Definition
Digestion, which takes place in the oral cavity, in the stomach and in the first part of the intestine, is a physiological process mediated by a series of chemical-physical transformations, through which the organism changes foods into substances that can be absorbed and assimilated .
Numerous organs participate in digestion, which together constitute a long tube called digestive system. Along this duct, which communicates with the outside through the mouth and anus, numerous anatomical structures can be found, each with a specific role that we will examine in the course of this article.
The digestive process, in short, involves: mouth, esophagus, stomach, duodenum and intestine, and digestive enzymes produced by the pancreas and liver.
Insights
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This apparently simple process actually involves numerous structures. Let's think for example of the masticatory muscles, the respective innervations, the mechanical action of the tongue and the numerous enzymes contained in the saliva. Among these is ptyalin, an enzyme that promotes starch digestion. This important complex carbohydrate contained mainly in cereals and potatoes is made up of the union of many simple sugars. To appreciate the digestive efficacy of ptyalin, just chew a piece of bread for a few minutes without swallowing it. As the time passes, the bolus will take on an increasingly sweet taste, testifying to the splitting of the long polysaccharide chains into simple sugars.
Another substance contained in saliva, called mucin, has instead the task of rendering the alimentary bolus viscous and lubricated.
Proper chewing is therefore the basis for good digestion.
Esophagus and Digestion
The bolus, the final product of chewing, continues its journey along the digestive tract thanks to swallowing, a process that conveys the bolus into the esophagus while preventing its reflux into the respiratory canal. This mechanism can only take place thanks to the coordinated action of tongue, larynx and pharynx.
Protected from the sternum and situated below the trachea the esophagus is made up of a dilatable tissue that widens and shrinks based on the presence or absence of food bolus. This important anatomical structure, similar to a channel about 25 centimeters long, has the function of connecting the oral cavity with the stomach.
Inside the esophagus the bolus is pushed downwards by a fine mechanism of muscular contraction. This function is linked to the presence of a series of muscular rings that contract and relax to allow food to advance (esophageal peristalsis). The mechanism is involuntary but so effective that it also acts against gravity, like when you lie downside up.
The esophagus also has very small glands that pour their secretion into a main excretory duct responsible for the fluidization of the esophageal walls. In this way the passage of food is further facilitated.
The regurgitation of gastric contents is prevented by the presence of a valve located at the lower end of the esophagus. This strip of muscle tissue called the lower esophageal sphincter normally allows the bolus to pass in one direction only. As soon as the mixture of food and saliva arrives in this area the valve opens, lets the bolus pass and closes again.
CONTINUE: Digestion of stomach and duodenum »
