NUR 195 Nursing Assessment: Hematologic Function
Plasma and Plasma Proteins; After cellular elements are removed from blood, the remaining liquid portion is called plasma. More than 90% of plasma is water. The remainder consists primarily of plasma proteins, clotting factors (particularly fibrinogen), and small amounts of other substances such as nutrients, enzymes, waste products, and gases.
If plasma is allowed to clot, the remaining fluid is called serum. Serum has essentially the same composition as plasma, except that fibrinogen and several clotting factors have been removed in the clotting process. Plasma proteins consist primarily of albumin and the globulins.
Reticuloendothelial System; The RES (also called the mononuclear phagocytic system, or MPS) is a system of phagocytic cells, including monocytes and macrophages. The RES is divided into primary and secondary lymphoid systems. - The primary lymphoid system is the site of RES cell production and includes the bone marrow and thymus. - The secondary lymphoid system is the site of RES cell function and includes the liver, spleen, and lymph nodes. In the liver, spleen, lymph nodes, and other areas throughout the body, these cells function to recognize foreign cells and trigger an immune response.
The spleen has a number of additional functions including recycling of iron, pooling of platelets, and blood volume regulation. It also acts as a filter for bacteria. In addition, the spleen is a major source of fetal hematopoiesis. It can resume hematopoiesis later in adulthood if necessary, particularly when marrow function is compromised (e.g., in bone marrow fibrosis).
Leukocytes (White Blood Cells);(1/2) Leukocytes are divided into two general categories: granulocytes and agranulocytes. In normal blood, the total leukocyte count is 5,000 to 10,000 cells per cubic millimeter. Of these, approximately 60% to 70% are granulocytes, and 30% to 40% are lymphocytes. Both of these types of leukocytes primarily protect the body against infection and tissue injury. Granulocytes Granulocytes are divided into three main subgroups: - eosinophils, - basophils, and - neutrophils. Neutrophils are the most numerous cells of this class.
1. Neutrophils; Fully mature neutrophils result from the gradual differentiation of myeloid stem cells, specifically myeloid blast cells. The process, called myelopoiesis, takes an average of 10 days. Once the neutrophil is released into the circulation from the marrow, it stays there for only about 6 hours before it migrates into the body tissues to perform its function of phagocytosis (ingestion and digestion of bacteria and particles; Here, neutrophils last no more than 1 to 2 days before they die.
Agranulocytes; Monocytes and lymphocytes are leukocytes with granule-free cytoplasm—hence the term agranulocyte 1. Monocytes; Monocytes (also called mononuclear leukocytes) have a single-lobed nucleus. They are the largest of the leukocytes. In normal adult blood, monocytes account for approximately 5% of the total leukocyte count. When released from the marrow, monocytes spend a short time in the circulation (approximately 24 hours) and then enter the body tissues. Within the tissues, the monocytes continue to differentiate into macrophages, which can survive for months. Macrophages are particularly active in the spleen, liver, peritoneum, and the alveoli; they remove debris from these areas and phagocytize bacteria within the tissues
2. Lymphocytes; Mature lymphocytes are small cells with scanty cytoplasm. Immature lymphocytes are produced in the marrow from the lymphoid stem cells. A second major source of production is the cortex of the thymus. Cells derived from the thymus are known as T lymphocytes (or T cells); those derived from the marrow can also be T cells but are more commonly B lymphocytes (or B cells). Lymphocytes complete their differentiation and maturation primarily in the lymph nodes and in the lymphoid tissue of the intestine and spleen after exposure to a specific antigen. Mature lymphocytes are the principal cells of the immune system, producing antibodies and identifying other cells and organisms as "foreign."
Leukocytes (White Blood Cells);(2/2) 2. Eosinophils; Eosinophils play a key role in response to parasitic and allergic diseases. The presence of certain microbes (such as parasites) results in the release of the granular contents of the eosinophil, allowing for destruction and phagocytosis of the organism. Basophils; Basophils are the least numerous of the circulating leukocytes and have characteristically large, dark-purple granules.
3. Basophils ; The granules contain heparin and histamine and are released in response to exposure to allergens. The number of circulating granulocytes found in the healthy person is relatively constant. An elevation in the total number of WBCs may indicate infection, trauma, or tissue injury, or may be a side effect of certain medications, such as corticosteroids. A WBC count that is below normal may be related to viral infections, the result of side effects from medications such as antiviral medications, or may hint of a more serious condition such as leukemia or myelodysplastic syndrome.
globulins.; The globulins can be separated into three main fractions (alpha, beta, and gamma) - Important proteins in the alpha and beta fractions are the transport globulins and the clotting factors that are made in the liver. - The transport globulins carry various substances in bound form in the circulation. For example, thyroid-binding globulin carries thyroxin, and transferrin carries iron. - The clotting factors, including fibrinogen, remain in an inactive form in the blood plasma until activated by the clotting cascade. - The gamma globulin fraction refers to the immunoglobulins, or antibodies. These proteins are produced by the well-differentiated lymphocytes and plasma cells. The actual fractionation of the globulins can be measured on a specific laboratory test (serum protein electrophoresis).
Albumin; Albumin is particularly important for the maintenance of fluid balance within the vascular system. Albumin, which is produced by the liver, has the capacity to bind to several substances that are transported in plasma (e.g., certain medications, bilirubin, and some hormones). People with poor hepatic function may have low concentrations of albumin, with a resultant decrease in osmotic pressure and the development of edema.
Red Blood Cell Destruction; Aged erythrocytes lose their elasticity and become trapped in small blood vessels and the spleen. They are removed from the blood by the reticuloendothelial cells, particularly in the liver and the spleen.
As the erythrocytes are destroyed, most of their hemoglobin is recycled. Some hemoglobin also breaks down to form bilirubin and is secreted in the bile. Most of the iron is recycled to form new hemoglobin molecules within the bone marrow; small amounts are lost daily in the feces and urine and monthly in menstrual flow.
The process of blood coagulation is highly complex. It can be activated by the intrinsic or the extrinsic pathway. Both pathways are needed for maintenance of normal hemostasis. Many factors are involved in the coagulation cascade that forms fibrin. extrinsic pathway; When tissue is injured, the extrinsic pathway is activated by the release of thromboplastin from the tissue. As the result of a series of reactions, prothrombin is converted to thrombin, which in turn catalyzes the conversion of fibrinogen to fibrin. intrinsic pathway; Clotting by the intrinsic pathway is activated when the collagen that lines blood vessels is exposed. Clotting factors are activated sequentially until, as with the extrinsic pathway, fibrin is ultimately formed.
As the injured vessel is repaired and again covered with endothelial cells, the fibrin clot is no longer needed. The fibrin is digested via two systems: - the plasma fibrinolytic system and - the cellular fibrinolytic system. The substance plasminogen is required to lyse (break down) the fibrin. Plasminogen, which is present in all body fluids, circulates with fibrinogen and is therefore incorporated into the fibrin clot as it forms. When the clot is no longer needed (e.g., after an injured blood vessel has healed), the plasminogen is activated to form plasmin. Plasmin digests the fibrinogen and fibrin. The by-products of clot digestion, called fibrin degradation products, are released into the circulation. Through this system, clots are dissolved as tissue is repaired, and the vascular system returns to its normal baseline state.
Blood; Blood makes up approximately 7% to 10% of the normal body weight and amounts to 5 L to 6 L of volume. blood carries oxygen absorbed from the lungs and nutrients absorbed from the GI tract to the body cells for cellular metabolism.Blood also carries proteins such as hormones, antibodies, and other substances to their sites of action or use
Excessive clotting is equally as dangerous as excessive blood loss because it can obstruct blood flow to vital tissues. To prevent this, the body has a fibrinolytic mechanism that eventually dissolves clots (thrombi) formed within blood vessels. The balance between these two systems, clot (thrombus) formation and clot (thrombus) dissolution, or fibrinolysis, is called hemostasis.
Erythropoiesis; Erythroblasts arise from the primitive myeloid stem cells in bone marrow. The erythroblast is an immature nucleated cell that accumulates hemoglobin and then gradually loses its nucleus. At this stage, the cell is known as a reticulocyte. Further maturation into an erythrocyte entails the loss of the dark-staining material within the cell and slight shrinkage. The mature erythrocyte is then released into the circulation. Differentiation of the primitive myeloid stem cell of the marrow into an erythroblast is stimulated by erythropoietin, a hormone produced primarily by the kidney.
If the kidney detects low levels of oxygen (as would occur in anemia, in which fewer red cells are available to bind oxygen, or with people living at high altitudes), the release of erythropoietin is increased. The increased erythropoietin then stimulates the marrow to increase production of erythrocytes. The entire process typically takes 5 days. For normal erythrocyte production, the bone marrow also requires - iron, - vitamin B12, - folic acid, - pyridoxine (vitamin B6), - protein, and other factors. A deficiency in any one of these factors during erythropoiesis can result in decreased red cell production and anemia.
Hemostasis; Hemostasis is the process of preventing blood loss from intact vessels and of stopping bleeding from a severed vessel. The prevention of blood loss from intact vessels requires adequate numbers of functional platelets. Platelets nurture the endothelium and thereby maintain the structural integrity of the vessel wall. Two processes are involved in arresting bleeding: primary and secondary hemostasis
In primary hemostasis, - the severed blood vessel constricts. -Circulating platelets aggregate at the site and adhere to the vessel and to one another. An unstable hemostatic plug is formed. secondary hemostasis. - For the coagulation process to be correctly activated, circulating inactive coagulation factors must be converted to active forms. - This process occurs on the surface of the aggregated platelets at the site of vessel injury. - The end result is the formation of fibrin, which reinforces the platelet plug and anchors it to the injury site. This process is termed secondary hemostasis.
TABLE 19-1 Blood Cells; WBC (Leukocyte): Fights infection Neutrophil: Essential in preventing or limiting bacterial infection via phagocytosis Monocyte: Enters tissue as macrophage; highly phagocytic, especially against fungus Eosinophil: Involved in allergic reactions (neutralizes histamine); digests foreign proteins Basophil: Contains histamine; integral part of hypersensitivity reactions Lymphocyte: Integral component of immune system - T lymphocyte: Responsible for cell-mediated immunity; recognizes material as "foreign" - B lymphocyte: Responsible for humoral immunity; many mature into plasma cells to form antibodies
Plasma cell: Secretes immunoglobulin (Ig, antibody); most mature form of B lymphocyte RBC (erythrocyte): Carries hemoglobin to provide oxygen to tissues; average lifespan is 120 days Platelet (thrombocyte): Fragment of megakaryocyte; provides basis for coagulation to occur; maintains hemostasis; average lifespan is 7 days
Erythrocytes (Red Blood Cells); The normal erythrocyte has a biconcave disk shape. It has a diameter of approximately 8 μm and is so flexible that it can pass easily through capillaries that may be as small as 2.8 μm in diameter. The membrane of the red cell is very thin so that gases, such as oxygen and carbon dioxide, can easily diffuse across it; the disk shape provides a large surface area that facilitates the absorption and release of oxygen molecules. Mature erythrocytes consist primarily of hemoglobin, which contains iron and makes up 95% of the cell mass. Mature erythrocytes have no nuclei The presence of a large amount of hemoglobin enables the red cell to perform its principal function of oxygen transport.
Occasionally, the marrow releases slightly immature forms of erythrocytes, called reticulocytes, into the circulation. An elevation in the reticulocyte count may occur as a normal response to an increased demand for erythrocytes (as in bleeding) or in some disease states. An important property of heme is its ability to bind to oxygen loosely and reversibly. Oxygen readily binds to hemoglobin in the lungs and is carried as oxyhemoglobin in arterial blood. Oxyhemoglobin is a brighter red than hemoglobin that contains lesser amounts of oxygen (reduced hemoglobin), which is why arterial blood is a brighter red than venous blood. Whole blood normally contains approximately 15 g of hemoglobin per 100 mL of blood.
Iron Stores and Metabolism; The average daily diet in the United States contains 10 to 15 mg of elemental iron, but only 0.5 to 1 mg of ingested iron is normally absorbed from the small intestine daily. The rate of iron absorption is regulated by the amount of iron already stored in the body and by the rate of erythrocyte production. Additional amounts of iron, up to 2 mg daily, must be absorbed by women of childbearing age to replace that lost during menstruation. Total body iron content in the average adult is approximately 3 g, most of which is present in hemoglobin or in one of its breakdown products. With iron deficiency, bone marrow iron stores are rapidly depleted; hemoglobin synthesis is depressed, and the erythrocytes produced by the marrow are small and low in hemoglobin. This is known as microcytic anemia (characterized by small red blood cells).
Part of a standard complete blood count (CBC) includes the Mean Corpuscular Volume (MCV), which measures the size of the RBCs. In microcytic anemia, a small (< 82 μm3) MCV is seen. Causes of microcytic anemia include iron deficiency related to - dietary inadequacy, - malabsorption, - increased iron loss, and - increased iron requirement. In the adult, lack of dietary iron is rarely the sole cause of iron deficiency anemia. Iron deficiency in the adult generally indicates that blood has been lost from the body (e.g., from bleeding in the GI tract or heavy menstrual flow). The source of iron deficiency should be investigated promptly, because iron deficiency in an adult may be a sign of bleeding in the GI tract or colon cancer.
Platelets (Thrombocytes); Platelets, or thrombocytes, are not technically cells; rather, they are granular fragments of giant cells in the bone marrow, called megakaryocytes. Platelet production in the marrow is regulated in part by the hormone thrombopoietin, which stimulates the production and differentiation of megakaryocytes from the myeloid stem cell.
Platelets play an essential role in the control of bleeding. They circulate freely in the blood in an inactive state, where they nurture the endothelium of the blood vessels, maintaining the integrity of the vessel. When vascular injury occurs, platelets collect at the site and are activated. They adhere to the site of injury and to each other, forming a platelet plug that temporarily stops bleeding. Substances released from platelet granules activate coagulation factors in the blood plasma and initiate the formation of a stable clot composed of fibrin, a filamentous protein.
Anatomic and Physiologic Overview; Plasma is the fluid portion of blood; it is thin and colorless and contains various proteins, such as albumin, globulin, fibrinogen, and other factors necessary for clotting, as well as electrolytes, waste products, and nutrients. Approximately 55% of blood volume is plasma, and 45% consists of various cellular components. Blood; The cellular component of blood consists of three primary cell types - erythrocytes (red blood cells [RBCs]), - leukocytes (white blood cells [WBCs]),and - thrombocytes (platelets).
RBCs generally live for 120 days, WBCs live from days to years depending on the type, and platelets live 7 to 10 days. The primary site for hematopoiesis (formation and production of blood cells) is the bone marrow.
Function of Leukocytes (WBCs); Granulocytes protect the body from invasion by bacteria and other foreign entities. Neutrophils arrive at a given site within 1 hour after the onset of an inflammatory reaction and initiate phagocytosis, but they are short-lived. An influx of monocytes follows; these cells continue their phagocytic activities for long periods as macrophages. This process constitutes a second line of defense for the body against inflammation and infection. Although neutrophils can often work adequately against bacteria without the help of macrophages, macrophages are particularly effective against fungi and viruses. The primary function of lymphocytes is to produce substances that aid in attacking foreign material. T lymphocytes kill foreign cells directly or release a variety of lymphokines, substances that enhance the activity of phagocytic cells.
T lymphocytes are responsible for - delayed allergic reactions, - rejection of foreign tissue (e.g., transplanted organs), and - destruction of tumor cells. This process is known as cellular immunity. B lymphocytes are capable of differentiating into plasma cells. Plasma cells, in turn, produce antibodies called immunoglobulin (Ig), which are protein molecules that destroy foreign material by several mechanisms. This process is known as humoral immunity. The increase in eosinophil levels in allergic states indicates that these cells are involved in the hypersensitivity reaction since they neutralize histamine. Thus, eosinophil counts are examined in allergic reactions and parasitic infections and to monitor response to treatment. Basophils play a large part in hypersensitivity reactions and are used to study chronic inflammation.
Vitamin B12 and Folic Acid Metabolism; Vitamin B12 and folic acid are required for the synthesis of DNA in many tissues. Deficiencies of either of these vitamins have the greatest effect on erythropoiesis. Both vitamin B12 and folic acid are derived from the diet and depend on a functioning intestinal mucosa for absorption.
Vitamin B12 combines with intrinsic factor produced in the stomach, and is absorbed in the distal ileum. It is important for nurses to recall that patients who have had a partial or total gastrectomy may have limited amounts of intrinsic factor, and therefore the absorption of vitamin B12 may be diminished, leading to anemia. The effects of either decreased absorption or decreased intake of vitamin B12 are not apparent(ปรากฏ) for 2 to 4 years.
Bone Marrow; The bone marrow is the site of hematopoiesis, or blood cell formation. In children, blood formation involves all skeletal bones, but with aging, marrow activity is usually limited to the pelvis, ribs, vertebrae, and sternum. In adults with disease that causes marrow destruction, fibrosis, or scarring, the liver and spleen can also resume production of blood cells by a process known as extramedullary hematopoiesis. The myeloid stem cell is responsible not only for all nonlymphoid white blood cells (WBCs) but also for the production of red blood cells (RBCs) and platelets.
When stimulated, stem cells can begin a process of differentiation into either myeloid or lymphoid stem cells. Lymphoid stem cells produce either T or B lymphocytes, whereas myeloid stem cells differentiate into three broad cell types: - erythrocytes, - leukocytes, and - platelets. Thus, with the exception of lymphocytes, all blood cells are derived from myeloid stem cells. A defect in a myeloid stem cell can cause problems with erythrocyte, leukocyte, and platelet production.