Blood PDF

2287_13_243-264 7/2/12 1:12 PM Page 245 13 chapter BLOOD The blood of an average adult measures about 5 liters and...

2287_13_243-264 7/2/12 1:12 PM Page 245 13 chapter BLOOD The blood of an average adult measures about 5 liters and accounts for 7% of body weight. For centuries, scientists and philosophers alike have regarded blood as the fluid of life. It has only been since the invention of the microscope, however, that the complexity of this vital fluid has become apparent. Blood is actually a connective tissue consisting of several types of cells in combination with fluid: a tissue with a fluid matrix. Its fluid composition allows blood to function as no other connective tissue can. Instead of staying fixed it one location, blood can move. In fact, its main function is to serve as a transport medium as it makes endless, frequent laps around the body. Blood delivers oxygen and removes waste products from the body’s cells; it delivers nutrients, hormones, enzymes, and many other critical substances to points throughout the body; it plays multiple roles in protecting the body against infection; it helps stabilize the body’s acid- base balance; it also helps regulate body temperature. By analyzing the components of blood, one can gain clues about diseases and disorders throughout the body, which is why blood tests are performed more often than any other medical test. Interpreting those results, though, depends upon a solid understanding of the components and functions of blood. Components of Blood When a sample of blood is spun down in a centrifuge, its two main components become apparent. The main component of plasma is water; however, plasma also contains proteins (the main one being albumin), nutrients, electrolytes, hormones, and gases. Plasma proteins play roles in blood clotting, the immune system, Plasma is the clear, extracellular matrix of this liquid and the regulation of fluid volume. Plasma without the connective tissue. It accounts for 55% of blood. clotting proteins (which occurs when blood is allowed to clot and the solid portion is removed) is called serum. WBCs and platelets form a narrow buff-colored band just underneath the plasma. Called the buffy coat, these cells Formed elements—which include cells and cell constitute 1% or less of the blood volume. fragments—make up 45% of blood. Specific blood cells include erythrocytes (red blood cells, or RBCs), RBCs are the heaviest of the formed elements and sink to leukocytes (white blood cells, or WBCs), and platelets. the bottom of the sample. They account for most of the formed elements. This value—the percentage of cells in a sample of blood—is called the hematocrit. The Body AT WORK An important property of blood—determined by the combination of plasma and blood cells—is viscosity. Basically, viscosity refers to how thick or sticky a fluid is. The more viscous a fluid, the thicker it is. (For example, honey is more viscous than water.) Whole blood is normally five times as thick as water, mainly due to the presence of RBCs. If the number of RBCs drops, blood becomes “thinner,” or less viscous, causing it to flow too rapidly. Too many RBCs increase viscosity, making blood flow sluggish. Left untreated, either condition can cause cardiovascular problems. 2287_13_243-264 7/2/12 1:12 PM Page 246 246 Blood Cell Formation Maintenance of the Body The body works continually to replace blood cells that are old or damaged or that have been used up in body processes. The production of blood is called hemopoiesis; tissues that produce blood cells are called hemopoietic tissues. The body has two types of hemopoietic tissue: red bone marrow and lymphatic tissue. Red bone marrow—found in the ends of long bones and in flat irregular bones such as the sternum, cranial bones, FAST FACT vertebrae, and pelvis—produces all types of blood cells. An adult normally produces 400 billion Lymphatic tissue—found in the spleen, lymph nodes, platelets, 200 billion RBCs, and 20 and thymus gland—supplement blood cell production billion WBCs every day. by producing lymphocytes, a specific type of WBC. All blood cells can trace their beginnings to a specific type of bone marrow cell called a stem cell (also called a pluripotent stem cell). Stem cells are unspecialized cells that give rise to immature red blood cells, white blood cells, and platelet-producing cells. Stem cell Proerythroblast Myeloblast Lymphoblast Monoblast Megakaryoblast The “offspring” of the stem cell divide further, ultimately becoming a mature red blood cell, white blood cell, or platelet. Reticulocyte Progranulocyte Megakaryocyte Erythrocytes Basophil Eosinophil Neutrophil Lymphocyte Monocyte Thrombocytes Granulocytes Agranulocytes Red blood cells White blood cells Platelets 2287_13_243-264 7/2/12 1:13 PM Page 247 247 Red Blood Cells Blood Charged with delivering oxygen to cells and removing carbon dioxide, red blood cells, or erythrocytes, are critical to survival. Blood contains more RBCs than any other formed element. A normal RBC is shaped like a disc with a sunken center. This shape gives the cell a large surface area through which oxygen and carbon dioxide can readily diffuse. FAST FACT A single droplet of blood contains RBCs lose almost all of their organelles during development. about 5 million erythrocytes. Because they lack a nucleus and DNA, they cannot replicate themselves. The cytoskeleton of the RBC contains stretchable fibers that make it flexible, allowing it to fold and stretch as it squeezes through tiny capillaries. When the cell emerges from the tight confines of a narrow vessel, it springs back to its original shape. Hemoglobin Over a third of the interior of a RBC is filled with hemoglobin—a red pigment that gives blood its color. Hemoglobin consists of four ribbon-like protein chains called globins. Bound to each globin is an iron-containing molecule called heme. Each heme molecule can combine with one molecule of oxygen; therefore, one hemoglobin molecule can unite with four molecules of oxygen to form oxyhemoglobin. (Hemoglobin also carries CO2, but, instead of binding with heme, CO2 binds with globin.) (For more information about gas transport by hemoglobin, see Chapter 17, Respiratory O2 System.) FAST FACT Each red blood cell contains 200 to 300 million molecules of hemoglobin. 2287_13_243-264 7/2/12 1:13 PM Page 248 248 The Body AT WORK Maintenance of the Body How much oxygen the blood can carry depends on the quantity of red blood cells and hemoglobin it contains. That’s why some of the most commonly performed blood tests measure hematocrit, FAST FACT hemoglobin concentration, and RBC count. Normal values vary The study of blood is called between men and women, as shown below: hematology. Hematocrit: Female: 37%-48%; Male: 45%-52% Hemoglobin: Female: 12-16 g/dl; Male: 13%-18 g/dl RBC count: Female: 4.2-5.4 million/mm3; Male: 4.6-6.2 million/mm3 Differences in blood values between men and women result because of several factors. Men have higher levels of androgens, and androgens stimulate RBC production. Also, women of reproductive age lose blood through menstruation, which lowers blood cell counts. Finally, women typically have more body fat than men, and the higher the body fat content, the lower the hematocrit level. FAST FACT The Body AT WORK The color of blood always remains The oxygen-carrying component of hemoglobin contains iron. within the red spectrum: bright red Consequently, an adequate supply of dietary iron is crucial for when oxygenated and a deep maroon hemoglobin synthesis. Because of the loss of blood through when deoxygenated. Blood is never menstruation, women of reproductive age have the highest blue. nutritional requirement for iron. Other nutritional requirements for red blood cell formation include vitamin B12, folic acid, and vitamin C. Life lesson: Sickle cell disease Sickle cell disease is an inherited blood disorder Sickled cells involving hemoglobin. Affected RBCs are stiff rather than flexible; as they try to squeeze into narrow blood vessels, they can’t fold over like a normal RBC. Instead, their shape becomes distorted: the cells elongate and the ends point, making them look somewhat like a sickle (which is where the disease gets its name). These distorted cells are also sticky, causing them to clump together and block small blood vessels. This deprives tissues of necessary oxygen, resulting in intense pain. Normal red Other complications of sickle cell disease include blood cells kidney or heart failure or stroke. If a person inherits the gene for the disease from only one parent, he will have sickle cell trait. People with sickle cell trait are generally healthy. If a person inherits the defective gene from both parents, sickle cell disease will result. The disease occurs mostly among people of African descent. 2287_13_243-264 7/2/12 1:13 PM Page 249 249 Blood Life Cycle of Red Blood Cells Red blood cells circulate for about 120 days before they die, break up, and are consumed by phagocytic cells in the spleen and the liver. In fact, 2.5 million RBCs are destroyed every second. While this is only a fraction of the trillions of RBCs in the body, the body must constantly produce new RBCs to maintain homeostasis. The process of producing new erythrocytes—called erythropoiesis—is maintained through a negative feedback loop. ANIMATION 1 6 As the number of RBCs O2 O2 As damaged RBCs are increases, oxygen levels rise. removed from circulation, Less EPO is produced and oxygen levels fall. RBC production declines. 2 5 The kidneys detect the declining After one to two days, levels of oxygen and respond the reticulocyte becomes by secreting a hormone called a mature erythrocyte. erythropoietin (EPO). 3 4 EPO stimulates the red An immature form of an bone marrow to begin the erythrocyte, called a process of creating new reticulocyte, is released erythrocytes. into circulation. The Body AT WORK At any given time, reticulocytes comprise about 0.5% to 1.5% of the circulating RBCs. This number rises, though, in certain FAST FACT situations. For example, following blood loss, the body tries to produce more RBCs to make up for those that were lost. In its The process of erythropoiesis effort to catch up, the bone marrow releases an increased takes three to five days. number of reticulocytes into the circulation. Another common cause of increased RBC production is a move to higher altitude, where the atmosphere contains less oxygen. The body compensates for the lower atmospheric oxygen by producing more red blood cells. In contrast, a low reticulocyte count may mean that fewer RBCs are being made by the bone marrow, which may result from certain types of anemia or bone marrow disorders. 2287_13_243-264 7/2/12 1:13 PM Page 250 250 Breakdown of Red Blood Cells As an RBC ages, its membrane weakens, becoming fragile. As it passes through the narrow capillaries in the spleen, it begins to break down. Maintenance of the Body ANIMATION Macrophages in the liver and spleen ingest and destroy old RBCs. In the process, hemoglobin is broken down into its two components of globin and heme. Heme Globin Globin is further Heme is broken down into broken down iron and bilirubin. into amino acids. Fe+ Bilirubin Iron The amino acids are used Iron is transported for energy or to create new Bilirubin is to the bone marrow, proteins. excreted into where it’s used to the intestines create new as part of bile. hemoglobin. The Body AT WORK When the destruction of RBCs becomes excessive (hemolysis), the body can’t readily assimilate the increased amounts of bilirubin being produced. Instead of being excreted into the intestines, the excess bilirubin enters the tissues, causing the skin and sclera to take on a yellowish hue. This condition is called jaundice. FAST FACT Jaundice may also result from conditions such Bile in the intestines gives feces its brown color. as liver disease or bile duct obstruction that Another pigment resulting from the breakdown of interfere with the flow of bile into the intestines. hemoglobin (called urochrome) gives urine its Newborns, too, often develop jaundice shortly yellow color. after birth (a condition called physiological jaundice). This occurs as their immature livers begin the task of clearing bilirubin from the blood. 2287_13_243-264 7/2/12 1:13 PM Page 251 251 Blood Life lesson: Polycythemia When the rate at which new RBCs are being created exceeds the rate at which old ones are being destroyed, an imbalance results. The state in which the body has an excess of RBCs is called polycythemia. An abnormality in the red bone marrow, such as cancer, is one possible cause of polycythemia. In this instance, the diseased marrow triggers overproduction of RBCs; this condition is called polycythemia vera. Another type of polycythemia—secondary polycythemia—results when the body attempts to compensate for conditions that have caused the amount of oxygen in the blood to drop. For example, smoking, lung or heart diseases, and air pollution all lower oxygen levels in the blood. In an attempt to maintain its delivery of oxygen to the tissues, the body increases production of RBCs. (Living at high altitude also causes polycythemia as the body compensates for lower levels of atmospheric oxygen.) An increased number of RBCs increases blood volume as well as viscosity. Symptoms include headache, ruddiness, and itchiness. Unchecked, complications such as high blood pressure, blood clots, and even heart failure may occur. FAST FACT FAST FACT To ensure adequate erythropoiesis, we must “Packaging” hemoglobin inside red consume 5 to 20 mg of iron in our food each day to blood cells ensures that the hemoglobin cover the amount lost through the urine, feces, and remains within the confines of the blood bleeding. vessels instead of leaking out into the surrounding tissues. Life lesson: Anemia Anemia is a deficiency of RBCs or hemoglobin. Normal number of Anemic number of Sometimes anemia occurs because of a loss of RBCs, red blood cells red blood cells such as from a hemorrhage, or when too many RBCs are being destroyed (hemolytic anemia). More commonly, anemia results from an insufficient supply of iron in the diet. Because iron is a key component of hemoglobin, an insufficient supply of this nutrient leads to iron- deficiency anemia. (Another nutritional anemia— pernicious anemia—results from a lack of vitamin B12. In this instance, the anemia typically occurs because the body can’t assimilate the vitamin due to a lack of a chemical produced in the stomach called intrinsic factor.) Another cause of anemia is an insufficient supply of the hormone erythropoietin (EPO). Without EPO, red bone marrow isn’t stimulated to create new erythrocytes, which explains why anemia usually accompanies kidney disease. Without enough RBCs or hemoglobin, the oxygen-carrying capacity of blood is diminished, causing fatigue, pallor, and, possibly, shortness of breath. Blood viscosity is also reduced, resulting in a faster heart rate and lower blood pressure. 2287_13_243-264 7/2/12 1:13 PM Page 252 252 White Blood Cells Maintenance of the Body White blood cells (WBCs) or leukocytes are the fewest of the formed elements. (A microliter of blood contains between 5000 and 10,000 WBCs and 5 million RBCs.) Regardless, WBCs are crucial to life: they are the body’s line of defense against invasion by infectious pathogens. The body contains five types of WBCs, all different in size, appearance, abundance, and function. All leukocytes—unlike RBCs—contain a nucleus. They also contain a number of other internal structures, some of which look like granules when stained and examined under a microscope. The presence or absence of granules identifies the FAST FACT two classifications of WBCs: granulocytes (those having obvious granules) and The body contains many more agranulocytes (those having few or no granules). WBCs than is reflected in a blood count. In fact, WBCs Granulocytes spend most of their lives in Besides containing granules in the cytoplasm, granulocytes also contain a single connective tissues, not in the multilobular nucleus. The three types of granulocytes are neutrophils, bloodstream from which the eosinophils, and basophils. samples are taken. Types of Granulocytes Neutrophils Eosinophils Basophils Quantity Most abundant of the WBCs, Eosinophils account for 2% to 5% of The fewest of the WBCs, basophils neutrophils make up 60% to 70% of all circulating WBCs. comprise only 0.5% to 1% of the WBC the WBCs in circulation. count. Characteristics The nucleus of young neutrophils looks While few exist in the bloodstream, Basophils possess little or no like a band or a stab wound; therefore, eosinophils are numerous in the phagocytic ability. they are sometimes called band cells or lining of the respiratory and digestive stab cells. tracts. They are also called polymorphonuclear leukocytes (PMNs) because the shape of the nucleus varies between neutrophils. Function Highly mobile, neutrophils quickly Eosinophils are involved in allergic Basophils secrete heparin (an migrate out of blood vessels and into reactions; they also kill parasites. anticoagulant), which prevents clotting tissue spaces, where they engulf and in the infected area so WBCs can enter; digest foreign materials. they also secrete histamine, a substance that causes blood vessels to leak, which attracts WBCs. Worn-out neutrophils left at the site of infection form the main component of pus. Life cycle All granulocytes circulate for 5 to 8 hours and then migrate into the tissues, where they live another four or five days. 2287_13_243-264 7/2/12 1:13 PM Page 253 253 Blood Agranulocytes Unlike granulocytes, agranulocytes lack cytoplasmic granules; the nuclei of these WBCs also lack lobes. There are two types of agranulocytes: lymphocytes and monocytes. Types of Agranulocytes Lymphocytes Monocytes Quantity The second most numerous of the WBCs, lymphocytes Monocytes comprise 3% to 8% of the WBC count. constitute 25% to 33% of the WBC count. Characteristics Lymphocytes are the smallest of the WBCs. Monocytes are the largest of the WBCs. Function Lymphocytes are responsible for long-term immunity. There Monocytes are highly phagocytic and can engulf large are two types: bacteria and viral-infected cells. T lymphocytes, which directly attack an infected or cancerous cell B lymphocytes, which produce antibodies against specific antigens Life cycle All lymphocytes begin in the bone marrow; while some mature After circulating in the bloodstream for 10 to 20 hours, there, others migrate to the thymus to finish developing. monocytes migrate into tissues, where they transform into macrophages: aggressive phagocytic cells that ingest bacteria, cellular debris, and cancerous cells. After maturing, all lymphocytes colonize the organs and tissues of the lymph system (such as the spleen and lymph nodes). Afterward, they continually cycle between the Macrophages can live as long as a few years. bloodstream and lymph system. Lymphocytes may survive from a few weeks to decades. (For more information on lymphocytes, see Chapter 16, Lymphatic & Immune Systems.) FAST FACT When cells become inflamed from a bacterial infection, they release chemicals that attract neutrophils and other phagocytic WBCs to the infection site. Life lesson: Changes with aging The volume and composition of blood remains relatively constant with age. Abnormal blood values that do occur usually result from disorders in other systems. For example, elderly individuals are more likely to form unwanted blood clots or develop chronic types of leukemia. However, these disorders usually occur because of changes in blood vessels in the case of blood clots) or the immune system (in the case of leukemia). Elderly individuals also have a greater risk for developing pernicious anemia. Again, this disorder is secondary to the fact that the stomach mucosa, which produces intrinsic factor, atrophies with age. 2287_13_243-264 7/2/12 1:13 PM Page 254 254 The Body AT WORK Maintenance of the Body An abnormally low WBC count (called FAST FACT leukopenia) may result from certain viral The most commonly performed blood test is illnesses, including AIDS, as well as lead poisoning. the complete blood count (CBC). It provides An elevated WBC count (called leukocytosis) information about all the formed elements of usually indicates infection or an allergy. Because the blood: RBCs (including hemoglobin, each WBC has a slightly different function, hematocrit, and reticulocytes), WBCs knowing the count of each WBC (called a (including a differential), and platelets. differential WBC count) can be useful. For example, an increased number of neutrophils indicate a bacterial infection. A high eosinophil count signals an allergy or a parasitic infection. Life lesson: Leukemia A cancer of the blood or bone marrow, leukemia is characterized by an extremely high WBC count. The term leukemia encompasses a number of varieties of the disease. To differentiate between types, leukemia is subdivided into several large groups. The first differentiation is between acute and chronic forms of the disease. Acute leukemia—the form occurring most commonly in children—appears suddenly and involves the rapid increase of immature WBCs. In contrast, chronic leukemia, which involves the proliferation of relatively mature but still abnormal WBCs, develops more slowly. It occurs most often in older people, although it may occur at any age. The next major classification of leukemia is based on the type of blood cell affected. Lymphocytic leukemia involves the rapid proliferation of lymphocytes; myeloid leukemia involves uncontrolled granulocyte production. In all types, the proliferation of abnormal WBCs crowds out normal bone marrow cells, resulting in deficiencies of normal WBCs, RBCs, and platelets. The deficiency of normal WBCs leads to a weakened immune system, placing the individual at risk for infection. The deficiency of RBCs leads to anemia, which may cause fatigue and pallor. Finally, the deficiency of platelets results in an increased risk for bleeding and bruising. Acute lymphocytic leukemia—the most common form of leukemia in children—has the highest cure rate. Treatment includes chemotherapy, radiation, and bone marrow transplants. FAST FACT An increased number of band cells (typically a sign of an infection) is often called a shift to the left. That’s because, historically, paper laboratory slips used for differential WBC counts listed the count for band cells to the left of the counts for mature neutrophils. 2287_13_243-264 7/2/12 1:13 PM Page 255 255 Platelets and the Control of Bleeding Blood Platelets (also called thrombocytes) are the second most abundant of the formed elements, with each microliter of blood containing between 150,000 and 400,000 platelets. Platelets play a key role in stopping bleeding (hemostasis). Instead of being individual cells, platelets are actually fragments of larger bone marrow cells called megakaryocytes. The edges of the megakaryocyte break off to form cell fragments called platelets. The platelets live only about 7 days. Red blood cell Hemostasis When a blood vessel is cut, the body must react quickly to stop Platelets the flow of blood. It does so through the following sequence of events: vascular spasm, the formation of a platelet plug, and the formation of a blood clot. Vascular Spasm As soon as a blood vessel is injured, smooth muscle fibers in the wall of the vessel spasm. This constricts the blood vessel and slows the flow of blood. (This response is only temporary but gives the other hemostatic mechanisms time to activate.) Formation of a Platelet Plug Vessel The break in the blood vessel exposes collagen fibers, creating a injury rough spot on the vessel’s normally slick interior. This rough spot triggers changes in the passing platelets, transforming them into sticky platelets. The sticky platelets do as their name implies: stick to the vessel wall and to each other, forming a mass of platelets called a platelet plug. The platelets facilitate their clumping by secreting several chemicals: some cause the vessel to constrict further while others attract even more platelets. The platelet plug forms a temporary seal in the vessel wall. A more stable solution requires the Collagen Platelet formation of a clot. fibers plug 2287_13_243-264 7/2/12 1:13 PM Page 256 256 Formation of a Blood Clot Blood clotting, or coagulation, involves a complex series of chemical reactions using proteins called clotting factors. (See “The Body at Work” on this page.) Maintenance of the Body The first several reactions in the clotting process vary, depending upon whether the process has been stimulated by factors inside or outside the blood. Specifically, when the damaged blood vessel and surrounding tissues—areas outside or extrinsic to the blood—release clotting factors, this kicks off a cascade of events called the extrinsic pathway. When the clotting factors are activated within the blood—such as by the platelets as they adhere to the collagen in the damaged vessel wall—this sets off a different cascade of events called the intrinsic pathway. ANIMATION FAST FACT Sticky platelets Normal clotting requires Both the extrinsic and adequate blood levels of intrinsic pathways result calcium. That’s because many in the formation of factor of the reactions in the clotting Intrin X. (This occurs in a single sic pat process use calcium. reaction in the extrinsic hw Extr ay pathway, while, in the ins ic p intrinsic pathway, four ath w different reactions are ay Injured cells required to activate factor X.) Either way, once factor X is activated, the The end result of both the extrinsic and intrinsic pathways is the production of an Prothrombin formation of a blood clot activator follows a common enzyme called prothrombin activator. pathway, as shown here. Prothrombin activator acts on a globulin Prothrombin called prothrombin (factor II)… …converting it to the enzyme thrombin. Thrombin transforms the The sticky fibrin threads Thrombin form a web at the site of soluble plasma protein fibrinogen into fine threads of insoluble fibrin. the injury. Red blood cells and platelets flowing through the web become ensnared, creating a clot Fibrin of fibrin, blood cells, and platelets. A blood clot can effectively seal breaks in a smaller vessel; however, blood clotting alone may not stop a hemorrhage Fibrin from a large blood vessel. The Body AT WORK The blood contains numerous proteins called clotting factors. Under normal conditions, these factors are inactive. However, the activation of one factor sets off a chain of reactions, with the product of the first reaction triggering another reaction in the next factor on a set pathway. A series of reactions in which each depends on the product of the preceding reaction is called a reaction cascade. The process of coagulation involves more than 30 chemical reactions, with one following the other in a precise order. Many of the clotting factors involved in this process are identified by Roman numerals, such as factor VIII, factor X, etc. The numerals indicate the order in which they were discovered, not their order in the reaction cascade. 2287_13_243-264 7/2/12 1:14 PM Page 257 257 Blood The Body AT WORK Because the liver synthesizes most of the clotting FAST FACT factors, abnormal liver function interferes with The extrinsic pathway leads to clot formation in normal blood clotting. Even more interesting is about 15 seconds, while the intrinsic pathway takes that seemingly mild disorders, such as gallstones, 3 to 6 minutes. To stop bleeding more quickly, can also interfere with blood clotting. That’s massage the tissues surrounding the wound. because the synthesis of clotting factors requires Stimulating the cells in the area will trigger the vitamin K. Vitamin K is absorbed into the blood extrinsic pathway and speed up clot formation. from the intestine but, because vitamin K is fat soluble, it can be absorbed only if bile is present. Bile is secreted by the liver. If the bile ducts become blocked, such as by liver disease or gallstones, vitamin K can’t be absorbed and bleeding tendencies develop. Dissolution of Blood Clots The blood clotting process doesn’t stop with the formation of the clot. Soon after the blood clot forms, the platelets trapped within the Later, after the vessel has healed, a small chain of reactions converts fibrin web contract, pulling the edges of the damaged vessel closer an inactive plasma protein (plasminogen) into plasmin. Plasmin together. works to dissolve the fibrin meshwork, and the clot breaks up. This process is called fibrinolysis. Prevention of Blood Clots When a blood vessel has broken, speedy clot formation is essential to stop the bleeding. However, it’s just as crucial to prevent clots from forming when they aren’t needed. The following factors discourage blood clot formation. Smooth endothelium: The inner lining of undamaged blood vessels is very smooth, which helps prevent platelets from sticking. Blood flow: The blood normally produces small amounts of thrombin. When blood is circulating normally, the rapidly moving bloodstream dilutes the thrombin before a clot can form. If blood flow decreases—such as when blood pools in the legs during prolonged sitting or lying down—thrombin can accumulate to the point that a clot develops. Anticoagulants: Basophils and mast cells normally secrete the anticoagulant heparin, which prevents blood clots by blocking the action of thrombin. Heparin is also given by injection to inhibit clot formation in patients who are susceptible to developing unwanted blood clots. 2287_13_243-264 7/2/12 1:14 PM Page 258 258 Life lesson: Blood clotting disorders Maintenance of the Body The formation of unwanted blood clots is the most common, and perhaps the most serious, of clotting disorders. In fact, about 650,000 Americans die every year from blood clots that have lodged in arteries in the brain, heart, or lungs. Once lodged, the clot shuts off blood flow, often resulting in sudden death. An unwanted blood clot inside of a vessel is called a thrombus. If a piece of the clot breaks off and circulates through the bloodstream, it’s called an embolus. Such clots may be treated with injections of heparin or the oral anticoagulant warfarin (Coumadin). While heparin blocks the action of thrombin, Coumadin blocks the effects of vitamin K on the liver. This causes the liver to produce less prothrombin, which, in turn, leads to less thrombin. Either way, blood clotting diminishes. A more rare disorder—hemophilia—results from a deficiency of one of the clotting factors. Because hemophilia is a sex-linked recessive disorder, it affects primarily males. (Specifically, it afflicts about 1 out of 30,000 males.) People with hemophilia may be deficient in any one of several different clotting factors, but the most common missing factor is factor VIII. Because people with hemophilia lack the ability to form blood clots, even minor injuries can become life-threatening. The disorder is treated with infusions of the missing clotting factor. FAST FACT Tissue plasminogen activator (t-PA)—one of the substances that stimulates the conversion of plasminogen into plasmin—can be administered as a drug. It’s often given as an early treatment to dissolve clots causing strokes and heart attacks. Blood Types For centuries, people have realized that excessive blood loss often proved fatal. However, when they tried to fight the effects of hemorrhage by transfusing blood from one person into another, they were mystified as to why some recovered while others died. It wasn’t until 1900, when a scientist discovered the blood types A, B, and O, that the matter became clear. This scientist discovered that the surface of each red blood cell carries a protein called an antigen (also called agglutinogen). There are two antigens: A and B. Blood type A Blood type B Blood type AB Blood type O People with type A blood have People with type B blood have People with type AB blood People with type O blood the A antigen on their RBCs. the B antigen. have both A and B antigens. have neither antigen. A antigen B antigen FAST FACT In the United States, about 45% of the population has O blood, 40% has A blood, 11% has type B blood, and 4% has type AB blood. 2287_13_243-264 7/2/12 1:14 PM Page 259 259 While the blood cell carries antigens, the blood plasma carries antibodies (called agglutinins) against the antigens of the Blood other blood types. (See “The Body at Work” on this page for further explanation of antigens and antibodies.) Blood type A Blood type B Blood type AB Blood type O Type A blood has anti-B Type B blood has anti-A Type AB blood has no Type O blood has both antibodies. antibodies. antibodies. anti-A and anti-B antibodies. Anti-B antibody Anti-A antibody Transfusions are successful as long as the recipient’s plasma doesn’t contain antibodies against the ABO type being transfused. If such antibodies are present, they will attack the donor’s RBCs, causing a transfusion reaction. Type A blood Anti-B antibody Type B blood If someone with type A blood were to receive a...the anti-B antibodies in the recipient’s blood would transfusion of type B blood... immediately attack the donor’s RBCs. The antibody- antigen reaction would cause the RBCs to clump together ( agglutinate ). The clumping of RBCs blocks blood vessels, cutting off the flow of oxygen. The RBCs also burst (called hemolysis) and release their hemoglobin into the bloodstream. The free hemoglobin could block tubules in the kidneys, leading to renal failure and possibly death. The Body AT WORK FAST FACT Every cell in the body carries antigens on its surface. The antigens, which are unique to ABO antibodies are not each individual, allow the body to distinguish its own cells from foreign invaders. When present at birth. Rather, the body detects a substance with an unfamiliar antigen, it launches an immune they first appear during response to destroy it. infancy and build, reaching The first step in the attack occurs when antibodies in the blood plasma bind to the maximum concentration foreign cells (or the cells containing the foreign material). Next, antibodies bind to more between the ages of 8 and than one antigen molecule in an effort to “corral” the foreign invaders until the immune 10 years. system can break them down. This process, which produces large clumps of antigen- antibody molecules, is called agglutination. (Antigens and antibodies will be discussed more fully in Chapter 16, Lymphatic & Immune Systems.) 2287_13_243-264 7/2/12 1:14 PM Page 260 260 The Body AT WORK Maintenance of the Body Because type O blood contains neither antigens A or B, it has been referred to as FAST FACT universal donor blood, implying that it can be given to any recipient. This isn’t true, however, because the donor’s plasma contains both anti-A and anti-B In the United States, type O antibodies; this means that the type O blood would agglutinate the RBCs of a blood is the most common type A, B, or AB recipient. Usually this doesn’t occur because only the RBCs are while type AB is the most rare. transfused. Traces of plasma still remain, however, so a reaction is possible, although unlikely. The only way to be certain is to perform a test in which a sample of the donor’s blood is mixed (or cross-matched) with a sample of the FAST FACT recipient’s blood to ensure that agglutination won’t occur. Likewise, type AB blood is sometimes called the universal recipient— The ABO type and Rh type are implying that a person with this blood type can receive a transfusion of any both used when classifying type of blood—because it contains neither anti-A nor anti-B antibodies. blood. For example, O⫹ blood However, the donor’s plasma may contain either of those antibodies; if refers to type O, Rh positive; transfused, they would agglutinate the recipient’s RBCs. Again, the only way B⫺ blood refers to type B, to ensure that won’t happen is to cross-match the samples. Rh negative. The Rh Group Besides being classified according to ABO type, blood is also classified as being Rh positive or Rh negative. Rh-positive blood contains the Rh antigen; Rh-negative blood lacks this specific antigen. About 85% of white Americans and 95% of African Americans have Rh-positive blood. Blood does not normally contain anti-Rh antibodies; however, it’s possible for someone with Rh-negative blood to develop anti-Rh antibodies. There are two ways this can occur. The first way is when someone with Rh-negative blood receives a transfusion of Rh-positive blood. The second way is when an Rh-negative mother becomes pregnant with an Rh-positive fetus. – + – – + – + – + + – + Agglutination of – – Rh-positive RBCs – + Anti-Rh + – – ++ – antibodies – + ++ – + – + + + – – + – – – – + – – – – – – – – – – – – – – – – – – – – – – – – – – – In the case of a transfusion, if a To protect itself, the body Difficulty arises if the recipient person with Rh-negative blood develops antibodies against the encounters the Rh antigen again, receives a transfusion of Rh antigen (anti-Rh antibodies). such as through a subsequent Rh-positive blood, the recipient’s infusion of Rh-positive blood. If body interprets the Rh antigen as that occurs, the anti-Rh antibodies something foreign. that formed during the first transfusion will attack the Rh antigen in the donor blood, causing agglutination. 2287_13_243-264 7/2/12 1:14 PM Page 261 261 Blood A similar condition may result when a woman with Rh-negative blood and a man with Rh-positive blood conceive a baby who is Rh positive. ANIMATION Rh-negative – – blood cell – – – – + + – – + + + + – – + + – + + + – + + – – Rh-positive – – blood cell + Because maternal and fetal blood doesn’t mix, the first pregnancy However, during delivery (or miscarriage), the fetus’ blood often with an Rh-positive fetus will proceed normally. mixes with that of the mother, thus introducing Rh antigens into the mother’s bloodstream. – – – – Anti-Rh – – antibodies ++ – – + ++ – – + – – – – – mother’s body lines The endocardium responds by forming anti-Rh antibodies against the heart’s If the mother later becomes pregnant with another Rh-positive this foreigncovers chambers, substance. the valves, and continues baby, the anti-Rh antibodies can pass through the placenta even if into the vessels. It consists of a thin layer of the RBCs can’t. When they do, they attack the fetal RBCs, causing squamous epithelial cells. agglutination and hemolysis. The infant develops a severe hemolytic anemia called erythroblastosis fetalis. FAST FACT All Rh-negative women who become pregnant with an Rh-positive baby should be treated with an Rh immune globulin called RhoGAM. The immune globulin prevents the formation of anti-Rh antibodies by the mother, thus preventing an attack on the fetus’ RBCs. 2287_13_243-264 7/2/12 1:14 PM Page 262 262 Review of Key Terms Maintenance of the Body Anemia: A deficiency of red blood Hemoglobin: Iron-containing pigment Neutrophils:Most abundant of the cells or hemoglobin of red blood cells that carries oxygen white blood cells; highly mobile Basophils: The fewest of the WBCs; Hemolysis: The destruction of red Plasma: The clear extracellular matrix secretes heparin blood cells of blood Coagulation: Blood clotting Hemopoiesis: The production of Platelets:Blood cell fragments that blood play a key role in stopping bleeding Eosinophils: White blood cells that protect against parasites; also involved Hemostasis: An arrest of bleeding Reticulocyte: An immature form of an in allergic reactions erythrocyte Leukocytes: White blood cells Erythrocytes: Red blood cells Serum: Plasma without the clotting Leukocytosis: Elevated white blood proteins Erythropoietin: Hormone secreted by cell count the kidneys that stimulates the Viscosity: The thickness or stickiness Leukopenia: Abnormally low white production of erythrocytes of blood blood cell count Fibrin: Insoluble protein fibers Lymphocytes: Second most numerous involved in forming a blood clot of the WBCs; responsible for long- Fibrinolysis: Process of dissolution of a term immunity blood clot Monocytes: Largest and most long- Hematocrit: The percentage of red lived of the WBCs; highly phagocytic blood cells in a sample of blood Own the Information To make the information in this chapter part of your Key Topics for Chapter 13: working memory, take some time to reflect upon what The components of blood you’ve learned. On a separate sheet of paper, write down The formation of blood cells everything you can recall about the key topics discussed in The structure and function of red blood cells and hemo- this chapter, listed here. After you’re done, log on to the globin DavisPlus website and check out the learning objectives for The life cycle of red blood cells Chapter 13. Does what you’ve written down fully address The structure and function of white blood cells each of the learning objectives for this chapter? If not, read The structure and function of platelets the pertinent sections in this chapter again. Then take your Mechanisms for the formation of a blood clot learning even further by writing out or diagramming the The dissolution of a clot concepts for each learning objective. ABO and Rh blood types The results of blood incompatibility from a transfusion or in utero 2287_13_243-264 7/2/12 1:14 PM Page 263 263 Test Your Knowledge Blood 1. What does a hematocrit reveal? 6. Which of the following WBCs a. The ability of the body to fight have the longest lifespan? infection a. Neutrophils b. The ability of the blood to clot b. Eosinophils c. How much oxygen the blood c. Basophils can carry d. Monocytes d. The amount of iron in the 7. Which of the following is not blood part of hemostasis? Answers: Chapter 13 2. Which substance allows RBCs to a. Vascular spasm 1. Correct answer: c. WBCs help the body fight infection, so an analysis of these cells would reflect transport oxygen? b. Formation of fibrin that ability. Platelets allow the blood to clot, so a a. Erythropoietin (EPO) c. Formation of a thrombus measurement of platelets would reflect that ability. Iron is a key component of hemoglobin; therefore, b. Thrombin d. Formation of thrombin a low hemoglobin level could possibly reflect a c. Fibrin deficiency of iron. 8. How would someone experiencing d. Hemoglobin 2. Correct answer: d. Erythropoietin is a hormone a heart attack caused by a blood secreted by the kidneys to stimulate the production of RBCs. Thrombin (an enzyme) 3. A move to high altitude would clot benefit from a drug that stimulates the formation of fibrin, an insoluble trigger which change in the stimulates the conversion of protein used to form a blood clot. blood? plasminogen into plasmin? 3. Correct answer: a. Reticulocytes are immature RBCs; as the body compensates for lower levels of a. An increased number of a. Plasmin encourages the growth atmospheric oxygen, it would increase production reticulocytes of new blood vessels that can of RBCs. As a result, the number of immature RBCs (reticulocytes) would increase rather than b. A decreased number of bypass the clot. decrease. Neutrophils are WBCs, and a change in reticulocytes b. Plasmin increases the oxygen- altitude alone would not affect their rate of production. c. An increased number of carrying capacity of RBCs. 4. Correct answer: a. A lack of red blood cells and neutrophils c. Plasmin inhibits the formation hemoglobin may cause pallor and cyanosis; d. A decreased number of of new blood clots. however, the initial response from hemolysis would be to produce jaundice. Ruddiness would neutrophils d. Plasmin dissolves the fibrin result from an excessive number of red blood cells, not hemolysis. 4. Hemolysis may produce which meshwork around blood clots. 5. Correct answer: d. Basophils have little or no physical sign? 9. What substance, carried by each phagocytic ability. Eosinophils are mostly involved in allergic reactions, but they also kill parasites. a. Jaundice red blood cell, determines blood Lymphocytes colonize the organs and tissues of the b. Pallor type? lymph system, where they are involved in long- term immunity. c. Cyanosis a. Antibody 6. Correct answer: d. All granulocytes (which includes d. Ruddiness b. Antigen neutrophils, eosinophils, and basophils) circulate for c. Hemoglobin 5 to 8 hours and then migrate into the tissues, where 5. When an infecting organism they live another four or five days. In contrast, d. Globin macrophages can live as long as a few years. pierces the skin, which of the 7. Correct answer: c. A thrombus is an unwanted following WBCs would quickly 10. Which of the following will blood clot inside a blood vessel. The other migrate out of the blood vessels occur if someone with type A answers are all a part of hemostasis. 8. Correct answer: d. None of the other answers are and into the tissues to ingest the blood receives a transfusion with correct. foreign invader? type B blood? 9. Correct answer: b. Blood plasma carries antibodies a. Basophils a. Leukocytosis against the other blood types. Hemoglobin is the red pigment with blood cells. Globin is the b. Eosinophils b. Polycythemia ribbon-like protein chain that helps form c. Lymphocytes c. Agglutination hemoglobin. d. Neutrophils d. Fibrinolysis 10. Correct answer: c. Leukocytosis is an elevated number of white blood cells. Polycythemia is an increased number of red blood cells. Fibrinolysis is the dissolution of a blood clot. None of these occur in a transfusion reaction. Scan this code with your mobile device to experience the Podcast Library on DavisPlus. Go to http://davisplus.fadavis.com Keyword: Thompson to see all of the resources available with this chapter.