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Nutrition in Animals

Nutrition in Animals Synopsis



  • The process in which food is consumed by the organisms and the nutrients are absorbed by the body and used in the functioning of the body is called nutrition.

Steps in Nutrition                       

Nutrition in Amoeba

  • The mode of nutrition in Amoeba is holozoic

Nutrition in Grasshopper
  • In grasshopper, the different processes of nutrition takes place in fully developed digestive system. 
  • The digestive system is a system of organs and glands concerned with obtaining, digesting and absorbing nutrients from food. 
  • The digestive system of grasshopper is divided into three parts:
  1. Foregut: It consists of mouth, oesophagus or food pipe, crop and gizzard.
  2. Midgut: It consists of stomach and ileum.
  3. Hindgut: It consists of colon and rectum

Human Digestive System

  • The conversion of complex food substances into simple absorbable substances is called digestion.
  • The digestive system of humans consists of the alimentary canal and digestive glands.

Alimentary Canal

  • The alimentary canal extends from the mouth to the anus.
  • It is 6 to 7 metre long.


  • The mouth is the anterior end of the alimentary canal.
  • It opens into the buccal cavity or the oral cavity.
  • The oral cavity consists of teeth and the tongue.
  • The teeth are embedded in sockets and have well-developed roots. Such a type of arrangement is called thecodont.
  • All mammals including humans have two sets of teeth during their lifespan. Hence, human teeth are also diphyodont.
  • Humans exhibit heterodont dentition, i.e. four different types of teeth are found. They are incisors, canines, premolars and molars.
  • The arrangement of teeth in each half of the upper jaw and the lower jaw in the order I, C, PM, M is called the dental formula.

  • The dental formula in human beings is begin mathsize 12px style 2123 over 2123 end style.
  • Incisors = 2/2, canines 1/1, premolars = 2/2, molars 3/3
    Therefore,begin mathsize 12px style 2123 over 2123 end style× 2= 32
  • The tongue lies at the floor of the buccal cavity.
  • The posterior part of the tongue is attached to the floor of the buccal cavity by a soft fold called frenulum.
  • The dorsal surface of the tongue bears numerous papillae.
  • Taste buds located near the tip of the tongue are for sweet taste.
  • The tongue helps in recognition of taste.
  • It also allows mixing of saliva with food.

  • The oral cavity continues into the pharynx.
  • The pharynx is a short, common passage for food and air.
  • The oesophagus and trachea open into the pharynx.
  • An epiglottis is a cartilaginous flap which prevents the entry of food into the trachea and entry of air into the oesophagus.


  • The oesophagus is a 25-cm long muscular tube.
  • It opens into the stomach.
  • The opening of the oesophagus into the stomach is surrounded by cardiac sphincters.


  • The stomach is J-shaped and the widest part of the alimentary canal.
  • The stomach has three parts — cardiac region, fundic region and pyloric region.
  • The oesophagus opens into the cardiac region.
  • The cardiac region continues into the fundic region which further continues into the pyloric region.
  • The parietal cells of the stomach secrete HCl while the peptic cells secrete pepsinogen.

Small Intestine

  • The small intestine is the longest part of the alimentary canal.
  • It consists of duodenum, jejunum and ileum.
  • The opening of the stomach into the duodenum is guarded by the pyloric sphincter.
  • The mucosa of the small intestine bears folds called villi.
  • Each villus has numerous brush-like borders called microvilli.
  • Microvilli increase the area of absorption.
  • Complete digestion of food and its absorption take place in the small intestine.

Large Intestine

  • The small intestine opens into the large intestine.
  • It consists of three parts — caecum, colon and rectum.
  • The opening of the small intestine into the caecum is guarded by the ileocaecal valve.
  • The colon is divided into four parts—ascending colon, transverse colon, descending colon and sigmoid colon.
  • The descending colon opens into rectum which opens out through the anus.
  • The large intestine is involved in the absorption of water.

Digestive Glands
  • There are three main digestive glands.

Salivary Glands

  • Three pairs of salivary glands are — parotid glands, sublingual glands and submaxillary glands.
  • The three glands are located outside the buccal cavity and they secrete saliva.


  • The liver is the largest gland of the human body.
  • It is situated in the abdominal cavity just below the diaphragm.
  • It consists of two lobes—right lobe and left lobe.
  • Each lobe is made of hepatic lobules which are the structural and functional units of the liver.
  • Each hepatic lobule is made of hepatic cells which are arranged in cords.
  • Each hepatic lobule is covered by a thin connective tissue sheath called Glisson’s capsule.
  • The gall bladder is a pyriform sac which lies just below the right lobe of the liver.
  • The cystic duct (the duct of the gall bladder) and the hepatic duct from the liver unite to form the common bile duct.
  • The common bile duct and the pancreatic duct of the pancreas open together into the duodenum as the common hepatopancreatic duct.
  • The opening of the hepatopancreatic duct into the duodenum is guarded by the sphincter of Oddi.