7.2) Alimentary canal

7.2) Alimentary canal


Ingestion: is the taking of substances such as food and drink into the body through the mouth.

Mechanical digestion: is the breakdown of food into smaller molecules without chemical change to the food molecules.

Chemical digestion: is the breakdown of large insoluble molecules into smaller soluble molecules.

Absorption: is the movement of digested food molecules and ions through the wall of the intestine into the blood.

Assimilation: is the movement of digested food molecules into cells of the body where they are used, becoming part of the cell.

Egestion: is the passing out of food that has not been digested or absorbed, as faeces, through the anus.


Diarrhoea: is the loss of watery faeces.

Treatment of diarrhoea is known as oral hydration therapy. This involves drinking plenty of fluids – sipping small amounts of water at a time to rehydrate the body.


Cholera: is a disease caused by the bacterium Vibrio cholera which causes acute diarrhoea.

When the Vibrio cholera bacteria are ingested, they multiply in the small intestine and invade its epithelial cells. As the bacteria become embedded, they release toxins which irritate the intestinal lining and lead to the secretion of large amounts of water and salts, including chloride ions. The salt decrease the osmotic potential of the gut contents, drawing more water from surrounding tissues and blood by osmosis. This makes the undigested food much more watery, leading to acute diarrhoea, and the loss of body fluids and salt leads to dehydration and kidney failure.