Why Are the Walls of the Ventricles Much Thicker Than the Walls of the Atria?

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The human heart has four separate chambers. Atria are the upper chambers of the heart and ventricles are the lower chambers. There is one atrium and one ventricle on the right side of the heart and one of each on the left side. Both atria and ventricles have valves that assist in the pumping of blood. The ventricles have much thicker walls than the atria, since they need to pump the blood much further and with more force.

Heart Wall

  • The heart itself is composed of three layers of tissue called the endocardium, the myocardium and the epicardium. The endocardium, or inner layer, is a thin layer of smooth muscle that will allow blood to flow without difficulty. The myocardium, or middle layer, is the muscular layer and the thickest layer of the heart wall. This is the layer that makes the most difference between the atria and ventricles. The ventricles have much thicker myocardial layers. The myocardium's job is to physically pump the blood from place to place. The epicardium, or outer layer, is a thin layer that helps protect the heart.

Job of the Atria

  • The right atrium receives blood from the veins of the body. This blood is deoxygenated and has already given its oxygen to the body tissues and has also picked up carbon dioxide and waste products from the tissues. The left atrium receives blood from the lungs. The pulmonary veins transport blood that has been to the lungs and received oxygen back to the heart, depositing it in the left atrium. Both atria have valves that prevent backflow of blood. When the heart contracts, the atria push the blood to the ventricles, the chambers right below the atria.

Job of the Ventricles

  • The walls of the ventricles are thicker and more muscular than those of the atria. The right ventricle is the depository for deoxygenated blood from the right atrium. The job of this ventricle is to pump the blood to the lungs so that it can obtain oxygen. The left ventricle is the powerhouse of the heart. It has the most muscular and thickest walls of any chamber of the heart, being even more muscular than the right ventricle. This chamber receives the blood that has been oxygenated in the lungs and pumped through the left atrium. The left ventricle is responsible for pumping the blood to the body tissues and organs. It has to be the most forceful since the blood that leaves the left ventricle has the furthest to travel.

DIfferences and Similarities

  • The four chambers of the heart all have very different functions and yet they work in ways that are similar to each other. All four chambers have valves that are there to prevent the backflow of blood. Each of the four chambers has a wall that consists of an endocardial, a myocardial and an epicardial layer. The atria have thinner walls and do not propel the blood very far. The ventricles have the same type of wall, although it is much thicker and more muscular. They also must pump the blood much further and with much more force.

Interesting

  • The heart functions as a type of double pump. Both sides work as one. The atria and ventricles are responsible for keeping this pump functioning smoothly and effectively. If any one chamber is not functioning as well as it should be, the entire heart and human body will suffer.

References

  • Body Structures & Functions; Ann Senisi Scott; 2004
  • The Human Body in Health and Illness; Barbara Herlihy PhD, RN; 2003
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