Difference Between Atria and Ventricles

Main Difference – Atria vs Ventricles

Atria and ventricles are the two types of chambers found in the heart of animals. The heart is a muscular pump that pushes blood throughout the body via blood vessels. Most mammals have a heart with four chambers as their heat is divided into two sides as right and left by the interatrial septum. The four chambers of the mammalian heart are right atrium, left atrium, right ventricle, and left ventricle. Generally, atria are the smaller upper chambers while ventricles are the larger lower chambers of the heart. The main difference between atria and ventricles is that atria receive blood into the heart whereas ventricles pump blood outside the heart.

Key Areas Covered

1. What are Atria
– Definition, Structure, Function
2. What are Ventricles
– Definition, Structure, Function
3. What are the Similarities Between Atria and Ventricles
– Outline of Common Features
4. What is the Difference Between Atria and Ventricles
– Comparison of Key Differences

Key Terms: Atrioventricular (AV) Valves, Heart, Left Atrium, Left Ventricle, Right Atrium, Right Ventricle, Purkinje Fibers, SA Node

What are Atria

Atria refer to the two upper chambers of the heart. The atrium located on the right side is known as the right atrium while the one located on the left side is known as the left atrium. The right atrium receives deoxygenated blood from the body through the superior and inferior vena cava. It supplies blood to the right ventricle. The left atrium receives oxygenated blood from the lungs through four pulmonary veins. It supplies blood to the left ventricle of the heart. The valves that control the blood supply from atria to the corresponding ventricles are referred to the atrioventricular (AV) valves. The right AV valve is known as the tricuspid valve while the left AV valve is known as the mitral valve. The anatomy of the human heart is shown in figure 1.

Figure 1: Human Heart

The atria are made up of a thin-walled posterior part and a muscular anterior part known as pectinate muscle. The veins empty blood through the thin-walled posterior parts of each atrium. The anterior part of both right and left atria exhibits a wrinkled, flap-shape known as auricle. The right and left atria receive blood passively during the relaxation phase of the cardiac cycle. The main function of atria is to collect blood from the body and supply the correct volumes of blood to the right and left ventricles respectively. The most significant feature of the atria is the presence of the sinoatrial (SA) node and the pacemaker cells in the wall of the right atrium; they control the rhythm of the cardiac muscle cells during contraction.

What are Ventricles

Ventricles refer to the two lower chambers of the heart. The ventricle located on the right side is known as the right ventricle while the ventricle located on the left side is known as the left ventricle. The right ventricle receives deoxygenated blood from the right atrium, and it supplies blood to the pulmonary artery through the pulmonary semilunar valve. The left ventricle receives oxygenated blood from the left atrium, and it supplies blood to the aorta through the aortic valve. The main function of pulmonary semilunar and aortic valves is the prevention of the backflow of blood into the corresponding ventricle. The valve system of the heart is shown in figure 2.

Figure 2: Valves of the Heart

The walls of the ventricles are thicker than that of the atria. Therefore, the pumping pressure of the ventricles is also high. The pumping pressure of the right ventricle is 25/15 mmHg while that of the left ventricle is 120/80 mmHg. Typically, the heartbeat is initiated by the SA node of the right atrium. However, the Purkinje fibers of the ventricles can give rise to the premature ventricular contractions.

Similarities Between Atria and Ventricles

Atria and ventricles are chambers of the heart.
Both atria and ventricles are made up of heart muscles.
Both atria and ventricles deal with deoxygenated blood as well as oxygenated blood.
Both atria and ventricles are involved in pumping blood throughout the body.

Definition

Atria: Atria refer to the two upper chambers of the heart.

Ventricles: Ventricles refer to the two lower chambers of the heart.

Types

Atria: The two types of atria are the right atrium and left atrium.

Ventricles: The two types of ventricles are the right ventricle and left ventricle.

Size

Atria: The atria are small.

Ventricles: Ventricles are large.

Thickness of the Wall

Atria: The atria consist of a thin wall.

Ventricles: The ventricles consist of thick walls.

Function

Atria: The main function of the atria is to collect blood and supply it to the ventricles in a controlled manner.

Ventricles: The main function of the ventricles is to push blood throughout the body.

Receive Blood

Atria: The right atrium receives deoxygenated blood through the superior and inferior vena cava while the left atrium receives oxygenated blood through four pulmonary veins.

Ventricles: The right ventricle receives deoxygenated blood from the right atrium while the left ventricle receives oxygenated blood from the left atrium.

Types of Valves

Atria: The right atrium supplies blood through the tricuspid valve while the left atrium supplies blood through the mitral valve.

Ventricles: The right ventricle supplies blood through the pulmonary semilunar valve while the left ventricle supplies blood through the aortic valve.

Supply Blood

Atria: The right atrium supplies blood to the right ventricle while the left atrium supplies blood to the left ventricle.

Ventricles: The right ventricle supplies blood to the pulmonary artery while the left ventricle supplies blood to the aorta.

Blood Pressure

Atria: The atria receive blood passively as there are no valves between the corresponding veins and the atria.

Ventricles: Ventricles receive blood with a considerable blood pressure as they receive blood through valves.

Contraction Control

Atria: The right atrium consists of the SA node and pacemaker cells that control the contractions of heart muscles.

Ventricles: The ventricles consist of Purkinje fibers that give rise to premature ventricular contractions.

Conclusion

Atria and ventricles are the two main types of chambers of the heart. Atria are the upper chambers while ventricles are the lower chambers of the heart. The main function of atria is to collect blood from the body into the heart whereas that of ventricles is the pump blood to the corresponding parts of the body with a high pressure. The main difference between atria and ventricles is the role of each type of chambers in the heart.

Reference:

1. Bailey, Regina. “The Functions of the Heart’s Atria.” ThoughtCo, Available here.
2.“Ventricle.” Encyclopædia Britannica, Encyclopædia Britannica, inc., 26 Apr. 2016, Available here.

Image Courtesy:

1. “Heart diagram-en” By ZooFari – Own workSupporting references↑ [1] (cache)↑ [2] (cache) (CC BY-SA 3.0) via Commons Wikimedia
2. “Heartvalve” By Medicine Plus– (Public Domain) via Commons Wikimedia