Hematologic System: Structure, Function, Development - PDF

The Hematologic System: Structure, Function, and Development Overview The hematologic system plays a pivotal role in the human body, encompassing the production, regulation, and function of blood cells and the mechanisms of blood clotting. This detailed examination covers cellular differentiation, t...

The Hematologic System: Structure, Function, and Development Overview The hematologic system plays a pivotal role in the human body, encompassing the production, regulation, and function of blood cells and the mechanisms of blood clotting. This detailed examination covers cellular differentiation, the life cycle of erythrocytes, leukocytes, and platelets, and the intricacies of the blood coagulation system, providing a comprehensive understanding of hematology. Composition of Blood Key Components ​ Plasma: ○​ Functions: Carries nutrients, waste products, and hormones; involved in immune responses and blood clotting. ○​ Constituents: Composed of water (91%) and solutes (9%), including plasma proteins such as albumin, globulins, and clotting factors/proteins like fibrinogen. ​ Cellular Components: ○​ Erythrocytes (Red Blood Cells): ​ Most abundant cells in the blood (100-120 day life cycle). ​ Primary function is tissue oxygenation. ○​ Leukocytes (White Blood Cells): ​ Defend against infection; remove debris through phagocytosis. ​ Categorized into granulocytes and agranulocytes. ○​ Platelets (Thrombocytes): ​ Not true cells but cytoplasmic fragments. ​ Essential for blood coagulation and control of bleeding. Hematopoiesis: Blood Cell Production Hematopoietic Cells and Niches ​ Bone Marrow: ○​ Red (active) marrow is hematopoietic, found mainly in flat bones of adults. ○​ Yellow (inactive) marrow found in other bones.  ○​ Hematopoietic Stem Cells (HSCs): Develop into all blood cell types and are maintained by mesenchymal stem cells (MSCs). Differentiation ​ Multipotent Stem Cells: Differentiate into various blood cell types, including progenitor cells which further specialize under the influence of colony-stimulating factors (CSFs) like erythropoietin. Specific Pathways ​ Erythropoiesis: Red blood cell formation, involving stages from progenitor cell to erythrocyte, regulated by erythropoietin responding to tissue hypoxia. ​ Myelopoiesis: Development of granulocytes and monocytes in bone marrow, with lymphopoiesis pertaining to lymphocyte development in lymphoid organs. ​ Thrombopoiesis: Platelet production from megakaryocytes, regulated by thrombopoietin, with platelets being functional for about 10 days. Hemostasis: Blood Clotting Mechanism Sequence of Hemostasis 1.​ Vascular Injury: Causes vasoconstriction. 2.​ Platelet Plug Formation: Platelets adhere to injury site. 3.​ Coagulation Cascade: Formation of fibrin clot through intrinsic and extrinsic pathways. Components ​ Blood Vessels: Endothelial cells produce vasodilators like nitric oxide and prostacyclin under normal conditions. Injury exposes subendothelial matrix leading to platelet activation. ​ Platelets: Key roles include regulating blood flow, forming platelet plugs, and activating coagulation cascades. ​ Clotting Factors: Proteins that facilitate blood stabilization through fibrin formation, working via intrinsic and extrinsic pathways. Regulation and Resolution ​ Control Mechanisms: Include thrombin inhibitors, tissue factor pathway inhibitors, and protein C to degrade activated clotting factors. ​ Clot Retraction and Lysis: Final stages where fibrin strands tighten and the clot is lysed via the fibrinolytic system involving plasminogen and plasmin. Pediatrics and Aging in Hematology Pediatrics ​ Blood Cell Counts: Increased at birth due to the trauma of birth and cutting the umbilical cord, with notable risks such as impaired phagocytosis and bacterial infections compared to adults. Aging ​ Erythrocyte Turnover: Normal life span but slower replacement due to factors like iron deficiency. ​ Lymphocyte Function: Decreases with age, affecting the responsiveness of the humoral immune system. Introduction Hematologic disorders encompass a wide range of conditions affecting the blood and its components. This guide offers an in-depth look at various anemia types, platelet disorders, coagulation abnormalities, myeloproliferative disorders, and lymphomas, with a particular focus on their causes, manifestations, and treatments. Anemia Classification Anemia is characterized by a reduction in the total number of erythrocytes or the quantity/quality of hemoglobin, resulting in hypoxemia. It can be classified by: ​ Size (cytic): Macrocytic, Microcytic, Normocytic ​ Hemoglobin Content (chromic): Normochromic, Hypochromic Clinical Manifestations ​ Fatigue ​ Weakness ​ Dyspnea ​ Pallor Macrocytic Anemias Pernicious Anemia  ​ Cause: Lack of intrinsic factor needed for vitamin B12 absorption. ​ Symptoms: ○​ Weakness, fatigue, paresthesias ○​ Loss of appetite, weight loss ○​ Abdominal pain, sore tongue ○​ Neurologic symptoms ​ Treatment: Lifelong vitamin B12 replacement Folate Deficiency Anemia ​ Cause: Dietary deficiency; human dependence on dietary folate intake. ​ Symptoms: ○​ Fatigue, weakness ○​ Similar to pernicious anemia but without neurologic symptoms ​ Treatment: Daily oral folate administration Microcytic-Hypochromic Anemias Iron Deficiency Anemia ​ Cause: Dietary deficiency, chronic blood loss, impaired absorption. ​ Symptoms: ○​ Fatigue, weakness ○​ Pale earlobes, palms ○​ Koilonychia (spoon-shaped nails), Cheilosis, Stomatitis ​ Treatment: Iron supplementation and addressing underlying cause Anemia of Chronic Disease ​ Cause: Chronic illness or inflammation resulting in decreased erythropoiesis. ​ Symptoms: Similar to iron deficiency anemia but related to underlying chronic condition ​ Treatment: Manage underlying disease, possible erythropoietin therapy Thrombocytopenia and Thrombocythemia Thrombocytopenia ​ Definition: Platelet count