If we consider the body as a machine, the heart’s function is analogous to a fuel pump, and the entire circulatory system can be considered major and minor fuel lines that carry, return, and support the pump to make it useful. The heart is about the size of your closed fist, and if you can imagine it tilted right a tiny bit and fitted into the left side of your body, that’s about what your heart looks like. It’s primarily made of muscular tissue, which can be separated into two sides both horizontally and vertically. The top half of the heart is known as the atrium, while the lower half is known as the ventricle. The vertical split turns the two regions into four chambers. These include the right atrium, left atrium, right ventricle, and left ventricle. In a diagram, these sides will be backward, due to the perspective change (think of how you and the person facing you have different perspectives of left and right). These regions have many different functions, but for now, we will focus on the connections between the heart and the body. The connectors are the arteries, veins, and capillaries. The arteries are thick, muscular tubes that route oxygenated blood to other parts of the body. Veins are the carriers of spent blood, so they are less thick compared to arteries but have special valves inside of them to prevent backflow. Capillaries are only one cell thick, making them the thinnest group of vessels in the human body. The heart contains two main arteries and two main veins. The arteries are the aorta and the pulmonary artery, and the veins are the superior and inferior vena cava, superior and inferior referring to the distance to the head being closer and longer respectively. 

 Going back to the machine and fuel pump analogy, the right side of the heart can be considered the pump that sends the fuel to be processed by the lungs, which adds oxygen to supply it to the rest of the body. On the other hand, the left side accepts this fuel and sends it out to the body through the vessels of the circulatory system. When blood travels through the heart, it enters through the right atrium and moves downward through a valve known as the tricuspid valve. The blood then exits the right ventricle through the pulmonary artery to the lungs, which oxygenates the blood by a process known as diffusion. After diffusion has taken place, the oxygenated blood travels to the left atrium, where it moves through the mitral valve into the left ventricle. From the left ventricle, the oxygenated blood exits through a vessel known as the aorta, splitting and curving down the road into smaller arterioles and subsequent capillaries. Eventually, the deoxygenated blood is returned to the right atrium by the vena cava pair, and this cycle continues. Even though the path blood takes is long and curvy, the heart still can easily pump more than 1.5 gallons of blood a minute, or a good-sized aquarium of strawberry Kool-Aid in an hour. 

Overall, the human heart is a vital part of our very being alive, a symphony of tissue pumping life-giving blood all throughout our bodies. Understanding the heart’s anatomy and physiology is completely vital to knowing how to properly care for our bodies. Our efforts to learn how to better care for and understand this wonderful organ play out across our entire body, affirming the adage that a healthier heart indeed results in a happier life. 

In Anatomy and Physiology Part One, we discussed the general structure of the heart. Building upon that foundation, we will now dive into greater details about the specific layers, valves, and other components of the heart. Additionally, our discussion will also include their functions, which can be wide-ranging, from protecting the heart to facilitating blood flow. Understanding the anatomy and physiology of these parts is crucial to living a long and healthy life.

When looking at a picture of the heart, the outer muscular wall is a thick red sheet bordered by a paper-thin line, but this could hardly be farther from the truth. A tough, fiber-reinforced sac called the pericardium surrounds the muscle. This bag has two parts: the soft, serous pericardium and the fibrous pericardium. The fibrous layer is located on the outside, protecting the heart while still allowing it to beat. However, the actual organ part of the heart would damage itself by pulsing on a pure version of this outer layer. This is where the smooth and soft inner layer - called the serous pericardium - becomes incredibly crucial. This surface splits into two separate sheets, the parietal-serous layer which borders the sinewy outer layer, and the visceral-serous layer which encases the inner organ part. Even then, friction between the layers can damage and impair the heart, so the body developed an ingenious way of combating this. Between the two smooth layers is an area known as the pericardial cavity, which contains the pericardial fluid. This fluid drastically reduces the friction between the two parts which allows them to ease smoothly across each other. Together, these structures keep the heart safe from harm while allowing it complete freedom of the pumping action and other movements.

    Within the pericardial sac, the organ itself contains a war that is categorized into three distinct layers: the epicardium, myocardium, and endocardium (from outer to inner, respectively). This outer layer was already partially mentioned in the above paragraph, as the epicardium includes the visceral-serous layer. Its functions range from simple protection to the development and repair of heart cells. As for the middle layer, also known as the myocardium, its functions are very different. Its purpose is simple yet crucial: making up the bulk of the heart wall, it ensures the contraction of the heart, sending blood throughout the body. Finally, we stop at the endocardium, the innermost layer of the heart. The endocardium’s main structure is the endothelium, a thin layer of cells that line the valves and chambers of the heart. This thin layer of cells (endothelial cells) enables blood to easily flow over it and reach other areas of the body.

    Next, we will continue our discussion by looking at the valves of the heart. These structures, of which there are four total, are there for one function: to stop the regurgitation or backflow of blood. They are located between the two atriums and ventricles, the connection points of the right atrium and pulmonary artery, and that of the left ventricle and the aorta. The valve between the right atrium and right ventricle (remember, the atriums are the top two chambers, and the ventricles are the bottom ones) is known as the tricuspid valve, and the one between the left atrium and ventricle is called the mitral valve. These two valves are collectively called the atrioventricular valves, and the other two are grouped into the semilunar valves. These semilunar valves are named according to their respective arteries: the pulmonary valve located between the right ventricle and the pulmonary artery, and the aortic valve situated between the left ventricle and the aorta. The valves’ presence prevents many disorders from arising, some of which we will address in later editorials.

    In summary, the heart is composed of many different parts, some of which are grouped into layers. These parts have many distinct functions, which come together to form a general group function, illustrating an important idea in biology -  emergent properties. Without these structures, the heart would be unable to do its job which would result in dire consequences if left untreated. The most imperative thing is to preserve the health of these tissues as well as we can, enabling us to experience optimal cardiovascular health and wellness.

Now deoxygenated, this particular red blood cell will travel through the inferior vena cava, which is responsible for carrying deoxygenated blood from the lower body parts (ex: the legs) back to the heart. There is also the superior vena cava, which delivers deoxygenated blood from the upper portions of the body. The superior and inferior vena cava both fulfill the important role of transporting deoxygenated blood to the right atrium, where the blood would then proceed to flow into the right ventricle. From the right ventricle, the red blood cell travels through the pulmonary artery, which has the role of transporting deoxygenated blood from the right ventricle to the lungs for reoxygenation. In the lungs, the process of diffusion takes place as oxygen diffuses from the alveoli in the lungs to the red blood cell, reoxygenating it. The oxygenated red blood cell then travels through the pulmonary vein to the left atrium and flows to the left ventricle as it is ready to begin the entire cycle again.

Inside the vessel walls, they can be separated into three layers named tunica. Despite sharing similar fundamental structures, these vessels exhibit variations comparable to pipes with different requirements and specifications. For example, the aorta is elastic, with thick outer walls, making it ideal for delivering blood under high pressure as blood rushes out of the left ventricle. In contrast, the pulmonary artery and vena cavae (plural form of vena cava) are structured to withstand lower pressure, making them suitable for directing deoxygenated blood from the right ventricle or deoxygenated blood returning to the heart, respectively. The pulmonary veins, with their thinner structure relative to the aorta, play a unique role in transporting freshly oxygenated blood at a generally lower pressure than the aorta. Understanding these specifics allows us to understand better the proper ways to preserve these structures.

In conclusion, the Great vessels of the heart are indispensable parts of the circulatory system, enabling the heart’s pumping action to send blood rushing throughout the body. Different and unique in their own ways, together, they form a network of vessels comparable to a miniature highway system inside our bodies. Therefore, it is important to learn about these crucial structures and ways to protect them, allowing for an easier and more enjoyable life.