ossi...
Did you hear the one about the phlebotomist whose work was all in
vein?
Okay, in case you don't get that...a phlebotomist is someone who draws
blood for a living. Now the reason they draw blood from your vein is
because veins and arteries are structured differently, as we'll see.
Both have the same basic structure, which consists of three layers.
The anatomy department at Berkeley High School has a page which
describes these layers in some detail:
"The walls of both veins and arteries are made up of three distinct
layers:
1. The innermost layer is the tunica interna (or tunica intima)
which includes the endothelial lining of the vessel and the
underlying layer of connective tissue which contains mostly
elastic fibers.
2. The middle layer, tunica media (lucky you, no extra name for
you to memorize here) contains concentric sheets of smooth muscle
tissue held in a framework of elastic and collagen fibers.
3. The last surrounding layer of the vessel, tunica externa (or
tunica adventitia) forms a connective tissue lining. The fibers
of this layer combine with the fibers of surrounding tissues to
anchor itself and remain stable."
http://www.bhs.berkeley.k12.ca.us/departments/Science/anatomy/anatomy97/heart/html/heart&vessels/vesselstructure.html
The same page also notes that the arteries themselves are so thick
that they do now allow for blood flow into their own tissues, so
there are smaller vessels called vasa vasorum which feed the tissues
of the arteries themselves. So blood vessels have blood vessels!
Also noted is the fact that capillaries, the smallest of the blood
vessels, are not much bigger than 8 micrometers in size - about the
diameter of a single red blood cell.
The flow of blood is documented on another page from the same site.
Blood flows from the heart into the arterial trunks, and from there
into progressively smaller arteries down to the smallest ones, which
are called arterioles. They then progress into arterial capillaries
which feed the bodily tissues. From there, the blood moves into
progressively larger veins, which take blood back to the heart:
venous capillaries, venules, veins and finally, the pulmonary veins.
http://www.bhs.berkeley.k12.ca.us/departments/Science/anatomy/anatomy97/heart/html/heart&vessels/vesselflow.html
The size of the arterial trunks which begin the journey are about
25mm, and the size diminishes progressively down to the arterioles
at .3mm or 300 micrometers, and then to the capillaries at only 8
micrometers. This page from the University of California at Berkeley
has some good details:
http://mcb.berkeley.edu/courses/mcb135e/arteries.html
The process of shrinking reverses itself after the tissues have
been fed, beginning with venous capillaries and ending with the
pulmonary veins which connect to the heart:
"The diameter of the the superior vena cava varies from 18 to 22mm,
and the inferior vena cava is larger and varies between 27 to 36 mm
at their junction with the right atrium."
From this page about the heart from Virtual Hospital:
http://www.vh.org/adult/provider/anatomy/AnatomicVariants/Cardiovascular/Text/Arteries/Heart.html
Finally, this page from Springfield Technical Community College's
website has an excellent description of how the structure of
arteries and veins differ in regard to strength and elasticity,
and how their composition varies with the changes in size as they
become progressively smaller, losing the two outermost layers,
and then becoming progressively larger again. There is more
information, and some illustrations, on the page:
http://www.stcc.mass.edu/distance/AandP/AP/AP2pages/vessels/arteries.htm
Which brings us back to the point I made earlier, since, in that
page, it is noted that blood is drawn from veins rather than arteries.
This is due to the following facts from that page:
quote
1. Veins, with their thinner walls and larger diameters are easier
to stick with a needle and to extract blood from.
2. The thinner the vessel, the less the innervation, so the less
painful to stick with a needle.
3. Veins have blood under less pressure within them, so when you
stick a vein with a needle, blood will not typically seep out
much through your injection site.
4. Veins "store" blood, so much more blood is readily available
in your veins.
unquote
You may also find more links, in addition to the ones I referenced,
amidst the search results provided below.
Please do not rate this answer until you are satisfied that
the answer cannot be improved upon by means of a dialog
established through the "Request for Clarification" process.
sublime1-ga
Searches done, via Google:
properties human arteries veins elasticity thickness sizes
://www.google.com/search?q=properties+human+arteries+veins+elasticity+thickness+sizes
arteries veins differences
://www.google.com/search?q=arteries+veins+differences
diameter arteries
://www.google.com/search?q=diameter+arteries
diameter "arterial trunks
://www.google.com/search?q=diameter+%22arterial+trunks
"diameter of the superior vena cava
://www.google.com/search?q=%22diameter+of+the+superior+vena+cava |
Clarification of Answer by
sublime1-ga
on
01 Nov 2003 13:16 PST
ossi...
Sorry...I interpreted "modul of elasticity", in your original
question, to mean 'model' of elasticity.
The 'modulus of elasticity' or 'Young's modulus' is another story,
and the math is rather complex.
This page, from Wayne State University, in Michigan, notes that
blood vessels are composed of differing amounts of collagen and
elastin, depending on their function:
"The major components of vessel walls are:
Smooth muscle cells
Elastin
Collagen
The proportion of each material depends on the type of vessel
Ratio of collagen to elastin
Elastic arteries - 1:2
Distribution arteries - 2:1
Veins - 3:1"
http://ttb.eng.wayne.edu/~grimm/BME5370/Lect7Out.html#BloodVessels
From the same page:
"The behavior of elastin dominates at low stresses and strains,
while at higher levels of deformation the collagen dominates and
vessels become much stiffer (See Figure 10)"
http://ttb.eng.wayne.edu/~grimm/BME5370/Lect7Out.html#BVMechProps
And, under 'Mechanical Properties of Blood Vessels':
"Elastic and viscoelastic properties of arteries vary along the
length of the arterial tree (See Figure 8)
Composition and structural arrangement of fibres in walls also
changes along arterial tree"
http://ttb.eng.wayne.edu/~grimm/BME5370/Lect7Out.html#BVMechProps
Figure 8 provides a graphic representation of how the values for
the stress/strain curves vary with location on the arterial tree:
http://ttb.eng.wayne.edu/~grimm/ME518/L7F8.html
A graph from a lesson in biomechanics at the University of
Michigan illustrates the relative effects of collagen and elastin
on the stress curve for a human vena cava:
"Roach and Burton in 1957 digested collagen out of blood vessels
using trypsin, and digested elastin from blood vessels using
formic acid. They found that collagen contributed mainly to the
linear region of the nonlinear stress-strain curve while elastin
contributed mainly to the toe part of the stress-strain curve.
We can see this in stress strain curve from a human vena cava
below:"
See the illustration, and more of interest, on the page:
http://www.engin.umich.edu/class/bme456/bloodves/bloodves.htm
An article, 'Zero-stress states of human pulmonary arteries
and veins', by W. Huang and R. T. Yen, on the Journal of
Applied Physiology site, discusses the values for Young's
modulus (E) for arteries and veins:
"The residual stress is obtained by the multiplication of the
residual strains by Young's modulus E. Greenfield and Griggs
(9) gave E of human pulmonary artery as 2.6 × 10^6 dyn/cm^2.
For pulmonary veins, E is not available. If we assume that
the same E applied to both pulmonary arteries and veins, then
the estimated residual stresses for pulmonary arteries and
veins are presented in Table 4. [Link to Table 4]:
http://jap.physiology.org/cgi/content-nw/full/85/3/867/T4
For all orders of pulmonary arteries and veins, the inner wall
of the vessel is under compression, whereas the outer wall is
in tension. In general, the magnitude of compressive stress was
greater than the magnitude of tensile stress. For the arteries,
the compression lies between 0.341 × 10^6 and 0.876 × 10^6
dyn/cm^2, and the tension lies between 0.216 × 10^6 and
0.401 × 10^6 dyn/cm^2. For the veins, the compression is between
0.402 × 10^6 and 0.824 × 10^6 dyn/cm^2, and the tension is between
0.087 × 10^6 and 0.404 × 10^6 dyn/cm^2."
Much more on the page:
http://jap.physiology.org/cgi/content/full/85/3/867
Hooke's Law is also mentioned on the page above, and is
important to an understanding of the deformation of the
blood vessels under pressure:
http://www.coheadquarters.com/PennLibr/MyPhysiology/lect8/figbp03.htm
The above page is from a quick study index on the
CO Headquarters site:
http://www.coheadquarters.com/PennLibr/MyPhysiology/lect8/quick2.htm
You may also find this article from PubMed Central, on
'The degree of nonlinearity and anisotropy of blood vessel
elasticity', by J. Zhou and Y. C. Fung to be of interest:
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=24929
You may also find other useful material by exploring the
links provided below for the Google searches I made.
Please keep in mind the Google Answers pricing guidelines
when rating this answer:
http://answers.google.com/answers/pricing.html
sublime1-ga
Searches done, via Google:
"modulus of elasticity" "blood vessels"
://www.google.com/search?q=%22modulus+of+elasticity%22+%22blood+vessels%22
"modulus of elasticity" "veins"
://www.google.com/search?q=%22modulus+of+elasticity%22+%22veins%22
"modulus of elasticity" "arteries"
://www.google.com/search?q=%22modulus+of+elasticity%22+%22arteries%22
"Young's modulus"
://www.google.com/search?q=%22Young%27s+modulus%22
"Young's modulus" "blood vessels"
://www.google.com/search?q=%22Young%27s+modulus%22+%22blood+vessels%22
"Young's modulus" "of blood vessels"
://www.google.com/search?q=%22Young%27s+modulus%22+%22of+blood+vessels%22
"Hooke's law" "blood vessels"
://www.google.com/search?q=%22Hooke%27s+law%22+%22blood+vessels%22
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