Fundamentals of Entomology (2+1)

Anatomy: Circulatory system

Circulatory system

• Unlike the “closed” circulatory system of humans, insect circulatory systems are said to be “open”, meaning that they lack a complex network of veins and arteries to help transport blood throughout the body. Instead, insect blood (called hemolymph) flows relatively “freely” throughout the hemocoel.

Figure 8-2. Circulatory system. Arrows indicate direction of flow of hemolymph.

• Only one vessel is present in the insect circulatory system: the dorsal vessel. Posteriorly (in the abdominal region), the dorsal vessel acts as the heart, pumping hemolymph forward into the anterior region (in the head and thorax), where it acts as the aorta and dumps the hemolymph into the head. It flows posteriorly and is returned to the heart via ostia, which are small slits in the heart region of the dorsal vessel designed for hemolymph uptake.
• To view the dorsal vessel, examine the “back” (or dorsal region) of the insect’s body cavity for a very thin line that runs longitudinally from the head to the tip of the abdomen. Use the grasshopper or specimen that was ventrally dissected, as dorsal dissections will likely mutilate the vessel. Do not be discouraged if you have trouble finding it on your specimen. The dorsal vessel is very, very thin. Compare your specimen to those of your classmates.