Mini Case
16. Marc, a first-year college student, starts out on a
backpacking trip in southern New Mexico. It is September,
so the daytime temperatures are quite high, and the
desert air is very dry. He has a portable water filter to treat
river and stream water that he finds on his planned route
through the Gila wilderness. On the second day of his
week-long trip, Marc's water filter breaks. He is afraid of
contracting giardiasis (a protozoal disease spread through
water contaminated by animal feces), so he drinks only the
small amount of water that he can boil on his camp stove
at night. By the fifth night, Marc is feeling weak and thirsty,
and starts to hike out. He makes it to a local highway
and collapses. A passing motorist calls 911 for an
ambulance.
Apply Your Knowledge
a. Given that Marc has sweated a lot, and that sweating
causes the loss of more water than solutes, what has
happened to the solute concentration of Marc's blood
as a result of his dehydration?
b. From the solute concentration of Marc's blood, what
is likely to be happening to his body cells that are in
contact with his blood and related fluids (e.g., lymph
and cerebral spinal fluid)?
c. The paramedics have three saline solutions available.
The first is a "normal" isotonic saline solution (0.9%
NaCl), the second is a hypertonic saline solution
(3% NaCl), and the third is a "half normal" saline
solution (0.45% NaCl). Which one would you use to
treat Marc? Why?