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Cardiology: Heart and Circulatory System

The primary function of the heart is to pump blood throughout the organism, a process in which the liquid undergoes numerous transformations that enable it to support many crucial bodily functions. It accepts deoxygenated blood, pumps it to the lungs, where it is enriched with oxygen, and back, and then pushes it back into the arteries. In the process, various other substances, notably hormones, are introduced into the bloodstream while waste is removed, and the heart facilitates the process and ensures that all substances are delivered where they should be. Lastly, the heart’s beating maintains blood pressure, which is critical for the correct functioning of several more bodily functions. Overall, the common knowledge that the heart is a vital organ is accurate, and any issues in its functioning can have severe adverse consequences for the individual.

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In addition to the heart, the circulatory system consists of a large number of blood vessels of varying sizes that permeate the body and deliver blood to every tissue that needs access to it. Four distinct types of blood vessels are generally recognized: arteries, veins, capillaries, and sinusoids. Arteries carry blood away from the heart, whether to the lungs (pulmonary) or to the rest once it has been oxygenated (systemic). Conversely, veins move the substance back to the heart, where it is processed and prepared for reuse. They are divided into four types: pulmonary, systemic, superficial (close to the surface of the body), and deep (far from the surface). These two categories of blood vessels are relatively large, and damage to them can be devastating and lead to a quick death by bleeding. Capillaries are small vessels that are used to distribute blood throughout tissues and organs and facilitate the exchange of nutrients. Sinusoids are similar but located in the liver, spleen, and bone marrow, adapted to enable quick nutrient exchange to supply non-oxygen substances to the body.

Human cells rely on oxygen to produce energy and nutrients, constantly and rapidly consuming the element regardless of their location in the body. The lack of oxygen, also known as suffocation, can cause death within minutes, unlike starvation or dehydration. As a result, they require continuous replenishment of their reserves of the gas, which is supplied by the blood. When it comes back to the heart, the substance is effectively drained of its oxygen content, which informs the term used for it, “deoxygenated.” The heart then directs it to the lungs, where it is exposed to the gas and absorbs it until saturated or until there is no more available oxygen (Waschke & Paulsen, 2018). In this state, the blood is known as oxygenated, and it is ready to return to the heart and be pumped back into the organism to repeat the replenishment cycle.

Within the lungs, the blood is directed through a large number of small channels known as capillaries. These bloodstreams touch and encapsulate the air sacs that constitute lungs, which fulfill the dual function of one-way transit for specific gases. From within the sacs, oxygen moves through the membrane and enters the blood, where it is bonded to the hormone hemoglobin and carried through the organism. At the same time, blood takes away CO2, which is formed as a result of oxygen usage and does not benefit the organism, from the cells and carries it back to the lungs. There, it passes through the same membrane the opposite way to oxygen, entering the air sacs to be exhaled and, thus, expelled from the organism. In this way, blood fulfills the dual function of supplying oxygen to cells and removing its byproducts from them instead of letting them accumulate.

The heart is a muscle, though it is of an unusual type compared to more common smooth or skeleton muscles. They are striated like skeletal muscle, but also involuntary similar to the smooth variety, ribbon-like in structure and branched, and joined via structures known as intercalated discs as well as gap junctions at the discs’ borders (Khurana & Khurana, 2018). As a result of these properties, the heart beats regularly and rhythmically without the direct input of the body, though it responds to oxygen demand by beating faster or slower. This process consists of two stages: relaxation, where the heart lets blood in and expands to accommodate it, and contraction, where it forcefully pushes the liquid out into the arteries. With that said, the four sections of the heart are able to expand and contract somewhat independently, which enables the heart cycle with its four distinct stages.

These four sections are the right and left atria and the right and left ventricles. Each has a separate valve that it uses to control whether blood can flow into the chamber, which they close when contracting and pumping the substance out. These four valves are known as tricuspid, mitral, pulmonary, and aortic. In the heart cycle, the right atrium receives blood from the veins first, filling up with it. Next, the tricuspid valve opens, and blood flows from the right atrium to the right ventricle. The opening then closes, and the pulmonary valve opens instead as the right ventricle contracts to pump blood to the lungs. It is then received by the left atrium, which opens the mitral valve and enables blood to flow to the left ventricle. Finally, the closing and opening process repeats, and the aortic valve opens to let the left ventricle contract and send oxygenated blood throughout the body.

The disruption of the heart’s function can disrupt the functioning of every system in the body, especially given enough time. However, the complications most commonly linked to the organ directly involve it and include cardiogenic shock and cardiovascular diseases. The former occurs when the body is no longer able to pump blood and oxygen to the person’s organs, which leads to reduced cardiac output, hypotension, increased filling pressures, lactic acidosis, and a variety of other issues (Kirklin & Rogers, 2019). It can result from numerous different causes, which also determine the specific effects it can have. These factors include cardiovascular diseases, which are a broad category ranging from hypertension, which increases the patient’s risk but often does not have easily observable effects otherwise, to strokes, which can be sudden and kill the person almost immediately. These can also develop for a variety of different reasons, and a more detailed discussion is warranted.

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Cardiovascular diseases are typically classified into a variety of types by the area in which they manifest. Illnesses that affect the heart directly are known as coronary, those of brain-related blood vessels are cerebrovascular, and those of arm and leg vessels are peripheral. More specific condition types are also typically recognized, such as streptococcal bacteria-related rheumatic heart disease, inborn congenital heart disease, and leg vein blood clots known as deep vein thrombosis and pulmonary embolism. Depending on the source and location of the condition, the effects can vary widely. With that said, most cardiovascular conditions carry the risk of obstructing blood flow, which can damage the affected part and, potentially, the rest of the organism. The most problematic of these is the interruption of blood flow to the brain, which is known as a stroke. As brain cells are essential and do not recover the same way other types do, strokes can permanently disable a person at various degrees of severity, up to and including death.

Cardiogenic shock is not the only type that affects the heart; other varieties include distributive, obstructive, septic, neurogenic, and psychogenic shock. Distributive shock results from a loss of vascular tone, presenting as hyperdynamic cardiac activity with reduced oxygen extraction, leading to a maldistribution of blood and an eventual hypodynamic state (McQuillan & Makic, 2019). In obstructive shock, blood flow from the left ventricle is impeded, and tissues are not oxygenated adequately. In septic shock, metabolic tissue demands rise, often due to infection, and the heart is unable to meet them despite acting hyperdynamically. In neurogenic shock, central nervous system issues cause a loss of vasomotor control, and capacitance vessels are dilated, with blood volume unable to fill them (McQuillan & Makic, 2019). Lastly, psychogenic shock operates similarly to the neurogenic variety but is caused by emotional distress rather than nervous system injury or malfunction.

All of the types of shock discussed endanger the patient’s life, especially when combined with the other damage they are likely to have sustained. They prevent blood from conducting oxygen and nutrients effectively, starving the body of the materials it needs to survive. As such, many varieties of shock tend to be highly fatal unless they are addressed immediately by trained and qualified medical professionals. Even if such a treatment is administered, the heart’s efforts to address the shock, such as an increase in activity, can lead to overexertion and damage to the organ. The organs that are being starved of oxygen can also be permanently damaged in a variety of unpredictable ways. As such, shock is among the many reasons why people should proactively monitor their cardiovascular health for early signs of issues.

Despite its apparent simplicity, the heart is a complex organ, especially when viewed from a treatment perspective. It performs a variety of functions, most of which directly contribute to the short-term survival of the individual. Interfering with it for medical purposes is both difficult and dangerous, as its activities have to continue uninterrupted at all times. With that said, without oversight and maintenance, the heart can develop a variety of issues that can be highly lethal. It is advisable to maintain it through whatever means are available, with lifestyle, in particular, having a considerable effect on cardiovascular health in the long term. Moreover, medical workers should be prepared to recognize the signs of heart conditions, especially highly dangerous ones such as stroke or shock, and intervene quickly and effectively. The importance of the heart and the rates of cardiovascular diseases in numerous populations mandate that research into its operations and maintenance continue to achieve improvement.


Khurana, I., & Khurana, A. (2018). Concise textbook of human physiology (3rd ed.). Elsevier.

Kirklin, J. K., & Rogers, J. G. (2019). Mechanical circulatory support: A companion to Braunwald’s heart disease (2nd ed.). Elsevier.

McQuillan, K. A., & Makic, M. B. (2019). Trauma nursing: From resuscitation through rehabilitation (5th ed.). Elsevier.

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Waschke, J., & Paulsen, F. (2018). Sobotta atlas of anatomy: Internal organs (16th ed.). Elsevier.

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