CARDIOVASCULAR SYSTEM OUTLINE 22.1 Overview of the Cardiovascular System 657 22.1a Pulmonary and Systemic Circulations 657 22.1b Position of the Heart 658 22 22.1c Characteristics of the Pericardium 659 22.2 Anatomy of the Heart 660 22.2a Heart Wall Structure 660 22.2b External Heart Anatomy 660 Heart 22.2c Internal Heart Anatomy: Chambers and Valves 660 22.3 Coronary Circulation 666 22.4 How the Heart Beats: Electrical Properties of Cardiac Tissue 668 22.4a Characteristics of Cardiac Muscle Tissue 668 22.4b Contraction of Heart Muscle 669 22.4c The Heart’s Conducting System 670 22.5 Innervation of the Heart 672 22.6 Tying It All Together: The Cardiac Cycle 673 22.6a Steps in the Cardiac Cycle 673 22.6b Summary of Blood Flow During the Cardiac Cycle 673 22.7 Aging and the Heart 677 22.8 Development of the Heart 677 MODULE 9: CARDIOVASCULAR SYSTEM mck78097_ch22_656-682.indd 656 2/14/11 4:29 PM Chapter Twenty-Two Heart 657 n chapter 21, we discovered the importance of blood and the which carry blood back to the heart. The differences between I myriad of substances it carries. To maintain homeostasis, blood these types of vessels are discussed in chapter 23. Most arteries must circulate continuously throughout the body. The continual carry blood high in oxygen (except for the pulmonary arteries, pumping action of the heart is essential for maintaining blood as explained later), while most veins carry blood low in oxygen circulation. If the heart fails to pump adequate volumes of blood, (except for the pulmonary veins). The arteries and veins entering cells are deprived of needed oxygen and nutrients, waste products and leaving the heart are called the great vessels because of their accumulate, and cell death occurs. relatively large diameter. The heart exhibits several related charac- In a healthy, 80-kilogram resting adult, the heart beats about 75 teristics and functions: times per minute (about 4500 times per hour or 108,000 times per day). ■ The heart’s anatomy ensures the unidirectional flow of The amount of blood pumped from one ventricle per minute (about blood through it. Backflow of blood is prevented by valves 5.25 liters [L] at rest) is called the cardiac output. When the body is within the heart. more active, and the cells need oxygen and nutrients delivered at a ■ The heart acts like two side-by-side pumps that work at the faster pace, the heart can increase its output up to five- or six-fold. same rate and pump the same volume of blood; one directs blood to the lungs for gas exchange, while the other directs 22.1 Overview of the Cardiovascular blood to body tissues for nutrient and respiratory gas delivery. ■ The heart develops blood pressure through alternate cycles System of heart wall contraction and relaxation. Blood pressure Learning Objectives: is the force of the blood pushing against the inside walls of the vessels. A minimum blood pressure is essential for 1. Identify and describe the basic features of the pushing blood through the blood vessels. cardiovascular system. 2. Describe and trace the general patterns of the pulmonary 22.1a Pulmonary and Systemic Circulations and systemic circulations. The cardiovascular system consists of two circulations: the pulmo- 3. Identify the position and location of the heart. nary circulation and the systemic circulation (figure 22.1). The 4. Discuss the structure and function of the pericardium. pulmonary (pŭ l ḿō -nā r-ē; pulmo = lung) circulation consists of the As the center of the cardiovascular system, the heart con- chambers on the right side of the heart (right atrium and right ven- nects to blood vessels that transport blood between the heart and tricle) as well as the pulmonary arteries and veins. This circulation all body tissues. The two basic types of blood vessels are arteries conveys blood to the lungs via pulmonary arteries to reduce carbon (ar ter-́ ē ), which carry blood away from the heart, and veins (vā n), dioxide and replenish oxygen levels in the blood before returning to Lung Capillaries Figure 22.1 Cardiovascular System. The cardiovascular system is composed Pulmonary veins Left atrium of the pulmonary circulation and the Pulmonary Pulmonary arteries Left ventricle systemic circulation. The pulmonary Right atrium circulation pumps blood from the right circulation Aorta to Right ventricle systemic Systemic side of the heart through pulmonary arteries circulation vessels, to the lungs, and back to the Systemic left side of the heart. The systemic veins circulation pumps blood from the left side of the heart, through systemic vessels in peripheral tissues, and back Vessels transporting to the right side of the heart. oxygenated blood Capillaries Vessels transporting deoxygenated blood Vessels involved in gas exchange mck78097_ch22_656-682.indd 657 2/14/11 4:29 PM 658 Chapter Twenty-Two Heart Trachea Sternal angle Right lung Left lung 2nd rib Aortic arch Superior border Left phrenic Superior nerve vena cava Right border Right phrenic Pulmonary Left nerve Sternum trunk border Ascending aorta Diaphragm Anterior interventricular Inferior Right atrium artery border Left ventricle Right coronary artery Diaphragm Right ventricle (a) Borders of the heart (b) Heart and lungs, anterior view Mediastinum Left lung Posterior Ascending aorta Pleura (cut) Thoracic Pericardium vertebra Right lung Left lung (cut) Aortic arch (cut) Apex of heart Heart (in mediastinum) Diaphragm Sternum (cut) Anterior (c) Serous membranes of the heart and lungs (d) Cross-sectional view Figure 22.2 Heart Position Within the Thoracic Cavity. The heart is in the mediastinum of the thoracic cavity. ( a) An anterior view shows the position of the heart posterior to the anterior thoracic cage. The borders of the heart are labeled. (b) Cadaver photo of the heart within the mediastinum (anterior view). (c) Serous membranes (pericardium and pleura) surround the heart and lungs, respectively. (d) A cross-sectional view depicts the heart’s relationship to the other organs in the thoracic cavity. the heart in pulmonary veins. Blood returns to the left side of the WHAT DO YOU THINK? heart, where it then enters the systemic circulation. ●1 We previously mentioned that arteries tend to carry oxygenated ́ The systemic (sis-tem ik) circulation consists of the cham- blood, but the pulmonary arteries are the exception. Why are the bers on the left side of the heart (left atrium and left ventricle), pulmonary arteries carrying deoxygenated blood? along with all the other named blood vessels. It carries blood to all the peripheral organs and tissues of the body. Blood that 22.1b Position of the Heart is high in oxygen (oxygenated) from the left side of the heart is The heart is located left of the body midline posterior to the pumped into the aorta, the largest systemic artery in the body, sternum in the mediastinum (figure 22.2). The heart is slightly and then into smaller systemic arteries. Gas is exchanged with rotated such that its right side or right border (primarily formed tissues from the body’s smallest vessels, called capillaries. by the right atrium and ventricle) is located more anteriorly, while Systemic veins then carry blood that is low in oxygen (deoxygen- its left side or left border (primarily formed by the left atrium ated) and high in carbon dioxide and waste products back to the and ventricle) is located more posteriorly. The posterosuperior heart. Most veins merge and drain into the superior and inferior surface of the heart, formed primarily by the left atrium, is called venae cavae (vē ńē ca ́vē ; sing., vena cava), which drain blood the base. The pulmonary veins that enter the left atrium border into the right atrium. There, the blood enters the pulmonary cir- this base. The superior border is formed by the great arterial culation, and the cycle repeats. trunks (ascending aorta and pulmonary trunk) and the superior mck78097_ch22_656-682.indd 658 2/14/11 4:29 PM Chapter Twenty-Two Heart 659 it beats. The pericardial cavity is a potential space with just a thin lining of serous fluid. However, it may become a real space Fibrous pericardium as described in the Clinical View: “Pericarditis.” WHATW DID YOU LEARN? Parietal layer of serous pericardium ●1 What is the basic distinction between arteries and veins? Pericardial cavity ●2 Contrast the pulmonary and systemic circulations. Visceral layer of serous pericardium ●3 What is the difference between the base of the heart and its apex? (epicardium) ●4 Identify the layers of the pericardium. Why is the pericardial cavity described as a potential space? Fibrous pericardium Parietal layer of Study Tip! serous pericardium To demonstrate the almost frictionless movement of the heart Pericardial cavity within the pericardial sac, try the following demonstration: Visceral layer of 1. Obtain two glass microscope slides. Place them together and serous pericardium (epicardium) then try to slide them back-and-forth past each other. You will Heart wall find that they stick together (even if they are very clean) and Myocardium do not move relative to one another very easily! Endocardium 2. Now, take two similar glass slides and place a very small drop of water onto the surface of one slide. Place the slides together, as before, and then try to slide them back-and-forth past each other. We predict that you have demonstrated to yourself that glass slides move easily past each other when a water drop is present between them. This ease of movement of two opposing surfaces parallels the sliding movement of the parietal and visceral pericardial surfaces when a thin layer of serous fluid is present between them. Figure 22.3 Pericardium. The pericardium consists of an outer fibrous pericardium and an inner serous pericardium.