Up to 90% of human cancers are
carcinomas,
growths that origi-
nate in epithelium. Most carcinomas begin on surfaces that contact
the external environment, such as skin, linings of the airways in the
respiratory tract, or linings of the stomach or intestines in the diges-
tive tract. This observation suggests that the more common cancer-
causing agents may not deeply penetrate tissues.
PRACTICE
After each major section, a question or series
of questions tests the student’s understanding
of the material. If he or she cannot answer these
practice question(s), the student will want to
reread that section.
Learn,
Practice,
Assess!
Interesting applications help
students practice and apply their knowledge.
..
Boxed Information
connects chapter ideas to clinical situations,
discusses changes in organ structure and function, and
introduces new medical technology or experiments.
From Science to Technology
previews the technological
applications of knowledge
in anatomy and physiology
that students are likely to
encounter in the future and
explains how and why the
technology was developed.
Clinical Applications
encourage students to
explore information
on related pathology,
historical insights,
and clinical examples
that they are likely
to encounter in
their careers.
Reconnect Icon
prompts the student to
review key concepts found in previous
chapters that will assist in their
understanding of new information.
5.1
FROM SCIENCE TO TECHNOLOGY
Nanotechnology meets the Blood-Brain Barrier
N
anotechnology is helping drug devel-
opers to circumvent a problem in
drug delivery based on an anatomical
impediment—the close at achments of the cel s
that form tiny blood vessels in the brain. Like a
tight line of police of icers keeping out a crowd,
they cannot breach the bar ier. But this protec-
tion has a trade-of —the brain cannot take up
many therapeutic drugs that must penetrate to
be e² ective.
³or decades researchers have at empted to
deliver drugs across the bar ier by tagging com-
Nanoparticles that can cross the blood-brain
bar ier are made of combinations of oils and poly-
mers, with a neutral or slightly negative charge
(positively charged particles are toxic). In one
application, anesthetics or chemotherapeutics
are loaded into fat y bubbles (liposomes) that are
in turn placed in nanoparticles. This delivery sys-
tem masks the part of the drug that cannot cross
the bar ier and slows release of the drug, which
diminishes side e² ects.
In another application, insulin is delivered
in inhaled nanoparticles 10 to 50 nanometers in
diameter. Original y developed to provide insu-
lin to people with diabetes instead of injecting
it, clinical trials are showing that it is also helpful
in maintaining memory in people who have mild
cognitive impairment or Alzheimer disease.
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RECONNECT
To Chapter 3, Movements Into and Out of the Cell,
page 90.
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