Nutrition in Animals

Start music   Jan 11 2017 || 12:52 PM


Digestion – The breakdown of complex components of food into simpler substances


Digestion in Humans

Digestive system

  • Digestive tract and the associated glands together constitute the digestive system.


Digestive juices

  • They are secreted by the inner walls of the stomach, small intestine & other glands
  • Help in the breakdown food from complex substance into simpler substances


Parts of the digestive tract

  • The food passes through a continuous tract called alimentary canal
  • It can be divided into various parts:
  1. The buccal cavity,
  2. Food pipe or oesophagus,
  3. Stomach,
  4. Small intestine,
  5. Large intestine ending in the rectum
  6. The anus.


Mouth and buccal cavity

  • Ingestion – The process of taking food into the body
  • Teeth
    • 4 types of tooth: Incisor, Canine, Pre-molar, and Molar
    • Cutting and biting teeth - Incisor
    • Piercing and tearing teeth - Canine
    • Chewing and grinding teeth - Pre-molar, and Molar
  • Saliva breaks down starch into sugars
  • Tooth decay –
    • Normally bacteria are present in our mouth
    • They break down the sugars present from the leftover food and release acids
    • The acids gradually damage the teeth and this is called tooth decay
    • By brushing our teeth, we prevent tooth decay



  • Runs along the neck and the chest
  • Food is pushed down by movement of the wall of the foodpipe



  • Widest part of the alimentary canal
  • Its inner linings secrete 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 also makes the medium in the stomach acidic which helps the digestive juices to act.
  • The digestive juices break down the proteins into simpler substances.



  • A reddish brown gland situated in the upper part of the abdomen on the right side
  • Largest gland in the body
  • Secretes bile juice that is stored in a sac called the gall bladder
  • Bile plays an important role in the digestion of fats


Small Intestine

  • About 7.5 metres long
  • Receives secretions from the liver and the pancreas and also secretes juices
  • Food gets digested here:
    • Carbohydrates get broken into simple sugars such as glucose,
    • Fats are reduced to fatty acids and glycerol,
    • Proteins are converted into amino acids
  • Inner walls of the small intestine have numerous finger-like outgrowths called villi
  • The villi increases the surface area for absorption of the digested food
  • Digested food then passes into the blood vessels through the villi. This process is called absorption
  • The absorbed substances are transported via the blood vessels to different organs
  • They are used to build complex substances. This is called assimilation
  • The food that remains undigested and unabsorbed enters into the large intestine


Large intestine

  • About 1.5 meter long but wider than small intestine
  • Absorbs water and some salts from the undigested food material
  • The remaining waste passes into the rectum
  • The faecal matter is removed through the anus by the process of egestion


Digestion in grass-eating animals

  • Such animals swallow the grass and store it in a part of the stomach called rumen
  • Here the food is partially digested and is called cud
  • Later the cud returns to the mouth in small lumps and the animal chews it
  • This process is called rumination and these animals are called ruminants.


Digestion of cellulose in ruminants

  • The grass is rich in cellulose, a type of carbohydrate
  • The cellulose in the food is digested in the rumen by the action of certain bacteria
  • These bacteria are not present in humans.


Feeding and digestion in amoeba

  • Amoeba is a microscopic single-celled organism found in pond water
  • It constantly changes its shape by pushing out one, or more finger-like projections, called pseudopodia or false feet
  • This is for movement and for capturing the food
  • Amoeba 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 and The undigested residue of the food is expelled outside by the vacuole