Circulatory Systems

By Author: Isabella Evans
Total Articles: 11
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All animal cells require a constant supply of nutrients and oxygen, and the removal of wastes to maintain life. Your tutors in Perth will inform you that simple and small organisms such as sponges, flatworms, nematodes and cnidarians achieve this feat by simple diffusion through their moist body surfaces. And that they do not require a specialised system.

But for larger and more complex animals diffusion is too inadequate and slow to supply the necessities of all the cell and systems. And because of this reason these animals require a circulatory system. With evolution two basic types of circulatory systems has evolved in animals. But what these circulatory systems have in common as principal components are some type of fluid for transport called blood, a heart, and vessels to carry blood to and from cells.
The main purpose of a circulatory system is to transport nutrients, oxygen, carbon dioxide, hormones and waste products of cells. But in addition circulatory systems help to maintain fluid balance, regulate body temperature and may also assist in the defence of the body against invading microorganisms.

As ...
... you might have been tutored by tutors in Perth and as mentioned above, there are two basic types of circulatory systems found in complex animals. They are called “Open circulatory system” and “Closed circulatory system”.

Open circulatory systems are seen in arthropods (spiders, crabs and insects like bees and cockroaches etc.) and molluscs (snails, oysters etc. except for squid and octopus). In these animals blood is pumped by a sac-like or a tubular heart. Blood is released into a large space in the body cavity by short vessels. In the cavity the blood baths the cells and organs and reenter the heart through holes called ostia. To assist the circulation muscle action is used.

Closed circulatory systems are often called cardiovascular systems. In this type of a system blood is transported within vessels to body tissues and after each circulation it is returned to the heart. Any exchange of nutrients or gases happens via diffusion across capillaries, between the blood vessels and the extracellular fluid. The circulatory system of all vertebrates and that of annelids (eg: earthworms) and cephalopods (eg: squid and octopus) are closed circulatory systems. Yet the systems of fish, reptiles and birds etc. show various stages of evolution.

And so in closed circulatory systems we find single circuit and double circuit systems.
Single circuit systems are typically seen in fish and in this type of a system blood goes directly from the capillaries of the gills to that of the body tissues. Because of that the heart of fish has only a single pump.

Unlike in fish all other vertebrates have double circulatory systems but the heart is not always completely separated into two pumps, like in amphibians having a three chambered heart.
The blood in a double circulatory system is pumped through the lungs, where it is oxygenated. Then the blood returns to the heart. And the heart pumps the oxygenated blood through a systemic circuit to the body tissues.

Unlike in birds and mammals, in amphibians and most reptiles the heart is not fully divided and so there is some mixing of oxygenated and deoxygenated blood.

An understanding of circulatory systems in animals is very important in learning about mammalian transport and cardiovascular systems from your tutors in Perth as well as gain awareness of animal body systems.

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