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Digestion and Absorption — BIOLOGY STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceBIOLOGYDigestion and Absorption5 Marks
Question
What are the various enzymatic types of glandular secretions in our gut helping digestion of food? What is the nature of end products obtained after complete digestion of food?
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Answer

In the buccal cavity, saliva secreted by the salivary glands contains salivary amylase that acts as follows: $\text{Starch}\xrightarrow[\text{pH6.8}]{\text{Salivary amylase}}\text{Maltose}$ Gastric juice of the stomach contains proenzyme pepsinogen, which on exposure to hydrochloric acid gets converted into active enzyme, pepsin. Pepsin is a proteolytic enzyme that converts proteins into proteoses and peptones. Rennin is a proteolytic enzyme found in the gastric juice of infants which helps in the digestion of milk proteins. Small amounts of lipases are also secreted by gastric glands.$\text{Pepsinogen}\xrightarrow{\text{HCL}}\text{Pepsin}$
$\text{Proteins}\xrightarrow{\text{Pepsin}}\text{Proteases + Peptones}$
$\text{Casein}\xrightarrow{\text{Rennin}}\text{Paracasein}$
Bile, pancreatic juice and intestinal juice (succus erttericus) are the secretions released into the small intestine. Pancreatic juice and bile are released through hepato-pancreatic duct into duodenum. Pancreas secretes pancreatic juice that contains inactive enzymes like trypsinogen, chymotrypsinogen, procarboxypeptidases and enzymes like amylases, lipases and nuclease. An enzyme, enterokinase, secreted by the intestinal mucosa converts trypsinogen into active trypsin, which in turn activates the other enzymes in the pancreatic juice. The food reaching the small intestine is acted upon by the enzymes of pancreatic juice as follows: $\begin{matrix} \text{Proteins}\\\text{Peptones} \\ \text{Proteoses} \end{matrix}\Bigg]\xrightarrow[\text{Carboxypeptidase}]{\text{Typsin / Chymotrypsin}}\text{dipeptides}$ $\text{Polysaccharides}\xrightarrow{\text{Amylase}}\text{Disaccharides}\\ \ \ \ \ {\text{(starch)}} \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ {\text{(maltose)}}$ $\text{Fat}\xrightarrow{\text{Lipase}}\text{Diglycerides}\rightarrow\text{Monoglycerides}$ $\text{Nucleric acid}\xrightarrow{\text{Nucleases}}\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ {\text{Nucleotides}}\rightarrow\text{Nucleosides}$ Bile secreted by liver does not contain any enzyme. It only helps in emulsification of fats and activation of lipases. In the duodenum of the small intestine, the enzymes of the succus entericus act on the end products of the above reactions to form the respective simple absorbable form. $\text{Dipeptides}\xrightarrow{\text{Dipeptidases}}\text{Amino acids}$ $\text{Maltose}\xrightarrow{\text{Maltase}}\text{Glucose + Glucose}$ $\text{Lactose}\xrightarrow{\text{Lactose}}\text{Glucose + Galactose}$ $\text{Sucrose}\xrightarrow{\text{Sucrase}}\text{Glucose + Fructose}$ $\text{Nucleotides}\xrightarrow{\text{Nucleotidases}}\text{Nucleosides}\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \xrightarrow{\text{Nucleotidases}}\text{Sugars + Bases}$ $\text{Diglycerides + Monoglycerides}\xrightarrow{\text{Lipases}}\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ {\text{Fatty acids + Glycerol}}$ The end products of the carbohydrate digestion are glucose, protein digestion are amino acids, fat digestion are fatty acids and glycerol and nucleic acid digestion are sugars and bases.

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