How do open and closed circulatory systems differ?

Open circulatory systems pump blood into a cavity with organs, while closed systems circulate it within a network of vessels.

In an open circulatory system, the heart pumps the blood, also known as haemolymph, into a cavity called the haemocoel. The organs are directly bathed in this haemolymph, which allows for the exchange of nutrients, waste, and gases. The haemolymph then returns to the heart through openings called ostia. This type of system is common in invertebrates such as insects, spiders, and most molluscs. It is a relatively simple and low-pressure system, which is less efficient at transporting substances around the body compared to a closed system.

On the other hand, a closed circulatory system, found in vertebrates including humans, and some invertebrates like earthworms and squids, is more complex. In this system, the heart pumps blood into a series of vessels that form a closed loop. The blood never leaves the network of arteries, veins, and capillaries. The exchange of nutrients, waste, and gases occurs across the thin walls of the capillaries. This system allows for more efficient and rapid transport of substances around the body. It also enables the regulation of blood flow to different parts of the body based on need, something that is not possible in an open system.

In summary, the main difference between open and closed circulatory systems lies in the method of blood circulation. Open systems pump blood into a body cavity, directly bathing the organs, while closed systems circulate blood within a network of vessels, allowing for more efficient transport and regulation of substances.