What is Hemolymph?

So how exactly does the hemolymph transport all of these materials around the body? Even though species with open circulatory systems lack structured vessels, many species still possess hearts that work to pump hemolymph throughout different branches of the hemocoel. The hemocoel extends throughout most of an organism's body and in the extended branches molecules and nutrients are exchanged between the hemolymph to neighboring tissues. Honey bees have a heart with a single aorta containing many small holes in it that runs down the length of the insect. This aorta pumps hemolymph out of the heart and into the hemocoel chambers causing the hemolymph to flow through the body, coming in contact with various organs and exchanging nutrients before flowing back to the heart and starting the cycle again.

Importance of Hemolymph

Hemolymph is vital for the functioning of organisms with open circulatory systems where hemolymph functions as both the circulatory fluid and lymph fluid, working to transport and exchange molecules and nutrients throughout a body's cells and remove waste. Open circulatory systems are generally found in the invertebrate phyla of Arthropoda (insects, crab, lobster, etc.) and Mollusca (snails, clams, etc). However, due to the lack of structured vessels, open circulatory systems are less efficient in moving the hemolymph fluid around the body and this is a major reason why these systems are not found in giant organisms. Larger mollusks, such as octopus and squid, developed closed circulatory systems in order to transport fluids throughout their larger bodies.

Open circulatory systems and hemolymph do have some advantages, such as requiring less energy to move throughout the body; this makes it optimum for animals with slow metabolisms and smaller sizes. This system is also ideal for insects that already have tracheal systems to deliver and transport oxygen and do not need specialized vessels.

Lesson Summary

Hemolymph tissue is the circulatory fluid found in invertebrate species with open circulatory systems and is often compared to blood of vertebrate species. Many species in phylum Arthropoda and Mollusca have hemolymph and open circulatory systems. Unlike the closed circulatory system of vertebrate species, open circulatory systems do not contain structured vessels to transport fluids around the body. Instead, the hemolymph flows freely around the body's organs and is contained within the hemocoel. Hemolymph serves to transport oxygen and other molecules around the body and remove waste.

Water makes up the bulk of hemolymph, but hemolymph also contains proteins, carbohydrates, lipids, and other cells. Hemocytes are specialized immune cells that are found in hemolymph. These cells engulf invading pathogens and protect the organism. In some organisms, the hemolymph also contains a protein called hemocyanin. Hemocyanin is similar to hemoglobin in that it binds to oxygen and moves it around the body. However, unlike hemoglobin which is bound to red blood cells, hemocyanin is free-floating. In organisms with open circulatory systems, hemolymph acts as both their circulatory system fluid and their lymphatic system fluid. Although less efficient at transporting molecules than closed systems, open circulatory systems require less energy and are ideal in insect species that do not need oxygen transport due to their complex tracheal systems.