Difference Between Single and Double Circulation

The key difference between single and double circulation is that in single circulation, blood travels once through the heart during a complete cycle, while in double circulation, blood flows twice through the heart during a complete cycle.

The heart and lungs play an important role in circulation. The heart is the organ that pumps blood into various cells and tissues. Lungs or gills purify the blood and mix oxygen with the blood. In fish, blood flows once through the heart during a complete cycle. Hence, we call this type of circulation a single circulation. In mammals and birds, and other vertebrates, blood flows twice through the heart during a complete cycle. We call this type of circulation double circulation. Single circulation is less efficient than double circulation.

CONTENTS

1. Overview and Key Difference
2. What is Single Circulation
3. What is Double Circulation
4. Similarities Between Single and Double Circulation
5. Side by Side Comparison – Single vs Double Circulation in Tabular Form
6. Summary

What is Single Circulation?

In single circulation, blood flows once through the heart during one complete cycle of the body. Single circulation happens in fish. Venous blood flows through the heart. Single circulation is less efficient. Blood flows at low pressure. Hence, the rate of oxygen supply to cells and tissues is low in a single circulation.

In single circulation, blood flows from the heart to the gills, where the exchange of gases takes place. The heart has two chambers. The fish heart has one atrium and one ventricle. Then the oxygenated blood flows from the gills to various parts of the body and from these parts back to the heart.

What is Double Circulation?

In double circulation, blood flows twice through the heart during a complete cycle. Double circulation occurs in all vertebrates except in fish. Humans utilize a double circulatory system. Blood flows at high pressure in double circulation. Hence, tissues and cells receive oxygen at a higher rate. Moreover, the rate of waste removal is also high in double circulation.

Two pathways of circulations are pulmonary circulation and systemic circulation. Both oxygenated and deoxygenated blood flow through the heart. The heart has two separate compartments (four chambers) in order to prevent the mixing of oxygenated and deoxygenated blood. The right side of the heart pumps deoxygenated blood and is called the pulmonary circulation. Therefore, in pulmonary circulation, deoxygenated blood flows from the right ventricle to the lungs and oxygenated blood returns from the lungs to the left atrium. The left side of the heart pumps oxygenated blood into the systemic circulation. In the systemic circulation, oxygenated blood flows from the left ventricle of the heart to various parts of the body, and deoxygenated blood flows from various parts of the body to the right atrium.

What are the Similarities Between Single and Double Circulation?

• Single and double circulation are two types of circulatory systems.
• They are closed circulatory systems.
• Heart is the organ that pumps blood in both types of circulations.

What is the Difference Between Single and Double Circulation?

Single circulation is a type of circulatory system in which blood flows only once through the heart during one cardiac cycle. On the other hand, double circulation is a type of circulatory system in which blood flows twice through the heart during one cardiac cycle. So, this is the key difference between single and double circulation. Moreover, single circulation occurs via a double-chambered heart while double circulation occurs via a four-chambered heart. Thus, this is also a significant difference between single and double circulation. Single circulation is seen in fish while double circulation is seen in mammals, including humans.

The below infographic summarizes the differences between single and double circulation in tabular form.

Summary – Single vs Double Circulation

Single and double circulatory systems are two types of closed circulatory systems. In single circulation, blood flows only once through the heart during one complete cycle. In double circulation, blood flows twice through the heart during one complete cycle. Thus, this is the key difference between single and double circulation. Double circulation is more efficient in supplying oxygen to body tissues than single circulation. Furthermore, there is a strict separation of oxygenated and deoxygenated blood in double circulation. Mammals including humans utilize a double circulatory system, while fish utilize a single circulatory system.

Reference:

1. “Double Circulation – Blood Circulation in Humans.” BYJUS, 5 Mar. 2021, Available here.
2. “Single and Double Circulation Systems.” Nigerian Scholars Available here.

Image Courtesy:

1. “Fish circulation” By Lennert B – (CC BY-SA 3.0) via Commons Wikimedia

2. “Pulmonary And Systemic Circulation” (CC0) via Pixy.org