Digestive System of a Human


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Digestive System of a Human


Process of food Digestion

Human body is like some kind of a machine. Every machine use different source of energy to operate. Energy which is required for different biological processes that take place in human body is obtained from the foods we eat. These food contain various nutrients such as carbohydrates, lipids and proteins. Carbohydrates, lipids and proteins are complex organic molecules that do not dissolve in water. These compounds cannot be absorbed into the human body as in the form it is. Therefore they should be broken down into small particles.

The process by which the complex organic compounds are converted into simple organic products to be absorbed into the human body is called digestion of food or the Process of Food Digestion.

There are two main process of Food digestion. Namely mechanical processes and chemical
processes. During mechanical process the physical nature of the food is altered by breaking down of food into small pieces by teeth inside mouth. During chemical process, the insoluble complex compounds are broken down into simple molecules by the action of enzymes.
As an example, by using salivary amylase (ptyalin) enzyme inside the mouth Starch is converted into maltose.

Some nutrients such as mineral salts, some vitamins, glucose, fructose and galactose can be used by the body without any digestion.

The organs involved in food digestion, are collectively called as digestive system.

Human digestive system

Human digestive system is a complex system which consist of ,

Labeled Digestive System of a Human bestaiding.com
  • Buccal cavity
  • Oesophagus
  • Diaphragm
  • Salivary glands
  • Epiglottis
  • Small intestine
  • Stomach
  • Liver
  • Gall bladder
  • Pancreas
  • Large intestine
  • Appendix
  • Caecum
  • Rectum
  • Anus



Although it contain so many different parts it is actually a single tube which runs from mouth to anus. The functions take place in the digestive system are "food digestion, absorption of digested end products and removal of undigested materials" from the body.


Assignment - 6'1
Digestion in the buccal cavity

Digestion of food starts in the mouth. Mouth is the opening of the buccal cavity to the environment. The buccal cavity is made up of upper and lower jaws and it is surrounded by muscular lips at the bottom and top. Buccal cavity is surrounded by cheeks. Although Teeth are present in both jaws. Only the lower jaw can be moved. The tongue is attached to the floor of the buccal cavity and there are three salivary glands present in the buccal cavity. They secrete saliva and the tongue helps in identification of taste, mixing of food with saliva and swallowing.


Initially digested food is formed into a bolus and pushed to the posterior part of the buccal cavity. Then the food is pushed into the pharynx. Pharynx is a common area to both digestive and respiratory systems. There is a movable organ called epiglottis found just above the opening of trachea. When bolus is swallowed the epiglottis moves down to close the opening of trachea. Then bolus enters into oesophagus without entering into trachea.

Epiglottis helps to prevent entering food into the trachea. When food enters to pharynx, respiratory track is blocked by epiglottis. This prolong blockage of trachea may cause death. If the food is not removed instantly, the person may die due to blockage of respiratory tract.
Oesophagus is a constricted tube.


How is food moved along a constricted tube?

The bolus passes through the oesophagus by peristaltic movements. As oesophagus is a muscular structure, due to contractions and relaxations of its wall the peristaltic movements appear as waves. These peristaltic movements provide the force to propel the bolus forward. Then food is moved into stomach by peristaltic movements.

Digestion in the stomach

The stomach is an organ which is like a dilated sac. Due to the peristaltic activity of muscles in
the stomach wall the bolus is broken down and mixed well into a chyme. Several enzymes ooze out into the stomach. It is collectively called the gastric juice. The gastric juice contains mainly hydrochloric acid (HCl) and pepsin enzyme.


 HCl activates pepsin and pepsin starts the protein digestion to produce polypeptides. Renin present in infants causes coagulation of milk. Food retain in stomach for about three to four hours. Although the digested end products are not absorbed but some water, glucose and some drugs may absorb. Chyme containing partially digested proteins, digested and undigested carbohydrates, undigested lipids, water, minerals and vitamins are released into the proximal part of small intestine, duodenum part by part.

Hunger is a signal that indicates the need of food. When the stomach is empty, it continues to contract. So it causes a pain. It gives a sense about hunger. Hunger is a signal that indicates the need of food.


Labaled Digestive System of a Human bestaiding.com

Digestion in the small intestine

Small intestine is the place where the chemical digestion of food mainly happens. Pancreatic enzymes as well as intestinal enzymes involve in this digestion. In a grown adult the small intestine is about 7m in length. The duodenum is the proximal part of the small intestine which is shaped like a C.

The duct of the pancreas and the gall bladder opens into the duodenum via a single pore. Pancreatic juice is secreted into the duodenum through pancreatic duct. It contains three main enzymes. They are trypsin, amylase and lipase. The bile carried through the bile duct is added to it. Bile is produced in the liver and stored in the gall bladder and it contains bile pigments, bile salts, bicarbonate ions and water.

The lipids in food are broken down into small droplets by the process called emulsification due to mixing of bile with food at duodenum. So the enzymes get a greater surface area to act on lipid food.

Intestinal juice secreted by the wall of the intestine contains, maltase, sucrose,
lactase, peptidase and mucus. Mucus lubricates food and then ease the passage of
food materials along the gut. It protects the inner lining of gut wall. Proteins present
in wall of stomach and intestine is protected by the protein digestive enzymes as
there is a layer of mucus on the wall.

The small intestine is adapted to increase its efficiency of absorption by
  • being a long tube
  • Presence of circular folds in the inner wall
  • Presence of finger like projections called villi in the circular folds
  • Presence of microvilli in the epithelial cells of villi
  • thin epithelial lining on villi
  • Villi are highly vascularized


The digestive end products like Amino acids,Vitamins,Mineral salts,Monosaccharides (Glucose/ Galactose/ Fructose) are absorbed into the blood capillaries of

Fatty acids and glycerol formed by digestion of lipids are absorbed into lacteals and enter into blood circulatory system. When there is high amount of glucose in blood, they are converted into glycogen and stored in liver. In the same way when the concentration of glucose is decreased, glycogen breaks down to form glucose and is added to blood. The unabsorbed materials in small intestine are sent to the large intestine.

Processes in the large intestine

The large intestine starts with caecum and ends up at anus. Length of the large intestine of a grown adult is about 1.5 m and dilated part of the large intestine is the rectum. The materials entering into the large intestine mainly it contains undigested cellulose and water. A small blind ended tubular structure starts at the end of the caecum. It is known as the appendix. It is very small in humans and it may be infected and become swollen. This disease is known as appendicitis.

The main function of the large intestine is to absorb water from matter received from
ileum. Thereby making it into semi solid. The matter entered into large intestine is
known as faecal matter. Faecal matter is yellow in colour due to bile pigments in it.
Undigested food, microorganisms, epithelial cells and mucus are present in faecal
matter. When large intestine fills with faecal matter, it passes out from the anus.

The diseases and disorders associated with digestive system

Assignment - 6'2

Generally known as acidity. Inflammation of inner lining of mucosa of stomach is known as gastritis. It is a common disease among people due to


  • Skipping of meals
  • Consumption of acidic and spicy food
  • Excessive smoking and alcohol consumption
  • Mental stress

The main symptoms are,


  • Regurgitation of acid to mouth,
  • Burning feeling and pain in stomach.


When the condition becomes worse, ulcers appear in stomach and duodenal wall. Bleeding
can take place. By following healthy food diets and good habits one can avoid the above disease.


Difficulty in defecation due to hardening of faecal matter is known as constipation.
Faeces remain in the large intestine for a longer period of time and absorption of
water takes place excessively, Thereby this condition may occur.

Reasons for constipation are as follows,

  • Consumption of food with low dietary fires
  • Not taking required volume of water
  • Postponing of defecation

By avoiding above conditions and habits one can avoid this disease. Due to forceful defecation, the anal canal may damage and bleeding can occur. Haemorrhage may occur Due to constant constipation


Typhoid is caused by a bacterium. The pathogen is transmitted through food and water. It can enter into the body through mouth also while swimming and bathing. It may enter into the body through faecal matter of patient, consumption of contaminated food and fles.


The main symptoms are,


  • Pain in arms and legs.
  • Headache and fever.


It is a disease which gradually becomes worse. At initial stages constipation can occur. Tongue is covered by a plaque. After sometime stomachache and diarrhea can occur. Ulcers can form in the small intestine and cause bleeding. Therefore blood is released with faecal matter. Due to ulcers, the wall can be damaged. Disease can be identified by a blood test or stool test. Typhoid can be prevented by getting a vaccine.


Diarrhoea occurs when the intestines are infected with a virus, bacteria or a parasite.
This is also disease is transmitted by the faeces of an infected person. The main symptom
is release of faecal matter in liquid state. Dehydration may occur due to loss of fluid. Absorption of water in the large intestine will not occur properly. If dehydration becomes worse due to diarrhoea, it may be fatal. So it is needed to consume more water and consult a doctor immediately.

The above two diseases can be avoided by taking preventive measures given below

  • Consumption of boiled drinking water
  • Removal of breeding places of fleas and cover the food to prevent entering of flees to food
  • Avoid consumption of food which are sold in open places
  • Use of water seal latrines
  • Proper washing of hands with soap after using the toilet

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