HUMAN BIOLOGY

238 Chapter 12

On average, the wait time for a kidney

transplant can vary from a few months

to several years, during which time the

patient’s own kidneys are increasingly

likely to fail. About 4,000 people die each

year before they can be matched to a

willing donor.

Many factors are involved—for exam-

ple, self markers of potential donors and

recipients may not match closely, or perhaps someone who

has signed on to donate a kidney is no longer a good candi-

date for health-related or other reasons. Until recently, compil-

ing and sorting all the relevant biological and personal data

was a logistical nightmare. Now researchers at several universi-

ties have created donor registry computer software that can

quickly sift through all the information and generate a series of

options. All it takes is one ready-and-willing donor to start the

process. Then, the software can quickly crank out a plan that

matches that donor to the best potential recipient. Sometimes

the first match has a domino effect, freeing up another “ready”

kidney to go to another, more appropriate patient, and so on.

As more potential donors and recipients are added to the sys-

tem, the hope is that the waiting time for kidney transplants will

become much shorter and many more lives will be saved.

seLF-Quiz Answers in Appendix VI your Future

1. The body gains water by.
   a. absorption in the gut c. responding to thirst
   b. metabolism d. all of the above


2. The body loses water by way of the.
   a. skin d. urinary system
   b. lungs e. both c and d
   c. digestive system f. a through d


3. Water and small solutes enter nephrons during.
   a. filtration c. secretion
   b. reabsorption d. both a and b


4. Kidneys return water and small solutes to blood by.
   a. filtration c. secretion
   b. reabsorption d. both a and c


5. Some substances move out of the peritubular capillaries
   and are moved into the nephron during.
   a. filtration c. secretion
   b. reabsorption d. both a and c


6. Reabsorption depends on.
   a. osmosis across the nephron wall
   b. active transport of sodium across the nephron wall
   c. a steep solute concentration gradient
   d. all of the above


7. directly promotes water conservation.
   a. ADH c. Aldosterone
   b. Renin d. both b and c


8. enhances sodium reabsorption.
   a. ADH c. Aldosterone
   b. Renin d. both b and c


9. Changes in acid–base balance may cause the kidneys to
   .
   a. reabsorb and excrete bicarbonate
   b. form and release bicarbonate to the blood
   c. release ADH
   d. either a or b, depending on circumstances


10. Match the following salt–water balance concepts:
    aldosterone a. blood filter of a nephron
    nephron b. controls sodium reabsorption
    thirst mechanism c. occurs at nephron tubules
    reabsorption d. site of urine formation
    glomerulus e. controls water gain

CritiCaL tHinKing

1. A urinalysis reveals that the patient’s urine contains
   glucose, hemoglobin, and white blood cells (pus). Are
   any of these substances abnormal in urine? Explain.


2. As a person ages, nephron tubules lose some of their ability
   to concentrate urine. What is the effect of this change?
   3. Fatty tissue holds the kidneys in place. Extremely rapid
   weight loss may cause this tissue to shrink so that the
   kidneys slip from their normal position. On rare occasions,
   the slippage can put a kink in one or both ureters and block
   urine flow. Suggest what might then happen to the kidneys.
   4. Licorice is used as a remedy in Chinese traditional
   medicine and also is a flavoring for candy. When licorice
   is eaten, one of its components triggers the formation of a
   compound that mimics aldosterone and binds to receptors
   for it. Based on this information, explain why people who
   have high blood pressure are advised to avoid eating much
   licorice.
   5. Drinking too much water can be a bad thing. If someone
   sweats heavily and drinks lots of water, their sodium levels
   drop. The resulting “water intoxication” can be fatal. Why
   is the sodium balance so important?
   6. As the text noted, two-thirds of the water and solutes that
   the body reclaims by reabsorption in nephrons occurs
   in the proximal tubule. Proximal tubule cells have large
   numbers of mitochondria and demand a great deal of
   oxygen. Explain why.

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