CHAPTER 2 NUTRITION IN ANIMALS
HUMAN DIGESTIVE SYSTEM
(i) The mouth and the buccal cavity
The process of taking food through the mouth is called ingestion.
We have teeth that help us in chewing our food and breaking it down for swallowing.
Our tongue helps in mixing the saliva with the food. The taste buds are also located on the tongue.
(ii) The food pipe
After the food is properly chewed and mixed, it is swallowed which transfers it to the food pipe. The food pipe is also called the ‘oesophagus’. It connects the mouth to the stomach. The alimentary canal is a part of the food pipe which, due to the movements of its walls, pushes the food down to the stomach.
(iii) The stomach
The stomach is a thick walled bag shaped like a flattened U. the inner lining of the stomach secretes mucous, hydrochloric acid and digestive juices. The stomach opens into the small intestine.
(iv) The small intestine
The small intestine is about 7.5 metres long and is highly coiled. Both the liver and the pancreas secrete liquids into the small intestine. Liver is a reddish brown gland which is situated on the upper part of the right side abdomen. It is the largest gland in the body and secretes bile juice which is stored in the gall bladder. The pancreas is a gland situated right below the liver. The juices secreted by pancreas act on carbohydrates and proteins to convert them into simpler forms. The food is partially digested now and it reaches the lower small intestine.
The lower intestinal walls absorb the digested food through the blood vessels in them. The inner wall of the small intestine has finger-like outgrowths called villi which increase the surface area for absorption. The absorbed nutrients are transported to different organs of the body where they are further transformed into complex substances. This process is called assimilation.
(v) The large intestine
The large intestine is wider but shorter than the small intestine. It absorbs some salts and water from the undigested food. The remaining undigested food is excreted out of the body as faeces through the anus.
DIGESTION IN GRASS EATING ANIMALS
The grass eating animals like cows and buffaloes quickly swallow the grass and store it in a separate part of the stomach called rumen where it gets partially digested. This partially digested food is called cud. It later returns to the mouth in small lumps. The animals then chew it. Such animals are called ruminants and the process is called rumination.
DIGESTION IN MICROSCOPIC ANIMALS
A microscopic animal, an amoeba, for example, pushes out finger like projections called pseudopodia for movement and capturing food. It engulfs the food particle which gets trapped in a food vacuole and digestive juices are released in order to digest it. The undigested residue of the food is expelled.