Open Circulatory System: Function & Benefits

Open Circulatory System is part of the Circulatory System where blood directly suffuses throughout the body. It may be directly open to the environment, such as the digestive tract.

• Open Circulatory System make use of hemolymph instead of blood.
• Hemolymph functions as a blood, lymph, and intestinal fluid.
• The circulatory system is developed as multicellular organisms cannot exchange the material directly with the environment.
• They are efficient in transporting nutrients like oxygen and wastes like carbon dioxide throughout their bodies.
• The Open circulatory system pumps blood into a cavity called a hemocoel.
• The system surrounds the organs and returns to the heart through the ostia pathway, a form of opening.

Key Terms: Open Circulatory System, Circulatory System, Oxygen, Carbon Dioxide, Blood, Human Body, Nutrients, Organs, Hemolymph, Hormones, Cells, Organisms, Blood Vessels

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Open Circulatory System

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The open circulatory system is the type of circulatory system in which there are no blood vessels to carry out the function of blood transportation throughout the body of the organism. 

• The organs and tissues in the bodies of the organisms are directly fed with blood. 
• The blood flows directly through the cavities; hence, the role of the blood vessels is neutralized in the open circulatory system. 
• Since no blood vessels are involved in the open system, there is no difference between the blood and the interstitial fluid.
• However, the heart has an active role to play in this type of circulatory system. 

The heart directly pumps the hemolymph into the cavity called hemocoel, and it is transported to the cells that surround the organs so that the material is transported.

• The hemolymph travels back to the heart through the ostia. 
• The ostia closes during the contraction of the heart. 
• This type of blood circulatory system is found in arthropods.
• There is no exchange of gases in this type of circulatory system.

Open Circulatory System

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Circulatory System

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The circulatory system is responsible for the circulation of material such as amino acids and electrolytes, oxygen and carbon dioxide, and hormones through the body of these organisms.

• The circulatory system also carries the blood cells that help in providing nutrition to the cells in the body.
• It strengthens the immune system of an individual.
• This system is also named the cardiovascular system or the vascular system.

It includes the following essential components:

• Blood
• Heart
• Blood Vessels (veins and capillaries) 

The blood circulatory system in organisms includes the lymphatic system that helps transport lymph in the body. 

• Both systems work differently in the bodies of living organisms.
• The two major types of circulatory systems are the Open Circulatory System and the Closed Circulatory System.

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Functions of Open Circulatory System

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The functions of the Open Circulatory System are as follows:

• The Open Circulatory System is used for transporting oxygen, which is necessary for cellular respiration.
• The system helps fight against infection by transporting immune cells to any area of the body.
• It sends messages between cells, which include signalling hunger, thirst, oxygen deprivation, or other bodily needs.
• The system helps in removing excess material from the body.

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Advantages of Open Circulatory System

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The advantages of an Open Circulatory System are as follows:

• Open Circulatory System requires less energy for distribution in the body compared to Closed Circulatory System.
• There is no urgency to restore balance between the system.
• The processing of oxygen and carbon dioxide is done through different systems.
• It consists of specialized cells that perform the trade and communication upon which the survival of an organism depends.

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Hemolymph

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The hemolymph is plasma that mostly contains (water, organic compounds, and some inorganic salts, for example, Na⁺, Cl^-, K⁺, Mg²⁺, and Ca²⁺). It is directly pumped into the cavity, and the material in it is directly exchanged between the blood and the cells of the body. 

• Hemocytes are also present in the hemolymph as the free-floating cells.
• It plays a function in the immune system. 
• Hemolymph contains high levels of free amino acids.
• It helps in the functioning of chroma proteins, protease inhibitors, enzymes and lipid transport.

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Things to Remember 

• The open circulatory system is the type of circulatory system in which there are no blood vessels found in the body.
• Since there are no vessels to conduct the blood, as a result, blood flows freely through cavities.
• This type of system is mainly found in molluscs and arthropods.
• An open circulatory system prohibits the exchange of gases between cells of the organisms.
• The interstitial fluid contains all materials like water, sugar, hormones, fatty acids, salts and other enzymes.
• Living beings are efficient in transporting nutrients, gases like oxygen, and wastes like carbon dioxide throughout their bodies.

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