Section VI—Cardiovascular System
Heart
The pericardial cavity lies just anterior to the liver. It is enclosed by the pericardial sac and contains the heart (Figure 5.17). Continue the midventral incision of the abdominal wall anteriorly, cutting through the coracoid cartilage, to expose the pericardial cavity.
In doing so you will also cut through the transverse septum, the partition separating the pericardial and pleuroperitoneal cavities. Do not injure the posterior vena cava, which passes through the septum to reach the pericardial cavity. Carefully remove the musculature ventral to the cavity. The cavity is lined by parietal pericardium, while the heart itself is covered by visceral pericardium.The largest and most conspicuous part of the heart is the ventricle, which occupies the posteroventral part of the pericardial cavity (Figure 5.18). Lift the posterior end of the ventricle to observe the sinus venosus (Figure 5.19). The atrium lies anterodorsal to the ventricle and is partially divided into left and right atria. The conus arteriosus is the narrow tube extending anteriorly between the atria from the right side of the ventricle. It continues anteriorly as the wider bulbus arteriosus.
Venous System
Trace the posterior vena cava as it passes from the liver through the transverse septum. On entering the pericardial cavity, it subdivides into left and right hepatic sinuses, large vessels that extend anterolaterally into the sinus venosus (Figures 5.18 and 5.20). Probe just anterolateral to the entrance of the hepatic sinus on one side to observe the common cardinal vein, which enters the posterolateral end of the sinus venosus. The common cardinal vein mainly receives vessels that drain the head and forelimbs, such as the jugular and lingual veins as well as the subclavian vein, which is formed by the union of the brachial and cutaneous veins. It also
FIGURE 5.15 Pleuroperitoneal cavity of the male mudpuppy in ventral view, showing the urogenital system.
Much of the viscera has been removed.
FIGURE 5.16 Pleuroperitoneal cavity of the female mudpuppy in ventral view, showing the urogenital system. Much of the viscera has been removed.
FIGURE 5.17 Pericardial cavity of the mudpuppy in ventral view, opened to reveal the heart.
The ventral abdominal vein was observed passing through the free posterior margin of the falciform ligament (Figure 5.11). Return to this vessel. As you will see presently, its anterior end joins the hepatic portal vein. For now, follow the ventral abdominal vein posteriorly along the midventral abdominal wall. As noted above, it receives the vesicular vein from the urinary bladder. The ventral abdominal vein is formed, farther posteriorly, by the union of left and right pelvic veins. Follow one of the pelvic veins posterolaterally. At the level of the hind limbs, it receives the femoral vein. At this point, note that the common iliac vein, observed above as it entered the renal portal vein, joins the pelvic and femoral veins. The iliac is thus a short vein running between the renal portal vein and the union of the pelvic and femoral veins.
Observe the mesentery by spreading the coils of the small intestine. The mesenteric vein runs within the mesentery (Figure 5.18). Follow it as it passes anteriorly toward the pancreas. Next, locate the gastrosplenic vein, identified above as extending between the pancreas and spleen. The union of these veins, within the pancreas, forms the hepatic portal vein, which runs along the dorsal surface of the liver before entering this organ (Figure 5.20). The ventral abdominal vein joins the hepatic portal vein a short distance anterior to the union of the mesenteric and gastrosplenic veins.
receives the lateral vein, which extends along the lateral side of the trunk, and the posterior cardinal vein (Figures 5.18 and 5.20).
Various veins within the peritoneal cavity have already been identified. The posterior vena cava was identified first as it passed to the liver through the hepato- cavopulmonary ligament and then through the transverse septum. Reidentify this vein. Follow it as it passes through the liver, from which it receives several hepatic veins. Posteriorly, it passes middorsally in the pleuroperitoneal cavity, extending between the kidneys (Figure 5.20). It receives numerous efferent renal veins from the kidneys, as well as testicular or ovarian veins from the gonads (see also Figure 5.20).
A renal portal vein extends longitudinally along the dorsolateral margin of each kidney. Follow it posteriorly. At about the level of the hind limbs, each renal portal vein receives a common iliac vein. Posterior to the kidneys, the left and right renal portal veins form by the bifurcation of the median caudal vein from the tail. Anterior to the kidneys, the renal portal veins become the posterior cardinal veins. In this region the posterior cardinals anastomose with the posterior vena cava via the converging subcardinal veins; anteriorly, they drain into the common cardinal sinus.
Arterial System
Return to the bulbus arteriosus. As it leaves the front of the pericardial cavity, it bifurcates into left and right arteries (Figure 5.21). Each of these arches laterally and subdivides into two branches. They are probably not injected, but usually have remnants of blood so that they can, with diligence, be followed. The most anterior branch is the first afferent branchial artery, which follows the first branchial arch and enters the first external gill. The second branch bifurcates into the second and third afferent branchial arteries. Follow them, respectively, into the second and third external gills. The external carotid artery, which should be injected, is a narrow vessel running anteromedially along the anterior margin of the first afferent branchial artery.
Remove the lining on the roof of the oral cavity and pharynx.
Medial to the external gills are the left and right radices (sing., radix) of the dorsal aorta (Figure 5.22). Each radix arches toward the dorsal midline and joins its fellow to form the dorsal aorta, which continues middorsally along the trunk and tail. Follow the radix laterally. Its first branch is the vertebral artery, which passes anteriorly and almost immediately enters the musculature. Further laterally, a short
FIGURE 5.18 Pleuroperitoneal cavity of the mudpuppy in ventral view, revealing heart and vessels. Liver is pulled to the left.
FIGURE 5.19 Pericardial cavity of the mudpuppy in ventral view, exposing the heart. The ventricle and atrium are lifted and moved aside to reveal the sinus venosus.
trunk, the carotid duct, enters the anterior surface of the radix. The duct connects to the following two arteries. The first efferent branchial artery extends medially from the first external gill. The internal carotid artery extends anteromedially from the trunk, and helps supply the facial region and brain. The external carotid artery, observed in connection with the afferent branchial arteries, helps supply the floor of the mouth and pharynx. It arises from the first efferent branchial artery just after the latter emerges from the gill. Return to the radix and continue to follow it laterally. The pulmonary artery arises from its posterior surface and passes to the lung. Beyond the pulmonary artery, the second and third efferent branchial arteries, which emerge from the second and third gills, respectively, unite to form the radix.
As in the other vertebrates so far studied, the dorsal aorta supplies the structures of the trunk by paired and unpaired branches. Its most anterior paired vessels are the subclavian arteries. Each subclavian extends almost directly laterally, giving off several small arteries before continuing into the forelimb as the brachial artery.
The next few posterior arteries are single median arteries that mainly supply the viscera (Figure 5.23). The most anterior of these, the gastric artery, arises near the anterior end of the stomach and passes to this organ. The larger celiacomesenteric artery arises near the posterior end of the stomach and soon subdivides into various branches that primarily supply the spleen, stomach, duodenum, and liver. The dorsal aorta then gives off several unpaired mesenteric arteries that pass through the mesentery and supply the intestines. In addition, the aorta gives off paired testicular or ovarian arteries to the testes or ovaries that pass through the mesorchium or mesovarium, respectively, and paired renal arteries that pass into the kidneys. Dorsal to the posterior part of the kidneys, large, paired iliac arteries extend laterally. Each branches into three vessels, an anterior epigastric artery (onto the body wall), a lateral femoral artery (into the hind limb), and a posterior hypogastric artery (to the cloaca and urinary bladder). The small, paired cloacal arteries are the last branches of the aorta, which then continues into the tail as the caudal artery.Key Terms: Cardiovascular System
afferent branchial arteries
brachial artery brachial vein bulbus arteriosus carotid duct caudal artery caudal vein celiacomesenteric artery cloacal arteries common cardinal vein common iliac vein conus arteriosus cutaneous vein dorsal aorta efferent branchial arteries
efferent renal veins epigastric artery external carotid artery femoral artery
femoral vein gastric artery gastrosplenic vein heart
hepatic portal vein hepatic sinuses hepatic veins hypogastric artery iliac arteries internal carotid artery jugular vein lateral vein left atrium lingual vein mesenteric arteries mesenteric vein ovarian arteries ovarian vein parietal pericardium pelvic veins
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FIGURE 5.20 Schematic illustration showing the pattern of the venous system in the mudpuppy superimposed on a ventral view of the body outline.
FIGURE 5.21 Ventral view of the heart and ventral aorta in the mudpuppy.
FIGURE 5.22 Ventral view of the dorsal aorta and its branches in the mudpuppy. The right side of the mouth has been cut and the lower jaw swung open.
FIGURE 5.23 Pleuroperitoneal cavity of the mudpuppy in ventral view, showing the pattern of the arterial system posterior to the heart.
pericardial cavity posterior cardinal vein pulmonary artery radices (sing., radix) renal arteries
renal portal vein right atrium sinus venosus subcardinal veins subclavian artery
subclavian vein testicular artery testicular vein transverse septum ventral abdominal vein ventricle vertebral artery vesicular vein visceral pericardium