Read the text to find out about a) open and closed circulatory systems b) single and double circulatory systems
Circulatory system (or cardiovascular) is the system responsible for circulating blood throughout the body. Animal circulatory systems consist of 1) a blood or a bloodlike fluid 2) a system of tubular blood vessels 3) and one or more pulsating hearts that pump the blood through the vessels. Animals that are only a few cell layers thick do not need or possess circulatory systems, because they can rely on the body surface to exchange materials with the environment. Larger animals, however, require a circulatory system to transport nutrients and oxygen to their tissues, remove wastes, carbon dioxide and regulate body temperature.
Circulatory systems are classified into open or closed. In an open circulatory system, the heart pumps a fluid through arteries that empty into a large space, the hemocoel. The fluid bathes the organs in the hemocoel, and returns through veins to the heart. Since there is no distinction between blood and tissue fluid in such a system, the fluid is called hemolymph. Open circulatory systems are found in most mollusks and arthropods. In a closed circulatory system, blood never leaves the blood vessels, and is thus, separated from the tissue fluid. Blood flows away from the heart by way of arteries and returns to the heart by way of veins. Arteries are connected to veins by tiny, thin-walled capillaries. Arteries and veins have walls made of elastic and muscular tissue, and an inner lining of thin epithelium called endothelium. Capillaries are made of endothelium only. These thin walls allow for exchange of substances between the blood and tissue fluid.
Closed systems have a relatively high blood pressure. This enables nutrients and oxygen to be delivered quickly to their tissues and supports the high metabolic rate associated with the relatively high mobility of some animals. Squids, for example, have closed circulatory systems with three hearts, one to serve each gill and one for the rest of the body. Earthworms, although not highly mobile, have a closed circulatory system with five pairs of hearts.
Vertebrates have closed circulatory systems in close association with the respiratory systems. In fish, blood flows from the heart to the gills for gas exchange, then to the rest of the body, and finally back to the heart. This is called a single circulation since the blood flows through the heart only once during each complete trip around the body. Other animals, such as amphibians, reptiles, birds, and mammals, have a pulmonary circuit, where blood is pumped from the heart to the lungs and back, and a second, systemic circuit where blood is pumped to the body and back. This means that for each round trip of the body, the blood passes through the heart twice - the circuit of blood is like this: heart → lungs→ heart → body.
Figure 1: The single circulatory system found in fish
Figure 2: The double circulatory systems found in mammals
1. The Pulmonary Circulation.This is the circulation of deoxygenated blood from the heart to the lungs, oxygenated blood returns to the heart from the lungs.
2. The Systemic Circulation. Oxygenated blood is pumped from the heart around the body (including all the organs except the lungs). That blood returns to the heart deoxygenated (more accurately 'oxygen poor'), because much of the oxygen it contained, has been delivered to tissues in the body.
Exercise 1. Fill in the gaps with an appropriate word.
1. In an open circulatory system, the heart pumps a fluid through … that empty into … .
2. In a closed circulatory system, blood never leaves blood … .
3. Blood flows away from the heart by way of arteries and returns to the heart by way of … .
4. Capillaries are made up of … .
5. Vertebrates have … circulatory systems in close association with the … system.
(veins, closed, arteries, vessels, hemocoel, endothelium, respiratory)
Exercise 2. Complete the following sentences. Choose the ending according to the text.
1. Circulatory system (or cardiovascular) is the system responsible for … .
2. Large animals require a circulatory system to … .
3. In a closed circulatory system, blood never leaves the blood vessels, and is, thus, … .
4. Arteries are connected to veins by … .
5. Squids have closed circulatory systems with … .
6. In fish, blood flows from the heart to the gills for gas exchange, then to … .
7. Other animals, such as amphibians, reptiles, birds, and mammals, have a pulmonary circuit, where blood is pumped from the heart to the lungs and back, and a second, systemic circuit where … .
Exercise 3. Give the English equivalents of the Russian words in brackets.
1. Large animals require a circulatory system to transport (питательные вещества) and oxygen to their tissues, (удалять) wastes, carbon dioxide and (регулировать) body temperature. 2. Open circulatory systems are found in most (моллюски и членистоногие). 3. Arteries are connected to veins by tiny (тонкостенные капилляры). 4. Capillaries (состоять) of endothelium only. 5. In fish, blood flows from the heart to the gills (для газообмена), then to the rest of the body, and finally back to the heart. 6. Other animals, such as amphibians, reptiles, birds, and mammals, have (легочный круг), where blood is pumped from the heart to the lungs and back, and a second, (системный круг) where blood is pumped to the body and back.
Exercise 4. Translate the derivatives. Make up your own sentences with some of these words.
1. To deliver, delivery, deliverable, delivering.
2. To contain, container, contained, containing.
3. To possess, possession, possessing, possessive.