cavity

(2) Food pipe or esophagus

(3) Stomach,

(4) Small intestine

(5) Large intestine ending in the rectum

(6) The anus

· These parts together form the alimentary canal (digestive tract).

· The inner walls of the stomach and the small intestine, and the various glands such as salivary glands, the glands liver and the liver pancreas secrete digestive juices.

· The digestive juices convert complex substances of food into simpler ones.

· The digestive tract and the associated glands together constitute the digestive system.

The mouth and buccal cavity:

· Food is taken into the body through the mouth.

· The process of taking food into the body is called ingestion.

· We chew the food with the teeth and break it down mechanically into small pieces. Our mouth has the salivary glands which secrete saliva.

The food pipe/esophagus:

· The swallowed food passes into the food pipe or esophagus.

· The food pipe runs along the neck and the chest. Food is pushed down by movement of the wall of the food pipe.

· Actually this movement takes place throughout the alimentary canal and pushes the food downwards.

· At times the food is not accepted by our stomach and is vomited out.

The stomach:

· The stomach is a thick-walled bag.

· Its shape is like a flattened U and it is the widest part of the alimentary canal.

· It receives food from the food pipe at one end and opens into the small intestine at the other.

· The inner lining of the stomach secretes mucous, hydrochloric acid and digestive juices.

· The mucous protects the lining of the stomach.

· The acid kills many bacteria that enter along with the food and makes the medium in the stomach acidic.

· The digestive juices break down the proteins into proteins simpler substances.

The small intestine:

· The small intestine is highly coiled and is about 7.5 meters long.

· It receives secretions from the liver and the pancreas. Besides, its wall also secretes juices.

· The liver is a reddish brown gland situated in the upper part of the abdomen on the right side. It is the largest gland in the body.

· It secretes bile juice that is stored juice in a sac called the gall bladder.

· The pancreas is a large cream colored gland located just below the stomach.

· The pancreatic juice acts on carbohydrates and proteins and changes them into simpler forms.

· The partly digested food now reaches the lower part of the small intestine where the intestinal juice completes the digestion of all components of the food.

· The carbohydrates get broken into simple sugars such as glucose, fats into fatty acids and glycerol, and proteins into amino acids.

Absorption in the small intestine:

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

· The inner walls of the small intestine have thousands of finger-like outgrowths called villi.

· The villi increase the surface area for absorption of the digested food.

· The absorbed substances are transported via the blood vessels to different organs of the body where they are used to build complex substances such as the proteins required by the body. This is called assimilation.

· In assimilation the cells, glucose breaks down with the help of oxygen into carbon dioxide and water, and energy is released.

· The food that remains undigested and unabsorbed then enters into the large intestine.

The large intestine:

· The large intestine is wider and shorter than small intestine.

· It is about 1.5 meter in length. Its function is to absorb water and some salts from the undigested food material.

· The remaining waste passes into the rectum and remains there as semi-solid faces.

· The faecal matter is removed through the anus from time-to-time. This is called egestion.

Digestion In Grass-Eating Animals

· Cows, buffaloes and other grass-eating animals quickly swallow the grass and store it in a separate part of the stomach called rumen.

· Here the food gets partially digested and is called cud.

· But later the cud returns to the mouth in small lumps and the animal chews it.

· This process is called rumination and rumination animals are called ruminants.

· The grass is rich in cellulose, a type of carbohydrate.

· Many animals, including humans, cannot digest cellulose.

· Ruminants have a large sac-like structure between the small intestine and large intestine.

· The cellulose of the food is digested here by the action of certain bacteria which are not present in humans.

Feeding And Digestion In Amoeba

· Amoeba is a microscopic single-celled Amoeba organism found in pond water.

· Amoeba has a cell membrane, a rounded, dense nucleus and many small bubble-like vacuoles in its cytoplasm.

· Amoeba constantly changes its shape and position.

· It pushes out one, or more finger-like projections, called pseudopodia pseudopodia or pseudopodia false feet for movement and capture of food.

· Amoeba feeds on some microscopic organisms.

· When it senses food, it pushes out pseudopodia around the food particle and engulfs it.

· The food becomes trapped in a food vacuole.

· Digestive juices are secreted into the food vacuole.

· They act on the food and break it down into simpler substances. Gradually the digested food is absorbed.

· The absorbed substances are used for growth, maintenance and multiplication.

· The undigested residue of the food is expelled outside by the vacuole.