We have studied about the digestive system in the previous section. In this section and chapter we will look into the detailed digestive i.e digestion, absorption and assimilation involving the different enzymes. This study can be termed as enzymatic digestion. 


Most of the major nutrients in foods are bound in large molecules that cannot be absorbed from the intestine because of their size or because they are not soluble. The digestive system is responsible for reducing these large molecules into smaller, readily absorbed units and converting the insoluble molecules into soluble forms. Proper function of the absorptive and transport mechanism is crucial to delivering the products of digestion to individual cells. Derangement of any of these systems can result in malnutrition in the presence of an adequate diet. 


In the mouth, the teeth function to grind and crush food into small particles. The food mass is simultaneously moistened and lubricated by saliva, about 1.5 liters of which is produced daily by three pairs of salivary glands-the parotid, Submaxillary, and sublingual glands. It’s first function is to mix with food, lubricating dry foods and diluting thicker foods. It’s second function is to provide the Polysaccharide-digesting enzyme alpha amylase and the Lipid-digestion enzyme lingual lipase. A third function of saliva is to dissolve some molecules in food, allowing them to interact with the chemoreceptors in the mouth to give risk to the sensation and taste. Saliva also contains a protein that causes particles of food to stick together and lubricates the mass for easier swallowing. 

The masticated food mass, called a bolus, passes back to the pharynx under voluntary control, but from there on and through the esophagus, the process of swallowing (Deglutition) is involuntary. Peristalsis then moves the food rapidly to the stomach. 


Food particles are propelled forward and mixed with gastric secretion by wavelike contractions that progress forward from the fundus to the antrum and pylorus. Active chemical digestion begins in the middle portion of the stomach, where an average of 2000 to 2500 ml of gastric juice is secreted daily. This contains hydrochloric acid, intrinsic factor, the inactive protease pepsinogen, gastric lipase, mucus, and the gastrointestinal hormone gastrin.

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