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CIRCULATION

The Circulatory System

The circulatory system of insects is open, whereby blood, (haemolymph), flows freely through the body cavity, (haemocoel).

There is a dorsal vessel which is closed at the posterior end of the abdomen, and runs forward along the dorsal midline and opens in the head at the anterior portion, (aorta).

There are several chambers and openings, (ostia), along the dorsal vessel where blood enters it through valves. The blood is then pumped forward to the aorta and into the body cavity.

Blood contains:

Blood does not generally contain an oxygen-carrying pigment such as haemoglobin.

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Function of Blood

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Rate of Blood FLow

The flow of blood in the body cavity is helped by general muscular contractions and movement. There also pumping muscles on either side of the dorsal vessel and in active insects, additional pumping organs at the bases of the wings legs and antennae.

The pulse rate is controlled by hormones and varies with temperature and activity. Active moths have a pulse rate of 140/minute while pupae have a pulse rate of 1/hour.

The open circulatory system is rather inefficient. Dye injected into a cockroach takes 5 minutes to permeate the insect, while a human blood cell takes less than 1 minute to travel from heart to toe to heart.

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