Introduction

The Human heart is the organ that supplies blood flow throughout the entire Human body. Within the heart are four cavities: two ventricles and two atria. These cavities perform numerous functions individually that work in tandem with each other. First, the left atrium receives oxygenated blood from the lungs. Once this is done, the blood transfers to the left ventricle. The left ventricle then powers the blood through arteries to get the blood to the tissues of the body via use of the aorta. The right atrium acquires the blood after it has completed this process and is devoid of oxygen. In my paper, I will further examine the heart, its parts and the respective functions of the human heart as understanding this structure is essential to the survival of the human race.

Development of the Human Heart

The human heart is one of the first functioning organs in the human body. It begins beating in the human embryo at about 22 days, and blood flow begins in the embryo at the fourth week. The heart is not formed inside of the chest cavity. It initially is birthed within the embryonic disc, and when it folds it is then transferred to the chest cavity.(Livingstone, 2015)

The human heart goes through a process of creation while the human embryo is inside of the host mother. The heart has three primary germ layers that differentiate it during development: Mesoderm, Endoderm, and Ectoderm. These three germ layers inevitably produce every organ in the human body, including the heart.

While in development, the Endoderm sends signals to create cardiogenic cords. During development, a lumen is formed within them and they are then referred to as endocardial tubes. These tubes work together to form a single primitive heart tube. This heart tube then works to form five distinct regions: the truncus arteriosus, bulbus cordis, primitive ventricle, primitive atrium, and the sinus venosus. These five regions ,when fully developed, are the structure that combine to form the Human Heart. The primitive atrium develops into the two auricles and anterior ends of both the left and right atria. The primitive ventricle develops into the left ventricle. The right ventricle is developed from the bulbus cordis. The pulmonary trunk and aorta are created from the division of the truncus arteriosus. Lastly, the sinus venosus creates the SA node, coronary sinus, and the posterior of the right atrium when it has developed.

The Human Heart’s development is controlled by transcription factors. These transcription factors connect signalling pathways with genes for contractility, patterning, and muscle growth. This means that these genes are responsible for telling the human heart how to develop, what structures to make, how to make them, and their designated functions. (Olson 2006)

Structures of the Human Heart

The human heart has many different structures that work in tandem to keep human beings alive and operational. While the human heart itself could be described as an organ, it has many different muscles that allow it to pump blood throughout the stream of the body. One such muscle is a transverse muscle which splits each side of the human heart into two cavities. The upper cavity on each side is known as the atria, or the auricle, and the lower side is known as the ventricle. Dim venous blood is siphoned into the correct chamber by the coronary sinus and both the predominant and substandard vena cava (SVC). From the chamber, the blood goes into the ventricle is then passed through the respiratory conduit into the lungs. Once the blood becomes oxygenated/arterialized by its passage through the lungs, it is pumped back to one side of the heart by the pneumonic veins which open into the left chamber.

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From the left chamber, the blood is pumped into the left ventricle. Once here, the blood is distributed throughout the body by the aorta and its subdivisions. The right Atrium of the heart differs from the left Atrium, in which its walls are thinner that the left and it is longer. The right atrium is bigger than the left so that it is able to hold up to two ounces of fluid. It is comprised of two sections,an appendix auriculae and a main cavity/sinus.  The sinus is a huge quadrilateral-formed cavity situated between the IVC and the SVC. Its walls are incredibly slim and are associated on the lower surface with the right ventricle and internally within the left ventricle. (Bentham 2008)

The appendix auricle is a small cone-shaped muscular pouch. It projects from the sinus forward, where it overlaps the root of the pulmonary artery. There are four main openings into the right atrium; the IVC, SVC, atriculo-ventricula opening, and the coronary sinus. The larger IVC returns blood from the lower half of the body to the lowest part of the right atrium, near the septum.

The smaller SVC transfers blood from the upper half of the body to the upper and front part of the right atrium. The coronary sinus opens into the right atrium between the IVC and auriculo-ventricular opening. It transfers blood from the cardiac muscle of the heart. The coronary sinus is protected by the coronary valve, which is a semicircular fold of the lining membrane of the atrium. The auriculo-ventricular opening is an oval shaped hole, located between the right atrium and ventricle. There are two main valves located within the right atrium; the Eustachian valve and the coronary valve. The Eustachian valve is located between the front space of the IVC and the auriculo-ventricular opening. It is shaped like a crescent moon.

The right ventricle extends from the right atrium to near the top of the heart, and is shaped like a triangle. Its front surface is rounded and forms the anterior of the heart. Its posterior surface forms a small part of the heart’s surface, is flattened, and rests on the diaphragm muscle. Its inner wall is formed by the septum, and bulges into the cavity of the right ventricle. The ventricle forms a cone-shaped structure called the infundibulum, from which the pulmonary artery arises.

How Form Fits Function

Each and every structure of the human heart has evolved and developed over time to perform a specific function. For instance, the human heart has a wall that is composed of three layers: 1. The outer, thin layer known as the epicardium, 2. The thick middle layer made up of cardiac muscle fibers known as the myocardium, and 3. Another thin layer located on the innermost side of the heart known as the endocardium. The purpose of all three of these layers os to provide protection for the human heart from foreign substances, bacteria and other items that could cause damage to it. The human heart also has many tube-like structures extending from it, each with their own purpose. The aorta located beneath the human heart pumps blood to the lower portion of the body, while the inferior vena cava( located beneath the heart as well) serves the purpose of pumping blood back up from the lower portion of the body (Miranda,2019).  The heart has pulmonary veins that extend from both the left and right sides of the human heart  that each serve the purpose of pumping blood from the left and right lungs respectively. The human heart has a pulmonary artery which serves the purpose of pumping blood to the left and right lung, which explains why it has developed into a crossroads-type of vein-like structure ( meaning that it splits in the middle and has two tubes that travel to each lung respectively). At the top of   human heart are arteries that function to pump richly oxygenated blood throughout the top of the body. Given the nature of the severity of the upper half of the body ( the head and heart reside in this region), blood must be able to flow faster both to and from this region in order to keep the human body alive. For this purpose, the superior Vena Cava is the biggest tube-like structure connected to the heart, and it serves the purpose of pumping blood from the upper region of the body back into the heart. (Cherry 2017). The human heart has ventricles, which are large chambers designed to hold large amounts of blood at a time. They are designed this way in order to fill up with blood and then collapse in a ‘pumping’ motion to circulate the blood throughout the entire body (Ikwuagwu 2016)

The human heart itself is located in the center of the human body. It is located behind the rib cage, which serves as protection to this vital organ from everyday trauma and accidents. The human heart being located in the center of the human body allows it to be an equal distance away from every part of the body that needs blood pumped to it.

Conclusion

In conclusion, the human heart is the reason why human beings are alive. It has countless components, each with a different shape and the ability to perform a different task. The combination of all of these structures is known as the human heart, but upon further examination it is truly a masterpiece of an organ. It is the first organ that begins forming in a human embryo, and it is responsible for the creation of every organ that inevitably develops within the human body. Not only is the human heart the creator of these numerous organs, it is responsible for ensuring that blood reaches every inch of the body and that all organs and limbs remain healthy and functional throughout the duration of the human life cycle. Each part of the human heart has a unique shape, and form fits function.

Literature Cited

Speller, J. (2018, January 14). Development of the Cardiovascular System. Retrieved July 31, 2019, from https://teachmeanatomy.info/the-basics/embryology/cardiovascular-system/

Livingstone, C. (2015). Larsen’s Human Embryology(5th ed., Vol. 2nd). New York, NY: Edinburgh.

Olson, E. N. (2006, September 29). Gene Regulatory Networks in the Evolution and Development of the Heart. Retrieved July 31, 2019, from https://science.sciencemag.org/content/313/5795/1922

Bentham, J. & Bhattacharya (2008). S. Genetic mechanisms controlling cardiovascular development. Ann. NY Acad. Sci. 1123, 10–19.

Miranda, G. M. (2019, February 26). Structure and Function of the Heart. Retrieved July 31, 2019, from https://www.news-medical.net/health/Structure-and-Function-of-the-Heart.aspx

Cherry, E., & Fenton, F. (2017). The Virtual Heart. Retrieved from http://thevirtualheart.org/

Ikwuagwu, L. (2016, March 12). Anatomy of the Human Heart. Retrieved July 31, 2019, from https://www.acls.net/anatomy-of-the-human-heart.htm

Donahue-Taylor, C. (2016). Structure of the Heart. Retrieved from https://training.seer.cancer.gov/anatomy/cardiovascular/heart/structure.html