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6.NUTRITIONDIGESTION OF CARBOHYDRATES,

PROTEINS & LIPIDS

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DIGESTION IN THE MOUTH

Presence of food triggers the secretion of saliva by the three pairs of salivary glands.

Saliva contains the enzyme salivary amylase which

hydrolyse starch to maltose

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The thoroughly chewed food is rolled bytongue into a mass called bolus.

Bolus enters oesophagus & move along itby the aid of peristalsi. Oesophagus squeezes bolus down

oesophagus until it enters the stomach

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Pepsin hydrolyse large protein molecules into

smaller chain of polypeptides

Rennin Coagulates milk by converting the soluble

milk protein caseinogen in insoluble casein

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Food stays in the stomach in hours,churned & mixed with gastric juice

It eventually become a semi-fluid calledchyme. Chyme then gradually allowed to enter the

duodenum

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DIGESTION IN THE SMALL

INTESTINE Small intestine consist of duodenum, jejunum & the highly coiled ileum.

DUODENUM receive chyme from the stomach & secretion by the gall bladder (bile) &

pancreas (pancreatic juice)

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Bile

Is an alkaline greenish-yellow liquid Produce by liver Stored in gall bladder Doesnt contain any digestive enzymes But helps neutralise acidic chyme &

optimises duodenum pH for enzymeaction.

Emulsify lipids & break them into tinydroplets

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Pancreatic juices Contain enzymes: pancreatic amylase,

trypsin & lipasePancreatic amylase Completes the digestion of starch to

maltoseTrypsin digest polypeptides into shorter peptideLipase Complete digestion of lipid into fatty acids

& glycerol

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DIGESTION IN THE SMALL

INTESTINEILEUM Glands in the walls of the ileum secretes

intestinal juices Intestinal juices contain digestive enzymes Erepsin

Maltase, sucrase & lactase which needed to complete the digestion of peptides & disaccharides

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Erepsin

Digest peptides from the duodenum intoamino acidspeptides + erepsin > amino acids

Maltase, Sucrase & Lactase Digest disaccharides into itsmonosaccharides Maltose + maltase > glucose Sucrose + sucrase > glucose + fructose Lactose + lactase > glucose + galactase

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AT THE END OF DIGESTIVE PROCESS:

All carbohydrates are digested intomonosaccharides of glucose, fructose &galactose

Proteins are digested into amino acids Lipids digested into fatty acids & glycerol. All these are small enough to be absorbedby the lining of the small intestine

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