Jeremy, a seven year old African-American boy, is brought into his pediatricianÕs office by his mother. For the past few days Jeremy has been suffering from abdominal pain and diarrhea (which is often explosive) that begins approximately 2 - 5 hours after eating. These incidences seem to occur more rapidly and with a greater degree of severity after breakfast compared to other meals. JeremyÕs mother also notes that neither she nor her husband are exhibiting any of these symptoms while consuming the same foods as Jeremy. In talking with Jeremy, the pediatrician notes that the abdominal pain is associated with abdominal cramping and flatulence. Jeremy also states that he would occasionally feel Òsick to his stomachÓ prior to the onset of some of these episodes. When examining JeremyÕs medical record, his pediatrician notes that JeremyÕs height and weight were slightly less than normal for his age and that he had exhibited similar symptoms approximately 6 months ago. Jeremy is current on all of his immunization and has no previous history of illness.
Physical examination indicates that Jeremy was afebrile and normotensive. His respiratory rate was 12 breaths per minute and pulse was strong and regular at 73 beats per minute. Examination of the ear, nose, and throat proved to be uneventful. JeremyÕs reflexes were normal and within expected ranges. He did not present with any abdominal masses, splenomegaly or hepatomegaly. Additionally, there was no guarding when the internal organs were palpated. Clinical blood and urine screens were ordered and came back normal. The pediatrician asks JeremyÕs mother to describe their diet, specifically indicating how JeremyÕs diet may differ from either of the parents. With the exception of increased milk consumption by Jeremy, the diets are similar except in the quantity consumed by each individual.
JeremyÕs pediatrician suspects Jeremy may be lactose intolerant and collects a stool sample. The pH of the stool sample is in the acid range. Based on the results of the stool sample, a lactose tolerance test is conducted. (Both the pediatrician and JeremyÕs mother would prefer not to subject Jeremy to a small bowel biopsy.) Two tests are available, the breath test and a more traditional blood test. JeremyÕs pediatrician explains that if Jeremy were lacking lactase, the enzyme that breaks down lactose, the primary sugar in milk, administration of an oral dose of lactose would cause both the symptoms that Jeremy presents with as well as some other physiological changes. If Jeremy was lacking lactase the amount of hydrogen gas (H2) in JeremyÕs breath would increase. However, the pediatrician recommends a blood test that actually monitors the concentration of glucose in the blood following oral lactose. If Jeremy were lacking lactase, the rise in blood glucose following lactose administration would be less than normal. JeremyÕs mother agrees to the blood test and the results indicate that Jeremy is indeed lactose intolerant.
The pediatrician explains to Jeremy and his mother that the easiest way to treat the problem is to stop drinking and eating most milk and milk containing products. If Jeremy wants to continue to drink milk it would be best to purchase milk that has added lactase which predigests the lactose. Also, he could probably consume cheeses and yogurt, however, these may also cause some degree of bloating, discomfort and diarrhea. Finally, the pediatrician recommends calcium supplements to ensure that Jeremy is receiving adequate calcium for bone development.
1. Decribe the mechanical and biochemical processes of digestion. Indicate where each takes place.
2. Describe the normal enzymatic cycle catalyzed by lactase.
3. Identify the environmental factors that can influence enzyme activity and briefly discuss how enzyme activity is altered by these factors.
4. Why would blood glucose concentrations fail to rise following an oral dose of lactose in individuals with lactase deficiency?
5. Why would the inability to digest lactose cause diarrhea?
6. What is the cause of H2 gas in Jeremy's breath? (hint - lactose fermentation)
7.Bacteria in the colon are able to anaerobically metabolize lactose; how would this result in some of the symptoms Jeremy presents with?
8. Discuss why the pediatrician suggested specific treatments.
*adapted from McGraw Hill Online Learning Center, Essentials of Anatomy and Physiology,3rd ed.Seely/Stephens/Tate