Jun 23, 2011

Transportation in Earthworm

The circulatory system consists of longitudinal and transverse blood vessels, in which blood flows continuously. The circulatory system is complicated and the arrangement of blood vessels behind the 14th segment is different from the arrangement from the first 14th segments. So a general plan of circulatory system in earthworm is being discussed.

There are three main longitudinal blood vessels, besides smaller vessels, 4/5 pairs of hearts found in earthworm:

1.            Dorsal Vessel
It runs throughout the length of the body in the mid dorsal line. It is present above the alimentary canal. Its wall is thick and muscular. It shows rhythmical peristaltic contraction from behind to the front. The backward flow is prevented by a pair of valve present in front of each septum (septum is partition wall between the segments). It serves only as a collecting vessel. It receives blood from intestine, nephridia, body wall etc. in the first 14th segment, the dorsal vessel becomes a distributing vessel. It supplies blood to anterior region, of the earthworm. It also sends blood to the four pairs of hearts. The hearts pump the blood into the ventral vessel.

2.            Ventral Vessel
It runs throughout the length of the body below the alimentary canal. It is a distributing vessel only. The blood flows from anterior to posterior end. Valves are absent in its lumen (space). A number of small blood vessels are given off, which distribute blood to the body wall, septa and nephridia of each segment.

3.            Sub-Neural Vessel
It extends along the mid-ventral line of the body wall below the nerve cord and extends from 14th segment backwards. In each segment, it collects blood from the nerve cord and from ventral region of the body wall and the flow of blood is backward. Sub neural vessel in the 14th segment divides into two lateral oesophageal vessels. Sub-neural vessel communicates with the dorsal blood vessel through commissural vessel.

4.            Supra Oesophageal Vessel
It runs from 9th to 13th segment, between dorsal vessel and the oesophagus. At posterior it is connected with the ventral vessel through the two latero-oesophagal hearts.

5.            Hearts
The number of hearts depends on type of the species. It maybe 4 or 5 pairs. Hearts are situated in the 7th to 13th segments. They are also called aortic arch. The heart pumps blood from the dorsal to the ventral vessel. The flow of blood cannot be reversed due to the arrangement of the valves at the junction of dorsal vessel and hearts.

6.            Valves
The direction of flow of blood is controlled by valves. They are present in the (1) Dorsal vessel (2) Heart (3) at the points of junction of the chief vessels with the dorsal vessels.

7.            Blood
It is bright red in color due to the presence of hemoglobin, which is dissolved in plasma. There are also corpuscles in the blood which are colorless and nucleated.

8.            Distribution of Food
The branches of the ventral vessels that enter the wall of the digestive tract also break up into innumerable capillaries. The product of digestion such as amino acids and glucose enters the capillaries. The capillaries of the intestinal wall join to the dorsal vessel. Thus the end products of digestion are distributed to all parts of the body.

Transportation in Earthworm

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