Open circulatory system

Definition

An open circulatory system is a type of circulatory system where blood is not always contained within blood vessels but instead flows freely through cavities in the body, bathing the organs directly. This system is common in many invertebrates, such as arthropods and mollusks, and is characterized by the presence of hemolymph, a fluid that serves both as blood and interstitial fluid. The efficiency of this system varies among different species, depending on their size and metabolic demands.

5 Must Know Facts For Your Next Test

1. Open circulatory systems are less efficient than closed systems because they rely on diffusion for the exchange of gases and nutrients.
2. In many arthropods, the heart pumps hemolymph into the body cavity through openings called ostia, allowing it to return to the heart after circulating.
3. The pressure generated in an open circulatory system is generally lower than in closed systems, affecting the speed of circulation.
4. Some organisms with open circulatory systems can modify their flow rates by changing the heart's rhythm or size of the sinuses.
5. Open circulatory systems are particularly advantageous for smaller animals, as they require less energy to maintain compared to closed systems.

Review Questions

• How does an open circulatory system differ from a closed circulatory system in terms of efficiency and transport mechanisms?
  • An open circulatory system differs from a closed one primarily in that blood flows freely through body cavities rather than being confined to vessels. This leads to lower efficiency, as nutrient and gas exchange occurs via diffusion rather than through high-pressure vessels. In contrast, closed systems maintain higher pressure for faster transport, making them more effective for larger and more active organisms that have higher metabolic needs.
• Evaluate the advantages and disadvantages of an open circulatory system for small invertebrates living in aquatic environments.
  • The advantages of an open circulatory system for small invertebrates include lower energy costs for circulation and the ability to easily bathe tissues directly with hemolymph. However, disadvantages arise due to the lower pressure and efficiency in gas exchange, which may limit metabolic rates. In aquatic environments, this can be manageable since water facilitates diffusion; however, larger or more active species may struggle with oxygen supply if they rely solely on this system.
• Assess how the evolution of an open circulatory system might influence an organism's ecological niche and behavior.
  • The evolution of an open circulatory system can significantly shape an organism's ecological niche by determining its size, metabolic rate, and habitat preferences. For example, smaller animals with lower metabolic demands can thrive in environments where resources are scarce due to their efficient use of energy. Additionally, this system may influence behaviors such as feeding strategies and movement patterns. Organisms may evolve traits that align with the capabilities and limitations of their circulatory system, ultimately affecting their survival and reproduction within their ecological context.

Related terms

hemolymph: A fluid that circulates in an open circulatory system, combining functions of both blood and interstitial fluid, providing nutrients and oxygen to tissues.

sinus: A cavity or space within the body where hemolymph collects before being circulated back to the heart in an open circulatory system.

closed circulatory system: A type of circulatory system where blood is contained within vessels, allowing for more efficient transport of nutrients and gases, commonly found in vertebrates.