DIGESTIVE SYSTEM -BIOLOGY- TNPSC,TET,RRB,SSC SCIENCE (GK) STUDY MATERIAL

DIGESTIVE SYSTEM
The process of converting food into energy giving susbstances is carried out by this system.

  1. Buccal Cavity
    In the mouth salivary glands secrete saliva which contains the enzyme ptyalin.
    Also contains Lysozyme which kills bacteria
    Teeth: They are produced in two sets temporary and permanent. The teeth are of four types: Incisors, Canines, Premolars and Molars
    Structure of a Tooth:
    It is covered by a shining material called Enamel.
    Enamel is the hardest substance in the human body.
    Dental Formula:
    2123/2123. This means that there are 2 incisors, 1 canine, 2 premolars and 3 molars in half of the upper jaw and exactly the same arrangement in half of the lower jaw. i.e. 32
    The premolars and the molars are called the grinding teeth. The last molars are called the wisdom teeth.
    Linked with pharyns.
    Pharynx
    Trachea opens into pharynx through an aperture called Glottis. It also receives the opening of the Eustachian tubes from the middle ear through an aperture called Gullet.
    Oesophagus
    25 cm long tube.
    Leads to stomach
    Stomach
    In stomach, the food is called chime.
    Has 3 parts: Fundus, Cardiac and Pyloric
    It is a warehouse, where food can be stored to await the main process of digestion.
    Gastric juices produced in the stomach help in digestion of food. Also contains HCl which kills bacteria and provides acidic medium.
    Small intestine(Duodenum + Jejenum +Ileum)
    Here the food from the stomach is mixed with bile (from liver) and pancreatic juice (from pancreas) and moves forward by peristaltic movement.
    Duodenum receives the bile-pancreatic duct formed by the union of bile duct and pancreatic duct.
    Bot jejunum and ileum have numerous fingure like projections called the villi.
    Bile doesn’t take direct part in digestion of fat, it just makes the food alkaline.
    Large Intestine (Caecum+colon + Rectum)
    It receives undigested material from the small intestine and absorbs water.
    Cellulose digestion takes place in it.
    Vermiform appendix is a part of caecum,which produces antibodies.
    TONGUE
                 
    Saliva, secreted by the salivary glands, is
    mixed with the chewed food by the tongue.
    Tongue also contains taste buds due to which we sense bitter, sour, salty or sweet taste.
    DIGESTIVE GLANDS
    Parotid Glands
    These are largest salivary glands.
    Liver
    It is bilobed, right lobe being the larger and left lobe the smaller.
    Secretes Bile, which is yellowish in color.
    Bile helps in digestion in three ways.
    Liver is a gland which has got diverse functions.
    Digestion: With the help of bile (already discussed)
    Regulation of Blood Sugar: The liver separates the excess of sugar from the blood and stores it in its cells as glycogen (animal starch). This process is called Glycogenesis and is aided by pancreatic hormone insulin.
    During the days of food shortage, the stored glycogen is changed into glucose and added to the blood stream for distribution to the body.
    Formation of Glycogen from Noncarbohydrate sources: Excess of amino acids/ fats are also changed into glycogen.
    This process is called Glyconeogenesis.
    Their amino radical separating as ammonia and carbon chain changing into a keto acid. This process is known as Deamination.
    Excretion: Liver collects haemoglobinwhile keto acid takes part in metabolism.
    Blood clotting: liver produces heparin,prothrombin and fibrinogen.
    Formation of Red Blood Corpuscles: Liver produces RBCs in the embryo.
    Phagocytosis: Foreign matter, dead cells and bacteria are disposed off in the liver.
    Synthesis of Vitamin A
    Storage: Besides glycogen liver stores (a) lipids such as fats fatty acids and cholesterol Pancreas
    Endocrine –α, β, γ cells
    Exocrine – pancreatic juice
    It is both an exocrine and an endocrine gland. The endocrine part (called islets of langerhans) secretes hormones . The exocrine part secretes pancreatic juice.
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