Hemolymph circulation in the mosquito hemocoel

The insect circulatory system transports nutrients, signaling molecules, wastes and immune factors throughout the body. Here, we will present a comprehensive characterization of hemolymph propulsion in the abdomen of the mosquito Anopheles gambiae, with specific emphasis on the mechanics of hemolymph propulsion, the structure of the musculature responsible for propelling hemolymph, and the direction and speed of hemolymph flow in various areas of the insect. Overall, hemolymph circulation in mosquitoes is primarily driven by the contractile action of the dorsal vessel. This vessel is divided into a thoracic aorta and an abdominal heart that runs immediately underneath the dorsal midline of the tergum and pumps hemolymph in both anterograde (toward the head) and retrograde (toward the tip of the abdomen) directions. The heart is tethered to the abdominal tergum by six complete and three incomplete pairs of alary muscles, and propels hemolymph at an average velocity of 8mm/s by sequentially contracting muscle fibers oriented in a helical twist with respect to the lumen of the vessel. Hemolymph enters the heart through seven pairs of incurrent abdominal ostia and exits through distal excurrent openings located at the anterior end of the aorta and the posterior end of the heart. Once in the extracardiac regions of the hemocoel, hemolymph flow direction is directly influenced by the contractile action of the heart. However, during periods of anterograde heart contractions the ventral abdomen periodically contracts, facilitating extracardiac retrograde hemolymph propulsion in the abdominal hemocoel.