Dr Lwiiindi Blood Physiology PDF

INTRODUCTION TO BLOOD DR LWIINDI  BLOOD Composition And Functions Blood is a fluid, which circulates in the vascular channels of the human body due to the pumping action of the heart. It is red in color and consists of a liquid portion called plasma in which various t...

INTRODUCTION TO BLOOD DR LWIINDI  BLOOD Composition And Functions Blood is a fluid, which circulates in the vascular channels of the human body due to the pumping action of the heart. It is red in color and consists of a liquid portion called plasma in which various types of cells are present. The cells which are suspended in the plasma are of three different types  1.Erythrocytes or red blood cells The color of these cells is red due to presence of an iron containing pigment known as hemoglobin. 2.Leucocytes or white blood cells They are of different types (5) 3.Thrombocytes or Plateletes These cells help in the coagulation of blood  GENERAL FUNCTIONS OF BLOOD Blood performs various important functions, which could be summarized as follows; 1. RESPIRATORY Tissues and organs require a constant supply of oxygen to maintain their activity and simultaneously they form carbon dioxide and other waste products. Blood and particularly the red blood cells are responsible for transport of oxygen from the lungs to the tissues. This is due to the presence of hemoglobin, which combines with oxygen to form oxy-hemoglobin. Carbon dioxide from tissues is taken up by the blood and released in the lungs.  2. EXCRETORY As a result of metabolic activity there is a constant production of waste products. Blood transports them to the kidneys, lungs, skin and gastrointestinal tract for excretion. 3. NUTRITIVE Food is digested into simpler end products in the digestive tract. These substances are absorbed from the intestine and transported to all parts of the body by the blood  4. DEFENSIVE Blood protects the body against infections. This is achieved in different ways. Leucocytes have the ability to engulf and destroy invading organisms and the property of white blood cells is termed as phagocytosis. These cells form the defense force of the body and during infection their count increases. This virtue forms the basis of immunization against diseases.  5. COAGULATION It is a mechanism by which various factors present in the blood form a clot and thus prevent blood loss 6. ACID BASE EQUILIBRIUM Cell and enzyme activity require maintenance of a constant acid base equilibrium. Blood contains buffers which maintain pH (keep the pH constant).  7. BODY TEMPERATURE The water content of the blood is 90%. It has a high specific heat and high latent heat of evaporation, which help blood to maintain the body temperature. 8. TRANSPORT OF SUBSTANCES Blood is in rapid circulation and as such substances like hormones, vitamins and drugs are easily transported all over the body. 9. PROTEIN RESERVE Plasma proteins to a certain extent act as protein reserve and are used in extreme protein deficiency to form cell proteins. Section 1 Components and Characteristic Water: 93-95% Plasma: 50-60% Solutes: 5-7% Proteins: Nutrients Whole Products Electrolytes: blood Others: urea, gases. WBC, Platelet: 1% RBC: 40-50% (male) 37-48% (female)  Blood Components Water: – 93~95% (plasma); 65~68% (RBC); 81~86% (whole blood). – Solvent, humoral balance, osmotic pressure. Electrolytes: – Na+, K+, Mg2+, Cl-, HCO3-, etc. Cell shape, pH. Proteins: – Albumin: 40-48g/L. Colloidal osmotic pressure; carrier; buffer pH. – Globulin: 15-30g/L. Immune reaction: antibody; carrier. – Fibrinogen: 2-4g/L. Blood coagulation.  – Hemoglobin (Hb): 120-160g/L (male), 110-150g/L (female) Function: carry gases. Others: – carbohydrates, lipids, amino acid, pigments, hormones, gas (O2, CO2), and others like urea, uric acid.  Physical and chemical properties Blood pH: – Normal interval: 7.35~7.45. Regulated by lung and kidney. Viscosity: – Friction of molecules and cells in blood. – Relative viscosity: Whole blood: 4~5 times to water (RBC). Plasma: 1.6~2.4 times to water (Proteins). Anemia or body fluid loss.  Osmotic pressure – Definition: An ability of a liquid to attract and retain water. It drives osmosis. 300mmol/L – Composition and roles: Crystal osmotic pressure: 298.7 mmol/L. – Maintain shape and size of cells. Colloid osmotic pressure: 1.3 mmol/L. – Retain blood volume – Decide distribution of water between blood and interstitial fluid.  PLASMA It is the fluid part of the blood in which formed elements are suspended. The relative quantity of plasma and cells is in the ratio of 55:45. If blood mixed with an anticoagulant is taken in graduated tube and centrifuged for about half an hour, the cells being heavier, settle at the bottom of the tube and constitute about 45% of the blood volume. This is known as packed cell volume (PCV)  5 liter in adult 45% is packed cells volume (PCV) 55% is plasma volume Dr Sitelbanat 15  Hematocrit (packed red cell volume) - definition: fraction of the blood composed of RBC - functional significance - methods of determination: centrifuging blood in a calibrated ‘hematocrit tube’ - values ~ 35% – 45%; ~ up to 10% in severe anemia ~ up to 65% in polycytemia - corrected Ht = 0,96 Ht (3-4% from the measured Ht is represented by entrapped plasma) - venous vs. arterial hematocrit … - relation hematocrit – blood viscosity…  COMPOSITION Plasma contains 91-92% water and 8-9% of solid substances, which are both organic and inorganic in nature. Inorganic constituents are less than 1% and are mostly chlorides, carbonates and phosphates of sodium, potassium and calcium. Small amounts of iron, copper and iodide are also present. Sodium bicarbonate present in the plasma helps in the maintenance of blood pH during carbon dioxide transport.  Organic substances form the major bulk of solids present in plasma and they are; Plasma proteins (6.5-8 gms %) Glucose (80-120mg%) Cholesterol and lipids (150-250mg%) Non-protein nitrogenous substances like urea, uric acid, creatine and creatinine Hormones, enzymes and blood pigments.  PLASMA PROTEINS They are specific proteins present in plasma and are of three different types; 1. Albumin It forms the major bulk of plasma proteins and has a molecular weight of 60,000. Albumin content of plasma is 4-4.5gm%.  2.Globulin It constitutes about 2.5 gm of plasma proteins and has a relatively higher molecular weight of 1,30,000. Various types of globulins have been identified like alpha, beta and gamma globulin. The latter plays an important role in antibody formation. Prothrombin which helps in the coagulation is beta globulin and its plasma content is 0.1 gm%  3.Fibrinogen Blood coagulation requires this protein. The chemical nature of clot is fibrin, which is formed from fibrinogen. About 0.25 gm% of fibrinogen is present in blood. Fibrinogen and prothrombin are utilized in the clotting and plasma devoid of these two proteins is called serum. It only contains albumin and globulin. There are various methods by which plasma proteins can be isolated, like half or full saturation with ammonium sulphate or electrophoresis.  FUNCTIONS 1. Colloidal osmotic pressure It is 25mmHg. Albumin being the major plasma protein primarily influences the colloidal osmotic pressure. This is responsible for preventing fluid exit from the capillaries. 2. Antibody formation. Antibodies form an essential defense mechanism. This virtue is attributed to the gamma globulin  3. Coagulation Fibrinogen and prothrombin are involved in the clotting of blood. Various other clotting factors also belong to globulin. 4. Transport media Certain substances bind themselves with albumin, alpha and beta globulins and are transported. The transport of hormones, metals, drugs, dyes are examples of this function.  5. Erythrocyte sedimentation rate( ESR) is influenced by the fibrinogen content of plasma. 6. Viscosity Fibrinogen and globulins, due to their high molecular weight and irregular shape contribute to blood viscosity. 7. Buffer mechanism, plasma proteins act as buffers and maintain acid base balance. 8. Protein reserve. During emergency, cells of the reticuloendothelial system break them into amino acid. Subsequently these are used for the synthesis of cell protein  The erythrocyte sedimentation rate (ESR) - commonly used, inexpensive, but non- specific laboratory test (Westergren, 1921) - measures the speed of sedimentation of RBC/RBC aggregates in plasma over a period of 1 hour in a vertical column of anticoagulated blood under the influence of gravity - sialic acid-rich glycoproteins on cell surface membranes contribute to creating a negative charge on the cells’ surface cellular repel …  Erythrocyte sedimentation rate (ESR) - a raised ESR is associated with marked rouleaux formation of RBCs - mainly depends on plasma concentration of large proteins (fibrinogen, Ig) - ESR raised in systemic inflammatory & neoplastic diseases; useful in chronic diseases, for monitoring disease activity/response to therapy  The basic factors influencing the ESR - increased ESR with elevated fibrinogen (e.g., pregnancy, collagen vascular diseases, malignancy). decreased albumin conc. anemia (hematocrit is reduced, red blood cell aggregates fall faster); macrocytic red cells also settle more rapidly. a decreased ESR is associated with: hypofibrinogenemia, hypergammaglobulinemia associated with dysproteinemia, and hyperviscosity blood diseases in which RBC have an irregular or smaller shape that causes slower settling; increased albumin concentration – an abnormal value remains a nonspecific finding INTRODUCTION TO BLOOD DR LWIINDI  Section 2 Blood Cells Red blood cell White blood cell Platelet  Hemopoiesis The process of blood generation. Cell Lineage Lifespan Daily Production Rate RBC 120 days 2.5  109/L Neutrophil 7 hours 0.85  109/L Platelet 10 days 2. 5  109/L  Ontogeny of Hematopoiesis – Prenatal stages: First month: yolk sac. Third month: liver Fourth month: bone marrow – Postnatal stages: Bone marrow of almost any bone, predominatantly by flat bones and long bones.  100 100 Yolk Sac Liver Bone morrow Hemopoitic activity (%) Lymph nodes Spleen 0 1 2 3 4 5 6 7 8 9 Prenatal age (months) 100 100 Vertebrate Proportion of Red Tibia Sternum Morrow (%) Femur Ribs birth 10 20 30 40 50 60 70 80 90 Postnatal age (years) Hematopoiesis: the formation of blood cells Hematopoiesis is the process that generates blood cells of all lineages. Calculations based on the blood volume and the level and half-life of each type of blood cell in the circulation indicate that each day an adult produces ~ 200 billion erythrocytes, 100 billion leukocytes, and 100 billion platelets. These rates can increase by a factor of 10 or more when the demand for blood cells increases Growth and differentiation inducers (cytokines, hormones) for the formation of blood cells … Interleukin-3 (IL-3) promotes growth of most of the different types of stem cells Interleukin-7 (IL-7) - 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 Thrombopoietin (TPO/ megakaryocyte growth and development factor), assisted by Interleukin-11 (IL- 11), stimulates the production of megakaryocytes. Their fragmentation produces platelets.  Granulocyte-monocyte 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 (GCSF), they differentiate into neutrophils. - Further stimulated by interleukin-5 (IL-5) they develop into eosinophils. - Stimulated by macrophage colony-stimulating factor (M-CSF) the granulocyte/macrophage progenitor cells differentiate into monocytes, the precursors of macrophages.  B12 Vitamin & Folic acid Act on the final maturation of RBC. Both are essential for DNA synthesis through the formation of an essential DNA building block, thymidine triphosphat B12 Vitamin: - the body uses 1-3 μg/day of B12 vitamin - hepatic stores amounts 1000-3000 μg (enough for 3-4 years…) - intrinsic factor needed for absorption …  Vit. B12 & folic acid deficiency >> proliferation & maturation failure: - pernicious anemia > macrocytes (large, oval, fragile)> short life causes: atrophic gastric mucosa>> intrinsic factor deficiency> no B12 absorption  Erythropoietin Glycoprotein, MW = 34.000, T1/2 = 6 - 9 hours Mechanism of action: ↑ the committment of stem cells to proerythroblasts ↑ the differentiation of erythroblastic stages Synthesized - 90% kidneys (renal tubular* epithelial cells?), the rest of 10% formed mainly in the liver - stimulus = renal hypoxia ↑ in EPO conc. after minutes to hours, with a maximum level after 24 h ↑ after 3 - 5 days: ↑ RBC number. 10 x - other non-renal hypoxia sensors act through E, NE, PG (+) EPO production  Regulation of erythropoietin control mechanism… Therapeutically used: 50 – 300 U / kg, 3 times / week in kidneys diseases, transplant, anemia, pulmonary diseases, blood loss…  Age It is higher in the newborn. Sex Cell count is relatively less in females Exercise During muscular exercise there is a slight temporary elevation of cell count. Diural variation It is slightly reduced during sleep. Altitude At higher altitudes the count is increased due to hypoxic state, which stimulates cell production. Emotional state There is increased secretion of adrenaline during excitement which increases the erythrocyte count.  Normal erythrocytes have a mean diameter of 7.2 microns and an average thickness of 2.2 microns. They contain about 65% water and the rest is made up of solid substances, out of which the haemoglobin constitutes 33%. Functions The main function of red blood cell is to transport oxygen and carbon dioxide. Life period The average life of an RBC is 120days. The old cells are destroyed in the spleen and liver. The physiological rise in RBC count is called polycythaemia. This can be observed in high altitudes.  Polycythaemia vera indicates the pathological condition of raised RBC count, which is seen in malignant condition of the red bone marrow. A decreased red cell count or subnormal haemoglobin level, when present is called anaemia.  HAEMOGLOBIN It is a chromoprotein and is red in color. Hb consists of a protein component globin and an iron containing pigment haem. Iron exists in the ferrous form and each molecule of haemoglobin contains four iron atoms. Hb combines with the oxygen to form a loose reversible compound oxy-haemoglobin, which rapidly dissociates in the tissues to release oxygen. The formation and subsequent breakdown of oxyhaemoglobin is influenced by various factors which would be discussed later on in the chapter of respiration.  Haemoglobin content of the blood ranges between 14 to 18 gm% and can be determined by haemoglobinometer. The iron content of haemoglobin is about 0.34% and its molecular weight is 68000. the normal oxygen carrying capacity of haemoglobin is 1.34 ml per gm of Hb. The transport of oxygen is the most important function of Hb but the globin component also helps in the transport of CO2 by combining with it to form carbamino compounds.  Types Of Haemoglobin Foetal Haemoglobin Methaemoglobin Carboxyhaemoglobin  Life Span of Red Cells and Fate of Haemoglobin The average life span of erythrocytes is 120 days. The cells are constantly broken down, primarily in the spleen and new cells are formed in the bone marrow. This helps to maintain a constant cell count. The fate of haemoglobin has been summarized below:  IRON METABOLISM The iron content of the body is about 4-5 mgm/kg of body weight. It is an essential constituent of haemoglobin, myoglobin, and respiratory enzymes and its main functions are the transport of oxygen to the tissues and cellular oxidative mechanism. The important sources of iron are liver, spleen, kidney and heart, but egg yolk, green leafy vegetables, nuts, dates and figs also contain iron in adequate quantities.  Absorption Normally very little of dietary iron (10%) is absorbed in the gastrointestinal tract. The organic ferric iron is converted into ferrous form by gastric acidity and iron absorption mainly occurs in the upper duodenum and depends upon the ferritin content of the intestinal mucosa. This is an iron-protein complex having 23% iron and a protein called apoferritin. This theory of absorption is known as “mucosal block theory”.  Transport, Utilization and Storage Iron combines with beta globulin and forms siderophilin or transferrin, which is the transport form of iron. In the tissues iron is released from siderophilin and it is utilized for the synthesis of haemoglobin, myoglobin and respiratory enzymes. Iron is stored in liver, spleen and intestinal mucosa. About 0.8% of the circulating RBC undergo disintegration daily and they liberate approximately 8gm, of haemoglobin which on degradation gives 25mgm of iron.  The bulk of it is used for the resynthesis of haemoglobin and the balance is stored. Excretion The efficiency of the utilization of the endogenous iron is high and only small quantities in the urine.  ANAEMIA It is due to the reduction of red blood cells or sub- normal level of haemoglobin which consequently affects the supply of oxygen to the tissues. Anaemia by itself is not a disease but a symptom of some underlying cause. Some of the common types of anaemia are: I. Nutritional anaemia due to a certain deficiency in the diet a. Pernicious anaemia due to Vit B12 deficiency. b. Megaloblastic anaemia due to lack of folic acid. c. Hypochromic anaemia as in iron deficiency. II. Haemolytic anaemia resulting from excessive breakdown of RBC. It may be seen in the following conditions. a. Disease like malaria b. Sickle cell anaemia and thalassemia due to the presence of abnormal haemoglobin. III. Aplastic anaemia in which there is a suppression of bone marrow as in a. excessive use of certain drugs like sulpha drugs or chloramphenical. b. exposure to X-ray radiation. c. Malignant disease of the bone marrow. INTRODUCTION TO BLOOD DR LWIINDI  BLOOD INDICES A variation in the size and number of red cells or a reduction in haemogobin content requires clinical significance. In such conditions an elevation of blood indices helps the clinician in planning appropriate treatment.  Packed Cell Volume (PCV) It is also known as haemoglobin (Hct) and the term is used to express the ratio of blood cells to plasma (45:55). The normal value of PCV is 45% but in females it is slightly lower due to their reduced RBC count. PVC is increased in polycythemia and severe dehydration. It is reduced in anaemia.  Color Index It expresses the ratio between Hb% and RBC% considering RBC count of 5million/cu mm as 100%. The normal value ranges from 0.85 to 1.15. It is reduced in iron deficiency anaemia.  Mean Corpuscular Volume MCV) It indicates the average volume of a RBC The normal value is about 90cubic microns. An alteration of MCV helps in identification of microcytic and macrocytic anaemia.  Mean Corpuscular Haemoglobin (MCH) This gives an idea about the average haemoglobin content in a single red cell. Normal range varies between 28 and 31 micro micro (pico) grams.  Mean Corpuscular Haemoglobin Concentration (MCHC) It indicates the relative % of haemoglobin in the erythrocyte and its normal value is 35%. * 100  LEUCOCYTES They are commonly known as white blood cells. They are larger than erythrocytes, contain a nucleus and do not contain haemoglobin. Normal leucocyte count varies from 4000 to 11000 cell/cu of the blood, but in majority of healthy adults the range is restricted within 6000 to 9000 cells/cu mm. A study of the shape, size and appearance of the white cell reveals that leucocytes are of five different types. Leucocytes are classified into granulocytes and agranulocytes.  Granulocytes I. Neutrophil They constitute 60-70% of the total leucocyte count. They have a multilobed nucleus and the number of lobes usually ranges from 3 to 5. Cytoplasm contains fine granules, which take neutral stain. Neutrophils exhibit phagocytosis and their count increases in acute infections. They form the first line of defense in the body. Physiologically an increase in the neutrophil count is observed during menstruation, pregnancy and muscular exercise.  In various acute infections like pneumonia, appendicitis, tonsilitis, abscesses or boils (pus forming organisms) the count increases. Neutrophil granules contain many enzymes which include myelo peroxidase and proteases. They help in the destruction if invading microorganisms. the process of phagocytosis includes the mechanisms such as chemotaxis, opsonisation, ingestion and degranulation. The neutrophils also release thromboxanes, leukotriens.  The latter increase the vascular permeability and cause migration of more neutrophils to the site of inflamation. Neutrophil count decreases in typhoid, malaria, aplastic anaemia and under the influence of various drugs. The term neutropenia is used to denote a reduced count.  WBC - Leukocytes This photo shows an eosinophil (E) and a neutrophil (N). R for RBCs. The eosinophil is distinguished by its red granules and bilobed nucleus  = II. Eosinophil It has actually a bilobed nucleus and shows the presence of relatively large granules, which take an acidophilic or orange stain. Normal eosinophil count ranges from 2-5%. It has been observed that in allergic conditions eosinophil count increases (eosinophilia) to inhibit the intracellular synthesis of histamine.  They also show mild phagocytosis. Eosinophil help in attacking the parasites such as roundworm and threadworm by releasing their granules. A decrease on eosinophil count constitutes eosinopenia and can be seen in acute pyogenic infections, ACTH or steroid therapy. III. Basophil The nucleus in these cells is usually bilobed and cytoplasm contains coarse blue granules. Their count ranges from 0-1%. Basophil releases histamine and this occurs specially in hypersensitivity reactions such as anaphylactic shock. The basophil count increases in polycythemia and chronic myeloid leukemia. The cells mentioned earlier have one common feature. All of them contain granules in the cytoplasm and hence are known as granulocytes.  WBC – Leukocytes A basophile is characterized by a lobed nucleus and it is filled by large blue-black granules that sometimes cover the nucleus. Here you can see the distinct granules against the purple nucleus.  Agranulocytes I. Lymphocytes The has a large oval or rounded nucleus and there is a thin strip of clear nongranular cytoplasm between the nucleus and cell membrane. They are subdivided into large and small lymphocytes depending on their size. The functional classification of lymphocytes is dealt under immunity. The differential lymphocyte count ranges from 20- 30% and these cells show a significant increase in chronic infections like tuberculosis.  Lymphocytes are only slightly larger than red blood cells and they have a relatively large nucleus / cytoplasm ratio. Note that the lymphocyte in the above photo has only a thin rim of light purple cytoplasm around the dense nucleus.  Lymphocytes are responsible for providing immunity to the body. There are two functionally distinct types namely ‘T’ lymphocytes and ‘B’ lymphocytes. They are involved in immune and defense mechanisms and are described in the chapter on immunity. II. Monocyte They are the largest white cells (15 microns) and have a kidney shaped nucleus, which is eccentric in location. Consequently, one side of the cell shows larger amount of non-granular cytoplasm.  The normal monocyte count is 3-8%. Monocytes are phagocytic in function and they are the second line of defense in the body. The monocyte count increases in kala-azar, malaria and infectious mononucleosis. Monocytes leave the circulation and enter the tissues as tissue macrophage. Total and differential leucocyte count is a common investigation in diseases. The life span of white cells is very short and ranges from a few hours to 2-3 days. However, some of the agranular cells seem to have a longer life span.  Monocytes are phagocytic and may have vacuoles in the cytoplasm. They also have a horseshoe shaped nucleus or, in immature monocytes, they may have an indented nucleus.  Arneth Count The age of the neutrophil can be determined by the number of lobes present in its nucleus. The number of lobes increases as the cells grow old. The grouping of neutrophils based upon the number of lobes, is termed Arneth count. In a healthy individual the arneth count is: N1 5-10% N2 25-30% N3 45-50% N4 15-20% N5 less than 3%  An increase in one and two lobed cells is termed ‘shift to the left’ and indicates stimulation of granulopoiesis. On the other hand an increase in four and five lobed neytrophil constitutes a ‘shift to the right’ and indicates low leucopoiesis and poor body response to infection.  Function Of Leucocytes Phagocytosis It is a process by which leucocytes engulf bacteria and foreign material in an attempt to eliminate infection. Neutrophils and monocytes have this ability. Anti allergic effect Histamine release during allergic conditions is inhibited by eosinophils, consequently their count increases in allergy. Antibody formation Lymphocytes are mainly responsible for the antibody formation, giving immunity to the body.  Heparin production Basophils produce heparin, which prevents intravascular clotting. Trephone formation Leucocytes help in the formations of trephones from plasma proteins, which are needed for the growth and repair of tissues. Leucocytosis This term is used to indicate an increase in the white cell count and is a common feature I most infections. A physiological increase in leucocytes is seen in: - Menstruation - Pregnancy - Muscular exercise  A reduction in white cell count is known as leucopenia. This condition is seen in: - Bone marrow suppression by drugs and X-ray radiation - Pernicious anaemia - Infections such as typhoid and malaria Rarely, leucocytosis is associated with the presence of premature white cell in the peripheral blood. This condition, which may prove fatal is termed leukemia.  THROMBOCYTES Commonly known as platelets. They are small, biconvex non-nucleated cells, usually found in clusters in a dried film. The average size of platelets is 2.5 microns and their count ranges from 300,000 micro litre of blood. The life span of the platelets is about ten days. Variations in count An increase in the count is observed in A, Haemorrhage B, Splenomegally C, Hodgkin’s disease  A reduction in platelet count is known as thrombocytopenia. It is seen in; Splenomegally Aplastic anaemia Acute infections Leukemia Idiopathic thrombocytopenic purpura  FUNCTIONS Arrest of bleeding platelets aggregate at the site of injured vessel and form a haemostatic plug to prevent blood loss. Coagulation. Platelets release clotting factors, phospholipids, and prostaglandins which help in the clotting process. Clot retraction. The release of thrombesthenin from platelets helps in clot retraction.  Repair of endothelium. Platelet release PDGF(platelet derived growth factor) which helps in the repair of damaged capillary endothelium and other tissues. Release of serotonin and epinephrine. These substances released from platelets produce vasoconstriction and consequently reduce the blood loss. Purpura A reduction in platelet count results in purpura. It is a bleeding disorder in which haemorrhage tendency increases and there may be subcutaneous haemorrhage.  Platelets are produced in the BM from megakaryocytes, which are large cells with pseudopod, which chip off giving rise to platelets in the circulation. INTRODUCTION TO BLOOD DR LWIINDI  ABO SYSTEM Blood groups are genetically determined by the presence of the antigens found on the membranes of red blood cells. Agglutination, a process whereby cells clump together, occurs when red cells with a specific antigen encounter its corresponding antibody. In vivo agglutination results in either intravascular or extravascular haemolysis. The ABO blood group system consists of four main groups and these are determined by the presence or absence of the antigens, A and B.  The presence of antigen A or antigen B gives rise to Group A or Group B, the presence of both antigens gives rise to Group AB and the absence of both antigens gives rise to Group O. Antibodies to these antigens can be either naturally occurring or as a result of an immune response. Immune antibodies arise when an individual is exposed to foreign red cell antigens through either transfusion or passage of red cells across the placenta during pregnancy.  RHESUS BLOOD GROUP SYSTEM The Rhesus system comprises five main antigens, namely C, c, D, E and e, but amongst them D is the most common and strongly antigenic The term rhesus-positive usually refers to those individuals who express the D antigen on their red blood cells and rhesus-negative for those whose red cells do not express this antigen. Antibodies to these rhesus antigens occur very rarely in nature, although there are some forms of naturally occurring anti-E.  The production of immune antibodies, most commonly anti-D, occurs after sensitisation by pregnancy or transfusion. It is for this reason that anti-D is injected into a rhesus-negative mother after trans-placental passage of fetal blood into the maternal circulation. This destroys any fetal rhesus positive red blood cells before the maternal immune system can respond.  Rh Factor It is called Rh factor, as it was earlier isolated in Rhesus monkey. This agglutinogen is present in more than 85% individuals and those having it are called Rh positive. It differs from agglutinogen A and B, since no corresponding agglutinin exists in plasma. However, if Rh+ blood is transfused into the Rh- negative recipient, antibodies will develop and they produce adverse reaction during subsequent transfusions.  It is therefore essential that in addition to blood groups, Rh factor should also be determined and Rh+ blood should not be transfused to a Rh- recipient, to avoid hazards during subsequent transfusion. Rh factor determination is done by observing agglutination of red cells with the anti D sera.  Rh Incompatibility Rh+ blood should not be given to Rh- recipient. This would result in the formation of Rh antibodies, which endanger future transfusion. If the mother of Rh- and the fetus is Rh+, during the first pregnancy the mothers plasma is sensitized. In the later pregnancies, the fetal RBC, would trigger the production of enormous Rh antibodies in the mother. They cross placental barrier and destroy the fetal RBC. This may result in still birth or the new born developing severe jaundice (Icterus gravis neonatorum).  The destruction of the fetal RBC can also give rise to the appearance of the erythroblasts in the blood leading to erythroblastosis fetalis. To prevent such Rh incompatibility the mother should be immunised with anti Rh antibodies.  M and N Factors In addition to blood groups mentioned earlier, two other agglutinogens have been identified in red cells. They have been named as M and N factors and they constitute three groups, i.e. M,N and MN. These agglutinogens are not antigenic and do not affect transfusion. However, they are of significance in the determination of paternity in medico-legal cases.  Blood Transfusion The transfusion of whole blood could be a life saving measure in haemorrhage, shock, severe anaemia and many other blood related disorders. Caution has to be exercised to avoid adverse affects of mismatched transfusion.  Precautions During Blood Transfusion Blood group of the donor and recipient should be determined. Direct cross matching of blood should be done. The donor should be healthy and not suffering from any diseases like hepatitis or sexually transmitted disease. The recent malady of AIDS makes it all the more essential. Transfusion should be given slowly under aseptic conditions.  Hazards of Incompatible Transfusion Agglutination Haemolysis Fever and Chill Jaundice, due to increased bile pigments resulting from RBC destruction Renal failure (Lower nephron nephrosis) Uraemia, coma and death  ANTICLOTTING MECHANISMS DR LWIINDI  Prevention of coagulation Plasma inhibitors Fibrinolysis Role of the endothelial cells  clotting cascade Stage 1: Formation of prothrombin activator. Stage 2: Conversion of prothrombin to thrombin. Stage 3: conversion of fibrinogen to fibrin  Plasma inhibitors Inhibitor Mol. Weight Action Plasma Conc. (kD) (mg/ml) Antithrombin 50 Antiserine 240 III protease 2- 70 Antiplasmin 70 antiplasma 2- 725 Antiprotease 2500 macroglobulin Protein c 56 Anti-factor 5 V and Viii  Antithrombin III: – Nonspecific protease inhibitors – Produced in liver and endothelial cells binds to serine proteases in the coagulation system, blocking their activity as clotting factors. This binding is facilitated by heparin, a naturally occurring anticoagulant that is a mixture of sulfated polysaccharides with molecular weights averaging 15,000–18,000. The clotting factors that are inhibited are the active forms of factors IX, X, XI, and XII.  Protein C: – Vitamin K-dependent protein – Is activated to activited protein C (aPC) by thrombin in presence of endothelial cell-derived cofactor thrombomodulin. – aPC inactivates FV and FVIII in presence of another vitamin K-dependent cofactor: protein S. – See next slide. Anticoagulation pathway  Plasmin (fibrinolysin) is the active component of the plasminogen (fibrinolytic) system. This enzyme lyses fibrin and fibrinogen, with the production of fibrinogen degradation products (FDP) that inhibit thrombin. Plasmin is formed from its inactive precursor, plasminogen, by the action of thrombin and tissue-type plasminogen activator (t-PA). It is also activated by urokinase-type plasminogen activator (u-PA). If the t-PA gene or the u-PA gene is knocked out in mice, some fibrin deposition occurs and clot lysis is slowed. However, when both are knocked out, spontaneous fibrin deposition is extensive.  tPA: – Released from vascular endothelial cells following injury; – Binds to fibrin and is consequently activated. Urokinase: – Produced as the precursor, prourokinase by epithelial cells lining excretory ducts. – Role: to activate the dissolution of fibrin clots. plasminogen activator-inhibitors: – PAI-1 and PAI-2  Heparin: – A polysaccharide produced in basophilic mast cells – Distributed in the pericapillary tissue. – Abundant in lung, heart, liver, muscle tissues. – Inhibit thrombin conversion. – Promote antithrombin III activity. Calcium ions precipitants: – Sodium citrate  Endothelial cells Endothelium produces several inhibitors of hemostasis: – Prostaglandin I2: secreted by endothelial cells and is a potent inhibitor of platelet aggregation. – Thrombomodulin: Enhances the activiation of protein C by thrombin and results in the inactivation of factor V and VIII. – Heparans: a heparin-like molecule, produced by endothelial cells. Increase the anticoagulant effect of antithrombin III. – Plasminogen activator: necessary for dissolution of fibrin clots, such as tPA.