CIRCULATORY SYSTEM -- ARTERIES
A. Plasticity:
1. Accounts for variation in vessels among individuals of same species.
2. Veins vary more than arteries, left may differ from right.
B. Arteries and arterioles:
1. Larger in diameter than veins (typically).
2. More elastic, less muscle (less elastic in arterioles).
3. More elastic near heart for purpose of {absorbing pressure of blood}
a. F.S. -
b. F.S. -
4. Functional significance of elastic in arteries of body: {even out blood flow}
A. Anamniotes
1. Teleost fishes:
a. Pairs 1 & 2 degenerate, 3-6 supply gills.
b. Afferent (toward gills) and efferent (away from gills) branches connected by gill
capillaries.
2. Amphibians (anurans):
a. 1 & 2 degenerate.
b. Dorsal aorta continues cranially as internal carotid, which is supplied by arch #3.
c. Ventral aorta continues cranially as external carotid.
d. Portion of ventral aorta between 3 & 4 constitutes common carotid.
e. Dorsal connection between 3 & 4 degenerates; F.S.- separates blood flow to head
from blood flow to body.
f. 4th arch becomes systemic arch.
g. 5th arch degenerates (except urodeles).
h. 6th forms pulmonary arch (artery).
B. Amniotes
1. Arches 1, 2, 3, and 5 have the same fates as in anuran amphibians.
2. Reptiles:
a. Truncus arteriosus splits into 2 aortic trunks & 1 pulmonary trunk.
b. Arches #4 becomes paired systemic arches.
c. Arches #6 form pulmonary arteries.
3. Aves:
a. Truncus arteriosus forms two passages: pulmonary & aortic trunks.
b. Only right 4th arch persists as systemic arch.
4. Mammalia:
a. Truncus arteriosus forms two passages as in birds.
b. Only left 4th arch persists as systemic arch.
c. Ductus arteriosus shunts blood to body in fetus to bypass non-functional lungs;
constricts at birth.
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