FLUIDS
Unit 18 “ Physics in NYT Biology Articles” Dr. John P. Cise, Professor of Physics, Austin Community
College, 1212 Rio Grande St. Auistin Tx. 78701 [email protected] &
NYTimes October 7, 2014 by Natalie Angier
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Our Understanding of Giraffes Does Not Measure Up
INTRODUCTION: For all mammals the heart pumps blood from
toes back to heart to get more oxygen and nutrients. Consider
3
blood to have the same density (ρ) as water 1000 kg./m . Blood
pressure (BP) is given in terms of an equivalent column of
mercury supported by that pressure. A BP of 120 = 120 mm of
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mercury. Ρmercury =13,500 kg/m . Consider giraffe blood density =
human blood density. The purpose of this physics application is to
verify a BP of 120 is adequate to pump blood from toes to heart
and giraffe BP must be quite high to get blood from giraffe toes
back to heart 16 feet higher. Pressure in fluid column = ρ g h
QUESTIONS: (a) Find BP in
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Giraffes are the
Giraffs: 16 ft. = distance
“forgotten megafauna,”
from toes to heart.
said the executive director
of the Giraffe Conservation Foundation.
Humans: 4 ft. =
distance from
toes to heart.
N/m for a human with BP of
120? (b) Consider the human
heart is 4 ft. from your toes.
2
Find BP(N/m ) needed to
pump blood from toes to
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heart? Ρblood = 1000 kg/m .
2
3.28 ft. =1 meter, g = 9.8 m/s
(c) Consider the giraffe heart to be 16 feet from toes. Find giraffe BP(N/m2) needed to pump blood from toes to
heart? (d) How much larger must giraffe’s BP be compared to a human’s BP to pump blood from toes to heart?
ANSWERS: (a) 15,876 N/m2 (b) 11,951 N/m2 (c) 47,809 N/m2 (d) BPGiraffe = 4 BP Human
Note: In (a) a human BP of 15,876 N/m2 was enough(~12,000 N/m2 needed) to pump blood from toes to heart.
Also, the Giraffe had to have a BP much higher(as much as 5 times more as stated below)& we found 4 X more.
OKAVANGO DELTA, BOTSWANA — For the tallest animals on earth, giraffes can be awfully easy to overlook. Their
ochered flagstone fur and arboreal proportions blend in seamlessly with the acacia trees on which they tirelessly forage, and they’re as
quiet as trees, too: no whinnies, growls, trumpets or howls. “Giraffes are basically mute,” said Kerryn Carter, a zoologist at the
University of Queensland in Australia. “A snort is the only sound I’ve heard.”The species is not listed as endangered, but researchers
point with alarm to evidence that in the past 15 years, the giraffe population has plummeted some 40 percent, to less than 80,000 from
((( giraffe can stand 20 feet tall —
the height of a second-story window — with its neck accounting for roughly a third its span ))) and its long
140,000. Also of interest is the giraffe’s exceptional cardiovascular system. A large
legs the same. The multitiered challenge, then, is how to both pump blood very high and retrieve it from far below while avoiding
burst capillaries in the brain or blood pooling around the hooves.
As part of the Danish Cardiovascular Giraffe Research Program, scores of scientists have traveled to South Africa to study giraffe
((( measured blood pressure at different sites and found readings that
range from high to ridiculous — up to five times human blood pressure ))) — yet with none
physiology. They have
of the organ damage commonly seen in hypertensive patients.Instead, the giraffe has extremely thick blood vessel walls to prevent
blood from leaking into surrounding tissue, while rugged, inflexible collagen fibers in its neck and legs help keep the blood traffic
moving, rather as the tight antigravity suits worn by astronauts and fighter pilots will maintain blood flow under the most extreme
gravitational shifts. A complex mesh of capillaries and valves store and release blood in the neck, allowing the giraffe to bend over for
a drink of water and then raise its head again quickly without fainting; when the giraffe is standing still, sphincters at the top of the
legs limit circulation to the lower extremities, to minimize the risk of fluid buildup around the hooves.Researchers were also surprised
to find that contrary to old textbook wisdom, giraffes do not have unusually large hearts for animals their size. “It’s half a percent of
body mass, and that’s the same as we see in a cow, dog or mouse,” said Christian Aalkjaer of the department of biomedicine at Aarhus
University in Denmark.