Small intestine , Absorption of digested food , Metabolism , Large intestine and defecation

From Online Sciences - November 25, 2017

Small intestine

It consists of duodenum and ileum , It is about 8 meters long , It is about 3.5 cm in diameter at its beginning to reach 1.25 cm at its end , The coils and loops of small intestine are connected together by a membranous structure called mesentery , The juices that help to digest food in the small intestine are bile juice , pancreatic juice & intestinal juice .

Bile juice

The liver secretes bile which passes through the bile duct to be stored in the gallbladder until needed , Bile juice is secreted from the liver on the food during its passage in the duodenum and it does not contain digestive enzymes , It emulsifies fats , dividing the large masses of fats into small globules to facilitate and accelerate the enzymatic action on fats that do not dissolve in water .

FatsEmulsified( Bile juice )

Pancreatic juice

It is secreted from the pancreas on the food in the duodenum , Pancreatic juice includes Sodium bicarbonate ,Pancreatic amylase ,Trypsinogen enzyme and Lipase enzyme .

Sodium bicarbonate neutralizes HCl and renders ( makes ) the medium alkaline ( pH = 8 ) , Pancreatic amylase catalyzes the hydrolysis of glycogen and starch into maltose .

Starch and glycogen + WaterMaltose ( Malt sugar ),( Pancreatic amylase , Alkaline medium )

Trypsinogen enzyme is an inactive enzyme , It becomes active trypsin in the duodenum by the enterokinase enzyme that is secreted by the intestinal glands in the lining of small intestine , Trypsin catalyzes the hydrolysis of protein into polypeptides .

Trypsinogen ( Inactive)Trypsin ( active ) ,( Enterokinase )

Protein + WaterPolypeptides ,( Trypsin , Alkaline medium )

Lipase enzyme catalyzes the hydrolysis of emulsified fats into fatty acids and glycerol .

Emulsified fats + Water Fatty acids + Glycerol , ( Lipase , alkaline medium )

Intestinal juice

It is secreted by certain cells in the wall of small intestine which contains a mixture of enzymes ,These enzymes complete the action of the previous enzymes and end the action of digestion of all food constituents , These enzymes are Peptidases , Maltase , Sucrase , Lactase & Enterokinase enzyme .

Peptidases are a number of enzymes , each one is concerned with the hydrolysis of peptide linkages between certain kinds of amino acids in the polypeptide chains to give various amino acids .

Polypeptide chain Amino acids ,( Peptidases , Alkaline medium )

Enzymes which hydrolyze the disaccharides into monosaccharides , these are :

Maltase hydrolyzes maltose ( malt sugar ) into two molecules of glucose .

Maltose Two molecules of glucose( Maltase , Alkaline medium )

Sucrase hydrolyzes sucrose ( cane sugar ) into glucose and fructose ( fruit sugar ) .

SucraseGlucose + Fructose( Sucrase , Alkaline medium )

Lactase hydrolyzes lactose ( milk sugar ) into glucose and galactose .

Absorption of digested food

Structure of the villus

Routes of absorption of the digested food substances by the villi

Blood route

Lymphatic route


Large intestine and defecation


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