Cardiovascular System 2021 PDF

ANATOMY AND PHYSIOLOGY CHAPTER VIII: THE CARDIOVASCULAR SYSTEM The cardiovascular system (cardio- heart; vascular blood or blood vessels) or simply...

ANATOMY AND PHYSIOLOGY CHAPTER VIII: THE CARDIOVASCULAR SYSTEM The cardiovascular system (cardio- heart; vascular blood or blood vessels) or simply the circulatory system consists of three interrelated components: blood, the heart, and blood vessels. As the name implies, blood contained in the circulatory system is pumped by the heart around a closed circle or circuit of vessels as it passes again and again through the various "circulations" of the body. As you have learned in your previous lessons, circulation refers to the Adopted from: transportation of materials to and from the https://www.google.com/search?q=cardiovascular+s ystem+clipart&source=lnms&tbm=isch&sa=X&ved=2 cells made possible by the propulsion of ahUKEwjr5OzX3-nsAhVLzIsBHZJVAtoQ_ UoAXo ECAU blood through a blood system of tubes. QAw&biw=2048&bih=1005#imgrc=K6Sr9nnXQlC61M This chapter of the module has been designed to help you understand further how the cardiovascular system works. It is organized into three lessons: Lesson 1: The Blood; Lesson 2: The Heart; and Lesson 3: The Blood Vessels. LESSON 1. THE BLOOD INTRODUCTION OF THE LESSON AND PRESENTATION OF OUTCOMES The cardiovascular system consists of the blood, the heart, and the blood vessels. The focus of this lesson is blood. Blood is a liquid connective tissue that transports oxygen from the lungs and nutrients from the gastrointestinal tract, which diffuse from the blood into the interstitial fluid and then into body cells. Carbon dioxide and other wastes move in the reverse direction, from body cells to interstitial fluid to blood. Blood then transports the wastes to various organs—the lungs, kidneys, and skin—for elimination from the body.  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY After studying the section, you must have: a. explained the functions of blood; b. described the physical characteristics and physical components of blood; c. explained the origin of blood cells; d. described the structure, functions, life span and production of red blood cells; e. described the structure, functions, and production of white blood cells; f. described the structure, functions, and origin of platelets; g. described the mechanisms that contributed to hemostasis; and h. explained the various factors that promote and inhibit blood clotting. WARM-UP ACTIVITY Instructions: Read the clues provided and fill in the correct answer! 1 2 3 4 5 6 7 8 9 10 11 Mariano Marcos State University College of Health Sciences 2 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY ACROSS DOWN 1 A yellow-orange pigment that is formed 1 A liquid connective tissue when iron is removed from heme 3 The pigment that gives whole blood its 2 Other name for platelet red color 5 The liquid portion of the blood 4 Shape of platelets 7 Protein portion of hemoglobin 6 Differentiates into macrophages 8 Polymorphs or neutrophils 9 Cell that combat infection 10 Element necessary for RBC production 11 A gel formed when blood is drawn from the body CENTRAL ACTIVITIES The central activities are divided into five learning inputs. To evaluate what you have learned, an activity has been prepared for you after each learning input. The following will be the focus for each learning input: Learning Input 1: Functions and Properties of Blood; Learning Input 2: Formation of Blood Cells; Learning Input 3: Red Blood Cells; Learning Input 4: White Blood Cells; and Learning Input 5: Blood Platelets. Learning Input 1 Functions and Properties of Blood Blood has three general functions: 1. Transportation. As you just learned, blood transports oxygen from the lungs to the cells of the body and carbon dioxide from the body cells to the lungs for exhalation. It carries nutrients from the gastrointestinal tract to body cells and hormones from endocrine glands to other body cells. Blood also transports heat and waste products to various organs for elimination from the body. 2. Regulation. Circulating blood helps maintain homeostasis of all body fluids. Blood helps regulate pH through the use of buffers (chemicals that convert strong acids or bases into weak ones). It also helps adjust body temperature through the heat absorbing and coolant properties of the water in blood plasma and its variable rate of flow through the skin, where excess heat can be lost from the blood to the environment. In addition, blood osmotic pressure influences the water content of cells, mainly through interactions of dissolved ions and proteins. Mariano Marcos State University College of Health Sciences 3 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY 3. Protection. Blood can clot (become gel-like), which protects against its excessive loss from the cardiovascular system after an injury. In addition, its white blood cells protect against disease by carrying on phagocytosis. Several types of blood proteins, including antibodies, interferons, and complement, help protect against disease in a variety of ways. Blood is denser and more viscous than water and feels slightly sticky. The temperature of blood is 38°C (100.4F), about 1°C higher than oral or rectal body temperature, and it has a slightly alkaline pH ranging from 7.35 to 7.45. The color of blood varies with its oxygen content. When saturated with oxygen, it is bright red. When unsaturated with oxygen, it is dark red. Blood constitutes about 20% of extracellular fluid, amounting to 8% of the total body mass. The blood volume is 5 to 6 liters (1.5 gal) in an average sized adult male and 4 to 5 liters (1.2 gal) in an average-sized adult female. Whole blood has two components: (1) blood plasma, a watery liquid extracellular matrix that contains dissolved substances, and (2) formed elements, which are cells and cell fragments. Blood is about 45% formed elements and 55% blood plasma. Normally, more than 99% of the formed elements are composed of red blood cells (RBCs). White blood cells (WBCs) and platelets occupy less than 1% of the formed elements. Figure 1.1 shows the composition of blood plasma and the numbers of the various types of formed elements in blood. Blood Plasma. When the formed elements are removed from blood, a straw- colored liquid called blood plasma (or simply plasma) is left. Blood plasma is about 91.5% water and 8.5% solutes, most of which (7% by weight) are proteins. Some of the proteins in blood plasma are also found elsewhere in the body, but those confined to blood are called plasma proteins. Besides proteins, other solutes in plasma include electrolytes, nutrients, regulatory substances such as enzymes and hormones, gases, and waste products such as urea, uric acid, creatinine, ammonia, and bilirubin. Table 1.1 describes the chemical composition of blood plasma. Mariano Marcos State University College of Health Sciences 4 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY Figure 1.1. Components of blood. Adopted from: Tortora, G. J. & Derrickson, B., 2014. Principles of Anatomy & Physiology, 14th edition. New Jersey: John Wiley & Sons, Inc. Formed Elements. The formed elements of the blood include three principal components: red blood cells, white blood cells, and platelets (Figure 1.2). Red blood cells (RBCs) or erythrocytes transport oxygen from the lungs to body cells and deliver carbon dioxide from body cells to the lungs. White blood cells (WBCs) or leukocytes protect the body from invading pathogens and other foreign substances. There are several types of WBCs: neutrophils, basophils, eosinophils, monocytes, and lymphocytes. Lymphocytes are further subdivided into B lymphocytes (B cells), T lymphocytes (T cells), and natural killer (NK) cells. Each type of WBC contributes in its own way to the body’s defense mechanisms. Platelets, the final type of formed element, are fragments of cells that do not have Mariano Marcos State University College of Health Sciences 5 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY a nucleus. Among other actions, they release chemicals that promote blood clotting when blood vessels are damaged. Platelets are the functional equivalent of thrombocytes, nucleated cells found in lower vertebrates that prevent blood loss by clotting blood. See Table 1.2 for the other names, normal values, and life span of these formed elements of the blood. Table 1.1. Substances in Blood Plasma Adopted from: Tortora, G. J. & Derrickson, B., 2014. Principles of Anatomy & Physiology, 14th edition. New Jersey: John Wiley & Sons, Inc. RBC WBC BLOOD PLATELETS Erythrocytes Leukocytes Thrombocytes 4.5 to 5.5 million/cu.mm 5,000 to 10,000 per cu.mm 150,000 to 300,000 per cu.mm Gas transport Control infection Blood clotting 120 days Few hours – 200 days 6-18 days Biconcave disk Circular Oval Table 1.2. Other names, normal values, and lifespan of the formed elements of the blood. Mariano Marcos State University College of Health Sciences 6 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY Figure 1.2. Formed elements of the blood. Adopted from: Tortora, G. J. & Derrickson, B., 2014. Principles of Anatomy & Physiology, 14th edition. New Jersey: John Wiley & Sons, Inc. Activity 1. Test your knowledge! Before moving on to the next section, it’s time for you to evaluate first what you have learned by filling up the blanks below. Are you ready? Blood is more ___(1)_____ than water. It has a temperature of _(2)__°C, and it has a slightly alkaline pH ranging from _(3)_ to 7.45. The color of blood varies with its oxygen content. When saturated with oxygen, it is __(4)___. When unsaturated with oxygen, it is ___(5)___. Blood constitutes about 20% of extracellular fluid, amounting to 8% of the total body mass. The blood volume is ___(6)___ liters in an average sized adult male and 4 to 5 liters in an average- sized adult female. Whole blood has two components: ____(7)____, a watery liquid extracellular matrix that contains dissolved substances, and ____(8)____, which are cells and cell fragments. The formed elements of the blood include three principal components: red blood cells, _____(9)______, and _____(10)______. Mariano Marcos State University College of Health Sciences 7 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY Learning Input 2 Formation of Blood Cells The process by which the formed elements of blood develop is called hemopoiesis or hematopoiesis. Before birth, hemopoiesis first occurs in the yolk sac of an embryo and later in the liver, spleen, thymus, and lymph nodes of a fetus. Red bone marrow becomes the primary site of hemopoiesis in the last 3 months before birth, and continues as the source of blood cells after birth and throughout life. About 0.05–0.1% of red bone marrow cells are called pluripotent stem cells or hemocytoblasts and are derived from mesenchyme (tissue from which almost all connective tissues develop). These cells have the capacity to develop into many different types of cells (Figure 1.3). Figure 1.3. Origin, development and structure of blood cells. Adopted from: Tortora, G. J. & Derrickson, B., 2014. Principles of Anatomy & Physiology, 14th edition. New Jersey: John Wiley & Sons, Inc. During hemopoiesis, some of the myeloid stem cells differentiate into progenitor cells. Other myeloid stem cells and the lymphoid stem cells develop directly into precursor cells. Progenitor cells are no longer capable of reproducing themselves and are committed to Mariano Marcos State University College of Health Sciences 8 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY giving rise to more specific elements of blood. Some progenitor cells are known as colony- forming units (CFUs). Following the CFU designation is an abbreviation that indicates the mature elements in blood that they will produce: CFU–E ultimately produces erythrocytes (red blood cells); CFU–Meg produces megakaryocytes, the source of platelets; and CFU– GM ultimately produces granulocytes (specifically, neutrophils) and monocytes (see Figure 1.3). In the next generation, the cells are called precursor cells, also known as blasts. Over several cell divisions they develop into the actual formed elements of blood. Activity 2. Test your knowledge! Evaluate again how much you have learned. Before you proceed to the next section, state whether the following statements are correct or not. 1. The red bone marrow becomes the primary site of hemopoiesis after birth and throughout life. 2. Progenitor cells are no longer capable of reproducing themselves. 3. All formed elements of the blood originate from the myeloid stem cells. 4. Mesenchyme refers to the tissue from which almost all connective tissues develop. 5. Before birth, hemopoiesis first occurs in the liver of a fetus. Learning Input 3 Red Blood Cells Red blood cells (RBCs) or erythrocytes contain the oxygen-carrying protein hemoglobin, which is a pigment that gives whole blood its red color. A healthy adult male has about 5.4 million red blood cells per microliter (L) of blood, and a healthy adult female has about 4.8 million. RBCs are biconcave discs with a diameter of 7–8 m (Figure 1.4a). Mature red blood cells have a simple structure. Their plasma membrane is both strong and flexible, which allows them to deform without rupturing as they squeeze through narrow blood capillaries. Certain glycolipids in the plasma membrane of RBCs are antigens that account for the various blood groups such as the ABO and Rh groups. RBCs lack a nucleus and other organelles and can neither reproduce nor carry on extensive metabolic activities. The cytosol of RBCs contains hemoglobin molecules; these important molecules are synthesized before loss of the nucleus during RBC production and constitute about 33% of the cell’s weight. Red blood cells are highly specialized for their oxygen transport function. Because mature RBCs have no nucleus, all of their internal space is available for oxygen transport. Because RBCs lack mitochondria and generate ATP anaerobically (without oxygen), they do not use up any of the oxygen they transport. Even the shape of an RBC facilitates its Mariano Marcos State University College of Health Sciences 9 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY function. A biconcave disc has a much greater surface area for the diffusion of gas molecules into and out of the RBC than would, say, a sphere or a cube. Each RBC contains about 280 million hemoglobin molecules. A hemoglobin molecule consists of a protein called globin, composed of four polypeptide chains (two alpha and two beta chains); a ringlike nonprotein pigment called a heme (Figure 1.4b) is bound to each of the four chains. At the center of each heme ring is an iron ion (Fe 2) that can combine reversibly with one oxygen molecule (Figure 1.4c), allowing each hemoglobin molecule to bind four oxygen molecules. Each oxygen molecule picked up from the lungs is bound to an iron ion. As blood flows through tissue capillaries, the iron–oxygen reaction reverses. Hemoglobin releases oxygen, which diffuses first into the interstitial fluid and then into cells. Figure 1.4. The shapes of a red blood cell and a hemoglobin molecule. Adopted from: Tortora, G. J. & Derrickson, B., 2014. Principles of Anatomy & Physiology, 14th edition. New Jersey: John Wiley & Sons, Inc. Hemoglobin also transports about 23% of the total carbon dioxide, a waste product of metabolism. (The remaining carbon dioxide is dissolved in plasma or carried as bicarbonate ions.) Blood flowing through tissue capillaries picks up carbon dioxide, some of which combines with amino acids in the globin part of hemoglobin. As blood flows through the lungs, the carbon dioxide is released from hemoglobin and then exhaled. In addition to its key role in transporting oxygen and carbon dioxide, hemoglobin also plays a role in the regulation of blood flow and blood pressure. The gaseous hormone nitric oxide (NO), produced by the endothelial cells that line blood vessels, binds to hemoglobin. Under some circumstances, hemoglobin releases NO. The released NO causes vasodilation, an increase in blood vessel diameter that occurs when the smooth muscle in the vessel wall relaxes. Vasodilation improves blood flow and enhances oxygen delivery to cells near the site of NO release. Red Blood Cell Production. The production of red blood cell is known as erythropoiesis. It occurs in the domain yolk sac during the embryological stage of Mariano Marcos State University College of Health Sciences 10 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY development, by the liver from the second to the fifth month of fetal life and by the red bone marrow on the latter end of fetal development. During infancy and childhood, almost all the bones produce erythrocytes but when growth process of bones has been completed the RBC are produced by the red bone marrow of the cancellous and flat bones, skull bones, vertebrae, sternum, pelvis and the proximal ends of the femur and humerus. Normally, erythropoiesis and red blood cell destruction proceed at roughly the same pace. If the oxygen-carrying capacity of the blood falls because erythropoiesis is not keeping up with RBC destruction, a negative feedback system steps up RBC production. The controlled condition is the amount of oxygen delivered to body tissues. Cellular oxygen deficiency, called hypoxia, may occur if too little oxygen enters the blood. For example, the lower oxygen content of air at high altitudes reduces the amount of oxygen in the blood. Oxygen delivery may also fall due to anemia, which has many causes: Lack of iron, lack of certain amino acids, and lack of vitamin B12 are but a few. Circulatory problems that reduce blood flow to tissues may also reduce oxygen delivery. Whatever the cause, hypoxia results to the release of the kidney enzyme erythrogenin (REF) which then will activate the erythropoeitin/ hemapoeitin, a hormone that stimulates the red bone marrow to produce hematocytoblasts and hastens that successive nuclear and cytoplasmic maturation changes. RBCs that have hemoglobin on their blasts form are nucleated but when the differentiation is on the reticulocytes stage, the hemoglobin takes over the place of the nucleus. The mature RBC is then released to the blood stream. If ever there is an abrupt demand for RBC production, reticulocytes may be released. As the number of circulating RBCs increases, more oxygen can be delivered to body tissues. Life Cycle and Destruction of RBC. Red blood cells live only about 120 days because of the wear and tear their plasma membranes undergo as they squeeze through blood capillaries. Without a nucleus and other organelles, RBCs cannot synthesize new components to replace damaged ones. The plasma membrane becomes more fragile with age, and the cells channels in the spleen. Ruptured red blood cells are removed from circulation and destroyed by fixed phagocytic macrophages in the spleen and liver, and the breakdown products are recycled and used in numerous metabolic processes, including the formation of new red blood cells. The recycling occurs as follows (Figure 1.5): 1. Macrophages in the spleen, liver, or red bone marrow phagocytize ruptured and worn-out red blood cells. 2. The globin and heme portions of hemoglobin are split apart. 3. Globin is broken down into amino acids, which can be reused to synthesize other proteins. 4. Iron is removed from the heme portion in the form of Fe 3, which associates with the plasma protein transferrin, a transporter for Fe3 in the bloodstream. Mariano Marcos State University College of Health Sciences 11 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY 5. In muscle fibers, liver cells, and macrophages of the spleen and liver, Fe 3 detaches from transferrin and attaches to an iron-storage protein called ferritin. 6. On release from a storage site or absorption from the gastrointestinal tract, Fe3 reattaches to transferrin. 7. The Fe3–transferrin complex is then carried to red bone marrow, where RBC precursor cells take it up through receptor mediated endocytosis for use in hemoglobin synthesis. Iron is needed for the heme portion of the hemoglobin molecule, and amino acids are needed for the globin portion. Vitamin B12 is also needed for the synthesis of hemoglobin. 8. Erythropoiesis in red bone marrow results in the production of red blood cells, which enter the circulation. 9. When iron is removed from heme, the non-iron portion of heme is converted to biliverdin, a green pigment, and then into bilirubin, a yellow-orange pigment. 10. Bilirubin enters the blood and is transported to the liver. 11. Within the liver, bilirubin is released by liver cells into bile, which passes into the small intestine and then into the large intestine. 12. In the large intestine, bacteria convert bilirubin into urobilinogen. 13. Some urobilinogen is absorbed back into the blood, converted to a yellow pigment called urobilin, and excreted in urine. 14. Most urobilinogen is eliminated in feces in the form of a brown pigment called stercobilin, which gives feces its characteristic color. Figure 1.5. Formation and destruction of red blood cell and the recycling of hemoglobin components. Adopted from: Tortora, G. J. & Derrickson, B., 2014. Principles of Anatomy & Physiology, 14th edition. New Jersey: John Wiley & Sons, Inc. Mariano Marcos State University College of Health Sciences 12 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY Activity 3. Test your knowledge! Apply what you have learned in this section by answering the following questions. You can do it! 1. What is the lifespan of red blood cells? 2. How many polypeptide chains does a globin has? 3. What do you call the process of red blood cell production? 4. What is the main stimulus for red blood cell production? 5. What do you call the pigment that gives the feces it characteristic color? Learning Input 4 White Blood Cells Unlike red blood cells, white blood cells (WBCs) or leukocytes have nuclei and a full complement of other organelles but they do not contain hemoglobin. WBCs are classified as either granular or agranular, depending on whether they contain conspicuous chemical-filled cytoplasmic granules (vesicles) that are made visible by staining when viewed through a light microscope. Granular leukocytes include neutrophils, eosinophils, and basophils; agranular leukocytes include lymphocytes and monocytes. As shown in Figure 1.3, monocytes and granular leukocytes develop from myeloid stem cells. In contrast, lymphocytes develop from lymphoid stem cells. Granular Leukocytes. After staining, each of the three types of granular leukocytes displays conspicuous granules with distinctive coloration that can be recognized under a light microscope. Granular leukocytes can be distinguished as follows:  Neutrophil. The granules of a neutrophil are smaller than those of other granular leukocytes, evenly distributed, and pale lilac (Figure 1.6a). Because the granules do not strongly attract either the acidic (red) or basic (blue) stain, these WBCs are neutrophilic (neutral loving). The nucleus has two to five lobes, connected by very thin strands of nuclear material. As the cells age, the number of nuclear lobes increases. Because older neutrophils thus have several differently shaped nuclear lobes, they are often called polymorphonuclear leukocytes (PMNs), polymorphs, or “polys.  Eosinophil. The large, uniform-sized granules within an eosinophil are eosinophilic (eosin-loving)— they stain red-orange with acidic dyes (Figure 1.6b). The granules usually do not cover or obscure the nucleus, which most often has two lobes connected by either a thin strand or a thick strand of nuclear material. Mariano Marcos State University College of Health Sciences 13 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY  Basophil. The round, variable-sized granules of a basophil are basophilic (basic loving)—they stain bluepurple with basic dyes (Figure 1.6c). The granules commonly obscure the nucleus, which has two lobes. Figure 1.6. Types of white blood cells. Adopted from: Tortora, G. J. & Derrickson, B., 2014. Principles of Anatomy & Physiology, 14th edition. New Jersey: John Wiley & Sons, Inc. Agranular Leukocytes. Even though so-called agranular leukocytes possess cytoplasmic granules, the granules are not visible under a light microscope because of their small size and poor staining qualities.  Lymphocyte. The nucleus of a lymphocyte stains dark and is round or slightly indented (Figure 1.6d). The cytoplasm stains sky blue and forms a rim around the nucleus. The larger the cell, the more cytoplasm is visible. Lymphocytes are classified by cell diameter as large lymphocytes (10– 14 m) or small lymphocytes (6–9 m). Although the functional significance of the size difference between small and large lymphocytes is unclear, the distinction is still clinically useful because an increase in the number of large lymphocytes has diagnostic significance in acute viral infections and in some immunodeficiency diseases.  Monocyte. The nucleus of a monocyte is usually kidney-shaped or horseshoe- shaped, and the cytoplasm is blue-gray and has a foamy appearance (Figure 1.6e). The cytoplasm’s color and appearance are due to very fine azurophilic granules, which are lysosomes. Blood is merely a conduit for monocytes, which migrate from the blood into the tissues, where they enlarge and differentiate into macrophages. Some become fixed (tissue) macrophages, which means they reside in a particular tissue; examples are alveolar macrophages in the lungs or macrophages in the spleen. Others become wandering macrophages, which roam the tissues and gather at sites of infection or inflammation. In a healthy body, some WBCs, especially lymphocytes, can live for several months or years, but most live only a few days. During a period of infection, phagocytic WBCs may live only a few hours. WBCs are far less numerous than red blood cells; at about 5000– 10,000 cells per microliter of blood, they are outnumbered by RBCs by about 700:1. Mariano Marcos State University College of Health Sciences 14 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY Leukocytosis, an increase in the number of WBCs above 10,000/L, is a normal, protective response to stresses such as invading microbes, strenuous exercise, anesthesia, and surgery. An abnormally low level of white blood cells (below 5000/L) is termed leukopenia. It is never beneficial and may be caused by radiation, shock, and certain chemotherapeutic agents. The skin and mucous membranes of the body are continuously exposed to microbes and their toxins. Some of these microbes can invade deeper tissues to cause disease. Once pathogens enter the body, the general function of white blood cells is to combat them by phagocytosis or immune responses. To accomplish these tasks, many WBCs leave the bloodstream and collect at sites of pathogen invasion or inflammation. Once granular leukocytes and monocytes leave the bloodstream to fight injury or infection, they never return to it. Lymphocytes, on the other hand, continually recirculate—from blood to interstitial spaces of tissues to lymphatic fluid and back to blood. Only 2% of the total lymphocyte population is circulating in the blood at any given time; the rest is in lymphatic fluid and organs such as the skin, lungs, lymph nodes, and spleen. RBCs are contained within the bloodstream, but WBCs leave the bloodstream by a process termed emigration, also called diapedesis, in which they roll along the endothelium, stick to it, and then squeeze between endothelial cells (Figure 1.7. The precise signals that stimulate emigration through a particular blood vessel vary for the different types of WBCs. Molecules known as adhesion molecules help WBCs stick to the endothelium. Neutrophils and macrophages are active in phagocytosis; they can ingest bacteria and dispose of dead matter. Several different chemicals released by microbes and inflamed tissues attract phagocytes, a phenomenon called chemotaxis. The substances that provide stimuli for chemotaxis include toxins produced by microbes; kinins, Figure 1.7. Emigration of white blood cells. which are specialized products of damaged tissues; and some of the Adopted from: Tortora, G. J. & Derrickson, B., 2014. colony-stimulating factors (CSFs). Principles of Anatomy & Physiology, 14th edition. New Jersey: John Wiley & Sons, Inc Mariano Marcos State University College of Health Sciences 15 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY Among WBCs, neutrophils respond most quickly to tissue destruction by bacteria. Eosinophils leave the capillaries and enter tissue fluid. They are believed to release enzymes, such as histaminase, that combat the effects of histamine and other substances involved in inflammation during allergic reactions. Eosinophils also phagocytize antigen– antibody complexes and are effective against certain parasitic worms. A high eosinophil count often indicates an allergic condition or a parasitic infection. At sites of inflammation, basophils leave capillaries, enter tissues, and release granules that contain heparin, histamine, and serotonin. These substances intensify the inflammatory reaction and are involved in hypersensitivity (allergic) reactions. Lymphocytes are the major soldiers in lymphatic system battles. Most lymphocytes continually move among lymphoid tissues, lymph, and blood, spending only a few hours at a time in blood. Thus, only a small proportion of the total lymphocytes are present in the blood at any given time. Three main types of lymphocytes are B cells, T cells, and natural killer (NK) cells. B cells are particularly effective in destroying bacteria and inactivating their toxins. T cells attack viruses, fungi, transplanted cells, cancer cells, and some bacteria, and are responsible for transfusion reactions, allergies, and the rejection of transplanted organs. Immune responses carried out by both B cells and T cells help combat infection and provide protection against some diseases. Natural killer cells attack a wide variety of infectious microbes and certain spontaneously arising tumor cells. Monocytes take longer to reach a site of infection than neutrophils, but they arrive in larger numbers and destroy more microbes. On their arrival, monocytes enlarge and differentiate into wandering macrophages, which clean up cellular debris and microbes by phagocytosis after an infection. Activity 4. Test your knowledge! Before moving on to the next section, match the different types of white blood cells to their corresponding actions. Column A Column B 1. First to response to combat A. Basophils infection B. Eosinophils 2. Produces antibodies C. Neutrophils 3. Involve in phagocytosis D. Monocytes 4. Cell mediator of inflammation E. B cells 5. Attack transplanted cells and F. T cells cancer cells Mariano Marcos State University College of Health Sciences 16 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY Learning Input 5 Blood Platelets Besides the immature cell types that develop into erythrocytes and leukocytes, hemopoietic stem cells also differentiate into cells that produce platelets. Under the influence of the hormone thrombopoietin, myeloid stem cells develop into megakaryocyte colony-forming cells that in turn develop into precursor cells called megakaryoblasts (see Figure 1.3). Megakaryoblasts transform into megakaryocytes, huge cells that splinter into 2000 to 3000 fragments. Each fragment, enclosed by a piece of the plasma membrane, is a platelet. Platelets break off from the megakaryocytes in red bone marrow and then enter the blood circulation. Between 150,000 and 400,000 platelets are present in each microliter of blood. Each is irregularly disc-shaped, 2–4 m in diameter, and has many vesicles but no nucleus. Their granules contain chemicals that, once released, promote blood clotting. Platelets help stop blood loss from damaged blood vessels by forming a platelet plug. Platelets have a short life span, normally just 5 to 9 days. Aged and dead platelets are removed by fixed macrophages in the spleen and liver. Hemostasis. Hemostasis, not to be confused with the very similar term homeostasis, is a sequence of responses that stops bleeding. When blood vessels are damaged or ruptured, the hemostatic response must be quick, localized to the region of damage, and carefully controlled in order to be effective. Three mechanisms reduce blood loss: (1) vascular spasm, (2) platelet plug formation, and (3) blood clotting (coagulation). When successful, hemostasis prevents hemorrhage, the loss of a large amount of blood from the vessels. Hemostatic mechanisms can prevent hemorrhage from smaller blood vessels, but extensive hemorrhage from larger vessels usually requires medical intervention. Vascular Spasm. When arteries or arterioles are damaged, the circularly arranged smooth muscle in their walls contracts immediately, a reaction called vascular spasm. This reduces blood loss for several minutes to several hours, during which time the other hemostatic mechanisms go into operation. The spasm is probably caused by damage to the smooth muscle, by substances released from activated platelets, and by reflexes initiated by pain receptors. Platelet Plug Formation. Considering their small size, platelets store an impressive array of chemicals. Within many vesicles are clotting factors, ADP, ATP, Ca2, and serotonin. Also present are enzymes that produce thromboxane A2, a prostaglandin; fibrin-stabilizing factor, which helps to strengthen a blood clot; lysosomes; some mitochondria; membrane systems that take up and store calcium and provide channels for release of the contents of granules; and glycogen. Also within platelets is platelet-derived growth factor (PDGF), a Mariano Marcos State University College of Health Sciences 17 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY hormone that can cause proliferation of vascular endothelial cells, vascular smooth muscle fibers, and fibroblasts to help repair damaged blood vessel walls. Platelet plug formation occurs as follows (Figure 1.8): 1. Initially, platelets contact and stick to parts of a damaged blood vessel, such as collagen fibers of the connective tissue underlying the damaged endothelial cells. This process is called platelet adhesion. 2. Due to adhesion, the platelets become activated, and their characteristics change dramatically. They extend many projections that enable them to contact and interact with one another, and they begin to liberate the contents of their vesicles. This phase is called the platelet release reaction. Liberated ADP and thromboxane A2 play a major role by activating nearby platelets. Serotonin and thromboxane A2 function as vasoconstrictors, causing and sustaining contraction of vascular smooth muscle, which decreases blood flow through the injured vessel. Figure 1.8. Platelet plug formation. 3. The release of ADP makes other platelets in the area Adopted from: Tortora, G. J. & Derrickson, B., 2014. Principles of Anatomy & Physiology, 14th sticky, and the stickiness of edition. New Jersey: John Wiley & Sons, Inc. the newly recruited and activated platelets causes them to adhere to the originally activated platelets. This gathering of platelets is called platelet aggregation. Eventually, the accumulation and attachment of large numbers of platelets form a mass called a platelet plug. Mariano Marcos State University College of Health Sciences 18 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY A platelet plug is very effective in preventing blood loss in a small vessel. Although initially the platelet plug is loose, it becomes quite tight when reinforced by fibrin threads formed during clotting. A platelet plug can stop blood loss completely if the hole in a blood vessel is not too large. Blood Clotting. Normally, blood remains in its liquid form as long as it stays within its vessels. If it is drawn from the body, however, it thickens and forms a gel. Eventually, the gel separates from the liquid and is called a blood clot. It consists of a network of insoluble protein fibers called fibrin in which the formed elements of blood are trapped (Figure 1.9). The process of gel formation, called clotting or coagulation, is a series of chemical reactions that culminates in formation of fibrin threads. If blood clots too easily, the result can be thrombosis—clotting in an undamaged blood vessel. If the blood Figure 1.9. Blood clot formation. takes too long to clot, hemorrhage Adopted from: Tortora, G. J. & Derrickson, B., can occur. 2014. Principles of Anatomy & Physiology, 14th edition. New Jersey: John Wiley & Sons, Inc. Clotting involves several substances known as clotting (coagulation) factors. These factors 2 include calcium ions (Ca ), several inactive enzymes that are synthesized by hepatocytes (liver cells) and released into the bloodstream, and various molecules associated with platelets or released by damaged tissues. Most clotting factors are identified by Roman numerals that indicate the order of their discovery (not necessarily the order of their participation in the clotting process). Clotting is a complex cascade of enzymatic reactions in which each clotting factor activates many molecules of the next one in a fixed sequence. Finally, a large quantity of product (the insoluble protein fibrin) is formed. Mariano Marcos State University College of Health Sciences 19 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY Clotting can be divided into three stages (Figure 1.10): 1. Two pathways, called the extrinsic pathway and the intrinsic pathway lead to the formation of prothrombinase. Once prothrombinase is formed, the steps involved in the next two stages of clotting are the same for both the extrinsic and intrinsic pathways, and together these two stages are referred to as the common pathway. 2. Prothrombinase converts prothrombin (a plasma protein formed by the liver) into the enzyme thrombin. 3. Thrombin converts soluble fibrinogen (another plasma protein formed by the liver) into insoluble fibrin. Fibrin forms the threads of the clot. The Extrinsic Pathway. The extrinsic pathway of blood clotting has fewer steps than the intrinsic pathway and occurs rapidly—within Figure 1.10. The blood-clotting cascade. a matter of seconds if trauma is severe. It is so named because a Adopted from: Tortora, G. J. & Derrickson, B., tissue protein called tissue factor 2014. Principles of Anatomy & Physiology, 14th edition. New Jersey: John Wiley & Sons, Inc. (TF), also known as thromboplastin, leaks into the blood from cells outside (extrinsic to) blood vessels and initiates the formation of prothrombinase. TF is a complex mixture of lipoproteins and phospholipids released from the surfaces of damaged cells. In the presence of Ca 2, TF begins a sequence of reactions that ultimately activates clotting factor X (Figure 1.10a). Once factor X is activated, it combines with factor V in the presence of Ca 2 to form the active enzyme prothrombinase, completing the extrinsic pathway. The Intrinsic Pathway. The intrinsic pathway of blood clotting is more complex than the extrinsic pathway, and it occurs more slowly, usually requiring several minutes. The intrinsic pathway is so named because its activators are either in Mariano Marcos State University College of Health Sciences 20 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY direct contact with blood or contained within (intrinsic to) the blood; outside tissue damage is not needed. If endothelial cells become roughened or damaged, blood can come in contact with collagen fibers in the connective tissue around the endothelium of the blood vessel. In addition, trauma to endothelial cells causes damage to platelets, resulting in the release of phospholipids by the platelets. Contact with collagen fibers (or with the glass sides of a blood collection tube) activates clotting factor XII (Figure 1.10b), which begins a sequence of reactions that eventually activates clotting factor X. Platelet phospholipids and Ca 2 can also participate in the activation of factor X. Once factor X is activated, it combines with factor V to form the active enzyme prothrombinase, completing the intrinsic pathway. The Common Pathway. The formation of prothrombinase marks the beginning of the common pathway. In the second stage of blood clotting (Figure 1.10c), prothrombinase and Ca2 catalyze the conversion of prothrombin to thrombin. In the third stage, thrombin, in the presence of Ca 2, converts fibrinogen, which is soluble, to loose fibrin threads, which are insoluble. Thrombin also activates factor XIII (fibrin stabilizing factor), which strengthens and stabilizes the fibrin threads into a sturdy clot. Plasma contains some factor XIII, which is also released by platelets trapped in the clot. Thrombin has two positive feedback effects. In the first positive feedback loop, which involves factor V, it accelerates the formation of prothrombinase. Prothrombinase in turn accelerates the production of more thrombin, and so on. In the second positive feedback loop, thrombin activates platelets, which reinforces their aggregation and the release of platelet phospholipids. Clot Retraction. Once a clot is formed, it plugs the ruptured area of the blood vessel and thus stops blood loss. Clot retraction is the consolidation or tightening of the fibrin clot. The fibrin threads attached to the damaged surfaces of the blood vessel gradually contract as platelets pull on them. As the clot retracts, it pulls the edges of the damaged vessel closer together, decreasing the risk of further damage. Normal clotting depends on adequate levels of vitamin K in the body. Although vitamin K is not involved in actual clot formation, it is required for the synthesis of four clotting factors. The various clotting factors, and their functions are summarized in Table 1.3. Mariano Marcos State University College of Health Sciences 21 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY Clotting Factor Number Name Function Factor I Fibrinogen Forms Fibrin Factor II Prothrombin Forms thrombin which converts fibrinogen to fibrin Factor III Thromboplastin Converts prothrombin to thrombin Factor IV Calcium Serves as catalyst in converting to thrombin Factor V Labile Formation of active thromboplastin Factor VII Proconvertin Accelerates the action of tissue thromboplastin Factor VIII Anti-hemophilic Promotes the breakdown of thrombocytes and the formation of active platelet thromboplastin Factor IX Christmas Similar to Factor VIII Factor X Stuart Promotes the action of thromboplastin Factor XI Plasma, Promotes clumping and Thromboplastin factor breakdown of thrombocytes and release of thromboplastin Factor XII Hageman Factor Similar to XI Factor XIII Fibrin Stabilizing Factor Converts the loose fibrin mesh to a dense tight mesh Table 1.3. Clotting (coagulation) factors. Normal Anticoagulants. A remarkable characteristic of the blood is its ability to remain fluid in the blood vessels. This is made possible by the body’s coagulation inhibitors: heparin (inhibits the formation and action of thrombin) and anti-thrombin (a substance that neutralizes thrombin). Mariano Marcos State University College of Health Sciences 22 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY Activity 5. Test your knowledge! Answer the following questions to check your understanding of the concepts discussed. You can do it! 1. A plasma protein involved in blood clotting is: A. a platelet. C. globulin. B. fibrin (and fibrinogen) D. albumin. 2. It converts prothrombin into thrombin. A. Protrombinase C. Fibrinogen B. Vitamin K D. Calcium 3. The process whereby platelets contact and stick to parts of a damaged blood vessel. A. Platelet aggregation C. platelet adhesion B. Platelet plug D. Blood coagulation 4. The pathway where the thrombin converts fibrinogen into loose fibrin threads. A. Extrinsic pathway C. Common pathway B. Intrinsic pathway D. Any of these WRAP-UP ACTIVITY RECALL: 1. Blood transports oxygen, carbon dioxide, nutrients, wastes, and hormones. 2. It helps regulate pH, body temperature, and water content of cells. 3. It provides protection through clotting and by combating toxins and microbes through certain phagocytic white blood cells or specialized blood plasma proteins. 4. Physical characteristics of blood include a viscosity greater than that of water; a temperature of 38C (100.4F); and a pH of 7.35–7.45. 5. Blood constitutes about 8% of body weight, and its volume is 4–6 liters in adults. 6. Blood is about 55% blood plasma and 45% formed elements. 7. Blood plasma consists of 91.5% water and 8.5% solutes. Principal solutes include proteins (albumins, globulins, fibrinogen), nutrients, vitamins, hormones, respiratory gases, electrolytes, and waste products. 8. The formed elements in blood include red blood cells (erythrocytes), white blood cells (leukocytes), and platelets. 9. Hemopoiesis is the formation of blood cells from hemopoietic stem cells in red bone marrow. 10. Myeloid stem cells form RBCs, platelets, granulocytes, and monocytes. Lymphoid stem cells give rise to lymphocytes. Mariano Marcos State University College of Health Sciences 23 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY 11. Several hemopoietic growth factors stimulate differentiation and proliferation of the various blood cells. 12. The function of the hemoglobin in red blood cells is to transport oxygen and some carbon dioxide. 13. RBCs live about 120 days. A healthy male has about 5.4 million RBCs/L of blood; a healthy female has about 4.8 million/L. 14. After phagocytosis of aged RBCs by macrophages, hemoglobin is recycled. 15. RBC formation, called erythropoiesis, occurs in adult red bone marrow of certain bones. It is stimulated by hypoxia, which stimulates the release of erythropoietin by the kidneys. 16. WBCs are nucleated cells. The two principal types are granulocytes (neutrophils, eosinophils, and basophils) and agranulocytes (lymphocytes and monocytes). 17. The general function of WBCs is to combat inflammation and infection. Neutrophils and macrophages (which develop from monocytes) do so through phagocytosis. 18. Eosinophils combat the effects of histamine in allergic reactions, phagocytize antigen– antibody complexes, and combat parasitic worms. Basophils liberate heparin, histamine, and serotonin in allergic reactions that intensify the inflammatory response. 19. B lymphocytes, in response to the presence of foreign substances called antigens, differentiate into plasma cells that produce antibodies. Antibodies attach to the antigens and render them harmless. This antigen–antibody response combats infection and provides immunity. T lymphocytes destroy foreign invaders directly. Natural killer cells attack infectious microbes and tumor cells. 20. Except for lymphocytes, which may live for years, WBCs usually live for only a few hours or a few days. Normal blood contains 5000–10,000 WBCs/L. 21. Platelets are disc-shaped cell fragments that splinter from megakaryocytes. Normal blood contains 150,000–400,000 platelets/L. 22. Platelets help stop blood loss from damaged blood vessels by forming a platelet plug. 23. Hemostasis refers to the stoppage of bleeding. 24. It involves vascular spasm, platelet plug formation, and blood clotting (coagulation). 25. In vascular spasm, the smooth muscle of a blood vessel wall contracts, which slows blood loss. 26. Platelet plug formation involves the aggregation of platelets to stop bleeding. 27. A clot is a network of insoluble protein fibers (fibrin) in which formed elements of blood are trapped. 28. The chemicals involved in clotting are known as clotting (coagulation) factors. 29. Blood clotting involves a cascade of reactions that may be divided into three stages: formation of prothrombinase, conversion of prothrombin into thrombin, and conversion of soluble fibrinogen into insoluble fibrin. 30. Clotting is initiated by the interplay of the extrinsic and intrinsic pathways of blood clotting. 31. Normal coagulation requires vitamin K and is followed by clot retraction (tightening of the clot) and ultimately fibrinolysis (dissolution of the clot). Mariano Marcos State University College of Health Sciences 24 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY REFERENCE MATERIALS  Marieb, E. 2014 Essentials of Human Anatomy and Physiology11th edition. Philippines: Pearson Education South Asia.  Seeley, R. R., et al. 2011. Essentials of Anatomy and Physiology 11th edition. New York: McGraw-Hill.  Tortora, G. J. & Derrickson, B., 2014. Principles of Anatomy & Physiology, 14 th edition. New Jersey: John Wiley & Sons, Inc. Now you can move to the next topic! Let’s get going! Mariano Marcos State University College of Health Sciences 25 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY LESSON 2. THE HEART INTRODUCTION OF THE LESSON AND PRESENTATION OF OUTCOMES As you learned in the previous lesson, the cardiovascular system consists of the blood, the heart, and blood vessels. You have also examined the composition and functions of blood, and in this lesson you will learn about the pump that circulates it throughout the body—the heart. For blood to reach body cells and exchange materials with them, it must be pumped continuously by the heart through the body’s blood vessels. After studying the section, you must have: a. described the location of the heart; b. described the structure of the pericardium and the heart wall; c. discussed the external and internal anatomy of the chambers of the heart; d. described the structure and function of the valves of the heart; e. outline the flow of blood through the chambers of the heart and through the systemic and pulmonary circulations; f. discussed the coronary circulation; g. described the cardiac conduction system; h. explained how an action potential occurs in cardiac contractile fibers; i. enumerated the properties of the heart; j. described the pressure and volume changes that occur during a cardiac cycle; k. defined cardiac output; l. described the factors that affect regulation of stroke volume; and m. outline the factors that affect the regulation of heart rate. Mariano Marcos State University College of Health Sciences 26 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY WARM-UP ACTIVITY Instructions: Read the clues provided and fill in the correct answer! 1 2 3 4 5 6 7 8 9 10 ACROSS DOWN 1 Cardiac __________; the volume of blood 2 Membrane that surrounds the heart ejected from the left ventricle 3 Pumping organ of the body 4 Bicuspid valve 5 Natural pacemaker 5 CO = ______ volume X Heart rate 6 Ejects blood from the heart into blood 6 Carries deoxygenated blood into the heart vessels 9 Responsible for the pumping action of the 7 Upper chamber of the heart heart 8 Increases heart rate 10 A hormone that enhances heart’s pumping effectiveness Mariano Marcos State University College of Health Sciences 27 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY CENTRAL ACTIVITIES The central activities are divided into six learning inputs. To evaluate what you have learned, an activity has been prepared for you after each learning input. The following will be the focus for each learning input: Learning Input 1: Anatomy of the Heart; Learning Input 2: Heart Valves and Circulation of Blood; Learning Input 3: Cardiac Conducting System; Learning Input 4: Properties of the Heart; Learning Input 5: The Cardiac Cycle; and Learning Input 6: Cardiac Output. Learning Input 1 Anatomy of the Heart Location of the heart. The heart is relatively small, roughly the same size (but not the same shape) as your closed fist. It is about 12 cm (5 in.) long, 9 cm (3.5 in.) wide at its broadest point, and 6 cm (2.5 in.) thick, with an average mass of 250 g (8 oz) in adult females and 300 g (10 oz) in adult males. The heart lies in the mediastinum (Figure 2.1a). About two-thirds of the mass of the heart lies to the left of the body’s midline. You can visualize the heart as a cone lying on its side. The pointed apex is formed by the tip of the left ventricle (a lower chamber of the heart) and rests on the diaphragm. It is directed anteriorly, inferiorly, and to the left. The base of the heart is opposite the apex and is its posterior aspect. It is formed by the atria (upper chambers) of the heart, mostly the left atrium. In addition to the apex and base, the heart has several distinct surfaces. The anterior surface is deep to the sternum and ribs. The inferior surface is the part of the heart between the apex and right surface and rests mostly on the diaphragm (Figure 2.1b). The right surface faces the right lung and extends from the inferior surface to the base. The left surface faces the left lung and extends from the base to the apex. Pericardium. The membrane that surrounds and protects the heart is the pericardium. It confines the heart to its position in the mediastinum, while allowing sufficient freedom of movement for vigorous and rapid contraction. The pericardium consists of two main parts: (1) the fibrous pericardium and (2) the serous pericardium (Figure 2.2a). The superficial fibrous pericardium is composed of tough, inelastic, dense irregular connective tissue. It prevents overstretching of the heart, provides protection, and anchors the heart in the mediastinum. The fibrous pericardium near the apex of the heart is partially fused to the central tendon of the diaphragm and therefore movement of the diaphragm, as in deep breathing, facilitates the movement of blood by the heart. Mariano Marcos State University College of Health Sciences 28 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY Figure 2.1. Position of the heart and associated structures in the mediastinum. Adopted from: Tortora, G. J. & Derrickson, B., 2014. Principles of Anatomy & Physiology, 14th edition. New Jersey: John Wiley & Sons, Inc. The deeper serous pericardium is a thinner, more delicate membrane that forms a double layer around the heart (Figure 2.2a). The outer parietal layer of the serous pericardium is fused to the fibrous pericardium. The inner visceral layer of the serous pericardium, which is also called the epicardium; is one of the layers of the heart wall and adheres tightly to the surface of the heart. Between the parietal and visceral layers of the serous pericardium is a thin film of lubricating serous fluid. This slippery secretion of the pericardial cells, known as pericardial fluid, reduces friction between the layers of the serous pericardium as the heart moves. The space that contains the few milliliters of pericardial fluid is called the pericardial cavity. Mariano Marcos State University College of Health Sciences 29 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY Figure 2.2. Pericardium and heart wall. Adopted from: Tortora, G. J. & Derrickson, B., 2014. Principles of Anatomy & Physiology, 14th edition. New Jersey: John Wiley & Sons, Inc. Layers of the Heart Wall. The wall of the heart consists of three layers (Figure 1.2a): the epicardium (external layer), the myocardium (middle layer), and the endocardium (inner layer). The epicardium is composed of two tissue layers. The outermost, as you just learned, is called the visceral layer of the serous pericardium. This thin, transparent outer layer of the heart wall is composed of mesothelium. Beneath the mesothelium is a variable layer of delicate fibroelastic tissue and adipose tissue. The adipose tissue predominates and becomes thickest over the ventricular surfaces, where it houses the major coronary and cardiac vessels of the heart. The epicardium imparts a smooth, slippery texture to the outermost surface of the heart. The epicardium contains blood vessels, lymphatics, and vessels that supply the myocardium. Mariano Marcos State University College of Health Sciences 30 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY The middle myocardium is responsible for the pumping action of the heart and is composed of cardiac muscle tissue. It makes up approximately 95% of the heart wall. The muscle fibers (cells), like those of striated skeletal muscle tissue, are wrapped and bundled with connective tissue sheaths composed of endomysium and perimysium. The innermost endocardium is a thin layer of endothelium overlying a thin layer of connective tissue. It provides a smooth lining for the chambers of the heart and covers the valves of the heart. The smooth endothelial lining minimizes the surface friction as blood passes through the heart. The endocardium is continuous with the endothelial lining of the large blood vessels attached to the heart. Chambers of the Heart. The heart has four chambers. The two superior receiving chambers are the atria, and the two inferior pumping chambers are the ventricles. The paired atria receive blood from blood vessels returning blood to the heart, called veins, while the ventricles eject the blood from the heart into blood vessels called arteries. On the anterior surface of each atrium is a wrinkled pouchlike structure called an auricle, so named because of its resemblance to a dog’s ear (Figure 2.3). Each auricle slightly increases the capacity of an atrium so that it can hold a greater volume of blood. Also on the surface of the heart are a series of grooves, called sulci, that contain coronary blood vessels and a variable amount of fat. Each sulcus marks the external boundary between two chambers of the heart. The deep coronary sulcus (encircles most of the heart and marks the external boundary between the superior atria and inferior ventricles. The anterior interventricular sulcus is a shallow groove on the anterior surface of the heart that marks the external boundary between the right and left ventricles on the anterior aspect of the heart. This sulcus continues around to the posterior surface of the heart as the posterior interventricular sulcus, which marks the external boundary between the ventricles on the posterior aspect of the heart (Figure 2.3c). Right Atrium. The right atrium forms the right surface of the heart and receives blood from three veins: the superior vena cava, inferior vena cava, and coronary sinus. The right atrium is about 2–3 mm (0.08–0.12 in.) in average thickness. Between the right atrium and left atrium is a thin partition called the interatrial septum. A prominent feature of this septum is an oval depression called the fossa ovalis, the remnant of the foramen ovale, an opening in the interatrial septum of the fetal heart that normally closes soon after birth. Blood passes from the right atrium into the right ventricle through a valve that is called the tricuspid valve because it consists of three cusps or leaflets (Figure 2.4). It is also called the right atrioventricular valve. Mariano Marcos State University College of Health Sciences 31 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY Figure 2.3. Structures of the heart: surface features. Adopted from: Tortora, G. J. & Derrickson, B., 2014. Principles of Anatomy & Physiology, 14th edition. New Jersey: John Wiley & Sons, Inc. Right Ventricle. The right ventricle is about 4–5 mm (0.16–0.2 in.) in average thickness and forms most of the anterior surface of the heart. The inside of the right ventricle contains a series of ridges formed by raised bundles of cardiac muscle fibers called trabeculae carneae (see Figure 2.4). The cusps of the tricuspid valve are connected to tendonlike cords, the chordae tendineae, which in turn are connected to cone-shaped trabeculae carneae called papillary muscles. Internally, the right ventricle is separated from the left ventricle by a partition called the interventricular septum. Blood passes from the right ventricle through the pulmonary valve (pulmonary semilunar valve) into a large artery called the pulmonary trunk, which divides into right and left pulmonary arteries and carries blood to the lungs. Mariano Marcos State University College of Health Sciences 32 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY Figure 2.4. Structures of the heart: internal anatomy. Adopted from: Tortora, G. J. & Derrickson, B., 2014. Principles of Anatomy & Physiology, 14th edition. New Jersey: John Wiley & Sons, Inc. Left Atrium. The left atrium is about the same thickness as the right atrium and forms most of the base of the heart. It receives blood from the lungs through four pulmonary veins. Like the right atrium, the inside of the left atrium has a smooth posterior wall. Blood passes from the left atrium into the left ventricle through the bicuspid (mitral) valve, which, as its name implies, has two cusps. The term mitral refers to the resemblance of the bicuspid valve to a bishop’s miter (hat), which is two-sided. It is also called the left atrioventricular valve. Left Ventricle. The left ventricle is the thickest chamber of the heart, averaging 10–15 mm (0.4–0.6 in.), and forms the apex of the heart. Like the right ventricle, the left ventricle contains trabeculae carneae and has chordae tendineae that anchor the cusps of the bicuspid valve to papillary muscles. Blood passes from the left ventricle through the aortic valve (aortic semilunar valve) into the ascending aorta. Mariano Marcos State University College of Health Sciences 33 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY Activity 1. Test your knowledge! Before moving on to the next section, it’s time for you to evaluate first what you have learned. Use the diagram above to answer the following questions.. Are you ready? 1. Identify the letter that indicates the left common carotid artery. A) A B) B C) C D) D E) E 2. Identify the letter that indicates the left auricle. A) A B) B C) C D) D E) E 3. Identify the letter that indicates the aortic arch. A) A B) B C) C D) D E) E 4. Identify the letter that indicates the left coronary artery. A) A B) B C) C D) D E) E Learning Input 2 Heart Valves and Circulation of Blood As each chamber of the heart contracts, it pushes a volume of blood into a ventricle or out of the heart into an artery. Valves open and close in response to pressure changes as the heart contracts and relaxes. Each of the four valves helps ensure the one-way flow of blood by opening to let blood through and then closing to prevent its backflow. Operation of the Atrioventricular Valves. Because they are located between an atrium and a ventricle, the tricuspid and bicuspid valves are termed atrioventricular (AV) valves. When an AV valve is open, the rounded ends of the cusps project into the ventricle. When the ventricles are relaxed, the papillary muscles are relaxed, the chordae tendineae are slack, and blood moves from a higher pressure in the atria to a lower pressure in the ventricles through open AV valves (Figure 2.5d). When the ventricles contract, the pressure of the blood drives the cusps upward until their edges meet and close the opening (Figure 2.5b, e). At the same time, the papillary muscles contract, which pulls on and tightens the chordae tendineae. This prevents the valve cusps from everting (opening into the atria) in response to the high ventricular pressure. If the AV valves or chordae Mariano Marcos State University College of Health Sciences 34 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY tendineae are damaged, blood may regurgitate (flow back) into the atria when the ventricles contract. Figure 2.5. Responses of the valves to the pumping of the heart. Adopted from: Tortora, G. J. & Derrickson, B., 2014. Principles of Anatomy & Physiology, 14th edition. New Jersey: John Wiley & Sons, Inc. Operation of the Semilunar Valves. The aortic and pulmonary valves are known as the semilunar (SL) valves because they are made up of three crescent moon–shaped cusps (Figure 2.5d). Each cusp attaches to the arterial wall by its convex outer margin. The SL valves allow ejection of blood from the heart into arteries but prevent backflow of blood into the ventricles. The free borders of the cusps project into the lumen of the artery. When the ventricles contract, pressure builds up within the chambers. The semilunar valves open when pressure in the ventricles exceeds the pressure in the arteries, permitting ejection of blood from the ventricles into the pulmonary trunk and aorta (Figure 2.5e). As the ventricles relax, blood starts to flow back toward the heart. This back- flowing blood fills the valve cusps, which causes the free edges of the semilunar valves to contact each other tightly and close the opening between the ventricle and artery (Figure 2.5d). Systemic and Pulmonary Circulations. In postnatal (after birth) circulation, the heart pumps blood into two closed circuits with each beat—systemic circulation and pulmonary circulation (Figure 2.6). Mariano Marcos State University College of Health Sciences 35 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY The left side of the heart is the pump for systemic circulation; it receives bright red oxygenated (oxygen-rich) blood from the lungs. The left ventricle ejects blood into the aorta (Figure 2.6). From the aorta, the blood divides into separate streams, entering progressively smaller systemic arteries that carry it to all organs throughout the body— except for the air sacs (alveoli) of the lungs, which are supplied by the pulmonary circulation. In systemic tissues, arteries give rise to smaller-diameter arterioles, which finally lead into extensive beds of systemic capillaries. Exchange of nutrients and gases occurs across the thin capillary walls. Blood unloads O2 (oxygen) and picks up CO2 (carbon dioxide). In most cases, blood flows through only one capillary and then enters a systemic venule. Venules carry deoxygenated (oxygen-poor) blood away from tissues and merge to form larger systemic veins. Ultimately the blood flows back to the right atrium. The right side of the heart is the pump for pulmonary circulation; it receives all of the dark-red deoxygenated blood returning from the systemic circulation. Blood ejected from the right ventricle flows into the pulmonary trunk, which branches into pulmonary arteries that carry blood to the right and left lungs. In pulmonary capillaries, blood unloads CO2, which is exhaled, and picks up O2 from inhaled air. The freshly oxygenated blood then flows into pulmonary veins and returns to the left atrium. Coronary Circulation. Nutrients are not able to diffuse quickly enough from blood in the chambers of the heart to supply all layers of cells that make up the heart wall. For this reason, the myocardium has its own network of blood vessels, the coronary circulation or cardiac circulation. The coronary arteries branch from the ascending aorta and encircle the heart like a crown encircles the head (Figure 2.7a). While the heart is contracting, little blood flows in the coronary arteries because they are squeezed shut. When the heart relaxes, however, the high pressure of blood in the aorta propels blood through the coronary arteries, into capillaries, and then into coronary veins (Figure 2.7b). Mariano Marcos State University College of Health Sciences 36 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY Figure 2.6. Systemic and pulmonary circulations. Adopted from: Tortora, G. J. & Derrickson, B., 2014. Principles of Anatomy & Physiology, 14th edition. New Jersey: John Wiley & Sons, Inc. Coronary Arteries. Two coronary arteries, the left and right coronary arteries, branch from the ascending aorta and supply oxygenated blood to the myocardium (Figure 2.7a). The left coronary artery passes inferior to the left auricle and divides into the anterior interventricular and circumflex branches. The anterior interventricular branch or left anterior descending (LAD) artery is in the anterior interventricular sulcus and supplies oxygenated blood to the walls of both ventricles. The circumflex branch lies in the coronary sulcus and distributes oxygenated blood to the walls of the left ventricle and left atrium. The right coronary artery supplies small branches (atrial branches) to the right atrium. It continues inferior to the right auricle and ultimately divides into the posterior interventricular and marginal branches. The posterior interventricular branch follows the posterior interventricular sulcus and supplies the walls of the two ventricles with oxygenated blood. The marginal branch beyond the coronary sulcus runs along the right margin of the heart and transports oxygenated blood to the wall of the right ventricle. Mariano Marcos State University College of Health Sciences 37 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY Most parts of the body receive blood from branches of more than one artery, and where two or more arteries supply the same region, they usually connect. These connections, called anastomoses, provide alternate routes, called collateral circulation, for blood to reach a particular organ or tissue. The myocardium contains many anastomoses that connect branches of a given coronary artery or extend between branches of different coronary arteries. They provide detours for arterial blood if a main route becomes obstructed. Thus, heart muscle may receive sufficient oxygen even if one of its coronary arteries is partially blocked. Figure 2.7. Coronary circulation. Adopted from: Tortora, G. J. & Derrickson, B., 2014. Principles of Anatomy & Physiology, 14th edition. New Jersey: John Wiley & Sons, Inc. Coronary Veins. After blood passes through the arteries of the coronary circulation, it flows into capillaries, where it delivers oxygen and nutrients to the heart muscle and collects carbon dioxide and waste, and then moves into coronary veins. Most of the deoxygenated blood from the myocardium drains into a large vascular sinus in the coronary sulcus on the posterior surface of the heart, called the coronary sinus (Figure 2.7b). A vascular sinus is a thin-walled vein that has no smooth muscle to alter its diameter. The deoxygenated blood in the coronary sinus empties into the right atrium. The principal tributaries carrying blood into the coronary sinus are the following: Great cardiac vein in the anterior interventricular sulcus, which drains the areas of the heart supplied by the left coronary artery (left and right ventricles and left atrium) Mariano Marcos State University College of Health Sciences 38 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY Middle cardiac vein in the posterior interventricular sulcus, which drains the areas supplied by the posterior interventricular branch of the right coronary artery (left and right ventricles) Small cardiac vein in the coronary sulcus, which drains the right atrium and right ventricle Anterior cardiac veins, which drain the right ventricle and open directly into the right atrium. Activity 2. Test your knowledge! It’s time to evaluate what you have learned. Supply the missing items. (1) (2) (3) (4) (5) (6) Mariano Marcos State University College of Health Sciences 39 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY Learning Input 3 Cardiac Conducting System An inherent and rhythmical electrical activity is the reason for the heart’s lifelong beat. The source of this electrical activity is a network of specialized cardiac muscle fibers called autorhythmic because they are self-excitable. Autorhythmic fibers repeatedly generate action potentials that trigger heart contractions. These fibers have two important functions:  They act as a pacemaker, setting the rhythm of electrical excitation that causes contraction of the heart.  They form the cardiac conduction system, a network of specialized cardiac muscle fibers that provide a path for each cycle of cardiac excitation to progress through the heart. The conduction system ensures that cardiac chambers become stimulated to contract in a coordinated manner, which makes the heart an effective pump. The conducting system of the heart are as follows:  Sino-Atrial Node (SA Node). Compact mass of cells located on the upper part of the right atrium near the Superior Vena Cava; responsible in initiating the impulses for rhythmic heart beat (Pacemaker); elicits electrical impulses approximately 72x per minute to cause atrial contraction.  Atrioventricular Node (AV Node). Lies in the lower part of the interatrial septum receives electrical impulses from the SA Node; generates impulses when SA Node fails to function; generates 40-50 impulses per minute.  AV Bundle (Bundle of His). Tract of conducting fibers from AV Node that runs to the top of the interventricular septum; relay impulses from AV Node to the ventricles; continues down both sides of the septum as: right bundle branches and left bundle branches  Purkinje fibers (conduction myofibers). Emerge from bundle branches and pass into the fibers of the myocardium of the ventricles; enable electrical impulses to spread rapidly over all parts of the ventricles. Cardiac action potentials propagate through the conduction system in the following sequence (Figure 2.8): 1. Cardiac excitation normally begins in the sinoatrial (SA) node, located in the right atrial wall just inferior and lateral to the opening of the superior vena cava. SA node cells do not have a stable resting potential. Rather, they repeatedly depolarize to threshold spontaneously. The spontaneous depolarization is a pacemaker potential. When the pacemaker potential reaches threshold, it triggers an action potential. Each action potential from the SA node propagates throughout both atria via gap junctions in the intercalated discs of atrial muscle fibers. Following the action potential, the two atria contract at the same time. Mariano Marcos State University College of Health Sciences 40 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY 2. By conducting along atrial muscle fibers, the action potential reaches the atrioventricular (AV) node, located in the interatrial septum, just anterior to the opening of the coronary sinus. 3. From the AV node, the action potential enters the atrioventricular (AV) bundle (also known as the bundle of His). This bundle is the only site where action potentials can conduct from the atria to the ventricles. (Elsewhere, the fibrous skeleton of the heart electrically insulates the atria from the ventricles.) 4. After propagating through the AV bundle, the action potential enters both the right and left bundle branches. The bundle branches extend through the interventricular septum toward the apex of the heart. 5. Finally, the large-diameter Purkinje fibers rapidly conduct the action potential beginning at the apex of the heart upward to the remainder of the ventricular myocardium. Then the ventricles contract, pushing the blood upward toward the semilunar valves. Figure 2.8. The conduction system of the heart. Adopted from: Tortora, G. J. & Derrickson, B., 2014. Principles of Anatomy & Physiology, 14th edition. New Jersey: John Wiley & Sons, Inc. Mariano Marcos State University College of Health Sciences 41 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY Activity 3. Test your knowledge! Choose the best answer for following questions to check your understanding of the concepts discussed. Get ready! 1. Cells of the conducting system located between the AV node and bundle branches. A. trabeculae carneae C. pectinate muscles B. crista terminalis D. atrioventricular bundle 2. Large cardiac cells of the conducting system embedded in the ventricular walls between the endocardium and myocardium. A. atrioventricular bundle C. Atrioventricular branches B. Purkinje fibers D. Sinoatrial node 3.Parasympathetic impulses to the SA node are transmitted on this cranial nerve. A. Glossopharyngeal nerve C. Accessory nerve—spinal part B. Vagus nerve D. Trigeminal nerve Learning Input 4 Properties of the Heart The heart has electrophysiologic and mechanical properties that enable it to perform its function: Electrophysiologic Properties of the Heart  Automaticity. The ability of myocardial cells to initiate an impulse (action potential) spontaneously and repeatedly without neurohormonal control; evidently linked with fluid and electrolyte balance than nervous control.  Excitability/ irritability. The ability of myocardial cells to depolarize in response to stimulus or respond to electrical impulses  Conductivity. The ability of myocardial cells to propagate an electrical impulse from its origin throughout the heart rapidly and in a coordinated fashion.  Refractoriness. The inability of the heart to respond to a stimulus while still in a state of contraction or early recovery from a previous stimulus, thus help preserve heart rhythm. Mariano Marcos State University College of Health Sciences 42 Department of Nursing  CN 100 ANATOMY & PHYSIOLOGY: CHAPTER 1. INTRODUCTION TO ANATOMY & PHYSIOLOGY o Absolute refractory period. The heart muscle will not respond to any stimulus (first part of the repolarization, during depolarization). o Relative refractory period. The heart muscle slowly regains irritability (final stage of repolarization); only a stronger than normal stimulus can excite the heart muscle to contract during this period.  Rhythmicity. Rhythm in both the formation and conduction of impulses from the atria to the ventricles. Mechanical Properties of the Heart  Contractility. The ability of the myocardial fibers to shorten in response to depolarization and diffusion of calcium into myocardial cells when it combines with troponin to activate contractile elements.  Extensibility (expansibility). The ability of the heart to stretch as the heart fills with blood between contractions. Starling’s Law of the Heart. The greater the stretch of the cardiac muscle, the more forceful is the contractions and beat. However, when the muscle is overstretched, the force of contraction may decrease below normal c