Difference Between Atrium and Auricle

Main Difference – Atrium vs Auricle

Atrium and auricle are two structural components of the heart. The main difference between atrium and auricle is that atrium is a compartment of the heart whereas auricle is a small out-pouching of the atrium. Heart is composed of two atria and two ventricles. Atria are the upper compartments while ventricles are the lower compartments. Left atrium and right atrium are the two types of atria. Atria are the compartments that are first filled with blood in each cycle of the heart. Left atrium receives blood from the superior vena cava. Left atrium supplies blood to the left ventricle whereas right atrium supplies blood to the right ventricle. Auricle is an ear-like muscular pouch which arises from each atrium.

Key Areas Covered

1. What is Atrium
      – Definition, Anatomy, Physiology
2. What is Auricle
      – Definition, Anatomy, Physiology
3. What are the Similarities Between Atrium and Auricle
      – Outline of Common Features
4. What is the Difference Between Atrium and Auricle
      – Comparison of Key Differences

Key Terms: Atrium, Auricle, Atrioventricular (AV) Node, Blood, Heart, Sinoatrial (SA) Node, Superior Vena Cava, Ventricle

What is Atrium

Atrium refers to the each of the two upper cavities of the heart, which supplies blood to the ventricles. The two atria are separated by the interatrial septum. Thereby, the two atria are the left atrium and the right atrium. The major function of the atrium is to receive blood and carry it to the ventricles. The two atria in the heart are shown in figure 1.

Figure 1: Left and Right Atria

The right atrium receives blood from the superior and inferior vena cava. Superior vena cava drains blood from the chest, arm, neck, and head regions of the body while inferior vena cava drains blood from the rest of the body. Accordingly, right atrium receives de-oxygenated blood. The left atrium receives blood from four pulmonary veins which carry oxygenated blood from the lungs. The wall of the atrium is made up of inner endocardium, middle myocardium, and outer epicedium. The myocardium layer in the wall of the atrium is thinner than that in the ventricle wall. On that account, atrium generates a less pressure on blood.

The sinoatrial (SA) node is located in the upper right atrium wall of the heart. The electrical impulses that originate from the SA node travel through the wall of the heart to the atrioventricular (AV) node. The AV node is located in the lower portion of the right atrium. Both SA and AV nodes coordinate the contraction of the atria.

What is Auricle

Auricle refers to an ear-shaped pouch in the atrium of the heart. Each auricle is attached to the anterior surface of each atrium. Thereby, the two auricles are called the left auricle and the right auricle. Auricle is a wrinkled structure. It resembles a dog’s ear. The major purpose of the auricle is to increase the capacity of each atrium. The left and the right auricles are shown in figure 2.

Figure 2: Right and Left Auricles

The left auricle is also called the left atrial appendage (LAA). The right auricle is also called the right atrial appendage (RAA). The RAA is more muscular than the LAA.

Similarities Between Atrium and Auricle

Both atrium and auricle are two upper structures of the heart.
Both atrium and auricle occur in pairs.
Both atrium and auricle help to supply blood to the corresponding ventricles.

Definition

Atrium: Atrium refers to each of the two upper cavities of the heart which supplies blood to the ventricles.

Auricle: Auricle refers to an ear-shaped pouch in the atrium of the heart.

Type

Atrium: Atria is the upper chambers of the heart.

Auricle: Auricle is a conical muscular pouch that arises from each atrium.

Function

Atrium: Atrium supplies blood to the corresponding ventricle.

Auricle: Auricle increases the blood holding capacity of the atrium.

Surface

Atrium: Atrium is composed of a smooth surface.

Auricle: Auricle is composed of an irregular space.

Conclusion

Atrium and auricle are two structures of the upper portion of the heart. Atrium is a chamber that supplies blood to the ventricles. Heart is composed of two atria; left atrium and the right atrium. Auricle is an outer appendage of the atrium. It increases the capacity of the atrium. The main difference between atrium and auricle is their structure and function.

Reference:

1. Bailey, Regina. “The Functions of the Heart’s Atria.” ThoughtCo, Available here.
2.“Left Auricle.” InnerBody, Available here.

Image Courtesy:

1. “Diagram of the human heart (cropped)” By Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Heart, aorta and pulmonary artery” By Anatomist90 – Own work (CC BY-SA 3.0) via Commons Wikimedia