Heart as a PUMP

    The crustacean heart is a single-chambered sac made up of layers of muscular leaflets. The heart is suspended in the pericardial cavity by several suspensory ligaments under the dorsal carapace of the thorax.
    The cardiac ganglion in the heart generates the heartbeat rhythm.

     There are several arteries, but no vein. Hemolymph (blood) in the pericardial cavity flow into the ventricle through valvular openings called ostia. The hemolymph is then pumped out through the arteries. There are also valvular muscles between the ventricle and the arteries, the cardio-arterial valves.

Posterior-lateral view of a beating heart (crayfish)

    In order for the heart to work as a pump, the intake valves (ostia) must be closed and the outlet valves (cardio-arterial valves) opened during systole, and vice versa during diastole (here's a movie).
    The closure of the ostia is controled by the cardiac ganglion neurons. The tension of the cardio-arterial valves are regulated by the extrinsic nerves from the CNS and hormones.
    It has been reported by some investigators that the distribution of blood flow is controled by changing the tension of each cardio-arterial valve.

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