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Open Circulatory System vs. Closed Circulatory System: What's the Difference?

Edited by Janet White || By Harlon Moss || Updated on October 18, 2023
The open circulatory system has fluid moving freely in cavities; the closed circulatory system confines blood to vessels.

Key Differences

The open circulatory system and closed circulatory system are two primary ways in which organisms transport nutrients, waste, and gases throughout their bodies. These systems are foundational for maintaining an organism's metabolic processes. The open circulatory system is characterized by the movement of hemolymph (or circulatory fluid similar to blood) flowing freely within the body cavity. In organisms with this system, the heart pumps the hemolymph into spaces called sinuses, which surround organs.
In contrast, the closed circulatory system involves blood that remains enclosed in vessels throughout its circulation. The heart pumps this blood into large vessels, which subsequently branch out into smaller ones, reaching all parts of the body. This system is more efficient in transporting oxygen, nutrients, and waste products as the blood is confined and directed.
An open circulatory system is found mainly in lower invertebrates, such as insects and some mollusks. Since the hemolymph is not restricted to specific pathways, it moves slower, relying on body movements to aid circulation. The closed circulatory system, on the other hand, is typical of vertebrates like mammals, birds, and fish. This system, with its confined blood, operates under pressure, facilitating quicker and more targeted delivery of substances.
Furthermore, the open circulatory system, with its free-flowing hemolymph, tends to be less complex than the closed circulatory system. The closed system, with its intricate network of arteries, veins, and capillaries, supports the demands of larger, more active animals.

Comparison Chart

Fluid Movement

Hemolymph flows freely in body cavities.
Blood is confined to vessels.


Less efficient due to free-flowing nature.
More efficient due to confined and pressurized blood flow.

Found in

Primarily in lower invertebrates like insects.
Typically in vertebrates like mammals and birds.

Dependency on Body Movements

Relies on body movements for circulation.
Does not rely on body movements; has inherent pressure.


Generally simpler.
More intricate with a network of vessels.

Open Circulatory System and Closed Circulatory System Definitions

Open Circulatory System

A circulatory system where hemolymph flows freely in body cavities.
The open circulatory system in insects allows hemolymph to bathe the internal organs directly.

Closed Circulatory System

An internal transport system providing precise delivery of substances.
The closed circulatory system directs blood to specific tissues as needed.

Open Circulatory System

An internal transport system where hemolymph mixes with interstitial fluid.
In an open circulatory system, nutrients are directly exchanged between hemolymph and cells.

Closed Circulatory System

A circulatory system where blood remains within dedicated vessels.
Humans have a closed circulatory system, ensuring efficient nutrient transport.

Open Circulatory System

A system lacking dedicated blood vessels to confine circulatory fluid.
Crabs have an open circulatory system with few vessels.

Closed Circulatory System

A system where blood circulates without mixing with interstitial fluid.
The closed circulatory system in birds supports their high metabolic rate.

Open Circulatory System

Circulatory design in which fluid isn't always enclosed in vessels.
The open circulatory system relies on body movement to help circulate fluid.

Closed Circulatory System

Circulatory design with a network of arteries, veins, and capillaries.
Fish possess a closed circulatory system, aiding in efficient oxygen transport.

Open Circulatory System

A less complex circulatory arrangement found in many invertebrates.
The open circulatory system of a shrimp allows fluid to flow around organs in open spaces.

Closed Circulatory System

A more complex circulatory arrangement typically found in vertebrates.
The closed circulatory system of mammals includes a heart with multiple chambers for efficient pumping.


How does a closed circulatory system benefit mammals?

The closed circulatory system is more efficient, ensuring targeted and rapid transport of nutrients and wastes.

Which organisms typically have an open circulatory system?

Lower invertebrates like insects and some mollusks have an open circulatory system.

Does the closed circulatory system rely on body movements for circulation?

No, the closed system operates under pressure for blood circulation.

What is the main difference between an open and closed circulatory system?

The open circulatory system allows fluid to flow freely in body cavities, while the closed system confines blood to vessels.

How does oxygen transport differ between the two systems?

The closed system can transport oxygen more efficiently due to confined and pressurized blood flow.

Why is the open circulatory system considered less complex?

It lacks the intricate network of vessels found in the closed circulatory system.

Which system, open or closed, is more efficient in transporting substances?

The closed circulatory system is generally more efficient.

Why do some animals rely on an open circulatory system?

It's simpler, meets their metabolic needs, and is often paired with their body structure and lifestyle.

Which circulatory system supports higher metabolic rates?

The closed circulatory system can support higher metabolic rates.

How do organisms with an open circulatory system exchange nutrients and wastes?

Nutrients and wastes are directly exchanged between the hemolymph and the cells.

Which system provides more precise delivery of substances?

The closed circulatory system offers more precise delivery.

Are there intermediate forms between open and closed circulatory systems?

Some animals, like certain mollusks, exhibit features of both systems but are generally classified under one.

How is blood pressure managed in both systems?

Open systems generally have lower blood pressures, while closed systems maintain higher pressures for efficient blood flow.

Which circulatory system is more evolutionarily advanced?

The closed circulatory system is considered more advanced, supporting the needs of larger and more active animals.

What are the main vessels in a closed circulatory system?

The main vessels are arteries, veins, and capillaries.

Is the human circulatory system open or closed?

Humans have a closed circulatory system.

Does the open circulatory system use blood like mammals?

No, it uses a fluid called hemolymph which serves a similar purpose.

How do the heart functions differ between the two systems?

In the open system, the heart pumps hemolymph into body cavities; in the closed system, the heart pumps blood into vessels.

Can an organism switch between open and closed circulatory systems?

No, these systems are evolutionary adaptations specific to certain groups of organisms.

How does the open circulatory system support the needs of insects?

The open circulatory system allows direct exchange of nutrients between hemolymph and cells, suitable for insects' metabolic needs.
About Author
Written by
Harlon Moss
Harlon is a seasoned quality moderator and accomplished content writer for Difference Wiki. An alumnus of the prestigious University of California, he earned his degree in Computer Science. Leveraging his academic background, Harlon brings a meticulous and informed perspective to his work, ensuring content accuracy and excellence.
Edited by
Janet White
Janet White has been an esteemed writer and blogger for Difference Wiki. Holding a Master's degree in Science and Medical Journalism from the prestigious Boston University, she has consistently demonstrated her expertise and passion for her field. When she's not immersed in her work, Janet relishes her time exercising, delving into a good book, and cherishing moments with friends and family.

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