Hole's Human Anatomy and Physiology   8/e   Shier/Butler/Lewis
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Chapter 4: Cellular Metabolism


Case Studies

Lactose Intolerance

Case Presentation

Pei, a twenty-six year old Asian graduate student in computer science, had been experiencing occasional discomfort after meals. The discomfort reached a new peak last Thursday evening about an hour after eating a cheeseburger and a large chocolate milk shake. Pei spent much of that night in pain. She had abdominal cramps and diarrhea and also felt sick to her stomach. Pei went to the clinic and saw a doctor the next day.

The doctor asked Pei a number of questions and noted that Pei's discomfort seemed to be associated with dining out. Pei told the doctor that on most evenings she cooked for herself, usually preparing traditional Asian cuisine, and that she seldom experienced any discomfort after eating at home. Pei only experienced discomfort after dining out, especially, it seemed, after eating her favorite fast food meal, a double cheese burger and a chocolate shake. When asked if she used very much milk or cheese when preparing meals at home, Pei told the doctor that she almost never cooked with any dairy product.

The doctor suspected that Pei could be lactose intolerant and told Pei that she would like to have a test performed to verify her suspicion. Pei was able to be tested on that day because she had not had anything to eat or drink for two hours. At the clinic lab, Pei was given a lactose rich fluid to drink and had her blood glucose level measured several times over the course of two hours. Later, her doctor informed Pei that her blood glucose level had not risen after drinking the lactose rich fluid and that that was evidence that she was lactose intolerant. The doctor provided Pei with information about lactose intolerance and discussed with her how she could best alter her diet in order to avoid any discomfort while still obtaining sufficient calcium. The doctor also told Pei about various products that contain lactase, the enzyme responsible for lactose digestion, and assured her that if she used one of those products, she could probably still have the occasional cheeseburger and chocolate milk shake.

Case Background

Lactose intolerance is the inability to digest significant amounts of lactose. Some individuals are born lactose intolerant. These individuals lack the ability to produce lactase from birth. Most individuals that are lactose intolerant, however, become so gradually as lactase production decreases over time.

There is no cure for lactose intolerance, but treatment is fairly simple. Affected individuals are instructed to avoid as much lactose as required in order to avoid discomfort. Different individuals have different levels of intolerance and each affected person needs to determine through trial and error how much lactose he or she can tolerate. In addition to dietary control of lactose intolerance, individuals can also use products that contain lactase.

Questions

  1. In as complete a manner as possible, describe what type of molecule lactose is and list its subunits?


    Answer

  2. Describe what type of molecule lactase is and explain its function in the body.


    Answer

  3. Define the following terms.
    1. Substrate
    2. Active site


    Answer

  4. What component of enzyme structure is responsible for enzyme specificity?

    Answer

  5. How did the lactose intolerance test that Pei took provide evidence that she was lactose intolerant?

    Answer

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