Digestion in man , Buccal digestion and Gastric digestion

From Online Sciences - November 21, 2017

The heterotrophic organism ( consumer ) obtains its food in the form of ready organism materials which are large and complex molecules , These molecules can not diffuse through the cell membrane of living organism , So , the living organism must digest these molecules to become useful materials .


Digestion is the conversion of large food molecules ( polymers ) into smaller ones ( monomers ) by means of hydrolysis , This process is catalyzed by an enzymatic action .

The importance of digestion : The breaking down of large and complex food substances into a simpler and smaller molecules which are easily absorbed by the cells ( either by the diffusion or active transport ) , The cell will then use these simple compounds as a source of energy in the building of new tissues .

Examples :


Enzymes is a protein substance which has the properties of catalyst and has the ability to activate a particular chemical reaction .

The enzymes ability to activate a particular chemical reaction depends on the structure of reacting molecules ( reactants ) & the name of enzyme .

When the reaction is completed , the resulting molecules break away from the enzymes , leaving it in the same form as it was before the reaction .

Characteristics of enzymes

Examples : Pepsin enzyme is secreted by the stomach as an inactive pepsinogen which is changed into the active pepsin in the presence of HCl in the stomach .

pepsinogen ( Inactive ) pepsin ( Active ) , ( HCl acid )

Structure of the digestive system in man

Digestive ( Alimentary ) canal which consists of : mouth , pharynx , oesophagus , stomach , small intestine , large intestine , rectum and anus opening .

Accessory ( Associated ) glands which are salivary glands , liver and pancreas .

Buccal digestion

Mouth : The digestive canal starts with the mouth which contains teeth , tongue and salivary glands .

Teeth : that are differentiated into :

Tongue : helps to manipulate the food to be chewed by the teeth and it serves as an organ of taste .

Gastric digestion ( digestion in stomach )


Function of HCl :


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