Circulation in Reptiles | Zoology by miller and harley

Circulation in reptiles
The circulatory system of reptiles is based on that of amphib-
ians. Because reptiles are, on average, larger than amphib-
ians, their blood must travel under higher pressures to reach
distant body parts. To take an extreme example, the blood of
the dinosaur Brachiosaurus had to be pumped a distance of
about 6 m from the heart to the head--mostly uphill! (The
blood pressure of a giraffe is about double that of a human to
move blood the 2 m from the heart to the head.)
Like amphibians, reptiles possess two atria that are com-
pletely separated in the adult and have veins from the body
and lungs emptying into them. Except for turtles, the sinus
venosus is no longer a chamber but has become a patch of
cells that acts as a pacemaker. The ventricle of most reptiles
is incompletely divided (figure 20.14). (Only in crocodilians
is the ventricular septum complete.) The ventral aorta and
the conus arteriosus divide during development and become
three major arteries that leave the heart. A pulmonary artery
leaves the ventral side of the ventricle and takes blood to the
lungs. Two systemic arteries, one from the ventral side of the
heart and the other from the dorsal side of the heart, take
blood to the lower body and the head

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