INGESTION AND DIGESTION

[The account of the digestion presented  under this section is applicable  to maost mamals including man ]  .As his already been stated , the rabbit gnaws its food.By means of chisel-shaped  incisors , small portion of the vegetables  matter  are cut up and after being caught by  the mobile  lips are taken into the buccal cavity .Here  the food is throughly  mixed with saliva and subjecte to the action  of the grinding cheek-teeth .During later process  which is called mastication ,  the food is turned round and round  in the buccal cavity  by movements of the tongue  and chhek -muscles until  the whole forms a pulpy mass..Through mastication  is of very great importance  in herbivores animals like rabbit  which live entirely on vegetable matter containing a great deal of starch.It should  be noted  that in such animals  the molar and pre-molar have  special transverse ridges for grinding the food . Further the surfaces  of the  tongue is hard  and helps by rubbing the food  against the palatine ridges on the roof of the mouth cavity. .                             When mastication is completed , the pulpy mass is swallowed .This  is affected by the bonus being pushed  into pharynx  by the raising  of the tongue, prevented from entering the  posterior nares by the soft palate  and isa finally forced into the beginning  of the oesophagus by the contraction of the pharyngeal wall.During the  contraction of the pharynx and  entry of the bolus  into the oeso phagus  the  food is prevented from  entering  into the larynx through the glottis  by a flap- like  epiglottis .The  oeso phagus conveys the food  to the stomach through the  activity of the layer s  of the muscles in its walls.This activity causes peristalsis .                                                                            The first stages  in the conversaion of food into the protoplasm  of the animal  is its partial  breaking down into simpler compounds . In all cases the digestion consists  of a process of hydro lysis,during which the molecular size  of the subsances  is progressively reduced until the true  sollution is possible .These  changes are brought about by the  familiar biocatalysts known as enzymes or ferments.                                                            Inmouth , the food comes in contact with the colourless wateryfluid or saliva , secreted in the mouth cavity by the front pairs of salivary glands , which keeps the mouth continuosly moist  under normal conditions.When the food is in mouth ,its smell  and tastes considerably  increase the rates of its secretion .Since food stays for a very short time in a mouth , it is not in the mouth but in the stomach  where thwe main bulk of the salivary digestion  takes place  Besides ptyalin ,saliva contains 99% water ,mucin albumin ,globumin ,etc.The function of saliva are as follows ; 1 It changes  insoluble starch  and glycogen into soluble maltose .   2; It helps in swallowing and moistening and lubricating the food.3 It dissolves soluble substance  and thus make them fit for tasting .4It has  a cleaning effect on the mouth and the teeth .                                             In the mouth ,3-5 percent of the carbohydrates  are digested in the  suceeding part of the  alimentry canal  . The digestion doesnot takes place in the oeso phagus  because the oeso phagus  secretly only mucin ; it doesnot  produce any digestive  enzyme .The mucin is simply added to the bolus  so that  it easily passes from the oesophagus  to the stomach .However . the action  of the ptyalin , which has already  started in the mouth , continues .                                                                                                                                               Digestive in the stomach . The food  is subjected  to the action  of the gastric juice , secreted by the tubular gastric glands .As soon as   the food  reaches the stomach ,its  wall is mechanically simulated  to produce the gastrin harmone  , which , in turn  stimulates gastric glands to pour  gastric juice  into the lume of the stomach  The gastric juice is composed of water  , mucin ,hci an three digestive enzymes  such as pepsin ,rennin [in young ones of rabbit and calves of cattles]  and gastric lipase  The mucin protects the tissue  from the action of enzymes .It is amphoteric [a substance  that can  act as both acid and base according  to conditions]  in nature  and can thus nutralises both acids and alkalies  besides providing  a mechanical  buffer between hard  food substance and the living tissues