I know, rationally, that the brightly colored red and blue heart diagrams in the spiral bound textbook on the lab table aren’t entirely accurate. However, I was surprised at how disappointed I was to open the box of shrink-wrapped pig hearts and discover that the entire heart is a homogenous beige color – somewhere in between tea with too much milk in it and the thick clay in the riverbeds near my house. Luckily, that disappointment didn’t last. As my lab partner, Rebecca, and I unsealed the plastic wrap, our first impression of the heart was the smell. Acidic, chemically, headache-inducing: the preservatives that kept our heart from smelling like rotting meat also made the entire lab smell like the inside of a formaldehyde bottle!
As our noses adjusted, we began our cursory inspection of the heart. Once I was able to get over the bland coloration, our pig heart actually looked remarkably like the textbook model. From the shriveled atria to the rubbery arteries, our pig heart just looked like a small-scale reproduction of the plastic hearts that had been on display on the lab tables all week. Once we oriented the heart with the apex pointing down, Rebecca made the first cut, deftly slicing the heart in half like a bagel. We both gasped. The interior of the large, muscular ventricles was covered in delicate, stringy chordae tendineae! The textbook photos and models mentioned these fibrous bands, but the lightly sketched lines in our reference image in no way prepared us for the network of elastic filaments that criss-crossed through the ventricles. Rebecca tugged at one of the strands, but instead of breaking, it snapped back into place as soon as she released it. Those things are a lot stronger than they look!
Our second surprise was the septum’s thickness. We had both memorized the fact that the left ventricle has stronger muscle walls than the right ventricle (because while the right ventricle only pumps blood back into the lungs to get oxygenated, the left ventricle has to distribute blood to the entire body). However, the difference was huge! The septum was thick and muscular and not at all thin like the cartilaginous septum that separates the nostrils. As we continued to hack away… or rather, “dissect,” our heart, we noticed that if you pulled the filmy visceral pericardium away from the outer walls of the heart, it revealed rougher, almost striated muscle tissue below. It was even possible to pull up small strands of muscle tissue with the tweezers and separate the layers of the heart muscle. The same was true of the interior of the ventricles – once we peeled back the smooth endothelium that protected the inner walls of the heart, the coarser muscle tissue was revealed.
Even more interesting than the layers of the heart muscle was the layered structure of the veins and arteries splaying out of the heart. After Rebecca and I had thoroughly examined all the entrances and exits to the heart (mostly by sticking our fingers in the tubes to figure out which chamber each one led to), we sliced off a section of the aorta and attempted to identify the layers of the tissue that compose an artery.
By the time we were finished, our pig heart lay in chunks all over the dissecting tray. Rebecca was poking one end of her tweezers through the coronary artery and I was still stubbornly trying to “de-fat” the right atrium. As class time ran out, we reluctantly cleaned up our heart and threw out our gloves, eager to get the scent of preservatives off our hands. As Rebecca and I threw out the last of our paper towels, I turned to her and said, “I hope they aren’t serving pork carnitas again at lunch. I don’t really think I can imagine eating pork after that…”