Open vs Closed Circulatory System: Difference and Comparison

Various anatomical features can recognize different phyla in the animal kingdom. The type of circulatory system (open or close) is very distinguishable among organisms.

For example, spiders, lobsters, and crabs have open circulatory systems, whereas fish, birds, and humans have closed circulatory systems.

There are many features in these circulatory systems that make them different from each other. 

Key Takeaways

1. Open circulatory systems have blood flowing freely within body cavities, whereas closed circulatory systems transport blood through vessels.
2. Invertebrates, like insects and mollusks, possess open circulatory systems, while vertebrates, including mammals and birds, have closed circulatory systems.
3. Closed circulatory systems enable better blood pressure control and targeted delivery of oxygen and nutrients compared to open systems.

Open vs Closed Circulatory System

The difference between the open and closed circulatory systems is that the open circulatory system has open spaces called lacunae and sinuses, whereas the closed circulatory system has closed blood vessels called arteries and veins. An open circulatory system is present in arthropods and molluscs whereas a closed circulatory system is present in annelids and vertebrates. 

There are no blood vessels in the open circulatory system, and the organs and tissues are completely bathed in hemolymph (tissue fluid).

This type of circulatory system is present in organisms like insects (arthropods) and snails (molluscs). The central body cavity that is found in these types of animals is called hemocoel. 

In the closed-type circulatory system, there are distinct blood vessels that are called arteries and veins.

Unlike the open circulatory system, blood flows through these closed blood vessels and transports nutrients, oxygen, hormones, etc., to different organs and tissues.

Human beings (vertebrates) have a closed circulatory system. 

Comparison Table

Parameters of Comparison	Open Circulatory System	Closed Circulatory System
Open/Closed Spaces	The open spaces are called lacunae and sinuses and all the organs and tissues are bathed in the hemolymph.	Blood flows through the closed blood vessels that are called arteries and veins.
Type of Fluid	The fluid flowing in the open circulatory system is called hemolymph.	The fluid flowing in the closed circulatory system is called blood.
Flow Rate	The velocity of the fluid (hemolymph) flowing is slow.	The velocity of the fluid (blood) flowing is rapid.
Blood Vessels	The dorsal blood vessel is present in the open circulatory system.	Both the dorsal and ventral blood vessels are present in the closed circulatory system.
Capillary System	There is no capillary system.	The capillary system is present.
Nutrients	There is a direct exchange of nutrients between the hemolymph and the tissues.	Nutrients are exchanged through the tissue fluid.
Organisms	Mollusca and Arthropoda have an open circulatory system.	Annelida and Vertebrata have a closed circulatory system.

What is an Open Circulatory System?

In the open circulatory system, blood flows through the open spaces that are called lacunae and sinuses. The fluid flowing is called hemolymph, and the open cavity is known as hemocoel.

The organs are completely batched in hemolymph, as no closed blood vessels exist. This type of circulatory system is found in arthropods and molluscs. 

The open circulatory system pumps blood directly into the body cavity. No capillary system is present, and only dorsal blood vessels can be observed.

Since the hemolymph is in direct contact with the tissues, the nutrient is directly exchanged between the fluid and the tissue. 

The fluid flow rate in an open circulatory system is slower than in a closed circulatory system. No respiratory pigments are also present, and the blood volume cannot be controlled.

An open circulatory system is less efficient as compared to a closed circulatory system. The latter is better for blood transportation in large animals, which is why octopus has a closed circulatory system despite falling under molluscs.  

What is a Closed Circulatory System?

In the closed circulatory system, blood flows through the closed blood vessels that are called arteries and veins.

The blood, lymphatic fluid, and interstitial fluid are distinct in a closed circulatory system. This type of circulatory system is found in annelids and vertebrates. 

In the closed circulatory system, the heart pumps the blood and through the vessels, it reaches every tissue and organ in our body.

The capillary system is present in this type of circulatory system, and both the dorsal and ventral blood vessels are present. Since blood flows through closed blood vessels, the tissues are not in direct contact with it. 

The contraction and relaxation of the blood vessels can control the volume of blood in a closed circulatory system. Respiratory pigments are also present.

The advantage of a closed circulatory system is that it operates at much higher blood pressure as compared to the open circulatory system, and thus distribution takes palace at a much faster rate. 

Main Differences Between Open and Closed Circulatory System

1. The open spaces in the open circulatory system are called lacunae and sinuses, whereas the closed blood vessels in the closed circulatory system are called arteries and veins. 
2. The fluid flowing in the open circulatory system is called hemolymph, which is called blood in the closed circulatory system.
3. The velocity of hemolymph is slow in the open circulatory system, whereas blood flow is rapid in the closed circulatory system. 
4. The dorsal blood vessel is present in the open circulatory system, whereas the dorsal and ventral blood vessels are in the closed circulatory system. 
5. There is no capillary system in the open circulatory system, whereas it is present in the closed circulatory system.
6. In the open circulatory system, nutrients are directly exchanged between the hemolymph and the tissues. On the other hand, nutrients are exchanged through the tissue fluid in the closed circulatory system.
7. Mollusca and Arthropoda have an open circulatory system, whereas Annelida and Vertebrata have a closed circulatory system. 

References

1. https://www.hindawi.com/journals/ijz/2009/301284/
2. https://www.journals.uchicago.edu/doi/abs/10.1086/physzool.23.2.30152069