The circulatory system in mollusca PDF

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THE CIRCULATORY SYSTEM IN MOLLUSCA Most animals within the mollusca phylum have an open circulatory system. Cephalopods have a closed circulatory system. Within an open circulatory system blood is not restricted to circulating within the blood vessels. Open circulatory systems which have evolved through species such as crustaceans, insects, molluscs, and other invertebrates, pump blood into a haemocoel with the blood extending back to the circulatory system between the various cells. Blood within an open circulatory system is pumped by a heart into the body cavities, where tissues are surrounded by blood. There are various animals that fit the requirements of the mollusca phylum. one animal within the mollusca phylum is a snail. A snail has an open circulatory system which means that blood is not restricted from travelling within the blood vessels. The heart of the snail is found on the left side of the body and is made up of one auricle and one ventricle. The ventricle pumps blood through an aortic trunk to all parts of the body through a group of arteries and capillaries. From the capillaries the blood flows into various spaces in the tissues called the haemocoel. From the haemocoel blood passes into the veins and back to the auricle. The blood present in snails contains a fused compound known as hemocyanin which purpose is to transports oxygen. Hemocyanin is similar to haemoglobin which is found in human blood.

Another animal within the mollusca phylum is a slug. Slug's and snail's have a very similar circulatory system. The fluid that is transported through the circulatory system of a slug is called hemolymph. Hemolymph is a fluid in the circulatory system and is similar to the fluids and cells making up both blood and interstitial fluid including water, proteins, and

fats. Hemocyanin is present in the hemolymph as the respiratory pigment within the

circulatory system of a slug. Hemocyanin is respiratory proteins in the form of metalloproteinase containing two copper atoms that reversibly bind a single oxygen molecule. A third animal within the mollusca phylum is a chiton. A chiton is a small ovular species with eight plates on its dorsal side, and an open circulatory system. The artery takes the blood to the tissue, where it returns to the heart via a vein. In advanced animals, like humans, the blood goes from the heart to an artery, to a capillary (the name for a very small blood vessel) to the cells and back to the heart through a vein. This is important because as a rule, creatures with open circulatory systems aren't all that large. A mollusk has a heart, blood, and blood vessels. Oxygen and nutrients are carried to all parts of a mollusk's body by a circulatory system. Most have an open circulatory system- blood is collected from the gills, pumped through the heart, and released directly into spaces in the tissues. Then, it returns to the gills and then to the heart. These work well for slow-moving mollusks such as snails and clams because they demand for oxygen isn't very great. Cephalopods have a closed circulatory system. These faster moving mollusks like octopi and squid have a closed one because the system can transport blood through the animal's blood much more quickly. A blood filled space is called a haemocoel ("blood cavity"). The presence of discrete respiratory and circulatory systems has led to improved capacity for oxygen uptake and distribution, and hence an increase in body mass. Blood circulation

The heart and neighboring organs of a roman snail. Source: KILIAS (1985). flowing back. A roman snail's heart is located in the heart-bag (pericardium) at the upper mantle rim, behind the respiratory cavity. It is divided into two chambers, an atrium and a ventricle, both connected by a narrow duct, a valve avoiding blood fluid A roman snail's heartbeat frequency very much depends on the snail's body temperature and activity. It ranges from 70 to 80 beats per minute in an awake and active snail to about 5 beats per minute during aestivation, but especially during hibernation. When the snail's blood flows back to the lung, depleted from oxygen, it is almost colourless. After the blood has been loaded with oxygen again, its colour changes to blue. The reason, why a roman snail's blood is blue, is the snail's blood pigment – hemocyanin. Similar to haemoglobin it is a protein working as a complex with an inorganic atom, to which the oxygen molecule is supposed to bind. Contrary to haemoglobin, though, this inorganic atom in hemocyanin is copper, which appears blue in its oxidised state, but colourless, when reduced.of blood vessels, the capillaries, however, are open – the blood flows into the body

cavity and around the organs, which thereby it supplies with oxygen. Capillary veins suck blood from the body cavity and transport it back to the lung, where it is to be reloaded with oxygen. An open circulation, such as in a roman snail's body, basically can be found in all molluscs. Only the most highly developed cephalopods (cephalopoda), such as octopuses (octopodidae), possess a mostly closed circulation. Finally, a snail's blood not only transports respiration gases. It also gives form and firmness to the snail's soft body, which, the snail being a mollusc, lacks a skeleton. As it is the blood responsible for the body's firmness, it is also usually referred to as a hydro skeleton. Additionally the blood fluid of a snail is used to stretch out withdrawn parts of the body by hydraulic pressure. So for example, when a tentacle has been withdrawn by the action of a retractor muscle, it must be stretched again by pumping blood into its hollow interior....