6.4 food digestion
TRANSCRIPT
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Food digestion
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• Food digestion occur in the alimentary canal.• Alimentary canal consist mouth, oesophagus,
stomach, small intestine (duodenum,jejunum,illeum), large intestine (appendix, caecum, colon, rectum) and anus.
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• Type of digestion : physical digestion (involve breaking up large pieces of food into smaller pieces with chewing and slicing) and chemical digestion (digestive enzyme break down complex molecules into simple soluble molecules) .
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Digestion in oral cavity
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• Digestive process start in mouth.• Foods were chewing and break into small
pieces to increase the surface area for digestive enzyme to act.
• Presence of food triggers saliva glands (digestive gland) to secrete saliva.
• Saliva contain salivary amylase to hydrolyse starch to maltose.
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• Chewed food rolled into mass called bolus and prepare for swallowing into oesophagus.
• Bolus enter oesophagus and move along with peristalsis movement.
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Digestion in stomach
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• A muscular sac with highly folded inner walls to increase the surface area of the stomach.
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• The epithelial lining of stomach contain gastric gland which secrete gastric juice (mucus, hydrochloric acid and enzymes).
• Food were churned and mix with gastric juice by peristalsis movement in the stomach.
• The foods were in state of semi fluid called chyme.
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Hydrochloric acid function
• Prepare optimum pH (acidic medium) for enzyme pepsin and rennin to react.
• Kills bacteria • Stop the action of salivary amylase.
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Function of enzymes in gastric juice
• Enzyme pepsin –to hydrolyse protein into peptone and polypeptide.
• Enzyme rennin – to catalyse the coversion of caseinogen (soluble protein in milk) to casein (insoluble milk protein).
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Digestion in small intestine
• Consist duodenum, jejunum and ileum.
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duodenum
• First part of small intestine and do not have digestive gland.
• It receives:- Bile secretion (produce by liver and released from gall bladder).- Pancreatic juice.
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Function of bile
• Break up large globules of fats into small fat droplets (emulsifies fats).
• Prepare alkaline medium.• Neutralise acid from stomach.
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Pancreatic juices
• Contain enzymes lipase, amylase and trypsin.• Lipase hydrolyse fats into glycerols and fatty
acids.• Amylase hydrolyse undigested starch into
maltose.• Trypsin hydrolyse peptone and polypeptide
into peptides.
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Ileum
• Walls of ileum contain many intestinal glands.• Secrete intestinal juice (enzyme erepsin,
sucrase, maltase, lactase and lipase).