Re: goose bumps

On 13 Aug 2005 17:40:29 -0700, "chris.linthompson@xxxxxxxxx"
<chris.linthompson@xxxxxxxxx> wrote:

>Keith H Duggar wrote:

<others already snipped much of the history of names>

<snip a range of comments on a wide variety of well worked over stuff>

>> > > > 9) Structure is generally highly correlated with function.
>> > >
>> > > Sorry, I don't think "generally highly" is justified.
>> >
>> > Then you're wrong.
>>
>> Well, you are free to your opinion. However, arguments of
>> magnitude are often very hard to make. And they are not
>> made by listing a specific case as you did. Nor would
>> presenting more specific structures as you requested
>
>Well, snippage is fine to save bandwidth. However, my little joke there
>actually served a purpose. There really is a century or more of
>research showing that form follows function. In fact, it's the basis of
>every anatomy (and Anatomy & Physiology) class I ever took or heard of.
>You are going to have to go a long way before you disprove that form
>and function are not intimately related.
>
>>
>> > Conversely, please feel free to present structures
>> > that disprove this.
>>
>> "disprove" anything since you have already admitted that
>>
>> > ... there are some (I can think of a few) ...
>>
>> yet obviously you can still claim
>>
>> > but [structures correlated to function] outnumber them
>> > by orders of magnitude.
>>
>> even though you did not provide any evidence of this
>> magnitude, such as a comprehensive counting of known
>> structures.
>
>You snipped my example of blood vessels. Human blood vessels are
>exquisitely formed to perform particular functions. Arteries conduct
>oxygenated blood at high pressure to smaller vessels. Arterioles accept
>that blood and bring it to capillaries. Capillaries differ in structure
>from the preceding vessels in the number of tissue layers they possess,
>and are adapted to allow diffusion of gases into and out of the blood.
>Venules accept deoxygenated blood from capillaries and conduct it to
>veins, whose structure- especially in those veins draining into the
>inferior vena cava- is again well-adapted to bringing that blood to the
>heart.
>

I already stated that I prefer to continue commenting in this thread
only where real biology is involved. Here, let me just add some facts
to Chris' nice example of form/function relationships in the human
vasculature. That relationship far exceeds the simple facts that
Chris related. Let me describe some of the details he alluded to
because exploring these details forms some of my favorite
structure/relation exam questions in both my introductory biology and
my animal physiology courses. In particular, the walls of arteries,
arterioles, capillaries, and veins are distinctly different in the
quantity and type of connective tissue and in the quantity of smooth
muscle they contain. The walls of arteries are highly specialized to
be very elastic, albeit with stiff spring constants, and hence act as
low compliance vessels and pressure reservoirs. The walls of
capillaries are highly specialized to be single endothelial cells.
However there are different categories of capillaries with rather
different structures, all highly specialized according to the role of
the tissues they perfuse. The walls of veins are specialized to form
very loose springs, easily stretched. As a result, veins have high
compliance and act as volume reservoirs. The pattern of branching is
such that the greatest resistance elements are formed by the
arterioles which therefore allows them to control flow and systemic
pressure. The pattern of branching also provides for the fastest flow
in the arteries and veins and the slowest flow in the capillaries,
allowing for more efficient exchange between the blood and the
interstitial fluid. Even the biochemistry of the epithelial tissue
varies from organ to organ producing nitric oxide induced dilation
only in specific tissues. The pattern of autonomic innervation and
hormone sensitivity of the smooth muscle varies greatly from organ to
organ. The distribution of alpha vs. beta adrenergic receptors, the
existence of cholinergic sympathetic receptors, the relative magnitude
of sympathetic vs. parasympathetic innervation varies drastically so
that heavy physical activity is associated with vasodilation in active
skeletal muscle and severe vasoconstriction in reproductive,
digestive, and excretory organs.

And don't get me started on hemoglobin -- a molecule exquisitely
adapted not just to carry oxygen, but to increase oxygen delivery to
active tissue, to carry carbon dioxide and to increase carbon dioxide
uptake in active tissue, and to buffer pH changes especially those
that result from changes in metabolic rate. Oh yes, there is also the
high altitude adaptations, the changes between fetal and adult forms,
and rather a great deal more.

Chris is quite right. Structure-function relationships are a very
important aspect of all of biology, but are exceptionally important in
physiology, a subject near and dear to me. So I get rather upset when
someone impugns the heart of my subject. And comparative physiology
(comparing and contrasting different animals in different locations on
the phylogenetic tree) demonstrates the evolutionary basis for these
adaptations.

There are soft spots in biology where we do not yet have the type of
experimental data necessary to confirm all of our ideas. But the
relationship between structure and function is most definitely not one
of those.




.

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