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Blood and Hemostasis - Anatomy & Physiology

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  • Functions of Blood
    Transport of oxygen, nutrients, wastes, and hormones; Regulation of body temperature, pH, and fluid volume; Protection against blood loss and infection.
  • Major Components of Blood
    Blood consists of plasma (55%) and formed elements including erythrocytes (RBCs), leukocytes (WBCs), and platelets.
  • Physical Characteristics of Blood
    Viscous, opaque fluid with metallic taste; pH 7.35–7.45; volume ~5-6 L in males, 4-5 L in females; color varies with oxygen content.
  • Composition of Plasma
    About 90% water with dissolved solutes including electrolytes, plasma proteins (albumin, globulins, fibrinogen), nutrients, gases, hormones, and wastes.
  • Erythrocyte Structure
    Biconcave, anucleate cells ~7.5 μm diameter; filled with hemoglobin for oxygen and carbon dioxide transport.
  • Hemoglobin Structure
    Protein globin with four subunits (2 alpha, 2 beta) each bound to a heme group containing iron that binds oxygen.
  • Erythropoiesis
    Process of RBC production in red bone marrow from hematopoietic stem cells, regulated by erythropoietin (EPO).
  • Regulation of Erythropoiesis
    EPO released by kidneys in response to hypoxia; stimulates RBC production; testosterone enhances EPO production.
  • Dietary Requirements for Erythropoiesis
    Needs amino acids, lipids, carbohydrates, vitamin B12, folic acid, and iron for hemoglobin synthesis and DNA replication.
  • Life Span and Fate of RBCs
    Live 100-120 days; old RBCs broken down by spleen macrophages; iron recycled; heme degraded to bilirubin.
  • Anemia
    Condition with low oxygen-carrying capacity due to blood loss, decreased RBC production, or increased RBC destruction.
  • Sickle-Cell Anemia
    Genetic disorder with abnormal hemoglobin S causing RBCs to sickle, leading to vessel blockage and poor oxygen delivery.
  • Leukocytes (WBCs)
    Complete cells with nuclei; defend against infection; classified as granulocytes (neutrophils, eosinophils, basophils) and agranulocytes (lymphocytes, monocytes).
  • Neutrophils
    Most abundant WBCs; multilobed nucleus; phagocytize bacteria; granules contain enzymes and defensins.
  • Eosinophils
    Bilobed nucleus; red cytoplasmic granules; destroy parasitic worms; involved in allergy and asthma.
  • Basophils
    Rarest WBCs; U- or S-shaped nucleus; granules contain histamine and heparin; promote inflammation.
  • Lymphocytes
    Large nucleus with thin cytoplasm rim; key in immunity; T cells attack infected cells; B cells produce antibodies.
  • Monocytes
    Largest WBCs; kidney-shaped nucleus; differentiate into macrophages; phagocytize pathogens and activate lymphocytes.
  • Platelets
    Cell fragments from megakaryocytes; contain granules with clotting chemicals; form platelet plugs to stop bleeding.
  • Hemostasis Steps
    1) Vascular spasm (vasoconstriction), 2) Platelet plug formation, 3) Coagulation forming fibrin mesh clot.
  • Coagulation Pathways
    Intrinsic pathway triggered by blood contact with collagen; extrinsic pathway triggered by tissue factor; both activate factor X leading to thrombin formation.
  • Role of Thrombin
    Converts fibrinogen to fibrin; activates factor XIII to stabilize fibrin mesh; essential for clot formation.
  • Clot Retraction and Fibrinolysis
    Platelets contract to shrink clot; plasmin enzyme dissolves clot after repair is complete.
  • Factors Limiting Clot Growth
    Removal/dilution of clotting factors; anticoagulants like antithrombin III and heparin inhibit clotting to prevent excessive clot formation.
  • Blood Groups ABO
    Based on presence of A and/or B antigens on RBCs; antibodies in plasma react against absent antigens; type O is universal donor, AB universal recipient.
  • Rh Blood Group
    Presence (+) or absence (-) of D antigen; Rh- individuals form antibodies if exposed to Rh+ blood; important in transfusions and pregnancy.
  • Transfusion Reactions
    Agglutination and hemolysis of mismatched RBCs causing reduced oxygen delivery, vessel blockage, and kidney damage.
  • Leukemias
    Cancerous overproduction of abnormal WBCs; acute affects children, chronic affects adults; disrupt normal blood cell production.