Absorption

Image

The inside of the small intestine is permeable and has a large surface area over which absorption can take place.

The lining of the small intestine contains two types of vessels that absorb the products of digestion:

• Capillaries absorb food and take it to the liver via the hepatic portal vein.

• Lacteals absorb mainly the products of fat digestion and empty them into the bloodstream.

A number of factors increase the surface area of the small intestine and so speed up the rate of absorption:

• The human small intestine is over five metres long.

• The inner lining is folded.

• The folds are covered with finger-like projections called villi.

• The villi are further covered by smaller projections called microvilli.

Other uses of digestive enzymes

Microorganisms also make digestive enzymes. Decay organisms such as certain bacteria and fungi release these enzymes onto the food and take up the soluble products. These organisms are called saprophytes (saprotrophs).

Scientists have used microorganisms such as these to supply enzymes for a number of uses:

• Biological washing powders contain proteases and lipases.

• Proteases are used to pre-digest protein in some baby foods.

• Amylases are used to convert starch into sugar syrup.

• Isomerase is used to convert glucose into fructose, which is sweeter.

Microorganisms are also used to try and improve the health of the digestive system. Probiotics contain live bacteria that may produce useful vitamins and neutralise toxins. Prebiotics contain food substances that are said to encourage the growth of the ‘good’ bacteria.