Animals possess two type of circulatory system. They are
a) Open type and
b) Closed type
Open Type
In this type of circulatory system the blood may
be present in the blood vessels for some time but finally it comes out
of the blood vessels. The internal organs are directly bathed in blood.
The blood flows from the heart into the arteries. The artery open into
large spaces called sinuses. From the sinus the blood is carried by the
veins to the heart. There are no inter connecting vessels or capillaries
between the arteries and the veins, as the blood comes out of blood
vessels. This type of circulatory system is called open type. It occurs
in annelids like leeches, arthropods, most of the molluscs and
ascidians.
Closed Type
In the closed type of circulatory system, the
blood remains inside the blood vessels and does not come out. The blood
flows from arteries to veins through small blood vessels called
capillaries. The closed type of circulatory system occurs in most of the
Annelids, Cephalopods and Vertebrates including man.
Characteristics of Open System
1) The blood flows at a very low velocity and at low pressure due to the absence of smooth muscles.
2) There is direct exchange of materials between the cells and the blood because of the direct contact between them.
3) The respiratory pigment, when present, is dissolved in the plasma of the blood and there are no red corpuscles.
Characteristics of Closed System
1) The speed of circulation is more rapid due to the presence of muscular and contractile blood vessels.
2) The supply and removal of materials to and from the tissues by the
blood is enhanced, thereby increasing the efficiency of circulation.
3) The volume of blood flowing through a tissue or organ is regulated by
the contraction and relaxation of the muscles of the blood vessels.
0 comments:
Post a Comment