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CLASS – XI BIOLOGY, , By – MONIKA I, , DIGESTION OF FOOD., Digestion of food involves breaking down of complex food into their simple forms . It occurs through, the action of enzymes . The process occurs in following way ., In Buccal cavity – Shows two major functions, a). Mastication of food – Food substances are broken into smaller pieces by movement, of teeth Tongue helps food to mix thoroughly with saliva and mucus . The mucus lubricates, and adheres the masticated particles of food into bolus and pushes towards pharynx for, deglutition ., b) . Swallowing It is the process of passing bolus into the oesophaous by peristalsis as reflex, which takes the food down towards the stomach ., PERISTALSIS : It is reflex wave that comprise through whole digestive tract ., MECHANISM OF DIGESTION :, 1. Digestion in Buccal cavity –, Digestion starts in the cavity by hydrolytic action of enzyme salivary amylase ., Salivary amylase, , Starch, , Maltose, , pH 6.8, , Lysozyme acts as an antibacterial agent kills bacteria thus prevent infections., 2. Digestion in stomach ., Food remains in stomach for about 4-5 hours . Intestinal mucosa contains gastric gland, comprises three types of cells, a) . Mucus or neck cells for secretory mucus, b). peptic or chief cells for secreting proenzyme pepsinogen, c). Parietal or oxyntic cells for secreting HCL and intestinal factory ( for vitamin B12 …) The, food mixed thoroughly with acidic gastric juice secreted in stomach by chewing, movement . The enzymes of stomach and their actions are –, a) PEPSIN, Pepsinogen HCl, Pepsin, Proteins (pepsin) Proteases + Peptones, b) Rennin – It is a proteolytic enzyme found in gastric juice of infant., HCl, Prorennin, Rennin, c) Gastric lipase – It acts on emulsified fats and helps in digesting 25% of fats in milk., Digestion in small intestine . ----Due to peristalsis movement the food is mixed thoroughly along with the, secretions in the intestine , contraction of muscle in the small intestine with kneading and churning of, thyme finally pushes into large intestine . The pancreatic juice from pancreas and bile from liver are, released through hepatopancreatic duct ., Enzyme from pancreas are, 1. Trypsinogen, 2. Chymotrypsinogen, 3. Procarboxypeptidases, 4. Amylases, 5. Lipases, 6. Nucleases, Trypsinogen Enterokesiase, , Trypsin, , Proteins, Peptones, Proteases, , Trypsin/Chymotrypsin, , chymothygin, , Dipeptides

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Carbohydrates in thyme are hydrolysed by pancreatic amylase into disaccharides, Polysaccharides ( starch ) Amylase, Disaccharides, Nucleases pancreatic juice acts as reaction acid to form nucleotide and nucleotides, Nucleic Acid Nucleases, Nucleosides, Nucleosides, DIGESTIVE JUICE FROM LIVER .Bile secreted from liver passes into duodenum and small intestine. Bile contains bile pigment bilerubin, and biliverdin, bile salt. Cholesterol and phospholipids, Fats Lipases, Diglycerides, Monoglycerides, Biles helps in emulsifying of fats i.e. break down of fats into small micelles which are kept suspended ., ENZYMES FROM INTESTINE –, Intestinal mucosal epithelium has brush border cells with goblet cells which forms the intestinal juice, known as succus entericus . It contains enzymes like Disaccharides, Dipeptidase, Lipases ,and, Nucleosides, Dipeptides Dipeptidases, Amino acids, Maltase, , Maltose, Lactose, , Glucose + Glucose, , Lactase, , Nucleotide, , Glucose + Fructose, Nulceotidases Nulceotidase, , Di and Monoglycerides, , Lipases, , Nulceotidases, , Sugar + Base, , Fatty acids + Glycerol, , Lipolytic enzyme, All these reactions takes very close to mucosal epithelial cells of small intestine which facilitate their, absorption., DIGESTION I LARGE INTESTINE, The last stage of simplification of food occurs in last part of alimentary canal is large intestine which is carried, out by bacterial action., Functions of large intestine are 1. Absorption of water, minerals and certain drugs., 2. Secretion of mucus helps in adhering the waste particles together and lubricating for an unabsorbed, substances are known as faeces which are temporarily stored in rectum for defaecation through anal opening., ABORPTION OF DIGESTED FOOD COMPONENTS, Absorption of Monosaccharides and amino acids. The carbohydrates are mainly absorbed in form of, monosaccharides . Proteins are absorbed in form of simple amino acids Glucose and amino acids are absorbed, by simple diffusion passage of these substances into blood depends upon concentration gradients ., ABSORPTION OF PROTEINS : Proteins proteoses and peptones reach intestine and are acted upon by, proteolytic enzyme of pancreatic juice ., ABSORPTION OF WATER : Water absorption in large intestine occurs by osmosis from lumen of large intestine, through epithelial cells and blood capillaries in villi . Absorption of water from small intestine is associated with, absorption of electrolytes of digested food in order to maintain osmotic balance in the blood., ABSORPTION OF FATS : Fatty acid and glycerol are insoluble in water , which cannot be absorbed into the, blood directly . These are converted into small droplets called micelles with the help of bile salts and, phospholipids and move into intestinal mucosa . Formation of micelle takes place due to aggregation of water

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molecules which can be absorbed into intestinal cells by diffusion . They are resynthesised into protein coated, fat globules called chylomicron ., CALORIFIC FUEL VALUE : The amount of energy liberated during complete combustion of 1 gm. of a, calorimeter is the calorific fuel value ., EGESTION : The digestive waste are eliminate out of the body by the process of egestion . The peristaltic, movement gradually pushes the undigested materials from small intestine to large intestine and to anal area ., , **************************************************************