The Digestive, Respiratory, and Urinary Systems
Some individuals do not produce sufficient amounts of the enzyme lactase to digest the sugar lactose, present in milk and dairy products, and are referred to as “lactose intolerant”. Lactose is a disaccharide, which must be broken down by lactase into its constituent monosaccharides, glucose and galactose, before it can be absorbed. If not broken down, it remains in the small intestines and is passed along into the large intestine, a place it does not belong, with waste materials. The results can range from dehydration and diarrhea to intestinal cramps and bloating. The pain and bloating often experienced by the lactose intolerant after lactose ingestion are caused by intestinal bacteria that metabolize the lactose to which they are normally not exposed. Products of this fermentation include organic acids and various gases. Some products are available to allow lactose intolerant individuals to eat lactose containing products, and are meant to be ingested just before eating milk or dairy products.
Which of the following is a reasonable explanation of the observation that lactose intolerant individuals become dehydrated after lactose consumption?
|A||The presence of lactose in the large intestine inhibits the pituitary gland from releasing the hormone ADH.|
|B||Large amounts of lactose in the large intestine increase the osmotic pressure, causing water to be retained there and eliminated with wastes, whereas it would normally be reabsorbed into the blood.|
|C||Because they cannot drink milk, lactose intolerant individuals are deprived of an important water source.|
|D||The presence of lactose in the large intestine causes more frequent urination.|
The normal function of the large intestine is to reabsorb water from the digestive system into the blood; the presence of large amounts of any chemical not usually present will inhibit this function, and allow more water than normal to be eliminated with the feces. This also contributes to diarrhea. None of the other choices make sense, and none are supported by the passage.