(a) Life-threatening diarrhea is a shockingly common problemin the developing world. People with life-threatening diarrheaare often Na+-depleted, and to save their lives, replacing Na+ isessential. However, “raw” Na+ in the intestines is not absorbed.Drinking a solution of NaCl does not, therefore, replenish bodyNa+. In fact, drinking such a solution can actually worsen aperson’s situation by osmotically dehydrating the blood andother body fluids. Explain how drinking an NaCl solution couldhave this effect. (b) One of the greatest physiological discoveriesof the twentieth century was that drinking a solution of mixedglucose and NaCl can promote restoration of the body’s Na+. Withthe glucose concentration high enough in the solution, glucose“drives” the glucose–Na+ cotransporter in the apical membranesof intestinal epithelial cells, promoting Na+ uptake in sick people.Explain the concept behind this manipulation of the cotransporterfor therapeutic ends. The approach has saved millions of lives.
(a) Life-threatening diarrhea is a shockingly common problem
in the developing world. People with life-threatening diarrhea
are often Na+-depleted, and to save their lives, replacing Na+ is
essential. However, “raw” Na+ in the intestines is not absorbed.
Drinking a solution of NaCl does not, therefore, replenish body
Na+. In fact, drinking such a solution can actually worsen a
person’s situation by osmotically dehydrating the blood and
other body fluids. Explain how drinking an NaCl solution could
have this effect. (b) One of the greatest physiological discoveries
of the twentieth century was that drinking a solution of mixed
glucose and NaCl can promote restoration of the body’s Na+. With
the glucose concentration high enough in the solution, glucose
“drives” the glucose–Na+ cotransporter in the apical membranes
of intestinal epithelial cells, promoting Na+ uptake in sick people.
Explain the concept behind this manipulation of the cotransporter
for therapeutic ends. The approach has saved millions of lives.
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