Chapter 23 Circulation The Circulatory System aids cells to The Circulatory System aids cells to receive nutrients, exchange gases, and removes wastes. Blood is used to transport these materials using red blood cells filled with hemoglobin and the liquid part of blood tissue called plasma Blood is in vessels called arteries and veins that are connected by capillaries. Blood moves away from the heart in arteries and towards the heart in veins. © 2012 Pearson Education, Inc. 1

23.2 EVOLUTION CONNECTION: Vertebrate cardiovascular systems reflect evolution Blood passes through the heart of a fish once in each circuit through the body, an arrangement called single circulation. A single circuit would not supply enough pressure to move blood through the capillaries of the lungs and then to the body capillaries of a terrestrial vertebrate. Student Misconceptions and Concerns  Students might need to be reminded about the changes in surface-to-volume ratios as organisms increase in size. As any organism gets larger (maintaining the same proportions) the need for a circulatory system coupled with a respiratory system increases, since the increase in surface area does not keep up with the increase in volume.  Students might not realize that closed circulatory systems are capable of greater pressures when fluids remain confined to limited spaces. Teaching Tips  The three-chambered heart of amphibians and turtles should not be seen as a necessary “intermediate” stage in some predestined evolution of a four-chambered heart. Instead, the three-chambered heart conveys advantages not permitted by the complete subdivision of the ventricle. In amphibians and turtles, the circuit to the lungs can be bypassed when diving underwater. When breathing is not possible, blood can be rerouted past the lungs. Thus, a loss in efficiency conveys an advantage in flexibility. This fundamental principle, in which efficiency and flexibility are traded against each other, is illustrated in many systems in living organisms.  Challenge students to explain why closed circulatory systems have evolved in squids and octopuses, but not in clams or snails. The greater amount of muscular activity in squids and octopuses may have favored these more efficient systems of delivery.  To help students understand the need for a circulatory system, consider this analogy. Small islands are like small animals: No inner part is very far from the edges. However, large countries, like large animals, have considerable interior areas located far from their borders. Therefore, large countries such as the United States, Canada, India, and China require an internal system of roads and railways to transport many goods from ocean ports to cities located deep in these countries. These roads and railways move materials from ports in the same way that blood and blood vessels move them from respiratory surfaces.  There are many simple demonstrations of diffusion that can be performed. If you use a video imager or overhead projector, add a single drop of food coloring to a beaker of water with bright illumination. The slow dissipation of the dye will serve as a colorful and dramatic example of materials moving from a higher to a lower level of concentration. Active Lecture Tips  See the Activity Blood Flow: Following a Single Red Blood Cell on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

Gill capillaries Heart: Ventricle Atrium Body capillaries Figure 23.2a Figure 23.2a The single circulation and two-chambered heart of a fish Body capillaries © 2015 Pearson Education, Inc.

23.2 EVOLUTION CONNECTION: Vertebrate cardiovascular systems reflect evolution Land vertebrates have a double circulation in which blood is pumped a second time after it loses pressure in the lungs. The pulmonary circuit carries blood between the heart and gas exchange tissues in the lungs. The systemic circuit carries blood between the heart and the rest of the body. Student Misconceptions and Concerns  Students might need to be reminded about the changes in surface-to-volume ratios as organisms increase in size. As any organism gets larger (maintaining the same proportions) the need for a circulatory system coupled with a respiratory system increases, since the increase in surface area does not keep up with the increase in volume.  Students might not realize that closed circulatory systems are capable of greater pressures when fluids remain confined to limited spaces. Teaching Tips  The three-chambered heart of amphibians and turtles should not be seen as a necessary “intermediate” stage in some predestined evolution of a four-chambered heart. Instead, the three-chambered heart conveys advantages not permitted by the complete subdivision of the ventricle. In amphibians and turtles, the circuit to the lungs can be bypassed when diving underwater. When breathing is not possible, blood can be rerouted past the lungs. Thus, a loss in efficiency conveys an advantage in flexibility. This fundamental principle, in which efficiency and flexibility are traded against each other, is illustrated in many systems in living organisms.  Challenge students to explain why closed circulatory systems have evolved in squids and octopuses, but not in clams or snails. The greater amount of muscular activity in squids and octopuses may have favored these more efficient systems of delivery.  To help students understand the need for a circulatory system, consider this analogy. Small islands are like small animals: No inner part is very far from the edges. However, large countries, like large animals, have considerable interior areas located far from their borders. Therefore, large countries such as the United States, Canada, India, and China require an internal system of roads and railways to transport many goods from ocean ports to cities located deep in these countries. These roads and railways move materials from ports in the same way that blood and blood vessels move them from respiratory surfaces.  There are many simple demonstrations of diffusion that can be performed. If you use a video imager or overhead projector, add a single drop of food coloring to a beaker of water with bright illumination. The slow dissipation of the dye will serve as a colorful and dramatic example of materials moving from a higher to a lower level of concentration. Active Lecture Tips  See the Activity Blood Flow: Following a Single Red Blood Cell on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

Pulmocutaneous circuit Figure 23.2b Figure 23.2B The double circulation and three-chambered heart of an amphibian Lung and skin capillaries Pulmocutaneous circuit Atrium Atrium Ventricle Figure 23.2b The double circulation and three-chambered heart of an amphibian Right Left Systemic circuit Systemic capillaries © 2015 Pearson Education, Inc.

23.2 EVOLUTION CONNECTION: Vertebrate cardiovascular systems reflect evolution Frogs and other amphibians have a three-chambered heart. The right atrium receives blood returning from the systemic capillaries in the body’s organs. The ventricle pumps blood to the lungs and skin. Because gas exchange occurs both in the lungs and across the thin, moist skin, this is called a pulmocutaneous circuit. © 2015 Pearson Education, Inc.

23.2 EVOLUTION CONNECTION: Vertebrate cardiovascular systems reflect evolution Frogs and other amphibians have a three-chambered heart. The right atrium receives blood returning from the systemic capillaries in the body’s organs. The ventricle pumps blood to the lungs and skin. Because gas exchange occurs both in the lungs and across the thin, moist skin, this is called a pulmocutaneous circuit. © 2015 Pearson Education, Inc.

23.2 EVOLUTION CONNECTION: Vertebrate cardiovascular systems reflect evolution 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. The left side receives and pumps only oxygen-rich blood. © 2015 Pearson Education, Inc.

23.3 The human cardiovascular system illustrates the double circulation of mammals Blood flow through the circulatory system of humans drains from the large veins called the superior vena cava (from the head and arms) or inferior vena cava (from the lower trunk and legs) into the right atrium, the heart contracts pushing blood into the right ventricle through a valve moves out to the lungs via the pulmonary artery, which forms capillaries in alveoli returns to the left atrium through the pulmonary vein, and goes into the left ventricle where it leaves the heart through a large artery called the aorta. © 2012 Pearson Education, Inc. 9

Superior vena cava Pulmonary artery Pulmonary artery Figure 23.3 Capillaries of head, chest, and arms Superior vena cava Pulmonary artery Pulmonary artery Aorta Pulmonary circuit Systemic circuit Lung capillaries Pulmonary vein Pulmonary vein Right atrium Left atrium Right ventricle Figure 23.3 Blood flow through the circulation of the human cardiovascular system Aorta Left ventricle Inferior vena cava Capillaries of abdominal region and legs © 2015 Pearson Education, Inc. 10

Atrioventricular (AV) valve Atrioventricular (AV) valve Figure 23.4 To lung To lung Right atrium Left atrium From lung From lung Semilunar valve Semilunar valve Atrioventricular (AV) valve Atrioventricular (AV) valve Figure 23.3B Blood flow through the human heart Right ventricle Left ventricle 11