Starch, the role of salivary and pancreatic amylases and of maltase located in the intestinal epithelium; disaccharides, sucrase and lactase; Sucrose is a disaccharide formed by condensation of glucose and fructose. Lactose is a disaccharide formed by condensation of glucose and galactose. Lactose intolerance.

Starch is a polysaccharide, it is broken down by the body into monosaccharides, in two stages:

• Amylase (released from the salivary and pancreatic glands) breaks starch down into maltose,
• Maltase (found in the intestines) breaks maltose down into glucose.

Sucrose is a disaccharide, it is digested in to two monosaccharides:

• Sucrase breaks sucrose down into glucose and fructose.

Lactose is a disaccharide, it is digested in to two monosaccharides:

• Lactase breaks lactose down into glucose and galactose.

Some peoples bodies do not produce enough lactase, this means there will be undigested lactase in their digestive system (after eating a product containing this sugar, like milk.) This lactase is fermented by bacteria which produces methane. The symptom of this is painful wind and the name of this condition is lactose intolerance.

Having lactose in the intestine decreases the water potential, this causes water to move in by osmosis, diluting the faeces and giving diarrhoea to the sufferer.