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Atrium: Heart Function & Definition

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  • 0:01 The Human Heart
  • 0:40 Blood Flow in the Heart
  • 1:50 How It Does Its Job
  • 3:10 Lesson Summary
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Lesson Transcript
Instructor: John Williams
The atrium is a key player in the functioning of the heart, yet it does not get the attention it's due when compared to the ventricles. This lesson pays homage to this unsung hero in cardiac circulation.

The Human Heart

Circulation, or the movement of fluids within an organism, is an essential process for life. In humans, this process is controlled by the heart. The heart is an organ made of mostly muscle, and this muscle is necessary to pump blood throughout the body.

The human heart has four chambers: two atria, which are located at the top of the heart, and two ventricles, which are located at the bottom. While the ventricles are often the focus of lectures involving the heart, it is important to discuss the characteristics of the atrium, since it is a vital part of the overall function of the heart.

Blood Flow in the Heart

When blood moves through the heart, it follows a one-directional pathway through all four chambers. Briefly, blood enters the right atrium from the body, moves to the right ventricle, is sent to the lungs for oxygenation, returns to the left atrium, moves to the left ventricle, and is pumped from there to the rest of the body. This pathway is important, because it helps to set the scene for the descriptions of the atria and their functions.

The atrium is the receiving chamber of the heart. In other words, when blood arrives at the heart, it will enter the atrium first. The walls of the atrium are relatively thin compared to the ventricles and do not generate a large amount of contraction to pump blood.

Why, you ask? Simply put, it doesn't have to pump blood far. Blood in the atrium is pumped only a few inches into the ventricle, and the atrium does not need a large amount of muscle for this function. By comparison, the walls of the ventricles have large amounts of muscle, since they pump blood out of the heart and into other circulation pathways. Both the left atrium and the right atrium are roughly the same size, since they both pump blood the same distance to the ventricles.

How It Does Its Job

The atrium is designed to allow for a smooth flow of blood from the body to the heart without interruption, even when it is contracting. While blood flow through the rest of the heart and the body takes place in rhythmic beats, the atrium has to receive blood in an uninterrupted manner in order to maintain cardiac function. This is done in several ways.

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