Lecture 4 – Hematology Hematology (Slide 2) 1. Hematology is the study of blood. 2. Hematocrit indicates the health of your blood. 3. Hematopoesis indicates the health of your blood as well as the ability of your tissues to produce new blood cells. 4. Hemostasis is the importance of vessels to contain your blood. The human circulatory system is a closed one in which all blood cells and plasma remain within vessels. 5. Rheology (study with hemodynamics) is the study of blood flow. 6. Blood is a tissue and may even be considered an organ. Its matrix is a fluid, not a semi-solid. What Is Hematocrit And How Is It Measured? (Slide 3, Fig 16.2) 1. Hematocrit refers to the percentage of a blood sample that contains blood cells. 2. A blood sample is placed in a centrifuge. This causes the blood cells to separate to the bottom of the tube, leaving blood plasma on the top. Between the two layers is a buffy coat, which contains leukocytes and platelets. 3. Normal blood contains 55-58% plasma, 42-45% erythrocytes (blood cells) and <1% buffy coat. 4. Women are more prone to anemia because they lose many RBCs during their menstrual cycle, and they never fully recover. Their hematocrit is slightly lower than that of men. Hematopoeis (Erythropoeisis), Differentiation, And Development Of RBCs, WBCs And Platelets (Slide 4, Figure 16.5) 1. Erythropoeisis, the production of new blood cells, starts with a hematopoietic (blood-forming) stem cell. 2. The hematopoeitic stem cell differentiates into myeloid stem cells or lymphoid stem cells. All lymphoid stem cells become lymphocytes, which enter the lymph system. 3. The myeloid stem cells differentiate to form all other cells in the circulatory system (erythrocytes, white cells and platelets). 4. There are many growth factors involved in the production of blood cells, such as colony stimulating factor (csf), interleukins (il) and leukotrienes (lk). Distribution (Partitioning) Of White Blood Cells (Slide 5, Table 16.2) Component Amount per microliter Diameter (micrometers) Anatomical Features Primary Function Erythrocytes 5,000,000 7-8 No nucleus, no organelles, biconcave disc Transport O2 and CO2 Leukocytes 4000 – 10,000 Defend body against pathogens Neutrophils 3000 – 7000 10-14 Multilobed nucleus; red and blue staining granules Phagocytosis of foreign material Eosinophils 100 – 400 10 – 14 Bilobed mucleus; red staining granules Kill parasites Basophils 20 – 50 10 – 12 Multilobed nucleu; blue staining granules Secrete chemical mediators in infmallmation and allergic reactions Monocytes 100 – 700 14 – 24 Large oval nucleus; no granules Phagocytosis: mature into macrophages in tissue Lymphocytes 1500 – 3000 5 – 17 Large nucleus; little cytoplasm; no granules B cells secrete antibodies. T cells secret cytokines that support immune response of other cells; secrete factors that kill infected or tumor cells. Platelets 150,000 – 450,000 2 – 4 Cytoplasmic fragments; granules Hemostasis Cellular Components Of The Blood (Slide 6, Fig 16.1) 1. Red blood cells form biconcave discs (donut-shaped indentations on both sides). 2. They are about 8 micrometers in diameter and, in the center, only 1 micrometer thick. 3. They have no nuclei. Their primary cellular component is hemoglobin molecules that are located near the perimeter of the cell. 4. They are shaped as they are in order to increase surface area. The hemoglobin is located near the surface so that it can readily take in O2 from the surrounding environment. 5. The white globs in the picture are activated platelets. Structure And Function Of Hemoglobin A (HBA) (Slide 7, Fig 16.3) 1. Hemoglobin is composed of four polypeptide chains, 2 α and 2 β chains. 2. Each polypeptide has an iron-containing subgroup called a heme group. This group has the ability to bind to O2 and carry it with the cell. The iron must be Fe2+, not Fe3+. 3. Each heme group can carry one O2 molecule, and since there are 4 heme groups per hemoglobin molecule, each hemoglobin molecule can carry 4 O2 molecules at one time. 4. The term “percent saturation” refers to the percent of RBC that are carrying 4 O2 molecules. 5. Oxygenated Hb is bright red while deoxygenated Hb is dark red. Hemoglobin can also carry CO2, H+ and CO. Anemia = A Decrease In The Capacity Of Blood To Carry Molecular Oxygen (Slide 8) 1. Iron-deficiency anemia – diet, excretion 2. Pernicious anemia – deficiency of vitamin B12 3. Anemic anemia – due to low circulating blood volume, perhaps due to a hemorrhage 4. Hemolytic anemia – malaria 5. Sickle cell anemia – biconcave shape of RBC is disrupted so O2 no longer binds. 6. Aplastic anemia – bone marrow defect 7. Renal anemia – kidney disease 8. Clinical/Laboratory Note: pulse oximetry and oxygen saturation a. Pulse Oximetry – non-invasive technique that measures changes in oxygenation of blood b. Oxygen Saturation – invasive technique that is more sophisticated and can measure more variables such as partial pressure; more reliable method of measuring oxygen levels in blood Pulse Oximetry Chart (Slide 9) 1. This chart shows that acetaminophen caused a large decrease in the percent saturation of O2. 2. It was collected using a pulse oximetry. Oxygen Saturation Chart (Slide 10) 1. This chart shows that acetaminophen caused no decrease percent saturation of O2. 2. It was collected using a blood gases pH analyzer. Summary And Conclusions (Slide 11) 1. Red Blood Cells are the designated mode of transportation for exchange of gases between whole blood and the tissues. 2. White Blood Cells are designed to combat invasions of the body by foreign entities and to dispose of senescent cells and cellular elements. 3. Platelets play an important regulatory role in maintaining our circulating blood volume (hence blood pressure, blood volume). Hemostasis And The Control Of Blood Loss (Slide 12) 1. Wound severs wall of blood vessels 2. Blood contact with extravascular tissue (anything on the other side of the endothelium) 3. Vasoconstriction occurs to reduce blood flow 4. Extravascular compression 5. Actions of platelets (thrombocytes), plugs 6. Formation of blood clots Hemostatic Role Of Circulating Platelets (Slide 13, Fig 16.6a) 1. The endothelium is a barrier between circulating blood and the extravascular space. 2. Platelets are fragments of megakaryocytes and are non-nucleated. 3. There are many proteins important in platelet plug formation. The most important is the von Willebrand factor (vWf). It is present in the plasma at all times but accumulates at the site of vessel damage. 4. Another important protein is thromboxane A2, or TXA2. This prostaglandin stimulates platelet aggregation as well as vasoconstriction. 5. Extravascular compressions also occur. This is based on intramural pressure, the pressure across the endothelium, between the interstitial fluid and the cellular fluid. During extracellular compressions, the interstitial pressure increases due to blood loss. Nonactivated Platelet (Slide 14) 1. Nonactivated platelets are disc-shaped, with transverse tubules running through them. 2. They have alpha granules, which contain molecules such as ADP, serotonin, epinephrine and other chemicals used for vasoconstriction and adhesion. They are also very sticky when activated. Mechanism of Platelet Activation And Adhesion (Slide 15) 1. The first step in platelet plug formation is platelet adhesion. When blood vessels become damaged, the blood within them comes in contact with subendothelial tissue. This causes vWf to bind to collagen fibers, upon which platelets then bind. Contact with vWf also activates the platelets, making them sticky and stimulating the secretion of certain products. 2. The second step in platelet plug formation is platelet aggregation. ADP stimulates morphological changes in the platelets that cause them to adhere to one another. These aggregated platelets release more ADP, causing more platelets to aggregate upon them. This forms a positive feedback loop. ADP also stimulates the release of thromoboxane A2 (TXA2). This is a prostaglandin that stimulates platelet aggregation and also causes vasoconstriction to slow down blood flow to the damaged area. Physiological Actions of Platelets (Slide 16) 1. When blood vessels are damaged, the blood contained within them is exposed to the subendothelium. 2. This causes vWf to bind to collagen fibers, and platelets to bind to vWf. 3. This causes platelet adhesion, activation and aggregation. Activated Platelets And The “Release” Action (Slide 17) 1. When platelets become activated, they change their morphology. They are no longer round, but have filapodia extending from them. 2. These filapodia have buds at their ends. When these buds contact other buds, they form a meshwork of filapodia to help create the clot. Physiological Process Of Forming Clots (Slide 18) 1. Platelets bind to fibrinogen molecules. 2. Many fibrinogen strands combine to form a fibrin. 3. Many fibrins combine to form a fibrin mesh. This is the polymerized form of fibrin. Fibrin Clot At The Site Of A Vascular Wound (Slide 19, Fig 16.7) 1. Once the fibrin mesh has formed, cells called fibroblasts penetrate through the fibrin. 2. These fibroblasts enlarge and divide within the meshwork. 3. These are the cells that fill in where the original damaged cells were located. Physiological Pathways Leading To The Formation Of Clots (Slide 20, Fig 16.8) 1. Both blood (intrinsic) and damaged tissue (extrinsic) have thrombolytic effects. 2. Inactive proteases are activated by catalysts. Inactive X is where the intrinsic and extrinsic pathways merge into one pathway. An active protease acts as the catalyst for the next step. 3. Thrombin is the activated form of prothrombin, a clotting factor. Thrombin turns inactive Factor XIII into activated Factor XIIIa. Thrombin acts on fibrinogen to make turn it into a loose network of fibrin strants. Active Factor XIIIa turns that loose fibrin meshwork into a stabilized fibrin meshwork. 4. INR is the international normalized ratio, a measure of health. It is the normalized ratio of prothrombin time, the amount of time it takes blood to clot. Anticoagulant Therapy (Slide 21) 1. Mechanism of Coumadin 2. Mechanism of Heparin 3. Mechanism of Aspirin 4. Your blood has a balance between coagulant and anticoagulant factors. If the blood viscosity gets too high, blood flow could be reduced, so anticoagulant factors need to be increased. If the blood gets too thin, your blood pressure could be reduced, so coagulant factors need to be increased. Coumadin’s Mechanism (Slide 22) 1. One method of coagulation is the Vitamin K-dependent conversion of inactive prozymogens to carboxylated prozymogens. Coumadin, or Warfarin, helps inhibit this pathway. 2. Once the prozymogen is carboxylated, Vitamin K is in the form of an epoxide and needs to be reduced using Vitamin K epoxide reductase. This enzyme turns the epoxide form into plain Vitamin K. Once Vitamin K is in its normal form, quinone, it needs to be reduced again. This time, it is reduced using Vitamin K quinone reductase. This reduced form of Vitamin K can cause the conversion of prozymogens to carboxylated prozymogens. 3. Coumadin acts to inhibit these two enzymes, so Vitamin K does not exist in its reduced form. Thus, it cannot convert inactive prozymogens into carboxylated prozymogens, and coagulation does not occur. Heparin’s Mechanism (Slide 23) 1. Heparin causes immediate anti-coagulation. 2. Thrombin is a protein that causes a blood clot using a fibrin mesh. 3. Antithrombin III is a molecule that contains binding sites for thrombin as well as Heparin. This binding usually occurs slowly. When heparin is present in the blood, thrombin binds more quickly to Antithrombin III. Once thrombin binds, Heparin is released from Antithrombin III, but thrombin remains attached. Heparin is now free to bind to other Antithrombin III molecules. 4. Once thrombin is bound to Antithrombin III, it cannot create a fibrin mesh to clot blood, and coagulation is again prevented. Aspirin’s Mechanism (Slide 24) 1. Aspirin is absorbed very quickly into the bloodstream and has an anti-platelet mechanism. 2. There is a pathway of three of four enzymes whose end result is the creation of thromboxane A2 and prostacycline, which activate platelets and vascular cells. 3. Aspirin acts to block the first enzyme in this pathway, called cyclooxygenase, by turning it into an inactive cyclooxygenase and thus stopping platelets from being created. Summary And Conclusions (Slide 25) 1. Vascular repair preserves blood volume. 2. Platelets (thrombocytes) are integral to repair. 3. Intrinsic system 4. Extrinsic system 5. Pro- and anti-coagulants are important to medicine and surgery. Cellular Components Of Blood (Slide 26) 1. Red blood cells are biconcave discs. 2. Scattered amongst the red blood cells are activated platelets. Physiological Formation Of The Platelet Plug (Slide 27) 1. Aggregated platelets release secretory products. a. ADP increases stickiness and has positive feedback. b. Serotonin causes vasoconstriction. c. Epinephrine causes vasoconstriction. d. Factors to regulate blood coagulation are also released. 2. Aggregated platelets also produce thromboxane A2, which has positive feedback. Mechanism Of Platelet Activation (Slide 28) 1. When vWf binds to collagen, it causes other proteins to bind to collagen as well. 2. This causes the formation of TXA2. 3. At the same time, ADP and fibrinogen are created as well. 4. Fibrinogen causes the collagen fiber to bind to other platelets and collagen fibers, creating a blood clot. Slides 29-32 are not important.