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RE: Long Necked Giraffes And Their Hearts
Here's the abstract:
Comp Biochem Physiol A Mol Integr Physiol. 2009 Dec;154(4):523-9. Epub 2009 Aug
An allometric analysis of the giraffe cardiovascular system.
Mitchell G, Skinner JD.
Centre for Veterinary Wildlife Studies, Onderstepoort, South Africa.
There has been co-evolution of a long neck and high blood pressure in giraffes.
How the cardiovascular system (CVS) has adapted to produce a high blood
pressure, and how it compares with other similar sized mammals largely is
unknown. We have measured body mass and heart structure in 56 giraffes of both
genders ranging in body mass from 18 kg to 1500 kg, and developed allometric
equations that relate changes in heart dimensions to growth and to
cardiovascular function. Predictions made from these equations match
measurements made in giraffes. We have found that heart mass increases as body
mass increases but it has a relative mass of 0.51+/-0.7% of body mass which is
the same as that in other mammals. The left ventricular and interventricular
walls are hypertrophied and their thicknesses are linearly related to neck
length. Systemic blood pressure increases as body mass and neck length increase
and is twice that of mammals of the same body mass. Cardiac output is the same
as, but peripheral resistance double that predicted for similar sized mammals.
We have concluded that increasing hydrostatic pressure of the column of blood
during neck elongation results in cardiac hypertrophy and concurrent
hypertrophy of arteriole walls raising peripheral resistance, with an increase
in blood pressure following.
> Date: Sun, 22 Nov 2009 20:57:29 -0700
> From: email@example.com
> To: firstname.lastname@example.org
> Subject: Long Necked Giraffes And Their Hearts
> Some implications for long necked dinosaurs...
> However, exactly how they maintain this neck, and get blood to a head that
> is two metres from their heart, has remained unknown.
> Now research reveals that giraffes have a small, powerful, supercharged
> heart that is different to that possessed by other similar mammals.
> Scientists have published the discovery in the journal Comparative
> Biochemistry and Physiology, Part A.
> "There are not many animals that have evolved to have a very long neck,"
> says giraffe expert Professor Graham Mitchell from the Centre of Wildlife
> Studies in Onderstepoort, South Africa.
> Prof Mitchell undertook the study along with Prof John Skinner at the
> University of Wyoming, Laramie, US.
> Previous studies have found the giraffe has an extremely high blood
> pressure that is twice that found in other animals.
> "We established that the heart is actually quite small. It's smaller than
> you'd expect in similar-sized animals, but the walls are incredibly
> thick," Prof Mitchell says.
> "You have a small but a very powerful heart delivering the blood
> The giraffe also has other specialist mechanisms to help deal with the
> high blood pressure, Prof Mitchell says.
> "Blood pressure depends on the capacity of the cardiovascular system as
> well as the efficiency of the pump."
> "Giraffes have got a way of adjusting the capacity of the cardiovascular
> system and are able to shrink and expand their blood vessels to change the
> volume of the cardiovascular system very efficiently."