MLS Hematology Hematology|2023 LATEST UPDATE|GUARANTEED SUCCESS

Hematopoiesis Production and development of blood cells normally occurring in the bone marrow Yolk sac -the beginning of hematopoiesis -begins as early as the eighteenth day after fertilization Aorta-gonad-mesonephros (AGM) -the beginning of intraembryonic hematopoiesis -beings at about four weeks of gestation Where is the location of hematopoiesis during the fetal development at the third month? liver Bone Marrow -the blood-forming tissue located between the trabeculae of spongy bone -location for formation and maturation of blood cells Two major departments of the bone marrow -vascular compartment -endosteal compartment Vascular Compartment composed of the bone marrow arteries and veins, stromal cells, and hematopoietic cells Endosteal Compartment the primary site of bone remodeling but also contains hematopoietic stem cells (HSCs) Bone Marrow Hyperplasia -an excessive proliferation of normal cells -occurs with all conditions of increased of ineffective hematopoiesis Extramedullary hematopoiesis the formation and development of blood cells at a site other than the bone marrow Bone marrow is the site of cell development for ____________. -myeloid cells -erythroid cells -megakaryocytic cells (mother cells) -lymphoid cells What are other sites of cell development for lymphoid cells besides the bone marrow? -thymus -spleen -lymph nodes Bone Marrow Hypoplasia -hematopoietic tissue becomes inactive -fat cells increase to offer a cushion for the marrow What are some causes for bone marrow hypoplasia? Environmental factors -chemicals -toxins Genetically determined Blood Cell Passage blood cells migrate from bone marrow to the vascular space What causes extramedullary hematopoiesis? hyperplasia of the marrow does not meet the physiologic needs of the tissues Where does extramedullary hematopoiesis usually occur? -liver -spleen Thymus lymphopoietic organ -bilobular organ with an outer cortex and central medulla -supplies immunocompetent T lymphocytes to T-dependent areas What is inside the cortex of the thymus? -small lymphocytes (thymocytes) -cortical epithelial cells -few macrophages What is inside the medulla of the thymus? -mature thymocytes -medullary epithelial cells -dendritic cells -macrophages Hypersplenism spleen may become enlarged -happens through the exaggeration of its normal activities of filtering and phagocytosis What does hypersplenism cause? -anemia -leukopenia (decreased WBC) -thrombocytopenia (decreased platelets) -combinations of cytopenias (decreased cells) Splenectomy removal of the spleen Splenectomy's effect of the lifespan of RBCs stays the same Kupffer cells -special macrophages that line the sinusoids -performs similar filtering functions as the phagocytes in the splenic cords and marginal zones What does acquired hyposplenism represent? a complication in sickle cell anemia What does the lymphatic system consists of? -lymph nodes -lymphatic vessels What is lymph formed from? -blood fluid that escapes into connective tissues Lymphatic vessels -carry lymph toward the ducts near the neck where lymph enters the blood -drains into the left and right lymphatic ducts Lymph nodes -bean-shaped and occurs in groups or chains along the larger lymphatic vessels -contain an outer area called the cortex and an inner area called the medulla Function of lymph nodes -acts as a filter removing foreign particles from lymph by dendritic cells and macrophages -provides immune defense against pathogens in virtually all tissues What do dendritic cells stimulate? T and B cells How do stimulated B cells move? -from the germinal centers to the medulla -resides as plasma cells and secrete antibody Mucosa-Associated Lymphoid Tissue (MALT) -collection of loosely organized lymphocytes Where is Mucosa-Associated Lymphoid Tissue (MALT) located? -throughout the body in association with mucosal surfaces -Peyer's patches in the intestine (lymphoid aggregates) -tonsils and appendix Mucosa-Associated Lymphoid Tissue (MALT) Function -trap antigens -rapidly initiate immune responses Lymphadenopathy -enlargement of the lymph nodes by expansion of the tissue within the node Causes of lymphadenopathy -inflammation of the lymph node -prolonged immune response to infection agents -malignant transformation of lymphocytes or macrophages -metastatic tumors that originate in extranodal sites Circulating Cells -Mature -Short life span -Incapable of mitosis -Described as terminally differentiated Which circulating cells are capable of mitosis? lymphocytes Terminally Differentiated -must be replaced by less differentiated, mitotically active precursor cells Hematopoietic Precursor Cells -located primarily in the bone marrow in adults -Consist of a hierarchy of cells -Enormous proliferation potential