CHAPTER 50. THE CIRCULATORY SYSTEM THE ESSENTIALS. Key Terms. Strategy

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1 CHAPTER 50. THE CIRCULATORY SYSTEM THE ESSENTIALS THEME ALERT Structure fits function is a major theme interwoven throughout the course and has been the basis of many free-response questions on the exam the structure of red blood cells and circulatory system vessels are excellent examples of this theme. Students need to know: the major structures of the circulatory system: arteries, veins, capillaries, heart chambers, and the route of mammalian circulation. how the major circulatory vessels illustrate the relationship between structure and function. how red blood cells illustrate the relationship between structure and function. how oxygen and carbon dioxide are transported in the blood. Key Terms open circulatory system hemolymph closed circulatory system heart interstitial fluid lymphatic system lymph lymph vessels endotherms countercurrent heat exchange plasma albumin globulins serum red blood cells white blood cells platelets fibrin arteries arterioles capillaries venules veins vasoconstriction vasodilation atrium ventricle pulmonary circulation systemic circulation atrioventricular (AV) valves semilunar valve cardiac cycle diastole systole pulmonary arteries pulmonary veins aorta coronary arteries superior venal cava inferior vena cava atrioventricular bundle bundle of His electrocardiogram (ECG or EKG) strokes atherosclerosis arteriosclerosis Strategy Class Time: The AP Acorn Book recommends devoting 32% of the course to the Structure and Function of Plants and Animals unit which includes 17 chapters: Chapters (plants) and Chapters (animals). This chapter can be covered in four days. 266

2 Below is a suggested schedule based on a year-long class meeting three 45-minute periods every two days: Lecture 1 (40 45 minutes): Circulatory System Lecture 2 (40 45 minutes): Control of Heart Function Lab 1 (80 90 minutes): AP Lab: Physiology of Circulatory System (required) Lab 2 (40 90 minutes): Lab Extension: Student Research on Factors Affecting Heart Rate (optional) Approach: As with each of the chapters discussing the structure and function of a specific system in animals, the circulatory system will contain information that is very familiar to students and other details that are surprisingly new to them. To enhance the connections throughout biology, it is best to present each system as the adaptation that evolved to support respiration and synthesis in multicellular organisms circulation is the system which distributes to every cell of the body the oxygen and fuels for respiration and raw materials for synthesis. In addition, the other functions of the circulatory system can then be introduced as both necessary and fortuitous extensions of its impact as a highway offering transit to every cell of the body. It became necessary for survival to patrol those highways for invaders trying to make a meal out of the organic molecules neatly packaged in cells, hence the protective function of the circulatory system. It was also advantageous to piggyback on this transportation system and use it as a means of cell-to-cell communication across a whole multicellular organism; hence the regulatory function of the circulatory system. As an alternative approach, this chapter can be presented earlier in the year directly after cellular respiration to better tie together cellular and whole organism systems. An evolutionary thread is nicely interwoven throughout this chapter relating structures and functions as adaptations to different life strategies. The circulatory system offers a number of key examples that illustrate adaptations at the molecular, cellular, and organism level. Arteries, veins and capillaries each have different structure aligned with their functions thickwalled arteries to withstand the force of pumped blood, thinner-walled veins with one-way valves to aid in returning blood to the heart, and one-cell thick walls capillaries to facilitate exchange. The four-chambered heart evolved separately in both mammals and birds and supported the high metabolic rates necessary for the evolution of endothermy, flight, and increased body size. Red blood cells lose many cellular components (nucleus, mitochondria, etc.) thereby increasing the amount of hemoglobin the cell can carry. The molecular structure of hemoglobin and the complementarity of its peptide subunits creates large reservoir of oxygen in the blood and also enables hemoglobin to react to changing blood conditions releasing more oxygen as blood ph falls due to increasing CO 2 levels. Proteins involved in blood clotting are produced as zymogens so they are available for rapidresponse to a blood vessel injury. 267

3 Concept Map 268

4 Student Misconceptions and Common Pitfalls Students have been learning about circulation through many years of life sciences and biology, but may understand it at an elementary level of sequential functions rather than tying their understanding together through evolutionary adaptations and structure-function relationships. When reviewing the direction of blood flow through the heart in diagrams, be sure to remind students that the diagram is drawn as if the heart were sitting in the body so they are sure which side is right and which side is left. Students often confuse the functions of artery and vein, thinking that arteries carry oxygenated blood and veins carry deoxygenated blood. Remind them of the age-old memorization trick that artery begins with a which stands for away from the heart. It is sometimes difficult for students to think of both sides of the heart beating in unison even though the blood is going to different destinations. You can use the expression two hearts beat as one. Most students have not been introduced to the lymphatic system. Be sure to distinguish its differences from the circulatory system: the lymphatic system is an open circulatory system populated by white blood cells. But be sure that students also understand that white blood cells are not limited to travel in the lymphatic system. In regards to thermoregulation, students are usually reluctant to relinquish the common, but misleading terms, warm-blooded and cold-blooded. Emphasize the correct terminology of endotherm and ectotherm, and strongly discourage the vernacular. Clarify that both groups regulate their body temperatures, just using different mechanisms: behavioral adaptations or physiological adaptations. Many ectotherms can maintain their body temperature well-above environmental temperatures through behavioral mechanisms. Throughout their study of biology, students often assume that the way we do it is a more advanced evolutionary stage than the rest of the animal kingdom. This extends to endothermy which students often consider advanced and ectothermy which students often consider primitive implying that endothermy is a more successful strategy. Present these as equally successful adaptations. Endothermy has a considerable overhead a metabolic cost. Whereas ectothermy may be a very successful strategy in an environment of limited resources or widely varying temperature conditions. In fact, ectotherms are far more abundant in the world and diverse than endotherms. Activities 1. Blood Flow in a Fish A classic exercise which usually wows students is setting up a microscope on the tail of a gold fish to watch the flow of blood cells in the capillaries. It s real, alive, and active. 2. Heart Dissection A heart dissection helps to dispel students misconceptions about heart structure. It is usually easy to obtain and calf or sheep heart from the local butcher or meat market. 269

5 Web Resources Circulatory System animation This video is a simple but effective animation on how the heart works. Circulatory System Tutorials and Quizzes This Web site offers a series of tutorials on the circulatory system and also follows up with online quizzes for assessment. On the Lighter Side Hemo the Magnificent movie This movie was originally made in 1957 by Frank Capra, but "Hemo" is still very informative, and it is great to see how much we knew then and how much more we know now. The movie can also be used to spark discussion about how the systems interact together. The movie talks about seawater and the body it is interesting to ask the students how seawater relates to all the body systems and then watch them make the connection between form, function and interdependence between the systems as well as making the evolutionary connection between aquatic unicellular organisms and multicellular organisms with their internal sea. Multiple Choice Questions 1. All of the following are components of blood EXCEPT a. erythrocytes b. beta islet cells c. leukocytes d. albumin e. platelets 2. Major differences between veins and arteries include all of the following EXCEPT a. arteries carry oxygenated blood and veins carry deoxygenated blood b. the walls of arteries are thicker, and contain more smooth muscle than veins of the same size c. veins contain one way valves, arteries do not d. arteries carry blood away from the heart and veins carry blood to the heart e. the blood in arteries is under higher pressure than in veins 270

6 3. The lub-dub sound of the heart is produced by the a. contraction of the atria followed by the contraction of the ventricles. b. opening and closing of the pulmonary artery. c. sinoatrial node. d. closing of the atrioventricular valves, followed by the closing of the semilunar valves. e. difference between systolic and diastolic pressure. 4. The division of the heart ventricle into left and right halves provides what advantage to mammals over amphibians? a. Mammals have a closed circulatory system whereas amphibians have an open circulatory system. b. The mammalian heart sends blood directly to the lungs whereas the amphibian heart cannot. c. The divided ventricles of the mammalian heart separate oxygenated and de-oxygenated blood. d. The heart of a mammal is able to pump twice as fast as the heart of an amphibian. e. The mammalian heart produces greater blood pressure. 5. The circulatory system performs all of the following functions EXCEPT a. carrying nutrients to the body cells b. controlling body responses to stimuli c. carrying oxygen to the body cells d. carrying wastes away from the body cells e. regulating body temperature 6. Both open and closed circulatory systems a. usually have one-way valves. b. have capillary beds. c. carry respiratory gases. d. are low pressure systems. e. include four-chambered hearts. 7. Which one of the following blood vessels carries deoxygenated blood in mammals? a. aorta b. renal artery c. pulmonary artery d. pulmonary vein e. coronary artery 8. The driving force that moves blood back to the heart in the veins is a. active transport. b. pumping of the heart. c. closing of one-way valves. d. skeletal-muscle contractions. e. stretching of the walls of the veins. 271

7 9. The baroreceptor reflex responds to low blood pressure by a. increasing flow of blood to the brain. b. decreasing the heart rate. c. increasing levels of aldosterone which stimulates the kidney to retain water. d. stimulating blood vessels in the skin and digestive system to contract, reducing blood flow. e. stimulating the spleen to release red blood cells. 10. Carbon dioxide released by a mammalian cell would probably be found moving in the blood primarily as a. carboxyhemoglobin. b. bicarbonate ions. c. carbonic acid. d. acid hemoglobin. e. oxyhemoglobin. Answers: 1. b, 2. a, 3. d, 4. c, 5. b, 6. c, 7. c, 8. d, 9. d, 10. b Essay Questions 1. Insects and mammals are both successful groups of organisms with complex body structures. Describe the differences in their circulatory systems. Insects are generally smaller than mammals. Would insect circulatory systems work in much larger animals? Insects do not have closed blood vessels. Intercellular fluid is circulated throughout the body cavity, moving nutrients and gases. Oxygen is delivered to the cells by the tracheal system, not the circulatory system, so every cell must exchange gases directly with the air in the tracheal system. This is not efficient for larger animals. 2. The four-chambered heart evolved independently in both birds and mammals. What is the adaptive advantage of a four-chambered heart? Oxygenated and de-oxygenated blood are separated in the four-chambered heart. This improves the efficiency of oxygen delivery to the body cells which allows for much higher metabolic rates. Higher metabolic rates support endothermy and flight in mammals and birds. 3. What are the structural differences between veins and arteries and how do these reflect the different functions of each vessel? 272

8 Arteries are narrower than veins. The walls of arteries are thicker and contain more smooth muscle than veins. This allows arteries to withstand the high pressure pumping of the heart. The elastic and stretchable walls of arteries are able to expand when the heart pumps and contract to maintain blood pressure even when the heart relaxes. The wider diameter, thinner-walled veins are able to accommodate the low velocity, low pressure blood travelling back to the heart. Veins also have one-way valves that limit blood to flowing only toward heart as it is pushed by skeletal muscle contractions in the legs. 273