Different phyla in the animal kingdom can be recognized by various anatomical features. The type of circulatory system (open or close) is very distinguishable among organisms. For example, spiders, lobsters, crabs have open circulatory systems whereas fish, birds, humans have closed circulatory systems. There are many features in these type of circulatory system that makes them different from each other.
Open vs Closed Circulatory System
The main 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.
In the open circulatory system, there are no blood vessels, and the organs and tissues are completely bathed in the 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 Between Open and Closed Circulatory System
| 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 there are no closed blood vessels. This type of circulatory system is found in arthropods and molluscs.
In the open circulatory system, blood is pumped directly into the body cavity. There is no capillary system 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 rate of fluid flow in an open circulatory system is slower as compared to a closed circulatory system. There are also no respiratory pigments present and the volume of blood cannot be controlled. An open circulatory system is less efficient as compared to a closed circulatory system. The latter one is better for blood transportation in large animals and that 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 volume of blood in a closed circulatory system can be controlled by the contraction and relaxation of the blood vessels. 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
- 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.
- The fluid flowing in the open circulatory system is called hemolymph and that in the closed circulatory system is called blood.
- The velocity of hemolymph is slow in the open circulatory system whereas blood flow is rapid in the closed circulatory system.
- The dorsal blood vessel is present in the open circulatory system whereas both the dorsal and ventral blood vessels are present in the closed circulatory system.
- There is no capillary system in the open circulatory system whereas it is present in the closed circulatory system.
- In the open circulatory system, there is a direct exchange of nutrients between the hemolymph and the tissues. On the other hand, nutrients are exchanged through the tissue fluid in the closed circulatory system.
- Mollusca and Arthropoda have an open circulatory system whereas Annelida and Vertebrata have a closed circulatory system.
Conclusion
The open and closed circulatory systems have many differences but the common function they perform is the transfer of nutrients, and fluid flow. For an open circulatory system, hemolymph is the flowing fluid and they don’t have closed blood vessels whereas, in a closed circulatory system, blood is the flowing fluid inside arteries and veins.
The main function of any circulatory system in an organism is to deliver oxygen and nutrient to various organs and tissues and take away the waste material from them. The circulatory system also includes the lymphatic system (for circulating lymph) and its transport is much slower than the flow rate of blood.
References
- https://www.hindawi.com/journals/ijz/2009/301284/
- https://www.journals.uchicago.edu/doi/abs/10.1086/physzool.23.2.30152069