(a) Define digestion. [2 m] (b) Describe the digestion of a piece of ugali in a human digestive system from the mouth until its assimilation. [18mks]

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(a) Define digestion
  • It is break down of complex insoluble; v food substance into simple soluble food substances; v 2max
(b) Describe the digestion of ugali;
  • Digestion of ugali begins in the mouth;v ugali is chewed by the teeth to increase large surface areav for action of salivary amylase / ptyalin; vThe food mixes with saliva produced by salivary glands;v
  • Saliva contains mucus and enzyme ptyalin. Mucus moistens, softens and lubricates the food;v ptyalin speeds up the conversion of starch to maltose;v ugali is made into bolus in the mouth;v
  • The bolus moves along the oesophagus and prestalsis / by contraction and relaxation of circular and longitudinal muscles into the stomach;v
  • The digestion continues until ugali become acidic since the stomach does not contain carbohydrase / carbohydrate digesting enzymes no digestion of ugali takes place here.v
  • Ugali now moves into duodenum by peristalsis in form of acidic chyme;v where it mixes with the bile from the liver and pancreatic juice from the pancreases;v bile being alkaline neutralizes the stomach acid;v and provides a suitable alkaline medium for the enzymes to act on carbohydrates;v
  • Pancreatic juice contains three enzymes out of the which enzyme amylase speeds conversion of starch to maltose;v
  • When food reaches the ileum; it mixes with intestinal juice which contains several enzymes. Maltase speeds up conversion of maltose to glucose;v
  • Lactose which speeds up conversion of lactose to glucosev and galactose; sucrase which speeds up conversion of sucrose into fructose and glucose;
  • Absorption- glucose, the end product of all carbohydrates diffuses through the epithelium of villi and capillary walls and enters into blood stream and is carried to the liver via hepatic portal veins;v
  • Assimilation- in the liver excess glucose is converted into glycogen and stored;
  • The rest of the glucose is carried by the blood tissues where is oxidized during tissue respiration to release energy;v

18mks

Total 20mks

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