• Food is one of the basic requirements of all the living organisms. The major components of our food are Carbohydartes,Proteins ,fats.Food provides energy and organic materials for groeth and repair of tissues.The water we take in,plays an important role in the metabolic processes and also prevents dehydration of the body.Bio-macromolecules(proteins,nucleic acids,polysaccharides and lipids)in fiod cannot be utilized by our body in their original form.They have to broken down and converted into simple substanes in the digestive system.The process of conversion of complex food substances to simple adsorbable forms is called DIGESTION..and is carried out by our digetive system by mechanical and biochemical methods.
  • Various types of nutrients of food : Nutrients may be organic or inorganic in nature.The organic constituents of nutrients are Carbohydrates,lipids and protiens and vitamins,and the inorganic constituents are Minerals and Water .Carbohydrates ,lipids and proteins are Macronutrients orProximate principles of food  because these constitute the energy sources for the production of heat and different organic functions.Minerals,vitamins and water are Micronutrients or Protective principles of food because although these do not provide energy,yet theur deficiencies are related to specific diseases and abnormalities in man.About 21 minerals (eg.Sodium,potassium,calcium,sulphur,phosphorus,magnesium ) or microelements (eg.Iron,iodine,manganese,cobalt,copper,molybenum ) are required in very small amount for human nutrition.

Human Digestive System


  • Teeth


#Arrangement of different types of teeth in the jaws on one side sockets on the other side

  1. Majority of mammals including human beings, have two sets of teeth during their life,i.e One temporary set & One permanent set. A set of Temporary set  or Deciduous teeth repalced  by a set of Permanent or Adult teeth. Such type of dentition is called Diphyodont.
  2. An adult human has 32 permanent teeth which are of different types, namely incisors(I),Canine(C),premolars(PM),molars(M). Such type of dentition is called Heterodont dentition.
  3. The arrangement of teeth is each half of the upper and lower jaw in the order I,C,PM,M is represented by a dental formula.
  4. The dental formula of human beings is 2123/2123.
  5. Out of these 32 teeth, premolars and last molar teeth appear only once i.e are monophyodont and the remaining teeth are diphyodont.
  6. The hard chewing surface covering of the teeth is made up of Enamel  which helps in the Mastication of food . This enamel is the hardest substance of the human body, secreted by ameloblast cell(ectodermal in origin)

Vertical section of human tooth

Classification position

Acrodont : Teeth are attached to the free surface or submit of the jaw bone Examples: fishes amphibians and reptiles

Pleurodont: Teeth fixed to lateral surface of jaw ridge Examples  fangs of snakes

Thecodont: Embedded in sockets and have well developed roots ( mammals and crocodiles)

Classification according to arrangement of enamel and dentine

  • Bunodont: Small,blunt and rounded cusps Examples Human
  • Lophodont: Intricate folding of enamel and dentine is present and cusps per connected several transverse ridges ( lophos) Examples  Elephants
  • Selenodont: Vertical crescent shaped cusps of hard animals closing softer  areas of dentine Examples sheep and cattle
  • Secodont: Pointed cusps Examples carnivores


The tongue is voluntary muscular and glandular structure which occupies the floor of the mouth it is attached to the floor of the mouth by fold called the Frenulum tongue and inverted v shape for return the sulcus terminalis divides the upper surface of the tongue into interior Oral part and posterior pharyngeal part.

 Filliform papillae :Smallest most abundant and have no taste buds.

Fungiform papillae: appear as red dots on tongue and contain taste buds.

Foliate papillae: absent in man.

Circumvallate papillae:largest in size and nob like, also contain taste buds.

The different areas of tongue are demarcated as follows:          

Base                      bitter

Tips and Sides  salt

Sides                     sour

Tip                       sweet

There are no taste buds for testing chillies .The burning sensation is due to stimulation of pain receptors.Sweat glands of dogs are present on tongue (panting of dog).


It is located in the upper left portion of the abdominal cavity, has three major parts ek Cardiac portion into which the oesophagus opens fundic region and pyloric portion which open into the first part of small intestine.



  1. Duodenum
  2. Jejunum
  3. lleum

Pyloric sphinncter regulates the opening of stomach into duodenum, ileum,thelast part of small intestine leads into the large intestine.

The wall of intestine has three layers of longitudinal and circular muscles.Mucosa has folds called plicae circulares (folds of kerckringfold  or valvulae conniventes) and villi  towards lumen of the intestine, epithelial cells lining the villi have microvilli which further increase the absorptive area.Intestinal glands or crypts of lieberkuhn  have epithelial cells (secrete mucus) Paneth cells secrete digestive enzymes and argentaffin cells secrete hormones.In duodenum burner glands are also present located in submucosa which secrete mucus .Diffuse patches of lymphoid tissue are present throughout the small intestine sign and aggregated element to form Peyer’s patches.

Large Intestine

** Large intestine consists of caecum colon and rectum

Caecum: It is a small blind sac with hosts some symbiotic microorganisms.Vermiform appendix (a finger bloke tubular projection) arises from the caecum is vestigial in human being. This caecum opens into the colon.

Colon: The colon is divided into three parts and ascending, a transverse and descending. This descending part of colon opens into rectum.Ascending colon is the smallest part and lacks mesentery.

Rectum: It is the last part of alimentary canal. It is the storage site for faecal matter. It opens outside through anus.


The wall of the alimentary canal from oesophagus to rectum possesses four layers namely serosa muscularis mucosa and mucosa.


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