Difference Between Open and Closed Circulatory System

Main Difference – Open vs Closed Circulatory system

Open and closed circulatory systems are involved in flowing materials from one part of the body to another along with a fluid. This fluid can be either haemolymph in the open circulatory system or blood in the closed circulatory system. Both circulatory systems comprise a pumping mechanism, which is the heart. The main difference between open and closed circulatory system is that tissues directly come into contact with the haemolymph in the exchange of materials in an open circulatory system whereas blood does not directly come into contact with tissues in the exchange of materials in a closed circulatory system.

Key Areas Covered

1. What is an Open Circulatory System
      – Definition, Pathway and Mechanism, Organisms having Open Circulatory System
2. What is a Closed Circulatory System
      – Definition, Pathway and Mechanism, Advantages
3. What are the Similarities Between Open and Closed Circulatory System
      – Outline of Common Features
4. What is the Difference Between Open and Closed Circulatory System
      – Comparison of Key Differences

Key Terms: Blood, Blood Vessels, Capillaries, Closed Circulatory System, Dorsal Blood Vessel, Haemolymph, Heart, Open Circulatory System, Respiratory Pigments, Sinuses, Ventral Blood Vessel

What is an Open Circulatory System

An open circulatory system is a type of circulatory system in which a circulatory fluid called haemolymph bathes tissues and organs in the body. That being so, the circulatory fluid is not confined within vessels and no distinction is found between blood and the interstitial fluid. Hence, the circulatory fluid is referred to as the haemolymph. The heart pumps the haemoplymph into the sinuses through a dorsal blood vessel. Tissues and organs in the body cavity directly come into contact with the haemolymph. Therefore, the exchange of materials like nutrients occur between the haemolymph and cells in the tissue. Haemolymph consists of organic compounds, water, and inorganic salts like Na⁺, Cl^–, Mg²⁺, Ca²⁺, and K⁺. Hemocytes are the circulatory cells within the haemolymph, which play a role in the immunity of the animal.

Difference Between Open and Closed Circulatory System

Figure 1: Different Circulatory Systems

An open circulatory system is found in mollusks, crustaceans, spiders, and insects. Many insects have a tracheal system apart from the circulatory system to transport respiratory gases, both oxygen and carbon dioxide into cells in tissues. This means respiratory gases are not transported by the haemolymph. On that account, haemolymph lacks respiratory pigments. The pressure of the circulatory fluid cannot be controlled in an open circulatory system. Therefore, organisms with open circulatory system do not have a ‘true’ heart. The open and closed circulatory systems are shown in figure 1.

What is a Closed Circulatory System

A closed circulatory system is a type of circulatory systems in which blood is the circulatory fluid, which circulates within closed vessels. Blood does not mix with the interstitial fluid in a closed circulatory system. The closed circulatory system comprises a heart, which pumps the blood into the dorsal blood vessel. The dorsal blood vessel carries blood to tissues and organs. The exchange of materials at tissues occur via small vessels called capillaries found in the tissue. The blood with wastes produced in the metabolism of tissues is transported back into the heart by the ventral blood vessel. Annelids and vertebrates like humans have a closed circulatory system. Nutrients, inorganic salts as well as respiratory gases are transported through the blood. On that account, the circulatory fluid of the closed circulatory system comprises respiratory pigments as well. The respiratory pigments found in humans is hemoglobin.

The major advantage of a closed circulatory system is the efficient delivery of oxygen and nutrients into tissues. The blood flows under high pressure in a closed circulatory system. This allows the blood to pass faster and achieve a high level of distribution within the body. A closed circulatory system comprises a lymphatic system, which regulates the fluid balance. The closed circulatory system is more complex than an open circulatory system. The distribution of blood in the closed circulatory system requires more energy as well. The pulmonary circulation of humans is shown in figure 2.

Main Difference - Open vs Closed Circulatory System

Figure 2: Pulmonary Circulation of Humans

Similarities Between Open and Closed Circulatory System

Open and closed circulatory systems are the two types of circulatory systems found in higher invertebrates and vertebrates.
A fluid is circulated throughout the body in both circulatory systems.
Both circulatory systems are governed by a pumping mechanism, which is the heart.
Both circulatory systems comprise a dorsal blood vessel.

Definition

Open Circulatory System: An open circulatory system is a type of circulatory system wherein the hemolymph bathes the organs and tissues directly, and no interstitial fluid is found between blood and tissues.

Closed Circulatory System: A closed circulatory system is a type of circulatory system is a type of circulatory system where blood circulates within closed vessels and is distinct from the interstitial fluid.

Found in

Open Circulatory System: Mollusks and arthropods have open circulatory systems.

Closed Circulatory System: Vertebrates and annelids have closed circulatory systems.

Mechanism

Open Circulatory System: In an open circulatory system, blood is pumped into a body cavity.

Closed Circulatory System: In a closed circulatory system, blood is pumped by the heart through vessels.

Vessels

Open Circulatory System: Open circulatory system comprises a dorsal blood vessel.

Closed Circulatory System: Closed circulatory system comprises both dorsal and ventral blood vessels.

Capillary System

Open Circulatory System: A capillary system is not found in an open circulatory system.

Closed Circulatory System: A capillary system is found in a closed circulatory system.

Tissues

Open Circulatory System: In an open circulatory system, tissues are surrounded by blood.

Closed Circulatory System: In a closed circulatory system, blood does not directly contact with tissues.

Exchange of Materials

Open Circulatory System: Only nutrients are exchanged directly between blood ad tissues in an open circulatory system.

Closed Circulatory System: Gases and nutrients are exchanged via tissue fluid in a closed circulatory system.

Transport of Gases

Open Circulatory System: Gases are not transported via the open circulatory system.

Closed Circulatory System: Gases are transported via the closed circulatory system.

Circulatory Fluid

Open Circulatory System: The fluid which flows in an open circulatory system is known as haemolymph.

Closed Circulatory System: The fluid which flows in a closed circulatory system is known as blood.

Respiratory Pigments

Open Circulatory System: No respiratory pigments occur in the haemolymph.

Closed Circulatory System: Respiratory pigments occur in the blood, which is involved in the transport of gases.

Blood Volume

Open Circulatory System: The volume of the blood cannot be controlled in an open circulatory system.

Closed Circulatory System: The blood flow is controlled by the contraction and relaxation of blood vessels.

Blood Flow

Open Circulatory System: Blood flow is very slow in an open circulatory system.

Closed Circulatory System: Blood flow is rapid in a closed circulatory system.

Conclusion

Open and closed circulatory systems are involved in the distribution of materials throughout the animal body. An open circulatory system lacks a vascular system and hence, the circulatory fluid directly bathes tissues and organs inside the body cavity. In a closed circulatory system, blood flows through a vascular system. Thus, the exchange of materials occurs via the interstitial fluid. So, the main difference between open and closed circulatory system is the mode of transporting the circulatory fluid inside the body.

Reference:

1.”Open circulatory system.” Biology-Online Dictionary. N.p., n.d. Web. Available here. 28 June 2017.
2.”Open Circulatory Systems: Definition & Examples.” Study.com. N.p., n.d. Web. Available here. 28 June 2017.
3.”Closed circulatory system.” Biology-Online Dictionary. N.p., n.d. Web. Available here. 28 June 2017.
4.”5 Pros and Cons of Closed Circulatory System.” Green Garage. N.p., 13 Jan. 2017. Web. Available here. 28 June 2017.

Image Courtesy:

1. “Figure 40 01 01ab” By CNX OpenStax – (CC BY 4.0) via Commons Wikimedia
2. “Sankey diagram human circulatory system” By Cmglee – Own work (CC BY-SA 3.0) via Commons Wikimedia