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1 An overview of the cardiovascular system. Driven by the pumping of the heart, blood flows through the pulmonary and systemic circuits in sequence. Each circuit begins and ends at the heart and contains arteries, capillaries, and veins 2 maria immaculata iwo, sf itb Heart Vessel Blood 3 maria immaculata iwo, sf itb Cardiovascular System Main component Blood : fluid circulated Heart : pump (pulmonary & systemic circuits) Vessel: Artery & vein Heart: : Blood Heart Bood vessel (artery, arteriole) Lung Systemic circuit Pulmonary circuit Capillary exchange tissue Blood vessel (Vein) Heart Excretion (Kidney) Aorta (Artery) Lymphatic vessel (Lymphatic system) maria immaculata iwo, sf itb • Functions of the blood • Formation of Blood Cells • Blood component: • Blood elements: • Red Blood Cells – Oxygen Transport – Carbon Dioxide Transport – Anemia – Blood Groups • White Blood Cells – Lymphocytes Serum protein & lipids – Monocytes Blood group & Rh – Neutrophils factor – Eosinophils Blood transfusion – Basophils • Platelets • Plasma 5 maria immaculata iwo, sf itb • If one takes a sample of blood, treats it with an agent to prevent clotting, and spins it in a centrifuge, – the red cells settle to the bottom – the white cells settle on top of them forming the "buffy coat". – The fraction occupied by the red cells is called the hematocrit. • Normally it is approximately 45%. Blood fluid: - Serum? - Plasma? – Values much lower than this are a sign of anemia. 6 maria immaculata iwo, sf itb 7 Plasma (46-63%) Formed elements (37-54% 8 Formed elements Function & description Source Plasma Function Source 9 10 11 12 Blood Plasma Plasma protein 7% Other solutes 1% Water 92% Blood Plasma (55%) A sample of blood is approximately 55% plasma and 45% formed elements. Plasma is approximately 92% water and contains – – – – Formed elements (45%) proteins to regulate the osmotic pressure of blood, protein for the clotting process and antibody proteins that work with the immune system to protect your body from invading pathogens. Electrolytes, hormones, nutrient and some blood gases are transported in the blood plasma. 13 Plasma Constituent Water Major functions Solvent for carrying other substances (organic and inorganic molecules, formed elements, and heat) Salts (eletrolytes): Sodium, Potassium Calcium, Magnesium Chloride, Bicarbonate Plasma proteins - Albumin Osmotic balance, pH buffering, and regulation of membrane permeability Major contribution to osmotic pressure of plasma, transport lipids, steroid, hormone Essential component of blood - Fibrinogen clotting system, can be converted to insoluble fibrin - Globulins Defense (antibodies), transport ions, hormone, and lipid - Regulatory proteins <1%) Enzymes, proenzymes, hormones14 Plasma Constituent Other solutes - Electrolytes Major functions Normal extracellular fluids ion composition essential for vital cellular activities. Ions contribute to osmotic pressure of body fluids. Major plasma electrolytes are Na+, K+, Ca2+, Mg2+, Cl-, bicarbonate, phosphate, sulfate ¯¯ - Organic nutrients Used for ATP production, growth, and maintenance of cells; include lipids (fatty acids, cholesterol, glycerides), carbohydrates (primarily glucose), and amino acids - Organic wastes Carried to sites of breakdown or excretion, include urea, uric acid, 15 creatinine, billirubin, ammonium ions The Formed Elements • The formed elements may be organized into three group of cells: - the red blood cells or erythrocytes, - the white blood cells or leukocytes, and - the platelets. • When stained, each group is easy to identify with a microscope: - The red cells are erythrocytes, - the stained cells are leukocytes, and - the small cell fragments between the red and white cells are platelets. 16 maria immaculata iwo, sf itb Blood elements There are seven types of cells and cell fragments : red blood cells (RBCs) or erythrocytes platelets or thrombocytes five kinds of white blood cells (WBCs) or leukocytes - Three kinds of granulocytes: neutrophils eosinophils basophils - Two kinds of leukocytes without granules in their cytoplasm (agranulocytes) lymphocytes monocytes 17 maria immaculata iwo, sf itb Blood characteristic Blood is a composite of fluid connective tissue that flows through the vessels of the vascular system. In response to injury, blood has the intrinsic ability to change from a liquid to a gel so as to clot and stop bleeding. Blood comprises cells and cell pieces that are collectively called the formed elements. These cells are carried in an extracellular fluid called blood plasma. 18 maria immaculata iwo, sf itb Blood characteristic • Blood inside the vein and artery ± 38 C (Higher than body temperature Viscosity: 5 x ŋ water • pH: 7.35-7.45 (± 7.4) • Total Volume: ± 7% body weight • Man : 5 - 6 L • Women: 4 - 5 L 19 maria immaculata iwo, sf itb Functions of the blood Blood performs two major functions: transport through the body of – – – – – – oxygen and carbon dioxide food molecules (glucose, lipids, amino acids) ions (e.g., Na+, Ca2+ , HCO3−) wastes (e.g., urea) hormones heat • defense of the body against infections and other foreign materials. All the WBCs participate in these defenses. 20 maria immaculata iwo, sf itb Blood Function Blood has many diverse functions, all relating to supplying cells with essential materials and maintaining the internal environment. Red blood cells transport respiratory gases to trillions of cells in the body. The blood controls the chemical composition of all interstitial fluid by regulating pH and electrolyte levels. White blood cells are part of the immune system and protect our body from microbes by producing antibody molecules and phagocytizing foreign cells. 21 maria immaculata iwo, sf itb THE FORMATION OF BLOOD CELLS (HEMATOPOIESIS) • All the various types of blood cells are produced in the bone marrow (some 1011 of them each day in an adult human!). • arise from a single type of cell called a hematopoietic stem cell — an "adult" multipotent stem cell. • These stem cells – are very rare (only about one in 10,000 bone marrow cells); – are attached (probably by adherens junctions) to osteoblasts lining the inner surface of bone cavities; – express a cell-surface protein designated CD34; – produce, by mitosis, 22 maria immaculata iwo, sf itb 23 Which path is taken is regulated by the need for more of that type of blood cell which is, in turn, controlled by appropriate cytokines and/or hormones. Examples: • Interleukin-7 (IL-7) is the major cytokine in stimulating bone marrow stem cells to start down the path leading to the various lymphocytes (mostly B cells and T cells). • Erythropoietin (EPO), produced by the kidneys, enhances the production of red blood cells (RBCs). • Thrombopoietin (TPO), assisted by Interleukin-11 (IL-11), stimulates the production of megakaryocytes. Their fragmentation produces platelets. 24 maria immaculata iwo, sf itb • Granulocyte-macrophage colony-stimulating factor (GM-CSF), as its name suggests, sends cells down the path leading to both those cell types. In due course, one path or the other is taken. – Under the influence of granulocyte colony-stimulating factor (G-CSF), they differentiate into neutrophils. – Further stimulated by interleukin-5 (IL-5) they develop into eosinophils. – Interleukin-3 (IL-3) participates in the differentiation of most of the white blood cells but plays a particularly prominent role in the formation of basophils (responsible for some allergies). – Stimulated by macrophage colony-stimulating factor (M-CSF) the granulocyte/macrophage progenitor cells differentiate into monocytes, macrophages, and dendritic cells (DCs). 25 maria immaculata iwo, sf itb Hemocytoblasts Myeloid stem cells Lymphoid stem cells Progenitor cells blast cells maria immaculata iwo, sf itb 27 28 Red Blood Cells (erythrocytes) The most numerous type in the blood. Women average about 4.8 million of these cells per cubic millimeter (mm3; which is the same as a microliter [µl]) of blood. Men average about 5.4 x 106 per µl. These values can vary over quite a range depending on such factors as health and altitude. Peruvians living at 18,000 feet may have as many as 8.3 x 106 RBCs per µl.) 29 maria immaculata iwo, sf itb Red Blood Cells (erythrocytes) • Red blood cells (abbreviated RBCs, also called erythrocytes from erythro = red + cyte = cell) are - continually produced in bone marrow and - recycled in spleen. • In mature form they lack nuclei and most cytoplasmic structures; • they are little more than discoid, flexible bags of hemoglobin. 30 maria immaculata iwo, sf itb Red Blood Cells (erythrocytes) • RBC precursors mature in the bone marrow closely attached to a macrophage. • They manufacture hemoglobin until it accounts for some 90% of the dry weight of the cell. • The nucleus is squeezed out of the cell and is ingested by the macrophage. • This scanning electron micrograph (courtesy of Dr. Marion J. Barnhart) shows the characteristic biconcave shape of red blood cells 31 maria immaculata iwo, sf itb Red Blood Cells (erythrocytes) • Thus RBCs are terminally differentiated; that is, they can never divide. • They live about 120 days and then are ingested by phagocytic cells in the liver and spleen. • Most of the iron in their hemoglobin is reclaimed for reuse. The remainder of the heme portion of the molecule is degraded into bile pigments and excreted by the liver. • Some 3 million RBCs die and are scavenged by the liver each second. • Red blood cells are responsible for the transport of oxygen and carbon dioxide. 32 maria immaculata iwo, sf itb Oxygen Transport • In adult humans the hemoglobin (Hb) molecule • consists of four polypeptides: – two alpha (α) chains of 141 amino acids and – two beta (β) chains of 146 amino acids • Each of these is attached the prosthetic group heme. • There is one atom of iron at the center of each heme. • One molecule of oxygen can bind to each heme. 33 maria immaculata iwo, sf itb • The reaction is reversible. • Under the conditions of lower temperature, higher pH, and increased oxygen pressure in the capillaries of the lungs, the reaction proceeds to the right. The purple-red deoxygenated hemoglobin of the venous blood becomes the bright-red oxyhemoglobin of the arterial blood. • Under the conditions of higher temperature, lower pH, and lower oxygen pressure in the tissues, the reverse reaction is promoted and oxyhemoglobin gives up its oxygen. 34 maria immaculata iwo, sf itb Carbon Dioxide Transport Carbon dioxide (CO2) combines with water forming carbonic acid, which dissociates into a hydrogen ion (H+) and a bicarbonate ions: CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3− • 95% of the CO2 generated in the tissues is carried in the red blood cells: – It probably enters (and leaves) the cell by diffusing through transmembrane channels in the plasma membrane. (One of the proteins that forms the channel is the D antigen that is the most important factor in the Rh system of blood groups.) 35 maria immaculata iwo, sf itb Carbon Dioxide Transport Only about 5% of the CO2 generated in the tissues dissolves directly in the plasma. (A good thing, too: if all the CO2 we make were carried this way, the pH of the blood would drop from its normal 7.4 to an instantly-fatal 4.5!) • When the red cells reach the lungs, these reactions are reversed and CO2 is released to the air of the alveoli. 36 maria immaculata iwo, sf itb Carbon Dioxide Transport Once inside, about one-half of the CO2 is directly bound to hemoglobin (at a site different from the one that binds oxygen). • The rest is converted — following the equation above — by the enzyme carbonic anhydrase into – bicarbonate ions that diffuse back out into the plasma and – hydrogen ions (H+) that bind to the protein portion of the hemoglobin (thus having no effect on pH). 37 maria immaculata iwo, sf itb Recycling of red blood cell components 38 Anemia • Anemia is a shortage of RBCs and/or the amount of hemoglobin in them. • Anemia has many causes. One of the most common is an inadequate intake of iron in the diet. Blood Groups • Red blood cells have surface antigens that differ between people and that create the so-called blood groups such as the ABO system and the Rh system. 39 maria immaculata iwo, sf itb The ABO Blood Groups • The ABO blood groups were the first to be discovered (in 1900) and are the most important in assuring safe blood transfusions. • The table shows the four ABO phenotypes ("blood groups") present in the human population and the genotypes that give rise to them. • When red blood cells carrying one or both antigens are exposed to the corresponding antibodies, they agglutinate; that is, clump together. • People usually have antibodies against those red cell antigens that they lack. 40 The ABO Blood Groups Blood Group Antigens on RBCs Antibodies Genotypes in Serum A A Anti-B AA or AO B B Anti-A BB or BO AB A and B Neither AB O Neither Anti-A and Anti-B OO 41 maria immaculata iwo, sf itb Other blood groups • Several other blood group antigens have been identified in humans. – Some examples: MN, Duffy, Lewis, Kell. • They, too, may sometimes cause – transfusion reactions and even – hemolytic disease of the newborn • in cases where there is no ABO or Rh incompatibility. 42 • Human red blood cells before (left) and after (right) adding serum containing anti-A antibodies. The agglutination reaction reveals the presence of the A antigen on the surface of the cells. 43 maria immaculata iwo, sf itb The Rh System • Rh antigens are transmembrane proteins with loops exposed at the surface of red blood cells. • They appear to be used for the transport of carbon dioxide and/or ammonia across the plasma membrane. • They are named for the rhesus monkey in which they were first discovered. • There are a number of Rh antigens. • Red cells that are "Rh positive" express the one designated D. • About 15% of the population have no RhD antigens and thus are "Rh negative". • The major importance of the Rh system for human health is to avoid the danger of RhD incompatibility between mother and fetus. 44 maria immaculata iwo, sf itb The Rh System • During birth, there is often a leakage of the baby's red blood cells into the mother's circulation. • If the baby is Rh positive (having inherited the trait from its father) and the mother Rh-negative, these red cells will cause her to develop antibodies against the RhD antigen. • The antibodies, usually of the IgG class, do not cause any problems for that child, but can cross the placenta and attack the red cells of a subsequent Rh+ fetus. • This destroys the red cells producing anemia and jaundice. • The disease, called erythroblastosis fetalis or hemolytic disease of the newborn, may be so severe as to kill the fetus or even the newborn infant. • It is an example of an antibody-mediated cytotoxicity disorder. 45 maria immaculata iwo, sf itb White Blood Cells (leukocytes) • White blood cells are much less numerous than red (the ratio between the two is around 1:700), • have nuclei, • participate in protecting the body from infection, • consist of lymphocytes and monocytes with relatively clear cytoplasm, and three types of granulocytes, whose cytoplasm is filled with granules. 46 maria immaculata iwo, sf itb White Blood Cells (leukocytes) • White blood cells (abbreviated WBCs, also called leukocytes from leuko = white + cyte = cell) comprise several distinct cell types, neutrophils, eosinophils, basophils, lymphocytes and monocytes. – Certain developmental and morphological similarities permit the first three these cells to be usefully grouped together as granulocytes or polymorphonuclear leukocytes. – The latter two types are then categorized as mononuclear leukocytes. 47 maria immaculata iwo, sf itb Lymphocytes • There are several kinds of lymphocytes (although they all look alike under the microscope), each with different functions to perform . • The most common types of lymphocytes are – B lymphocytes ("B cells"). These are responsible for making antibodies. – T lymphocytes ("T cells"). There are several subsets of these: • inflammatory T cells that recruit macrophages and neutrophils to the site of infection or other tissue damage • cytotoxic T lymphocytes (CTLs) that kill virus-infected and, perhaps, tumor cells • helper T cells that enhance the production of antibodies by B cells 48 maria immaculata iwo, sf itb Lymphocytes • Although bone marrow is the ultimate source of lymphocytes, the lymphocytes that will become T cells migrate from the bone marrow to the thymus where they mature under the influence of thymic hormones • Both B cells and T cells also take up residence in lymph nodes, the spleen and other tissues where they – encounter antigens; – continue to divide by mitosis; – mature into fully functional cells. 49 maria immaculata iwo, sf itb Lymphocytes Lymphocytes are small cells, 7-9 μm in diameter in blood smears, and are the second most common white blood cell type, comprising about 30 % of the circulating leukoytes. Lymphocytes have a round heterochromatic (deeply staining) nucleus surrounded by a relatively thin rim of cytoplasm. 50 maria immaculata iwo, sf itb Monocytes • Monocytes leave the blood and become macrophages and dendritic cells. Macrophages are large, phagocytic cells that engulf foreign material (antigens) that enter the body dead and dying cells of the body. Mononuclear leukocytes comprise both lymphocytes and monocytes. Both cell types work together in immune responses. This scanning electron micrograph (courtesy of Drs. Jan M. Orenstein and Emma Shelton) shows a single macrophage surrounded by several lymphocytes. 51 maria immaculata iwo, sf itb Monocytes • Monocytes are the largest of the leukocytes, and constitute about 5 % of the WBC population in peripheral blood. • In blood smears, their nuclei are typically indented, sometimes deeply so, with a kidney-bean or bent-horseshoe shape. • Monocytes belong to the same functional population as tissue macrophages. • Monocytes/macrophages engulf and digest foreign microorganisms, dead or worn-out cells, and other tissue debris. They interact closely with lymphocytes to recognize and destroy foreign substances. • Most ordinary connective tissues contain resident macrophages which normally remain at rest in the tissue. • But the normal number of fixed macrophages is supplemented during inflammation by the influx of many monocytes from the blood. 52 maria immaculata iwo, sf itb Neutrophils • The most abundant of the WBCs. • Neutrophils squeeze through the capillary walls and into infected tissue where they kill the invaders (e.g., bacteria) and then engulf the remnants by phagocytosis. • This is a never-ending task, even in healthy people: Our throat, nasal passages, and colon harbor vast numbers of bacteria. Most of these are commensals, and do us no harm. But that is because neutrophils keep them in check. This photomicrograph shows a single neutrophil surrounded by red blood cells 53 maria immaculata iwo, sf itb Neutrophils However, – heavy doses of radiation – chemotherapy – and many other forms of stress can reduce the numbers of neutrophils so that formerly harmless bacteria begin to proliferate. The resulting opportunistic infection can be lifethreatening. 54 maria immaculata iwo, sf itb Neutrophils • Neutrophils (also called neutrophilic granulocytes, or polymorphonuclear neutrophilic leukocytes, PMNs, or polys) are the most numerous of the leukocytes, about 60% of the white blood cell count. • They are about 12 μm in diameter in blood smear preparations (about twice the size of red blood cells). • Too many neutrophils is called neutrophilia; 55 maria immaculata iwo, sf itb Neutrophils • Neutrophils take their name from the staining properties of their cytoplasmic lysosomal granules (vesicles containing stored lysosomal enzymes). These granules are neutrophilic, meaning they show no special affinity for either acidic or basic stains but are stained mildly by both. – This is in contrast to the specific granules of eosinophils, which stain red with acidic stains such as eosin, and those of basophils, which stain with basic stains. The nuclei of mature neutrophils are elongated and pinched into several distinct lobes, hence the term polymorphonuclear. Immature neutrophils have a band-shaped nucleus and are hence sometimes called "bands". Mature neutrophils, in contrast, are called "segs", in reference to the segmented nucleus. 56 Eosinophils • Eosinophils (eosinophilic granulocytes) normally comprise less than two to four percent of the peripheral leukocytes. • Their specific granules are intense eosinophilic (stained by eosin), hence the name. • Eosinophils are about the same size as neutrophils. • Their nuclei are typically band shaped (elongated) or two-lobed. • The number of eosinophils in the blood is normally quite low (0– 450/µl). • However, their numbers increase sharply in certain diseases, especially infections by parasitic worms. • Eosinophils are cytotoxic, releasing the contents of their granules on the invader. 57 maria immaculata iwo, sf itb Eosinophils 58 maria immaculata iwo, sf itb Basophils • Basophils (basophilic granulocytes) comprise less than 1 % of leukocytes. normally the peripheral • Their specific granules are intense hence the name. basophilic, • Like eosinophils, basophils are similar in size to neutrophils. • Their nuclei may be band shaped or segmented. • Basophils seem to be functionally similar to tissue mast cells, involved in triggering inflammation. 59 maria immaculata iwo, sf itb Basophils • The number of basophils also increases during infection. • Basophils leave the blood and accumulate at the site of infection or other inflammation. There they discharge the contents of their granules, releasing a variety of mediators such as: – histamine – serotonin – prostaglandins and leukotrienes which increase the blood flow to the area and in other ways add to the inflammatory process. The mediators released by basophils also play an important part in some allergic responses such as – hay fever and – an anaphylactic response to insect stings. 60 maria immaculata iwo, sf itb Platelets • Platelets are cell fragments produced from megakaryocytes. • Blood normally contains 150,000–450,000 per microliter (µl) or cubic millimeter (mm3). This number is normally maintained by a homeostatic (negativefeedback) mechanism. • If this value should drop much below 50,000/µl, there is a danger of uncontrolled bleeding because of the essential role that platelets have in blood clotting. Some causes: – certain drugs and herbal remedies; – autoimmunity. 61 maria immaculata iwo, sf itb Platelets • When blood vessels are cut or damaged, the loss of blood from the system must be stopped before shock and possible death occur. This is accomplished by solidification of the blood, a process called coagulation or clotting. • A blood clot consists of – a plug of platelets enmeshed in a – Network of insoluble fibrin molecules. Please learn by yourself Details of the clotting process! maria immaculata iwo, sf62itb Plasma • Plasma is the straw-colored liquid in which the blood cells are suspended. • Composition of blood plasma Component Percent Water ~92 Proteins 6–8 Salts 0.8 Lipids 0.6 Glucose (blood sugar) 0.1 maria immaculata iwo, sf 63 itb Plasma • Plasma transports materials needed by cells and materials that must be removed from cells: – various ions (Na+, Ca2+, HCO3−, etc. – glucose and traces of other sugars – amino acids – other organic acids – cholesterol and other lipids – hormones – urea and other wastes Most of these materials are in transit from a place where they are added to the blood (a "source") – exchange organs like the intestine – depots of materials like the liver to places ("sinks") where they will be removed from the blood. – every cell – exchange organs like the kidney, and skin. maria immaculata iwo, sf64itb Serum Proteins • Proteins make up 6–8% of the blood. They are about equally divided between serum albumin and a great variety of serum globulins. • After blood is withdrawn from a vein and allowed to clot, the clot slowly shrinks. As it does so, a clear fluid called serum is squeezed out. Thus: • Serum is blood plasma without fibrinogen and other clotting factors. maria immaculata iwo, sf65itb Serum Proteins • Serum albumin – is made in the liver – binds many small molecules for transport through the blood – helps maintain the osmotic pressure of the blood The other proteins are the various serum globulins (& fibrinogen) 66 maria immaculata iwo, sf itb Serum Proteins Serum globulin • They migrate in the order – alpha globulins (e.g., the proteins that transport thyroxine and retinol [vitamin A]) – beta globulins (e.g., the iron-transporting protein transferrin) – gamma globulins. • Gamma globulins are the least negatively-charged serum proteins. (They are so weakly charged, in fact, that some are swept in the flow of buffer back toward the negative electrode.) • Most antibodies are gamma globulins. • Therefore gamma globulins become more abundant following infections or immunizations. 67 maria immaculata iwo, sf itb Serum Lipids • Because of their relationship to cardiovascular disease, the analysis of serum lipids has become an important health measure. • The table shows the range of typical values as well as the values above (or below) which the subject may be at increased risk of developing atherosclerosis. LIPID Typical values (mg/dl) Desirable (mg/dl) Cholesterol (total) 170–210 <200 LDL cholesterol 60–140 <100 LDL cholesterol 60–140 <100 HDL cholesterol 35–85 >40 Triglycerides 40–160 <160 68 • Total cholesterol is the sum of – HDL cholesterol – LDL cholesterol and – 20% of the triglyceride value • Note that – high LDL values are bad, but – high HDL values are good. • Using the various values, one can calculate a cardiac risk ratio = total cholesterol divided by HDL cholesterol • A cardiac risk ratio greater than 7 is considered a warning. 69 Congenital disorders: Nutritional disorders Iron deficiency anemia Thallasemias Sickle cell anemia Hemophilia Iron loading Pernicious anemia Vit K deficiency Secondary disorders Urinary system: Erythrocytosis Immune problems: Hemolytic disease of the newborn Trauma Hemorrhagic anemia Aplastic anemia Infection Blood disorders Tumors Leukemia Myeloid Lymphoid Bacteremia Viremia Septicemia Puerperal fever Malaria Hemolytic anemia Degenerative disorders: Excessive coagulation 70 • Blood Transfusions • "whole blood“ were transfused directly into patients (e.g., to replace blood lost by trauma or during surgery). • Most were further fractionated into components, including: – RBCs. When refrigerated these can be used for up to 42 days. – platelets. These must be stored at room temperature and thus can be saved for only 5 days. – plasma. This can be frozen and stored for up to a year. 71 Ensuring the safety of donated blood • A variety of infectious agents can be present in blood. – – – – viruses (e.g., HIV-1, hepatitis B and C, HTLV, West Nile virus bacteria like the spirochete of syphilis protozoans like the agents of malaria and babesiosis prions (e.g., the agent of variant Crueutzfeldt-Jakob disease) • and could be transmitted to recipients. • To minimize these risks, – donors are questioned about their possible exposure to these agents; – each unit of blood is tested for a variety of infectious agents. 72 • Most of these tests are performed with enzyme immunoassays (EIA) and detect antibodies against the agents. However, it takes a period of time for the immune system to produce antibodies following infection, and during this period ("window"), infectious virus is present in the blood. For this reason, blood is now also checked for the presence of the RNA of these RNA viruses: – HIV-1 – hepatitis C – West Nile virus – by the so-called nucleic acid-amplification test (NAT). 73 maria immaculata iwo, sf itb