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BL 1021 – Unit 4.6 – 4.8 The Circulatory System 4.6 Circulatory Systems • As animals get larger and more complex, the need for a system to more nutrients and wastes from place to place develops. • There are three elements common to all circulatory systems: • A liquid carrier substance (blood) • Vessels to carry the liquid (may not carry the liquid all the time however) • A pump to move the liquid (heart) 4.7 Open and Closed Circulatory Systems • The Open Circulatory system is the more primitive circulatory system in which a heart is present and the fluid being pumped is a combination of blood and body cavity fluid. • As the fluid does not stay in the vessels the whole time, it mixes with fluids throughout the body to form hemolymph. • This type of system is found in Phylum Arthropoda. 4.7 Open and Closed Circulatory Systems • This open system has one major disadvantage – the organism must keep moving to assure that the hemolymph bathes all the cells of the body. 4.7 Open and Closed Circulatory Systems • A closed circulatory system is a more recent and more complex development. In a closed system, the blood never leaves the vessels and does not mix directly with the various intercellular fluids. 4.7 Open and Closed Circulatory Systems • By having vessels reaching to every corner of the creature, blood can reach all cells of the body without needing the body to move. • In this type of system, blood flows in a direct loop or circuit. 4.7 Open and Closed Circulatory Systems • Closed systems have three types of vessels to carry blood: • Arteries deliver blood from the heart. They have thick and strong wall to handle the highpressure blood that comes directly from the heart. 4.7 Open and Closed Circulatory Systems • Veins return blood to the heart. They are thinner than arteries as the blood has dropped in pressure by the time it reaches them. • Veins have one-way valves to prevent blood from flowing backwards and pooling up. 4.7 Open and Closed Circulatory Systems • Capillaries are the middle-section of the system. These are very small and very thin vessels that can reach all the parts of the body. Their thin walls allows them to easily diffuse nutrients and wastes between the tissues and the blood. 4.8 Human Circulatory System • The human cardiovascular system is composed of a powerful four chamber heart (two atria which receive blood and two ventricles which send blood), a multitude of veins, arteries and network of capillaries, and blood. • The circuit of blood is known as double circulation because blood will make its way through the heart twice (through the right side then the left side) before completing its circuit through the body. In a very simplified description, the flow of blood is as follows 4.8 Human Circulatory System • On this diagram, the left of the diagram shows the right side of the body. • The path of blood through the body: • 1) Blood enters the right ventricle. This compartment seals off and compresses to release high-pressure blood. 4.8 Human Circulatory System • 2) Blood leaves the heart and travels to the lungs via the pulmonary artery. • 3) In the lungs, the blood takes up oxygen and releases carbon dioxide. • 4) Blood returns to the heart through the pulmonary vein. 4.8 Human Circulatory System • The path so far is known as the pulmonary circuit. This pathway gets fresh oxygen that will be delivered to the rest of the body in the next step, the systemic circuit. • That circuit will carry nutrients to the body’s tissues and remove wastes. 4.8 Human Circulatory System • 5) Once blood returns from the pulmonary vein, it collects in the left atrium. • 6) The blood then pumps into the left ventricle. • 7) The ventricles contract, pumping out the blood at max pressure into the aorta. 4.8 Human Circulatory System • 8) Blood heads to the various parts of the body from the aorta through a number of smaller arteries. • Arteries connect to capillary beds which exchange substances with the body’s tissues. 4.8 Human Circulatory System • 9) After exchanging substances with the body, the blood collects in a series of veins that ultimately combine into the vena cava. • 10) The blood collects into the right atrium. 4.8 Human Circulatory System • From the right atrium blood returns to the right ventricle to complete the cycle. • Both atria contract at the same time and both ventricles contract at once.