Intestinal juice is a mixture of liquid secreted by Brunner's glands present in the submucosa of the duodenum and intestinal glands present in the mucosa of the entire small intestine and mucus secreted by the goblet cells of the intestinal mucosa. It is a clear, pale yellow to slightly alkaline (pH–7.5 to 8.00) liquid.
About 2 liters of intestinal juice is secreted in our intestine throughout the day. Most of it is water in which digestive enzymes, lysozyme, inorganic ions etc. are dissolved. By spreading its mucus on the intestinal mucous membrane, it protects the membrane from the side effects of digestive enzymes. If microbes are present in the chyme, the lysozyme of the intestinal juice destroys them.
It contains the following digestive enzymes to digest nutrients-
1. Erepsin: This is the collective name for a number of exopeptidase enzymes that carry out protein digestion. In these, aminopeptidase and carboxypeptidase break down polypeptides and tripeptides directly into amino acids. Other enzymes are dipeptidases which break down dipeptides into amino acids.
2. Carbohydrate-digestive enzymes i.e. Carbohydrases: In order to complete the digestion of carbohydrates, there are enzymes called maltase, sucrase (invertase), and lactase in the intestinal juice. These chyme break down maltose into glucose, sucrose into fructose and glucose, and lactose into galactose and glucose, i.e. monosaccharides, respectively.
3. Enterokinase: As mentioned above, this enzyme works to convert the trypsinogen of pancreatic juice into active trypsin after reaching the duodenum.
4. Intestinal Lipase: It breaks down the residual fat of chyme into monoglycerides and fatty acids.
5. Nucleases: They break down the nucleosides present in the chyme into their constituent nitrogenous bases and sugars.
2. Carbohydrate-digestive enzymes i.e. Carbohydrases: In order to complete the digestion of carbohydrates, there are enzymes called maltase, sucrase (invertase), and lactase in the intestinal juice. These chyme break down maltose into glucose, sucrose into fructose and glucose, and lactose into galactose and glucose, i.e. monosaccharides, respectively.
3. Enterokinase: As mentioned above, this enzyme works to convert the trypsinogen of pancreatic juice into active trypsin after reaching the duodenum.
4. Intestinal Lipase: It breaks down the residual fat of chyme into monoglycerides and fatty acids.
5. Nucleases: They break down the nucleosides present in the chyme into their constituent nitrogenous bases and sugars.
Most of the digestive enzymes of the intestinal juice are suspended in the plasma membrane of the microvilli of the cells of the mucosa. Hence they are called brush border enzymes.
try these - What is Bile? , Categories of Digestive Enzymes
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