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As
you have learned, Williams Syndrome is a rare disorder (1
in 25,000 births) characterized by physical and developmental
problems. Scientists have tracked this disorder to a mutation
on chromosome 7. People with Williams Syndrome are missing
a small segment of this chromosome.
Most people with Williams Syndrome also lack the gene responsible
for the manufacture of elastin. This gene maps to the same
missing area of chromosome 7.
Elastin
is a protein that allows the tissues within our blood vessels,
skin and heart to stretch. Without this elastic property,
the function of the tissues is compromised.
In
addition to having a compromised elastin level, most people
with Williams Syndrome experience the narrowing of blood
vessels. Both the lack of tissue resiliency and the narrow
diameter of the vessels produce hypertension (high blood
pressure). Narrowed vessels within the heart and lung further
exacerbate the condition and may require surgical correction.
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OBJECTIVE
This
activity page will offer:
-
An insight into elastin and its association with Williams Syndrome
- An
experience in taking blood pressures
- An
observation of how vessel diameter affects pressure
Blood
Pressure Connection
People with Williams Syndrome must have their blood pressure monitored
periodically. In a doctor's office, this procedure is most often
performed with a cuff, stethoscope and mercury-filled manometer.
At home, it can be done using an automatic blood pressure monitor.
The
automatic device will measure blood pressure and display it as
two numbers--e.g., 110/80. The first number is the systolic pressure
(110). The systolic pressure is the force of the maximum surge.
The second number (80) is the diastolic pressure. This is the
"resting pressure" or baseline from which the systolic arises.
PROCEDURE
Part
1-Measuring Blood Pressure
Materials
- Blood
pressure monitor (automatic cuff)
Steps
- Work
with a partner. Before obtaining a pressure, deflate the cuff.
You can release air from the cuff by pressing the release valve
on the bladder.
- Position
the cuff around the upper arm. Secure it with the Velcro strap.
- Inflate
the cuff with a series of quick pumps. The pressure should go
up to about 150. Stop pumping.
- The
air will automatically seep from the cuff. As the air escapes,
the device will begin monitoring the blood vessel, recording
both the systolic and diastolic pressures.
- As
the cuff deflates, the systolic pressure will be the first reading
recorded and displayed.
- The
next reading is the diastolic pressure.
- Obtain
three measurements for the right arm.
- Record
your blood pressure. Do you have high blood pressure?* In adults,
hypertension is diagnosed as a blood pressure of 140/90. In
kids (who have more resilient and less obstructed vessels),
hypertension is diagnosed at lower blood pressures. Hypertension
is also influenced by other factors such as exercise, diet and
lifestyle.
*If you have high blood pressure, see the school nurse to find
out what you can do about it.
QUESTIONS
-
Why is it important for people with Williams Syndrome to have
their blood pressure monitored periodically?
- What
do the two numbers of a blood pressure mean?
PROCEDURE
Part
2 - Compromised Diameter
Materials
- Drinking
straw (new)
- Paper
(clean sheet)
- Tape
Steps
- Roll
a sheet of clean paper into a tube. The tube should have a diameter
of about 1 inch (about 2.5 cm).
- Blow
through the tube as hard as you can. Note any resistance or
difficulty in blowing air through the tube.
- Remove
the straw from its wrapping. Blow through the straw as hard
as you can. Note any resistance or difficulty forcing air through
the straw.
QUESTIONS
- Through
which of the two tubes did you blow the hardest?
- Why
was it easier to blow air through the larger diameter tube?
- If
we were to apply this experience to Williams Syndrome, what
would the straw and paper tube represent?
Applying
What You Have Observed
How might a decreased diameter affect the health of a blood vessel?
To compensate for the restriction, the heart must pump harder
to move blood at the same rate through the vessels. This harder
pumping action raises blood pressure. At a high enough pressure,
the blood vessels may rupture and cause a stroke.
EXTENSIONS
Resilient Pump
The
heart and other circulatory structures contain elastin. Elastin
allows a structure to stretch, then return to its "resting" length.
If muscle cells can only actively contract, what is the relationship
between elastin and the pumping action of the heart tissue?
With
your instructor's permission, examine the bladder of a blood pressure
monitor. If possible, detach the bladder from its connecting tube.
Observe the function of the one-way valve. How does this valve
control the flow of air? How is the bladder similar to a heart?
How is it different? Although the bladder does not contain elastin,
it behaves as if it does. Explain.
Aging
and Elastin
Elastin is manufactured primarily when we are young. The older
we get, the less elastin is produced. Think about it. What is
the connection between this protein and the appearance of wrinkles?
How might research breakthroughs affect the appearance of skin
as we age?
The
Old Fashioned Way
Learn how to take blood pressures using a manual cuff and stethoscope
here.
(www.madsci.org/experiments/archive/859422898.Bi.html)
Web
Connection
Overview
of Williams Syndrome and its symptoms
http://www.williams-syndrome.org/facts.htm
Informational
site for parents, family members and others posted by the Williams
Syndrome Foundation
http://www.wsf.org/
A
site that describes elastin and its role in the body
http://www.wsf.org/MEDICAL/layreader/elastin.htm
The
activities in this guide were contributed by Michael DiSpezio,
a Massachusetts-based science writer and author of "Critical Thinking
Puzzles" and "Awesome Experiments in Light & Sound" (Sterling
Publishing Co., NY).
Academic Advisors for this Guide:
Corrine Lowen, Science Department, Wayland Public Schools, Wayland,
MA
Suzanne Panico, Science Teacher Mentor, Cambridge Public Schools,
Cambridge, MA
Anne E. Jones, Science Department, Wayland Middle School, Wayland,
MA
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