Chapter 16 Blood

About this Chapter Composition of Blood Plasma make up and roles Various cell types, origin and roles Red blood cells, hemoglobin & iron metabolism How coagulation works

Blood Components: Plasma Transports Solutes Water, ions, trace elements Gasses: O2 & CO2 Organic Molecules Glucose N–wastes Proteins Antibodies Hormones

Composition of Blood 55% of our blood's volume is made up of plasma Plasma also contains blood clotting factors, sugars, lipids, vitamins, minerals, hormones, enzymes and antibodies One group detected 490 separate proteins in serum Serum albumin accounts for ~55% of blood proteins, globulins make up ~38% and fibrinogen comprises ~7% The remainder of plasma proteins (1%) consists of regulatory proteins such as enzymes, proenzymes and hormones. All blood proteins are synthesized in liver except for the gamma globulins. Plasma contains many thousands of distinct lipid molecular species that fall into six main categories including fatty acyls, glycerolipids, glycerophospholipids, sphingolipids, sterols, and prenols The cellular components of blood include red corpuscles (erythrocytes), platelets (thrombocytes), and five types of white corpuscles (leukocytes)

Blood Components: Plasma Transports Solutes Figure 16-1: Composition of blood

Blood Components: "Blood Count" – % of Each Component Figure 16-2: The blood count

Blood Components: Cells Erythrocytes Red Blood Cells (RBC) O2 & CO2 transport White Blood Cells (WBC) Immune defense Phagocytosis Platelets: clotting

Blood Components: Cells Figure 16-1: Composition of blood

Hematopoiesis: Blood Cell Formation Mostly in bone marrow from stem cells Rate regulated by cytokines & growth factors

Hematopoiesis: Blood Cell Formation Figure 16-3: Hematopoiesis

Focus on RBCs: Lose their nucleus Cytoskeleton – shape Hemoglobin Binds O2 in heme group Binds some CO2 on globulin

Focus on RBCs: Figure 16-5c: Bone marrow

Figure 16-7a, b: Bone marrow Focus on RBCs: Figure 16-7a, b: Bone marrow

Iron Metabolism: Key to Hemoglobin O2 Transport Figure 16-8: Iron metabolism

Some Diseases of RBCs and O2 Transport Table 16-3: Causes of Anemia

Blood Components: Platelets Coagulate, form plug, prevent blood loss Formed by fragmentation from megakaryoctyes Figure 16-10c: Megakaryocytes and platelets

Overview of Hemostasis: Clot Formation & Vessel Repair Figure 16-11: Overview of hemostasis and tissue repair

Hemostasis: Vasoconstriction & Plug Formation Platelet activation Multiple factors Positive feedback Aggregation Loose plug

Hemostasis: Vasoconstriction & Plug Formation Figure 16-12: Platelet plug formation

Hemostasis involves the interaction of: Vascular Endothelium Platelets Coagulation Factors and Fibrinolytic Proteins

Hemostasis has 2 main functions: Induce a rapid & localized hemostatic plug at the site of vascular injury (clot formation) Maintain Blood in a fluid, clot-free state after the injury is healed (clot dissolution)

Endothelium vs. subendothelium Endothelial cells – line the vessels. Are thromboresistant in nature. They express thrombomodulin and heparin sulfate to keep inappropriate thrombi from forming. They also release tissue plasminogen activator and urokinase in the presence of thrombin shut off the coagulation cascade in the presence of IIa (thombin). Subendothelium – beneath the endothelium. Are thrombogenic in nature. Express von Willebrand Factor (vWF), collagen, and tissue factor to kick off the coagulation cascade. Subendothelium Endothelium Source: http://facstaff.gpc.edu/~jaliff/vein1.gif Beginning Review Quiz

Primary Hemostasis Injury Endothelial Cells Exposure of thrombogenic surface (subendothelial extracellular matrix)

Platelets adhere and get activated Change shape Release secretory granules (e.g. ADP, TXA2) Attract other platelets and Aggregate Hemostatic plug or Primary Platelet Plug

Secondary Hemostasis Fibrin is required to stabilize the primary platelet plug Fibrin is formed by two coagulation pathways i.e. Extrinsic & Intrinsic Extrinsic Pathway is initiated when Tissue Factor (III) present in damaged organ comes in contact with Blood Intrinsic Pathway is initiated when Factor XII binds to a negatively charged “foreign” surface exposed to Blood

Hemostasis: Coagulation & Clot Stabilization Prothrombin Ca++ Fibrinogen Fibrin Polymerization Figure 16-13: The coagulation cascade

Clinical Significance of Intrinsic and Extrinsic Pathways Two pathways lead to the formation of a fibrin clot: the intrinsic and extrinsic pathway. Although they are initiated by distinct mechanisms, the two converge on a common pathway that leads to clot formation. Both pathways are complex and involve numerous different proteins termed clotting factors. Fibrin clot formation in response to tissue injury is the most clinically relevant event of hemostasis under normal physiological conditions. This process is the result of the activation of the extrinsic pathway. The formation of a red thrombus or a clot in response to an abnormal vessel wall in the absence of tissue injury is the result of the intrinsic pathway. The intrinsic pathway has low significance under normal physiological conditions. Most significant clinically is the activation of the intrinsic pathway by contact of the vessel wall with lipoprotein particles, VLDLs and chylomicrons. This process clearly demonstrates the role of hyperlipidemia in the generation of atherosclerosis. The intrinsic pathway can also be activated by vessel wall contact with bacteria.

PT and aPTT testing PT (Prothrombin Time) test is done for deficiency of factors of extrinsic pathway aPTT (activated Partial Thromboplastin Time) test is done for deficiency of factors of Intrinsic pathway

Pharmacologic considerations PT (prothombin time) – measures the function of the extrinsic pathway and the common pathway. Extended by warfarin. aPTT (partial thomboplastin time) – measures the function of the intrinsic pathway and the common pathway. In vitro extension by heparin. Vitamin-K dependent coagulation components – Factors X, IX, VII, II, proteins C, S (mnemonic: 1972 [10, 9, 7, 2]). Warfarin (Coumadin) – inhibits vitamin-K reductase and effective levels of of vitamin-K dependent coagulation components. Will extend the PT. Heparin (drug) – purified from animals. Increases the activity of ATIII. Will increase the aPTT in vitro. Thromboxane A2 (TXA2) – synthesis of TXA2 is initiated by activated platelets. TXA2 increases platelet activation and aggregation. Its synthesis is inhibited by aspirin. Beginning Review Quiz

Overview of Traditional and Newer Antithrombotic Agents Baron TH et al. N Engl J Med 2013;368:2113-2124.

Constitutive inhibition secondary hemostasis Extrinsic pathway Intrinsic pathway anticoagulation Constitutive inhibition Common pathway primary hemostasis Antifibrinolysis Thrombin INJURY! Platelet Plug Fibrin Fibrin clot

Dissolving the Clot and Anticoagulants Bleeding stopped Vessel repair Plasmin Fibrinolysis Clot dissolved

Dissolving the Clot and Anticoagulants Figure 16-14: Coagulation and fibrinolysis

Fibrinolysis As soon as the injury is healed clot dissolution starts, to restore the normal flow of Blood Plasminogen is converted to the active form Plasmin by 2 distinct Plasminogen Activators (PAs): tissue plasminogen activator (t-PA) from injured endothelial cells Urokinase from Kidney endothelial cells and plasma

Coagulation and Disease Hemophilia Cardiovascular Diseases Key problem – clots block undamaged blood vessels Anticoagulants prevent coagulation Keep platelets from adhering Prevent fibrin coagulation "Clot Busters": Prevent further clotting Speed fibrinolysis Limit tissue damage (heart, brain…)

DIC (Disseminated Intravascular Coagulation) J. Mitra & Co. Ltd. DIC (Disseminated Intravascular Coagulation) Massive Injury or Sepsis Massive release of Tissue Factor III Excessive Activation of Thrombin Coagulation becomes systemic Annual Sales Conference 2005 (South & West)

High consumption of Platelets, coagulation factors Over production of fibrin clot Fibrin clot “disseminates” or spreads throughout the microcirculation Obstructing the blood flow to capillaries, smaller vessels

Once again release of Tissue Factor Lack of blood supply leads to tissue injury (decreased oxygenation, organ infarction & necrosis) Once again release of Tissue Factor Second time coagulation activation More consumption of coagulation factors and platelets

Summary Blood is about 50% plasma, water solvent & solutes: ions, elements, gasses, proteins, wastes & nutrients White blood cells function in internal defense Iron in hemoglobin is key to RBC transport of O2 Platelet activation initiates clot formation Clotting prevents blood loss but is a problem in cardiovascular disease