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THE
GREAT VESSELS OF THE HEART
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Following the reorganization of the aortic
arches to accommodate blood flow to the lungs, the great vessels which
enter and leave the heart were modified.
Subsequent variation in specific lineages led to further changes. The left subclavian
artery forms near the base of the heart while the right subclavian
forms as a later branch. The common carotid arteries may branch from the
same great vessel or from different ones.
In reptiles, the left and right systemic
vessels (aortas) leaving the heart fuse with the fourth embryonic aortic
arches, left and right, to form a pair of aortic arches which fuse in
the abdomen to form the descending aorta.
In reptiles, the right fourth aortic arch larger than the left
and the single common carotid originates from the right arch.
In birds, the left fourth aortic arch degenerates during development
and the right branch of the fourth aortic arch composes the aorta. In mammals, the right branch degenerates (its
only remnant being the base of the right subclavian
artery) and the left branch of the fourth aortic arch composes the aorta
(Torrey, 1979). In birds,
there is a left systemic vessel in addition to the aorta as in crocodiles,
but it degenerates. Some mammals have cartilage or even bone
associated with their hearts as in the cartilaginous aortic ring in horses
(which may calcify) or the 1 or 2 ossa cordis bones in some cattle, both of which are associated
with the aortic semilunar valve (Weichert,
1970). Amniotes were the first to possess a completely
separate pulmonary circuit, with no ductus arteriosus
connecting pulmonary and systemic circuits (which still persists in salamanders
and tadpoles) (Kardong). In sarcopterygian
fish, the pulmonary artery develops
as a branch of aortic arch VI which also services gills before emptying
into the dorsal aorta through the ductus arteriosus
(amphibians have the same) and the pulmonary vein carries oxygenated blood
from lungs to left atrium (Kardong p. 465). |
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CORONARY VESSELS ---Blood
vessels servicing the heart appear for the first time in sharks. |
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RENAL All vertebrate embryos possess another portal
system in which blood from the posterior portions of the body is routed
through kidney capillaries. This
renal portal system is retained in the adults of fish, amphibians, and
reptiles but is lost in the adults of birds and mammals (Torrey). |
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MONKEY |
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