go further into fish circulation, let's compare a human with a fish
to get a perspective on the anatomy and function.
(like us) there is a double circulation. The right side of the
heart receives blood returning back from the body; this blood is
low in oxygen (blue in the figure to the right). This
“deoxygenated” blood enters the right atrium and then the right
ventricle to be pumped to the lungs were the blood will be
oxygenated. The oxygenated blood (red in the figure) from the
lungs enters the left ventricle via the left atrium and is then
pumped out into the larger body circulation. Note that the volume
pumped by the right and left side of the heart is the same:
approximately 5 liters per minute in a 70 kg human.
the heart only has one atrium and one ventricle. The
oxygen-depleted blood that returns from the body enters the
atrium, and then the ventricle, and is then pumped out to the
gills where the blood is oxygenated, and then it continues through
the rest of the body.
On the next
page, you will see that the arrangement of the circulation in the
fish is based on a fine balance.