From: rh@smds.com (Richard Harter)
Newsgroups: talk.origins
Subject: Re: Holden Numbering
Date: 9 Sep 92 07:23:05 GMT
Reply-To: rh@ishmael.UUCP (Richard Harter)
Organization: Software Maintenance & Development Systems, Inc.

In article <1992Sep8.061806.3949@desire.wright.edu> sbishop@desire.wright.edu writes:
>In article <2895@fedfil.UUCP>, news@fedfil.UUCP (news) writes:

>>> I've been to the Zoo Ted. Giraffes are able to bend their heads down.
>>> I've seen it! Wow!  

>> Not for any length of time.  Scientists are now claiming that sauropods
>> carried their necks low, nearly horizontal, ALL the time, because they
>> could not have gotten blood to their brains otherwise.

>Says you!  After all, any statement from the man who said that new born horses
>can't run, that horses can't comfortably carry any weight over 125 pounds,
>that giraffes have enormous blood pressure in their heads *(ALL totally
>untrue)*, is very suspect.

But Sue, he is taking this straight from McGowan.  I quote (_Dinosaurs,
Spitfires, and Sea Dragrons_, pp101-102):

"...the average pressure of the blood leaving a healthy human heart during
its contractionis 120 mm of mercury, abbreviated to 120 mm Hg.

The blood leaving the giraffe's heart has to do more than just reach the
level of the head, it has to be at a high enoughpressure to pass through all
of the fine vessels, the capillaries, that supply the brain and other organs.
To achieve this the blood leaves the heart at a pressure of 200-300 mm Hg.,
which is probably the highest blood pressure of any living animal... A
giraffe's blood pressure is so high that it would probably rupture the
blood bessels of any other aimal, but two mechanisms appear to prevent
this.  First, the arterial walls are much thicker than in other mammals.
Second, the fluid that bathes the cells of the body is maintained at a
high pressure; this is largely achieved by the thick skin, which is
tightly stretched over the body and which functions like the ant-gravity 
suits worn by pilots of fast aircraft.

The unpleasant dizzy sensation we sometimes experience when standing
quickly from a lying or sitting position is caused by a temporary fall
in the pressure of the blood reaching the brain.  Giraffes sometimes lie
down to rest, and when they regain their feet they have to do so in stages,
firt squatting and waiting for a few moments befoer standing fully erect.
This behavioral modification presumably allows the vascular system to
stabilize.  If a giraffe suddenly raised its head to its full height it
would probably become faint. Conversely, when a firaffe is drinking,
its head is lower than its heart, which increases the blood pressure
to the brain.  The giraffe reduces the extent of this pressure increase
by splaying its front legs while drinking, which reduces the difference
in height between the head and the heart."

-- p 118 --

"Because of its long neck the giraffe's heart has to discharge blood
at pressures of between 200 and 300 mm Hg to supply blood to the brain.
Sauropods had even longer necks.  Estimates from mounted skeletons give
values for the veritcal distance between the heart and the head of of
almost seven feet (201 cm) in Apatosuars and twenty-two feet (655 cm)
in Brachiosaurus; their hearts would have needed to discharge blood at
pressusres of 216 mm Hg and 568 mm Hg, respectively (Hohnke, 1973)"



-- 
Richard Harter: SMDS Inc.  Net address: rh@smds.com Phone: 508-369-7398 
US Mail: SMDS Inc., PO Box 555, Concord MA 01742.    Fax: 508-369-8272
In the fields of Hell where the grass grows high
Are the graves of dreams allowed to die.