heart and aorta

Definition

The principal components of the open circulatory system in arthropods, consisting of a dorsal, tubular muscular heart that pumps hemolymph and an anterior vessel (aorta) that channels it toward the head and anterior body regions. The heart typically comprises serially arranged chambers (ostia) with valves that draw hemolymph from the surrounding pericardial sinus during diastole and propel it forward during systole. In insects, the heart extends through the abdomen and thorax, transitioning into the aorta in the thorax; in arachnids, the heart is more compact and often supplemented by accessory pumping organs. This system lacks capillaries; hemolymph bathes tissues directly in the hemocoel before returning to the pericardial cavity.

Etymology

Heart from Old English heorte; aorta from Greek aorte, the great artery, from aeirein 'to lift, heave'

Example

In the American cockroach (Periplaneta americana), the heart consists of 13 segmental chambers with paired ostia; hemolymph enters through these incurrent openings and is driven anteriorly through the aorta to supply the brain, antennae, and other cephalic structures before circulating through the open body cavity.

Related Terms

• Hemolymph
• ostium
• Pericardial sinus
• hemocoel
• open circulatory system
• pulsatile organ
• accessory heart

Usage Notes

The phrase 'heart and aorta' is often used jointly in arthropod anatomy because the functional distinction between heart (the contractile, valved pump) and aorta (the non-contractile conducting vessel) is less sharply demarcated than in vertebrates, and the two form a continuous dorsal vessel. Some authors use 'dorsal vessel' as a collective term. The number of heart chambers varies taxonomically: 13 in many insects, fewer in arachnids. The direction of hemolymph flow can reverse in some insects, controlled by accessory pulsatile organs. Do not confuse with the tubular hearts of some annelids or the closed circulatory systems of vertebrates.