543
CHAPTER FOURTEEN
Blood
Leeches have been used since the time of the ancient Egyptians to
break up blood clots. The saliva of the medicinal leech
Hirudo medici-
nalis
contains a potent and long-acting anticoagulant, hirudin. Most
people do not like three-inch long, slimy green-gray invertebrates
dining on a wound, so a biotech company developed a drug based
on the leech protein. However, the drug was
too
long acting—it
caused bleeding problems, could not be easily monitored, and could
damage the kidneys. Synthetic anticoagulants have taken its place.
and it is rapidly fatal. Symptoms include chest
pain, anxiety, racing pulse, sweating, cough with
bloody sputum, and loss of consciousness.
Bloom had several risk factors for DVT:
prolonged periods of immobility in the Bloom-
mobile and on F
ights; dehydration; and an inher-
ited clotting disorder that he had not known
about called factor V Leiden. Other risk factors
for DVT are prolonged immobility due to surgery;
oral contraceptive use; hormone replacement
therapy (estrogen); surgery (of the abdomen, pel-
O
n April 2, 2003, NBC news correspondent
David Bloom, traveling with the United
States infantry near Baghdad, mentioned
on the phone to his wife Melanie that he felt cramps
behind his knees. He also reported the symptom
to physicians in the United States, who advised
that he seek immediate medical attention. But he
didn’t. Instead, Bloom continued his reporting from
the “Bloom-mobile,” a tank turned into a traveling,
cramped newsroom. Three days later, as the mili-
tary unit prepared to leave for the ±
nal approach to
Baghdad, Bloom suddenly collapsed and died.
David Bloom died from a pulmonary embo-
lism, the result of a condition called deep vein
thrombosis (DVT). In the United States, approxi-
mately 2 million people a year develop DVT, and
200,000 die from pulmonary embolism.
In DVT, prolonged immobility causes blood
to pool, leading to clot formation, typically in the
femoral or popliteal veins or in the deep veins of
the pelvis. Symptoms occur in half of all a²
ected
individuals. These include deep muscle pain, red-
ness, swelling, and possibly discoloration and
dilation of surface veins (phlebitis). Part of the
clot may break off hours or days after it forms
and follow the path of circulation, lodging in the
pulmonary arteries. This is pulmonary embolism,
vis, or limbs); and cancer (of the ovaries, pancreas,
colon, liver, stomach, or lymphoma). Measures
to prevent DVT include taking anti-coagulants if
immobilization is expected; wearing compression
stockings that keep blood F
owing in the legs; and
doing exercises while immobilized during travel.
Some airlines advise passengers on how to exer-
cise on cramped flights, such as by curling the
toes up and down (±
gure 14C). DVT is sometimes
called “traveler’s thrombosis” and “economy-class
syndrome” for good reason.
14.3
CLINICAL APPLICATION
Deep Vein Thrombosis
Heparin-secreting cells are particularly abundant in the
liver and lungs, where capillaries trap small blood clots that
commonly form in the slow-moving blood of veins. These
cells continually secrete heparin, preventing additional clot-
ting in the cardiovascular system.
Table 14.10
summarizes
clot-inhibiting factors.
PRACTICE
46
How does the lining of a blood vessel help prevent blood clot
formation?
47
What is the function of antithrombin?
48
How does heparin help prevent blood clot formation?
TABLE
14.10
|
Factors That Inhibit Blood Clot Formation
Factor
Action
Factor
Action
Smooth lining of blood vessel
Prevents activation of intrinsic blood
clotting mechanism
Antithrombin in plasma
Interferes with the action of thrombin
Prostacyclin
Inhibits adherence of platelets to blood
vessel wall
Heparin from mast cells and
basophils
Interferes with the formation of prothrombin
activator
³ibrin threads
Adsorbs thrombin
FIGURE 14C
Exercising the toes and ankles on a long F
ight can lower the risk of deep vein
thrombosis.
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