digestive system


                      DIGESTIVE SYSTEM PDF


The human digestive system consists of the alimentary canal and its associated glands. The various organs of the human digestive system in sequence are: mouth, oesophagus or food pipe, stomach, small intestine, large intestine. The gland which are associated with the human digestive system and form a part of the human digestive system are salivary gland, liver and pancreas. The human alimentary canal of the digestive system which runs which runs from mouth to anus is about 9 metres long tube. The ducts of various gland open into the alimentary canal of digestive system and pour the secretions of the digestive juices into the alimentary canal. ( Digestive System Pdf)

                                   DIGESTIVE SYSTEM FUNCTION:

  • Intake of food
  • Chemical digestion by secreting enzymes.
  • Break down of food into simplified food.
  • Assimilation of food nutrients into the blood.
  • Release of undigested food.


  •                                            INGESTION

  • It means intake of food by Other associated organs for ingestion are teeth, tongue etc.
  •               DIGESTION: ( human digestive system)

  • This step begins in mouth with the help of teeth and saliva. Steps are like: Teeth cut the food into small pieces, chew and grind it,  salivary glands produce saliva and tongue  helps in mixing the saliva with food. Salivary gland produces Amylase enzyme which helps in chemical digestion of starch in mouth. The slightly digested food is swallowed by the tongue and  goes down by a contraction and expansion movement of oesophafus or food pipe wall called Oesophagus carries food to the stomach.  The food is further digested in stomach.  The food is  churned  in the stomach for about 3 hours. During this time the food is broken down into smaller pieces and forms a semi- solid paste.  The stomach wall secretes gastric juices which contains Hydrochloric acid, enzyme Pepsin, and Mucus. (digestive system) Hydrochloric acid makes the stomach acidic so, that Pepsin enzyme can be active to digest protein food into small peptide molecules.

                                         FUNCTION OF HYDROCHLORIC ACID

Another function of Hydrochloric Acid is to kill any bacteria which may enter the stomach. (digestive system) Mucus helps to protect the stomach wall from its own secretion of Hydrochloric acid.  If Mucus is not secreted ,hydrochloric acid will cause the erosion of inner lining of stomach leading to the formation ulcers in the stomach. ( STOMACH)

                                                 FOOD IN SMALL INTESTINE     

The partially digested food then enters into the small intestine. it is the site of complete digestion of food.  The small intestine receives secretion of liver and pancreas.  The wall of small intestine contains glands secreting intestinal juices.  All these secretions completes digestion of carbohydrates (into glucose), fats (into fatty acid and glycerol) and proteins (into amino acids) In this way, the process of digestion converts the large and insoluble food molecules into small and water soluble molecules. (digestive system) The chemical digestion of food is brought about by biological catalysts called Enzymes. ( SMALL INTESTINE)

  •                                                ABSORPTION 

  • Main region  for the absorption of digested food is trhe inner surface of small intestine has millions of tiny, finger like projections called villi.  The presence of villi gives the inner walls of small intestine a very large surface area which helps  in rapid absorption of digested food.  The walls of small intestine absorbs the digested food . It goes into our blood.
  •                                              ASSIMILATION

  •  The simplified and digested food is transported by the blood to whole body for further assimilation in each and every cell.  This assimilated food is used by the body cells for obtaining energy as well as growth and repair of body. The digested food which is not used by our body immediately is stored in the liver in the form of glycogen. ( digestive system diagram)
  •                                                   EGESTION

  •  Our body cannot digest some part of food.  The body passes thisundigested food into the large intestine where maximum water absorption makes the undigested food solid. When we go to the toilet, then we pass this undigested food from our body through the anus as faeces or stool. (human digestive system diagram)

                                               ENZYMES IN THE DIGESTIVE SYSTEM



Slightly alkaline  Saliva  Salivary amylase (ptyalin)  Starch → Maltose


Highly acidic (DIGESTIVE SYSTEM) Hydrochloric acid     Pepsin









   Proteins → Peptones and Proteoses 

Casein → Paracasein 


Duodenum (small intestine) 

Alkaline  Bile juice, Pancreatic juice    No enzyme 













Steapsin (Lipase)

       Emulsification of fat 

Proteins → Polypeptides 

Specific protein → Polypeptides 

Starch → Maltose 

Fats→Fatty acids and glycerol 


Ileum (small intestine)  Alkaline  Intestinal juice         Erepsin 















Peptones and peptides → Amino acids 

Sucrose → Glucose and fructose 

Maltose → Glucose 

Lactose → Glucose and Galactose 

Fats → Fatty acids and Glycerol 




ANSWER IN SHORT ( Digestive System Pdf)

Qs1 What is emulsification of fat?

Ans1:  The bile salts help in breaking down  oil droplets into small globules, forming  a milky solution  called  emulsification to facilitate further  digestion of fats.

Qs2:  Why is colour of bile yellow?

Ans2: Colour of bile is due to the presence of certain pigments  (bilivirdin and bilirubin)  produced  due to the breakdown of the dead and worn out red blood cells.

Qs3: How does liver control blood sugar level ?

Ans3: Liver retains excess glucose which is the product  of carbohydrate digestion and converts it into glycogen. Liver cells store the excess glycogen. These cells release glycogen in the form of glucose whenever needed by the body.

Qs4: Write short note on heparin.

Ans4: Liver produces heparin which is an anti-coagulant. Heparin  does not allow clotting of blood within the blood vessels.


Qs5: What do you know about  Goblet cell?

Ans5: Goblet cells are situated in the duodenum. These cells secrete mucus in the small intestine. This mucus helps in protection and carrying digestive products .

Qs6:  What is haemolytic jaundice?

Ans6:  When a person suffers from jaundice, the skin looks pale with a yellowish tint. It happens due to large amount of pigment bilirubin in the blood.  In this disease  red blood cells breaks down in abnormally large amounts.

Qs7: What is obstructive jaundice?

Qs7: In this disease, there is an obstruction of the bile duct or damage to the liver cells. It results in the precipitation of cholesterol of crystals out of bile which in turn forms gall bladder stone. ( Digestive System Pdf)

Qs8: What is succus entericus?

Ans8: Ileum contains intestinal glands that secrete intestinal juice which we term as succus entericus.


Qs9: How the anus empties the faecal matter outside the body?

Ans9: Rectum causes a special reflex called defecation reflex.Then the faeces pass to anus . After that, anus empties the anus by the relaxation of sphincter muscles.

Qs10: Mention the steps of digestion in buccal cavity and pharynx.

Ans10: In the Buccal cavity and Pharynx, the steps of digestion are:

  • Mastication (physical digestion or chewing by teeth)
  • Mixing of food with water and mucus of saliva
  • Partially digestion by enzymes in saliva.
  • Food is converted into bollus.
  • We swallow the bolus.

Qs11: Herbivores are unique in digestion, why? ( Digestive System)

Ans11:  Herbivores are special type of animal. So, they have cellulase enzyme which digests the  cellulose to form soluble glucose.  But in human being,  they cannot digest cellulose . It helps to keep the colon and rectum healthy. It prevents constipation.

Qs12: State the relation between villi and hepatic portal vein.

Ans12:    Blood capillaries absorb monosaccharides, peptides and amino acids  either by diffusion or active transport into the blood capillaries through villi. These blood capillaries converge to form hepatic portal vein. This vein delivers the absorbed food to the liver. Fatty acid, glycerol , water, , inorganic salts and vitamins are absorbed in the small intestine.

VERY SHORT TYPE QS ( Digestive System)

Qs13: What is chyme?

Ans13: The partial digested food turns into a paste like substance inside stomach, we call it chyme.




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