Question

Explain digestion from the mouth to the anus. What are the enzymes that carrying it ? What does the ph need to be for them to work ? The acids ?

Answer 1

• Digestion begins in the mouth or the buccal cavity during mastication of food.
• The saliva has an enzyme salivary amylase, which works at a pH of 6.8. It acts upon some of the carbohydrates present in the food to break it down and produce disaccharides.
• The food then moves to the stomach, where the pH is about 1.8 due to the presence of concentrated hydrochloric acid. The food mixes with HCl to form chyme.
• The pepsinogen in the stomach gets activated in the presence of HCl to become pepsin. This pepsin acts upon the proteins present in the chyme to produce proteoses and peptones.
• The partially digested food then moves to duodenum. Here, the bile juice and pancreatic juice are received and the intestinal juice, also called succus entericus is secreted.
• The pH in the intestine is about 7.8 due to the presence of bicarbonate ions.
• Bile juice emulsifies the fats and activates pancreatic lipase enzyme. Bile breaks the fat into micelles.
• The pancreatic juice contains trypsinogen, chymotrypsinogen, procarboxypeptidases, amylase, lipase and nuclease.
• The enzyme enterokinase secreted by intestinal mucosa activates trypsinogen to form trypsin. This in turn activates chymotrypsinogen and procarboxypeptidases into chymotrypsin and carboxypeptidase respectively.
• Trypsin, chymotrypsin and carboxypeptidase converts peptones, proteoses and proteins into dipeptides at a pH of 7.8.
• Pancreatic amylase acts upon the remaining carbohydrates to produce disaccharides, at pH 7.8
• The pancreatic lipase acts upon the fats to produce diglycerides and monoglycerides, at pH 7.8.
• Pancreatic nuclease acts upon the nucleic acids to produce nucleotides and nucleosides.
• The succus entericus contains lipase, dipeptidase, disaccharidase, nucleotidase, nucleosidase.
• Lipase breaks down diglycerides and monoglycerides into fatty acids and glycerol.
• Dipeptidase breaks down dipeptides into amino acids.
• Disaccharidase breaks down disaccharides into monosaccharides.
• Nucleotidase breaks down nucleotides into nucleosides.
• Nucleosidase breaks down nucleosides into nitrogenous base and pentose sugar.
• Later these simpler forms absorbed by the intestine.