The various parts of human digestive system are:
The Digestion in Humans starts with the Ingestion of food. Ingestion means ‘taking in’ - food is taken in by the person, and it reaches the mouth.
(1) Mouth:
The mouth or buccal cavity contains teeth, tongue and salivary glands.
Teeth:
The teeth are used to chew the food and break it into smaller pieces so that it is digested easily.
Tongue:
The tongue then moves the food around the mouth properly so as to mix food with the saliva.
Salivary Glands:
The salivary glands secrete saliva .
- It contains salivary amylase , an enzyme which helps in the chemical digestion of starch.
- Enzymes are biological substances that help in the progress of the reaction.
(2) Oesophagus:
It is also known as the food pipe .
- From the mouth, the food is pushed into the food pipe (oesophagus) with the action of the tongue.
- The walls of the oesophagus contract and expand to help the food move down the pipe into the stomach. This expansion and contraction movement is called Peristalsis.
(3) Stomach:
Due to the peristaltic movements of oesophagus, the food enters the stomach where a variety of juices act on it.
- The food is churned in the stomach for about 3-4 hours where a semi-solid paste is formed.
- The stomach wall contains three tubular glands in it. The glands present in this wall of stomach secrete gastric juices .
- The gastric juice contains hydrochloric acid , enzyme pepsin and mucus .
Hydrochloric acid:
- It kills any bacteria which may enter the stomach along with food.
- Turns the gastric juice acidic in nature.
Pepsin:
- The enzyme pepsin works in this acidic medium to digest the protein present in the food to convert it into smaller molecules.
- This protein digestion begins in the stomach.
Mucus:
- Mucus helps protect the lining of the stomach from the acidic secretion of HCl.
- If mucus is not secreted the lining of the stomach will be degraded leading to formation of ulcers.
(4) Small Intestine:
This partially digested food in the stomach now moves forward into the small intestine .
- The exit of food from the stomach is regulated by sphincter muscle which releases it in small amounts into the small intestine.
- The small intestine is the largest part of the alimentary canal. It is called the small intestine because it is very narrow .
- The small intestine receives secretions of two glands : liver and pancreas.
Liver :
- The liver secretes bile juice which is normally stored in the gallbladder and is a greenish yellow liquid .
- Bile performs two functions :
- It provides an alkaline medium for the acidic food coming from the stomach for the pancreatic enzymes to act on it
- Bile salts break down the fats present in food into smaller globules making it easy for the pancreatic enzymes to act and digest them.
Pancreas :
- Pancreas secrete pancreatic juices which contain digestive enzymes like pancreatic amylase, trypsin and lipase.
- The enzyme amylase breaks down starch
- The enzyme trypsin digests proteins
- The enzyme lipase breaks down emulsified fats .
- The enzymes present in the intestinal juice complete the digestion of complex carbohydrates into glucose , proteins into amino acids and fats into fatty acids and glycerol .
- After digestion the molecules of food become very small and can then be absorbed by the walls of the small intestine and move further into our blood.
- The small intestine is the region for absorption of digested food because of the presence of villi .
- Villi are small fingerlike projections which increase the surface area of the small intestine thereby increasing the rate of absorption.
- From the bloodstream, the digested food reaches all parts of the body where it becomes assimilated as part of cells.
- The digested food which is not used by our body immediately is stored in the form of a carbohydrate called glycogen in our liver.
(5) Large Intestine:
The undigested food passes from the small intestine into a wider tube called the large intestine.
- Here, most of the water gets absorbed from the undigested food and thus the leftover part becomes almost solid. The solid waste is excreted through the anus as faeces or stool.
- The exit of the waste is called egestion or defecation. It is controlled by the anal sphincter.
Dental Caries:
- Dental Caries or tooth decay is the damage that occurs to teeth which can potentially result in cavities, dental abscesses or even tooth loss .
- This begins as a result of plaque deposition on teeth. Plaque is a sticky deposit on teeth in which bacterial growth happens fast.
- This bacterial multiplication can convert the sugars in our food to acid.
- Enamel is the outermost, hard, white layer of a tooth
- This acid may cause enamel deterioration.
