4. THE CIRCULATORY SYSTEM
143
other diphasic deflection resulting from activity of the portal heart
appeared on the record. As might be expected it had no phase relationship with the electrocardiogram of the systemic ( branchial) heart.
TebFcis (1967) recorded a wave complex (termed the “Bd complex”)
in the electrocardiogram of the Port Jackson shark. The Bd complex
normally occurs between the QRS complex and the T wave and is
associated with the depolarization of the conus. The exact position of
the Bd complex in the ST segment is variable and may even coincide
with the T wave. In a few preparations, Tebecis recorded a Br complex
between the T wave of one cardiac cycle and the P wave of the next
cycle. The Br complex is associated with repolarization of the conus.
Tebgcis (1967) calculated the conduction velocity of the conal wave
of excitation from the time delay between two conal electrograms recorded from different points along the length of the conus and found
that the velocity of conduction was very slow, of the order of 2 A
cmlsec. The conduction velocity of the excitation wave passing over
the surface of the ventricle of the Port Jackson shark is much faster, in
the range of 4&100 cm/sec.
C. Mechanical Properties
There are differences in function between the teleost and elasmobranch heart. The elasmobranch heart is contained in a noncompliant
pericardium and has a contractile conus. The teleost heart is within a
thin and compliant pericardium and has a noncontractile but very
elastic bulbus.
In teleosts, the rate of atrial filling is determined by venous pressure.
The sinus venosus appears to play little or no role in actively moving
blood through the heart, but it forms part of an extensive venous
reservoir serving the atrium. The volume of the atrium prior to systole
is adequate to fill the ventricle, and the atrioventricular valves do not
open until atrial systole ( Randall, 1968). Therefore, contractions of the
atrium in the presence of sinoatrial valves to prevent the reflux of blood
into the sinus venosus serve to fill the ventricle, and, unlike the situ a t’ ion
in mammals, there is no direct inflow of blood into the ventricle from
the venous system during ventricular diastole.
Contractions of the ventricle result in large increases in intraventricular pressure ( Fig. 3 ) , the atrioventricular valves close and, in
teleosts at least, the ventricle contracts isovolumetrically until pressures
rise above that in the bulbus, when the valves at the exit of the ventricle
open and blood leaves the ventricle. Pressures in the ventricle, bulbus,
143
other diphasic deflection resulting from activity of the portal heart
appeared on the record. As might be expected it had no phase relationship with the electrocardiogram of the systemic ( branchial) heart.
TebFcis (1967) recorded a wave complex (termed the “Bd complex”)
in the electrocardiogram of the Port Jackson shark. The Bd complex
normally occurs between the QRS complex and the T wave and is
associated with the depolarization of the conus. The exact position of
the Bd complex in the ST segment is variable and may even coincide
with the T wave. In a few preparations, Tebecis recorded a Br complex
between the T wave of one cardiac cycle and the P wave of the next
cycle. The Br complex is associated with repolarization of the conus.
Tebgcis (1967) calculated the conduction velocity of the conal wave
of excitation from the time delay between two conal electrograms recorded from different points along the length of the conus and found
that the velocity of conduction was very slow, of the order of 2 A
cmlsec. The conduction velocity of the excitation wave passing over
the surface of the ventricle of the Port Jackson shark is much faster, in
the range of 4&100 cm/sec.
C. Mechanical Properties
There are differences in function between the teleost and elasmobranch heart. The elasmobranch heart is contained in a noncompliant
pericardium and has a contractile conus. The teleost heart is within a
thin and compliant pericardium and has a noncontractile but very
elastic bulbus.
In teleosts, the rate of atrial filling is determined by venous pressure.
The sinus venosus appears to play little or no role in actively moving
blood through the heart, but it forms part of an extensive venous
reservoir serving the atrium. The volume of the atrium prior to systole
is adequate to fill the ventricle, and the atrioventricular valves do not
open until atrial systole ( Randall, 1968). Therefore, contractions of the
atrium in the presence of sinoatrial valves to prevent the reflux of blood
into the sinus venosus serve to fill the ventricle, and, unlike the situ a t’ ion
in mammals, there is no direct inflow of blood into the ventricle from
the venous system during ventricular diastole.
Contractions of the ventricle result in large increases in intraventricular pressure ( Fig. 3 ) , the atrioventricular valves close and, in
teleosts at least, the ventricle contracts isovolumetrically until pressures
rise above that in the bulbus, when the valves at the exit of the ventricle
open and blood leaves the ventricle. Pressures in the ventricle, bulbus,