The Pinniped's Heart

By now we have observed all of the organs of the pluck except one: the heart. The pericardium is the sac that contains the heart, and this should be trimmed away to see the epicardium (external surface of the heart). A small amount of clear fluid is contained within the pericardium, which allows for lubrication during normal heartbeat activity. If there is a lot this fluid (pericardial effusion), and if it is off-colored, make a note of it as this may indicate a wide variety of cardial issues such as pericarditis (inflammation of the pericardium), complications from tuberculosis, trauma, etc.

The mammalian heart is separated into 2 ventricles and 2 atria. Deoxygenated blood flows from the ventricles directly into the right atrium, where the tricuspid valve then shuttles it into the right ventricle. The pulmonary valve shuttles this blood into the pulmonary artery, which passes by the lungs. Oxygenated blood then travels from the pulmonary vein into the left atrium where the mitral valve is, and then this blood is sent into the left ventricle, then through the aortic valve and into the arteries and aorta where it is sent throughout the body. All of the valves, ventricles, atria and the aorta and pulmonary valve should be examined and noted for any inconsistencies during the necropsy. This can be accomplished by removing the heart from the aorta and pulmonary artery by cutting the two transversely, leaving 6 centimeters of each vessel still attached. To examine the internal structures, two methods can be utilized:

Using scissors, make a small incision in the right atrium and cut along the peripheral edge going towards the apex (lowest part of the heart), then following up the right ventricle side of the septum until you reach the pulmonary artery. Then cut the left ventricle side of the apex, go along the septum until the aorta is reached. This leaves both sides of the heart intact, but is fairly complicated. A simpler way is to slice the entire organ in half starting from the apex and then travelling laterally towards the vessels.

The pulmonary artery is a flappy vessel that enters the right atrium cranially while the aorta is the most muscular and tough artery. Both should be cut longitudally and examined for defects. The left atrium and ventricle should have thicker and more muscular walls than the right side (thickness ratio of around 2:1), with the left ventricle the thickest part of the heart. The right pulmonary vein and right atrium are the most flaccid. Unusual structures within the chambers of the heart may suggest hereditary illness or vestigal fetal structures. They, along with lesions should be recorded. The myocardium can be examined by bread-slicing the ventricles.

And that was the heart! While I was initially intimidated by the intricacies of the heart's anatomy, it was more straightforward than I thought it would be. Next entry will explore the abdominal cavity. Then the pinniped part of this study will be complete and we can move on to small cetaceans.