How does a closed circulatory system differ from an open circulatory system?

The primary difference between closed and open circulatory systems lies in how the circulatory fluid is contained and distributed to tissues.

Closed Circulatory Systems

In a closed vascular system, the circulatory fluid is entirely confined within a continuous network of vessels, including arteries, veins, and fine capillaries. This structure allows for higher blood pressure and more precise regulation of blood flow to specific organs, making it highly efficient for large, active animals such as vertebrates and annelids. Because the fluid is contained, the composition of the blood can differ significantly from the interstitial fluid surrounding cells.12

Open Circulatory Systems

In an open vascular system, the circulatory fluid (hemolymph) is pumped from the heart into open body spaces called sinuses, where it bathes internal organs directly before being collected and recirculated. These systems generally operate at lower pressures and offer less control over blood distribution. In open systems, the circulatory fluid and interstitial fluid are the same. While typically less efficient for rapid responses, some animals, such as spiders, can maintain high pressures in specific instances.1324