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Describe the digestion of proteins and carbohydrates along the human gut

  • The meal is ingested into the mouth. It is then chewed/masticated by teeth; into smaller particles; and then mixed with saliva from the salivary gland; Saliva contains water, mucus and salivary amylase/ptyalin. Salivary amylase catalyses the breakdown of starch into maltose; the food is then rolled by the tongue into boluses, and then swallowed; The boluses move by peristalsis down the oesophagus into the stomach; Constant contractions and relaxations of the stomach walls mix the food to form chyme; The presence of food in the stomach further stimulates the production of gastric juice; which contain hydrochloric acid, pepsinogen, and rennin; Digestion of starch stops in the stomach due to presence of hydrochloric acid that denatures salivary amylase/ptyalin;
  • Pepsinogen is activated to pepsin; by hydrochloric acid. Pepsin catalyze the breakdown of proteins into peptides; Rennin coagulates caseinogen (soluble milk protein) into casein (insoluble); it is then pushed into the duodenum through the pyloric sphincter; In the duodenum, bile juice and pancreatic juice are secreted.  The pancreatic juice contains trypsinogen (the inactive form of trypsin); which digests the remaining proteins into peptides; Also contains pancreatic amylase; that digests the remaining starch to maltose;
  • In the ileum, intestinal juice/succus entericus is secreted; it contains peptidase enzymes; which break down peptides into amino acids; it also contains polypeptidase enzyme; which breaks down polypeptides to amino acids; Also contains maltase that digests maltose to glucose; lactase that digests lactose to glucose and galactose; sucrase that digests sucrose to glucose and fructose;   completing the process of digestion of proteins and carbohydrates;
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