Digestion In Human Being 

The Human digestive system consists of:
             Alimentary canal, and 
            Its associated glands.

Various organs of the human digestive system are:
    • Mouth
    • Oesophagus (food pipe)
    • Stomach
    • Small Intestine
    • Large Intestine
Glands associated with the human digestive system and form a part of the human digestive system are:
    • Salivary Glands
    • Liver
    • Pancreas
There are five process of nutrition in Animals (Human Beings)

Ingestion

  • Mouth is the special organ for the ingestion food.
  • By using hand, we put the food in the mouth.

Digestion 

  • In human being, digestion of food is started in the mouth.
  • The mouth cavity [buccal cavity] contains:
    • Teeth
    • Tongue
    • Salivary Glands
  • Teeth helps in physical digestion of food by cutting the food into small pieces, chewing and grinding.
  • In mouth, salivary gland produce saliva which the tongue help in mixing the food with saliva and get wetted, can be easily swallowed more easily.
  • By secreting enzymes, Salivary glands helps in chemical digestion of food.
  • Human saliva contain salivary enzyme called salivary amylase. This helps in digesting the starch present in the food into sugar.
  • In mouth, food is not completed digested.
  • Oesophagus is the food pipe through which the food swallowed from mouth to stomach.
  • The food swallowed to the stomach through the contraction and expansion movement of wall of Oesophagus is called Peristaltic movement.
  • Stomach is the J-shaped organ. It is present on the left side of the abdomen.
  • During the digestion in stomach, the food breaks down into still smaller pieces and thus form a semi-liquid paste.
  • Stomach wall contain three glands which secrete gastric juice.
  • Gastric Juice contain three substance:
    • Hydrochloric Acid
    • Enzyme pepsin
    • Mucus
  • Due the presence of Hydrochloric Acid, the gastric is acidic in nature. In the acidic medium, the enzyme pepsin begins the digestion of protein present in the food to form smaller molecules.
  • Only in the presence of an acid, the protein digestive enzyme pepsin is active.
  • Hydrochloric acid helps in killing the bacteria entered the stomach with food.
  • Mucus helps to protect the inner wall of the stomach from Hydrochloric acid.
  • If mucus is not present, the hydrochloric acid will cause the erosion of inner lining of the stomach leading to the formation of ulcers in the stomach.
From the stomach, the partially digested food enters the small intestine.
  • Small Intestine : It is the largest part of the alimentary canal.
  • Small intestine : 6.5 meters long in adult man.
Site of complete digestion: Small Intestine
  • Liver and Pancreas are the two glands that secrets juices in small intestine.
  • Liver secret - Bile Juice
  • Bile - Greenish Yellow 
  • Bile - Stored in gall bladder
  • Bile is alkaline and contain salt
  • Bile - Helps to emulsify or break the fat.
  • Bile perform two function:
    • makes the acidic food coming from stomach Alkaline so that pancreatic enzymes can act on it.
    • bile salts breaks the fats present in the food into small globules making it easy to for the enzymes to act and digest them.
  • Pancreas - Lies parallel to and beneath the stomach 
  • Pancreas secrets pancreatic juice which contains digestive enzymes like:
    • Pancreatic amylase - Breaks down Starch
    • Trypsin - Digest proteins
    • Lipase - Breaks down the fat.