2018 ESSAY QUESTION 8 DESCRIBE WHAT HAPPENS TO A MEAL RICH IN PROTEINS ALONG THE ALIMENTARY CANAL FROM INGESTION TO EGESTION. 20MARKS)

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  • The meal is ingested through the mouth;
  • (In the mouth) it is chewed (masticated by teeth); to reduce/ break it into smaller particles; mixed with saliva (from salivary glands);
  • The food is then rolled (by the tongue) into boluses; and pushed down/swallowed;
  • The boluses move by peristalsis (into the stomach);
  • Constant contraction and relaxation of the stomach walls mix food (giving rise to chyme);
  • Presence of food in the stomach further stimulates secretion of gastric juice; which contains pepsinogen; and rennin(chymosin);
  • Pepsinogen is activated to pespsin; by hydrochloric acid; (contained in the gastric juice).
  • Pepsin breaks down proteins to peptides;
  • Rennin converts/ coagulates the protein, (caseinogen); in milk to casein; (which is abundant in young children).
  • It is then pushed into the duodenum (through the pyloric sphincter);
  • Pancreatic juice on the duodenum contains trypsin; which digests proteins to peptides; (Trypsin is secreted in an inactive form trypsinogen).
  • 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; completing the process of digestion of proteins;
  • The amino acid molecules pass through the epithelium of the villi, and the capillary walls into the blood stream/ absorbed by active transport.
  • The undigested/ indigestible proteins/ food substances pass through the colon/ large intestines; where water is absorbed; leaving a semi-solid waste material being passed onto the rectum; then out through the anus (as faeces);
20 MARKS

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