Can you plz explain the complete process happening before the food get digested.?explanations about mastication and deglutition etc?

Question

Answer

Digestive Processes

The processes of digestion include six activities: ingestion, propulsion, mechanical or physical digestion, chemical digestion, absorption, and defecation.

The first of these processes, ingestion, refers to the entry of food into the alimentary canal through the mouth. There, the food is chewed and mixed with saliva, which contains enzymes that begin breaking down the carbohydrates in the food plus some lipid digestion via lingual lipase. Chewing increases the surface area of the food and allows an appropriately sized bolus to be produced.

This image shows the peristaltic movement of food. In the left image, the food bolus is towards the top of the esophagus and arrows pointing downward show the direction of movement of the peristaltic wave. In the center image, the food bolus and the wave movement are closer to the center of the esophagus and in the right image, the bolus and the wave are close to the bottom end of the esophagus.

Figure 1. Peristalsis moves food through the digestive tract with alternating waves of muscle contraction and relaxation.

Food leaves the mouth when the tongue and pharyngeal muscles propel it into the esophagus. This act of swallowing, the last voluntary act until defecation, is an example of propulsion, which refers to the movement of food through the digestive tract. It includes both the voluntary process of swallowing and the involuntary process of peristalsis. Peristalsis consists of sequential, alternating waves of contraction and relaxation of alimentary wall smooth muscles, which act to propel food along (Figure 1). These waves also play a role in mixing food with digestive juices. Peristalsis is so powerful that foods and liquids you swallow enter your stomach even if you are standing on your head.

Digestion includes both mechanical and chemical processes. Mechanical digestion is a purely physical process that does not change the chemical nature of the food. Instead, it makes the food smaller to increase both surface area and mobility. It includes mastication, or chewing, as well as tongue movements that help break food into smaller bits and mix food with saliva. Although there may be a tendency to think that mechanical digestion is limited to the first steps of the digestive process, it occurs after the food leaves the mouth, as well. The mechanical churning of food in the stomach serves to further break it apart and expose more of its surface area to digestive juices, creating an acidic “soup” called chyme. Segmentation, which occurs mainly in the small intestine, consists of localized contractions of circular muscle of the muscularis layer of the alimentary canal. These contractions isolate small sections of the intestine, moving their contents back and forth while continuously subdividing, breaking up, and mixing the contents. By moving food back and forth in the intestinal lumen, segmentation mixes food with digestive juices and facilitates absorption.

In chemical digestion, starting in the mouth, digestive secretions break down complex food molecules into their chemical building blocks (for example, proteins into separate amino acids). These secretions vary in composition, but typically contain water, various enzymes, acids, and salts. The process is completed in the small intestine.

Food that has been broken down is of no value to the body unless it enters the bloodstream and its nutrients are put to work. This occurs through the process of absorption, which takes place primarily within the small intestine. There, most nutrients are absorbed from the lumen of the alimentary canal into the bloodstream through the epithelial cells that make up the mucosa. Lipids are absorbed into lacteals and are transported via the lymphatic vessels to the bloodstream (the subclavian veins near the heart). The details of these processes will be discussed later.

In defecation, the final step in digestion, undigested materials are removed from the body as feces.

Answer

The digestion process is both mechanical and chemial process which starts from buccal cavity and ends at ileum of small intenstine. why called mechanical ? - because the first process carried out in buccal cavity called as MASTIGATION of food is caused by chewing of food which is a mechanical process.
why called as chemical process ? - because so many chemicals( digestive juices & enzymes) act during the process of digestion.
digestion in buccal cavity involves process like : - 1- mastigationhelps in breaking of food into smaller parts so that to increase surface area of food to faciliate mixing of saliva and action of enzymes. 2- mixing with saliva here only starch is digested by an enzyme called salivary amylase(ptyalin) present in our saliva. and it converts 30% of starch to maltose , isomaltose and dextrines. and the other components remain as such as no enxyme except ptyalin is +nt in buccal cavity. this partially digested food is called Bolus.
then occurs swallowing/degluttation - passing of bolus into pharynx by pushing of tounge. it is started as a voluntary process but later becomes involuntary.
note- their is no digestion in oesophagus .
digestion in stomach : digestions of lipids ; proteins ; milk protien(in infants) , nucleic acid takes place only by action of enzymes present in gastric juice.
the partially digested food from stomach is called chyme.
digestion in small intenstine :- here digestion of starch ; lipids ; protiens and nucleic acid frst takes place by action of pancreatic juice first. then digestion by succus entericus(intestinal juice )occurs which digests the remaning compoments into simpler forms.
the undigested food left in small intenstine like cellulose is also sometimes reaferred as chyme.(in some books). THIS IS ALL ABOUT THE DIGESTION PROCESS. PLEASE GO THROUGH NCERT ONCE AGAIN SO THAT YOU CAN KNOW WHERE WHICH ENZYME ACT ON WHICH COMPONENT OF FOOD.
hope this may helps you . good luck !
(please ignore grammatical errors if present )

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