HUMAN BIOLOGY

expLoreon your oWn

The rider and horse shown at the right are living examples

of the mammalian body’s ability to cool itself by producing

sweat. Since sweat is mostly water, how is heavy sweating likely to

affect the concentration of urine, especially if the athlete—in this case, a

polo player—doesn’t remember to drink fluid during the match? (You may

well have observed this effect in your own body after exercise.)

Drink 1 quart of water in 1 hour. What changes might you expect (and

can you observe) in your kidney function and the nature of your urine?

David Jennings/The Image Works

236 Chapter 12

at any given time in the United States, around 95,000

people who are desperately ill with kidney failure are waiting

to receive a donor kidney. For both the recipient and the

donor, all it takes is one healthy kidney for the urinary

system to function well. But as with all organ transplants, a

donated kidney can only go to a patient whose blood type

is compatible. according to the United network for organ

Sharing, this requirement—and the high demand—means

that it can take years for a patient to reach the top of the

list. many don’t make it in time.

maybe that’s what motivated tyler Weig, a healthy, 30-year-

old executive, to step up and become the first link in an

amazing chain of five paired-kidney exchanges. a paired

kidney exchange is a system of strangers helping strangers.

a recipient with a willing but incompatible donor—often

a relative or spouse—gets a compatible organ from a

stranger while the incompatible organ goes to a different

patient for which it is a good match.

In 2013 tyler donated the first kidney in a series of paired

organ exchanges that took place over three days at mercy

hospital in omaha, nebraska. In a sequence of ten carefully

Chain of Life

12.9

orchestrated operations, surgeons transplanted one of

tyler’s kidneys into a man whose first-choice donor—the

man’s wife—had an incompatible blood type. the wife,

in turn, donated a kidney to another, compatible recipient.

that recipient’s willing but incompatible donor provided a

kidney to yet another patient, and so on. In all, five people

who might otherwise have suffered for years waiting for a

donor match instead received

the gift of a healthy kidney and

a life free from the burden of

frequent dialysis.

paired kidney exchanges are

becoming more common,

sometimes helping more than

a dozen lucky recipients in a

matter of days.

FOCUS ON hUmaN impaCt

F i g u r e 12 .14 Donor kidneys

for transplant are usable for

several days as long as the

AJPhoto/Science Source organ is kept sterile and cool.

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