16
624
Few medical
breakthroughs
have
been as electrifying as the discovery of
insulin
in 1921, an event that changed
diabetes mellitus
(DM) from a
death sentence
to a survivable disease.
Nonetheless, DM is still a huge health
problem: Determining blood glucose levels
accurately and maintaining desirable levels
sorely challenge our present biotechnology.
Let's take a closer look at the characteristics
and challenges of type 1 and type 2, the
major forms of diabetes mellitus.
More than 1 million Americans have
type 1 diabetes mellitus
, formerly
called
insulin-dependent diabetes mellitus
(
IDDM
). Symptoms appear suddenly,
usually before age 15, following a long
asymptomatic period during which the
immune system destroys the beta cells.
Consequently, type 1 diabetics effectively
lack insulin.
Type 1 diabetes susceptibility genes have
been localized on several chromosomes,
indicating that type 1 diabetes is an
example of a multigene autoimmune
response. However, some investigators
believe that
molecular mimicry
is at
least part of the problem: Some foreign
substance (for example, a virus) has entered
Sweet Revenge: Taming the Diabetes Monster?
impaired bladder function, and impotence.
Female type 1 diabetics also tend to have
lumpy breasts and to undergo premature
menopause, which increases their risk for
cardiac problems.
Hyperglycemia is the culprit behind
these complications, and the closer to
normal blood glucose levels are held, the
less likely complications are. Continuous
glucose monitors make this much easier
than relying on finger pricks, and a new
device called the e-Mosquito that uses
tiny and nearly painless needles is also
promising. Currently, frequent insulin
injections (up to four times daily, or better
yet, by a continuous infusion pump) are
recommended to reduce vascular and
renal complications. While some glucose
sensors can talk directly to insulin pumps,
problems with automatically calculating
the amount of insulin to dispense mean
that patients must still make these
decisions. Such combined devices still fall
short of being a true “artificial pancreas.”
A number of alternative insulin delivery
methods including insulin inhalers exist.
Pancreatic islet cell transplants
have become increasingly successful in
helping type 1 diabetics. Still, only 33%
A
C L O S E R
LOOK
the body and is so similar to certain self
(beta cell) proteins that the immune system
attacks the beta cells as well as the invader.
Sadly, once beta cells are destroyed, they're
gone for good.
The goal of several lines of current
research is to halt the destruction
of beta cells. While broad-spectrum
immunosuppressants have been used,
these have serious side effects and a
more targeted approach is necessary.
Several clinical trials using various peptides
and DNA vaccines are underway. A
complicating factor is choosing which
patients can be helped: These treatments
work only if some beta cells still exist.
Unfortunately in children, the main target
population, beta cell destruction is rapid
and virtually complete by the time of
diagnosis.
Type 1 diabetes is difficult to control
and patients typically develop long-
term vascular and neural problems. The
lipidemia and high blood cholesterol
levels typical of the disease can lead to
severe vascular complications including
atherosclerosis, strokes, heart attacks,
renal shutdown, gangrene, and blindness.
Nerve damage leads to loss of sensation,
Check Your Understanding
19.
In the elderly, the decline in levels of which hormone is
associated with muscle atrophy? With osteoporosis in women?
For answers, see Appendix H.
In this chapter, we have covered the general mechanisms of
hormone action and have provided an overview of the major
endocrine organs, their chief targets, and their most important
physiological effects, as summarized in
System Connections
on
p. 626. However, every one of the hormones discussed here
comes up in at least one other chapter, where its actions are
described as part of the functional framework of a particular
organ system. For example, we described the effects of PTH and
calcitonin on bone mineralization in Chapter 6 along with the
discussion of bone remodeling.
Chapter Summary
For more chapter study tools, go to the Study Area
of MasteringA&P at
www.masteringaandp.com
.
There you will find:
Interactive Physiology
A&PFlix
Practice Anatomy Lab
PhysioEx
Videos, Practice Quizzes and Tests, MP3 Tutor Sessions, Case
Studies, and much more!
1.
±e nervous and endocrine systems are the major controlling
systems of the body. ±e nervous system exerts rapid controls
via nerve impulses; the endocrine system exerts more prolonged
effects via hormones.
The Endocrine System: An Overview
(pp. 592–593)
1.
Hormonally regulated processes include reproduction; growth
and development; maintaining electrolyte, water, and nutrient
balance; regulating cellular metabolism and energy balance; and
mobilizing body defenses.
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