Biology Essay Samples

Flow of Blood through the Heart

General Purpose:
Specific Purpose: To inform my audience about the process by which blood flows through the human heart
Thesis Statement: Why the heart is important, learning about its general anatomy. What happens during a single cycle of heart contraction, and how blood flows through the different chambers of the heart.

Introduction

Attention Getter: Do you know that the human heart never stops beating. And the over the course of a lifetime it can beat upt0 2.5 billion times, non-stop! On an average day, the heart pumps 2,000 gallons of blood through 60,000 miles of blood vessels.
Did you also know that the heart starts beating at four weeks after conception and does not stop until death?
Thesis Statement/Introduce Topic: The human heart is responsible not only for the functioning of the circulatory system, but also all other organs, including 7.5 trillion cells that constitute the human body. Today we will take a look at the processes by which blood flows through the heart and transports oxygen from the lungs to different parts of the body.
Preview: The human heart beats 72 times per minute, in this presentation we will see what exactly happens within the heart during each heartbeat.
The heart not only pumps blood throughout the body, it is actually responsible for the maintenance and nourishment of all other organs and bodily functions. The mammalian heart consists of four distinct chambers viz. the left and right atrium and the left and right ventricles. The heart is composed of three layers of tissues viz., epicardium, myocardium, and endocardium. The outer wall of heart is covered by a thin layer called the pericardium(J. S. Robb and R. C. Robb).
While the left heart chambers like left atrium and ventricle carry only oxygenated blood, the right atrium and ventricle transport only de-oxygenated blood. The heart is responsible for the proper functioning of the body and its organs. The mammalian and avian heart is designed to separate the oxygenated and deoxygenated blood to improve aerobic fitness and support high activity levels. Heart is one of the most important organs of the body that is vital for the proper functioning of the circulatory system. The human heart has evolved from the rudimentary two-chambered hearts of fish, to the three-chambered hearts of amphibians and reptiles to finally have the four-chambered configuration that is found in birds as well.
[Transition: Now let us look at how the heart works]
Main Point: Heart receives deoxygenated blood from all parts of the body through veins. Veins usually carry blood at a slower speed compared to arteries. A simple way to remember the difference between veins and arteries is that veins carry blood “to” heart and arteries carry blood to ‘from’ heart. For example, the pulmonary artery carries deoxygenated blood from the right ventricle to the lungs and the pulmonary vein supplies oxygenated blood to the left atrium.
Sub-point: Deoxygenated blood from all parts of the body reach the right atrium through two veins viz. superior vena cava, and inferior vena cava(Kent). The superior vena cava carries blood from the head and two arms, while the inferior vena cava transports blood via veins from legs and the gut. Once the deoxygenated blood reaches the atrium, the atrium goes through a systole and pushes the blood through the tricuspid valves that prevent backflow of blood from right ventricle to atrium.
Sub-point: The blood now inters the right ventricle, and during the ventricular systole the deoxygenated blood goes to the lungs through the pulmonary artery for oxygenation. There is a pulmonary valve at the base of right ventricle and the pulmonary artery prevents blood from flowing back to the right ventricle. Once the deoxygenated blood reaches the lungs, it passes through capillaries and by simple diffusion, oxygen from inspired air is transferred through the alveoli to the blood vessels, where Hemoglobin binds with oxygen. Thus the deoxygenated blood is oxygenated again.
[Transition: The oxygen-laden blood cells are now transported back via the pulmonary vein to the left atrium.]
Main Point: The left atrium is the only place where oxygenated blood is received from the lungs. The pulmonary vein carries oxygenated blood and supplies it to the left atrium.
Sub-point: Once the left atrium is filled with oxygenated blood, it goes through a systole and pushes blood to the left ventricle via the mitral valve. The oxygenated blood now reaches the left ventricle, where the blood is pumped out through the aorta to various parts of the body via the arteries. Aortic valve present between the left ventricle and the aorta, prevents the backflow of blood to the ventricle after the systole.
Sub-point: The heart has two pacemakers, the Sino atrial node and atrioventricular node that are responsible for the regular systole and diastole of the atrium and ventricles(Yamauchi). On an average a resting human heart can beat between 60-100 beats per minute. However, the sound of the beating heart is not caused by the contraction of the muscles, but the opening and closing of the tricuspid valve between right atrium and ventricle and the mitral valve, which is situated between the left atrium and ventricle.
Signpost: In summary the heart performs a very complex task as it transports blood rich with oxygen and nutrients to different parts of the body and also removes waste products, metabolites, carbon dioxide from the cells by supplying blood to the kidneys ( the excretory system), lungs, liver and other vital organs.

Summary: Heart is a very important organ that is vital to the homeostasis of the body

The four-chambered mammalian heart has improved efficiency as unlike amphibians, it does not allow oxygenated and deoxygenated bloods to mix. By circulating blood throughout the body, our heart keeps us healthy and functioning.

Bibliography

Kent, A F. “Researches on the Structure and Function of the Mammalian Heart.” The Journal of physiology 14.4-5 (1893): 233–254. Print.
Robb, Jane Sands, and Robert Cumming Robb. “The Normal Heart: Anatomy and Physiology of the Structural Units.” American Heart Journal 23.4 (1942): 455–467. Print.
Yamauchi, A. “Ultrastructure of the Innervation of the Mammalian Heart.” Ultrastructure of the Mammalian Heart. Academic Press New York, 1973. 127–178. Print.