1A circulatory system consists of a muscular pump (heart), a circulatory fluid (blood), and a set of tubes or vessels to carry the blood. Two basic types of circulatory systems have set of tubes or vessels to carry the blood. Two basic types of circulatory systems have evolved in animals:1. Open circulatory system – the system is called “open” because fluid is pumped through open-ended vessels and flows out among the cells; there's is no distinction between blood and interstitial fluid. In an insect, such as the grasshopper in Figure 12. Closed circulatory system – The vertebrate circulatory system is often called a cardiovascular system. The blood is confined to vessels, which keep it distinct from the interstitial fluid. There are three kinds of vessels; Arteries carry blood away from the heat to body organs and tissues; veins return blood to the heart; and capillaries covey blood between arteries and veins within each tissue• The cardiovascular system of a fish illustrates key features of a closed circulatory system. The heart of a fish has two main chambers. The atrium receives blood from the veins, and the ventricle pumps blood to the gills via large arteries. The large arteries branch into arterioles, small vessels that give rise to capillaries. Networks of capillaries called capillary beds infiltrate every organ and tissue in the body. The thin walls of the capillaries allow chemical exchange between the blood and the interstitial fluid. The capillaries converge into venules, which in turn converge into veins that return blood to the heart.2Figure 3: A fish has a single circuit of blood flow and two heart chambers. Blood pumped form the ventricle travels first to the gill capillaries. Blood pressure drops considerably form the ventricle travels first to the gill capillaries. Blood pressure drops considerably while blood passes through the gill capillaries for reasons we will explain shortly, but the blood is helped on its way by the animal’s swimming movements. An artery carries the oxygen-rich blood to systemic (body) capillaries in the tissues and organs of the body, from which the blood then returns to the atrium of the heart.Figure 4: Frogs and other amphibians have a three-chambered heart. The right atrium receives blood returning from the systemic capillaries. The ventricle pumps blood to capillary beds in the lungs and skin. Because gas exchange occurs both in the lungs and across the thin, moist skin, this is called a pulmocutaneous circuit. Oxygen-rich blood returns to the left atrium. Although blood from the left and right atria mixes in the single ventricle, most of the oxygen-poor blood is diverted to the pulmocutaneous circuit and most of the oxygen-rich blood goes to the systemic circuit.Figure 5: In all birds and mammals, the heart has four chambers: two atria and two ventricles. The right side of the heart handles only oxygen-poor blood, while the lefts side receives and pumps only oxygen-rich blood.3Diagram 1:1. The right ventricle pumps oxygen-poor blood to the two lungs via…2. the pulmonary arteries3. As the blood flows through capillaries in the lungs, it takes up oxygen and unloads carbon dioxide.4. Oxygen-rich blood flows back through the pulmonary veins to…5. left atrium6. Next, the oxygen-rich blood flows from the left atrium into the left ventricle7. The Left ventricle pumps blood to the systemic circuit. Oxygen-rich blood leaves the left ventricle through the aorta• The aorta is our largest blood vessel, with a diameter of roughly 2.5 cm, about the same diameter as a quarter. The first branches from the aorta are the coronary arteries, which supply blood to the heart muscle itself8. Next are branches leading to the head, chest, and arms9. Oxygen-poor blood from the upper body is channeled into a large vein called the superior vena cava, and the inferior vena cava, another large veins, returns blood form the lower body.10. The two vena cavae empty into the right atriumAs the blood flows from the right atrium into the right ventricle, we complete our journey4Figure 6 – shows the path of blood through the heart. About the size of a clenched first, the human heart is enclosed in a sac just under the breastbone. The heart is formed mostly the human heart is enclosed in a sac just under the breastbone. The heart is formed mostly of cardiac muscle tissue. Its thin-walled artria collect blood returning to the heart. The thicker-walled ventricles pumps blood to the lungs and to all other body tissues. Notice that the left ventricle walls are thicker, a reflection of how much farther it pumps blood in the body. Flap-like valves between the atria and ventricles and at the openings to the pulmonary artery and the aorta regulate the direction of blood flow.5Diagram 2: When entire heart is relaxed, in the phase called diastole, blood flows into all four of its chambers. Blood enters the right atrium from the venae cavae and the left four of its chambers. Blood enters the right atrium from the venae cavae and the left atrium from the pulmonary veins. The valves between the atria and the ventricles are open. Diastole lasts about 0.4 second, during which the ventricles nearly fill with blood. The contraction phase of the cardiac cycle is called systole. Systole begins with a very brief (0.1 second) contraction of the atria that completely fills the ventricles with blood. Then the ventricles contract for about 0.3 second. The force of their contraction closes the AV valves, opens the semilunar valves located at the exit from each ventricle, and pumps blood into the large arteries. Blood flows into the atria during the second part of systole, as the green arrows in step 3 indicate.The volume of blood that each ventricle pumps per minute is called cardiac output. This volume is equal to the amount of blood pumped by a ventricle each time it contracts times the heart rate (number of beats per minute)6In certain kinds of heart disease, the heart’s self-pacing system fails to maintain a normal heart rhythm. The remedy is an artificial pacemaker, a tiny electronic device surgically heart rhythm. The remedy is an artificial pacemaker, a tiny electronic device surgically implanted near the heart. Artificial pacemakers emit electrical signals that trigger normal heartbeats.7A heart attack, also called a myocardial infarction, is the damage or death of cardiac muscle tissue as a result of such blockage. Approximately one-third of heart attack victims