4. THE CIRCULATORY SYSTEM
147
the ventricular lumen and conal chamber are interconnected, blood
moves out of the ventricle into the conus at the onset of ventricular
systole. Thus there can be no truly isovolumetric phase to ventricular
systole in elasmobranchs.
The number of valves in the conus varies in different fish. The Port
Jackson shark has three sets of valves with three semilunar valves in
each set. Satchell and Jones ( 1967) refer to the valves as lower (proximal), middle, and upper (distal) conal valves. The lower valves are
those near the junction of the conus and ventricle. The middle valves
divide the conus into upper and lower conal chambers. A diagram by
Hanson (1967) shows four rows of conal valves in the dogfish, Squalus
acantlzias, whereas a drawing by Sudak (1965a) of a freshly obtained
heart from a smooth dogfish, Mustelus canis, shows only proximal and
distal conal valves.
During ventricular diastole the proximal (lower and middle) conal
valves of the Port Jackson shark are open (Satchell and Jones, 1967),
the ventricular and conal chambers are interconnected, and the pressure
difference between ventricle and conus and ventral aorta is maintained
by the closed distal (upper) conal valves. The proximal and middle
valves are not large in the Port Jackson shark, and when the conus is
relaxed their free edges do not meet and the valves are incompetent.
Conal systole narrows the conal lumen, and under these conditions the
valves are competent. The conus swells at the onset of ventricular systole
as blood moves from the ventricle into the conus. Pressures rise simultaneously in the ventricular and conal chambers and eventually exceed that
iin the ventral aorta; the distal (upper) conal valves open and blood
flows into the ventral aorta. Conal systole begins before the end of ventricular systole. The contraction starts at the junction of the ventricle
and conus and passes forward toward the ventral aorta. Conal systole
aids the closure of first the proximal (lower) and then the middle conal
valves as the ventricle relaxes. As the conus relaxes the proximal (lower)
and middle valves become incompetent, there is a small backflow, and
the distal (upper) conal valve closes. This valve, unlike the proximal
and middle valves, is competent in the absence of conal systole; hence,
it remains closed after the conus relaxes. Satchell and Jones (1967)
recorded blood flow in the ventral aorta of the Port Jackson shark and
found that flow occurs only during the period between the opening of
the distal conal vnlvcs and the closing of the proximal conal valves. During this period the changes in flow and pressure in the ventral aorta can
be ascribed to ventricular systole. The period between closure of the
proximal and distal valves corresponds to conal systole, and during this
period, Satchcll and Jones did not record any blood flow in the ventral
147
the ventricular lumen and conal chamber are interconnected, blood
moves out of the ventricle into the conus at the onset of ventricular
systole. Thus there can be no truly isovolumetric phase to ventricular
systole in elasmobranchs.
The number of valves in the conus varies in different fish. The Port
Jackson shark has three sets of valves with three semilunar valves in
each set. Satchell and Jones ( 1967) refer to the valves as lower (proximal), middle, and upper (distal) conal valves. The lower valves are
those near the junction of the conus and ventricle. The middle valves
divide the conus into upper and lower conal chambers. A diagram by
Hanson (1967) shows four rows of conal valves in the dogfish, Squalus
acantlzias, whereas a drawing by Sudak (1965a) of a freshly obtained
heart from a smooth dogfish, Mustelus canis, shows only proximal and
distal conal valves.
During ventricular diastole the proximal (lower and middle) conal
valves of the Port Jackson shark are open (Satchell and Jones, 1967),
the ventricular and conal chambers are interconnected, and the pressure
difference between ventricle and conus and ventral aorta is maintained
by the closed distal (upper) conal valves. The proximal and middle
valves are not large in the Port Jackson shark, and when the conus is
relaxed their free edges do not meet and the valves are incompetent.
Conal systole narrows the conal lumen, and under these conditions the
valves are competent. The conus swells at the onset of ventricular systole
as blood moves from the ventricle into the conus. Pressures rise simultaneously in the ventricular and conal chambers and eventually exceed that
iin the ventral aorta; the distal (upper) conal valves open and blood
flows into the ventral aorta. Conal systole begins before the end of ventricular systole. The contraction starts at the junction of the ventricle
and conus and passes forward toward the ventral aorta. Conal systole
aids the closure of first the proximal (lower) and then the middle conal
valves as the ventricle relaxes. As the conus relaxes the proximal (lower)
and middle valves become incompetent, there is a small backflow, and
the distal (upper) conal valve closes. This valve, unlike the proximal
and middle valves, is competent in the absence of conal systole; hence,
it remains closed after the conus relaxes. Satchell and Jones (1967)
recorded blood flow in the ventral aorta of the Port Jackson shark and
found that flow occurs only during the period between the opening of
the distal conal vnlvcs and the closing of the proximal conal valves. During this period the changes in flow and pressure in the ventral aorta can
be ascribed to ventricular systole. The period between closure of the
proximal and distal valves corresponds to conal systole, and during this
period, Satchcll and Jones did not record any blood flow in the ventral