Blood is a specialized body fluid that delivers necessary substances to the tissues and transports waste products away from the tissues. The main components of blood are plasma, red blood cells, white blood cells, and platelets. Blood is produced through hematopoiesis, a process where stem cells in the bone marrow mature into the various blood cell types.
Red Blood Cells
Red blood cells, also called erythrocytes, are the most abundant cell type found in blood. Their main function is to transport oxygen from the lungs to tissues and carbon dioxide from tissues back to the lungs. Red blood cells lack a cell nucleus and other organelles, which allows maximum space for the oxygen-carrying protein Hematology. Anemia is a condition where the number of red blood cells or their oxygen-carrying capacity is reduced. This can result from blood loss, disturbances in red blood cell production or increased red blood cell destruction.
White Blood Cells
White blood cells, or leukocytes, are essential components of the immune system. The main types of white blood cells are granulocytes like neutrophils, eosinophils and basophils, and agranulocytes like lymphocytes and monocytes. Neutrophils are the most abundant white blood cell and act as the body’s first line of defense against invading microbes. Lymphocytes include T cells and B cells that play major roles in adaptive immunity through cell-mediated and humoral immunity respectively. Monocytes differentiate into macrophages that engulf and digest pathogens and cellular debris. Leukemia involves the abnormal proliferation of white blood cells in the bone marrow and blood.
Platelets
Platelets, sometimes called thrombocytes, are small cytoplasmic fragments that help form blood clots and stop bleeding. When a blood vessel is damaged, platelets adhere to the site of injury and aggregate to form a platelet plug. They also secrete factors that activate the clotting cascade, leading to fibrin formation and clot stabilization. Thrombocytopenia refers to a low platelet count, increasing the risk of excessive bleeding. Thrombocytosis is a high platelet count, often associated with inflammation or malignancy. Platelets have a short lifespan of only 7-10 days in circulation.
Bone Marrow
The bones of adults contain yellow and red bone marrow, where hematopoiesis actively occurs only in the red marrow. In infants and children, more bones contain red marrow for increased blood cell production. The bone marrow contains hematopoietic stem cells that can differentiate into the various blood cell precursors and mature blood cell types through a complex series of regulated stages. Stem cell numbers and activity decline with age, accompanied by a shift toward more fatty yellow marrow. Diseases affecting the bone marrow include aplastic anemia, myelofibrosis and myelodysplastic syndromes. Cancer therapies often damage the bone marrow, necessitating stem cell transplantation.
Hematological Malignancies
Cancer can start in the bone marrow with malignant transformation of hematopoietic stem or progenitor cells. Leukemia is a cancer of the white blood cells characterized by aberrant growth and accumulation of abnormal blast cells in the bone marrow and blood. The main types are acute myeloid leukemia, acute lymphoblastic leukemia, chronic myeloid leukemia and chronic lymphocytic leukemia. Lymphoma involves cancer of the lymphocytes, with non-Hodgkin’s lymphoma more common than Hodgkin’s lymphoma. Multiple myeloma is a cancer arising from plasma cells within the bone marrow. These hematological malignancies can be challenging to diagnose and treat due to effects on normal blood cell production. Stem cell transplantation and targeted therapies have improved treatment outcomes in recent years.
Diagnostic Evaluation and Clinical Applications
A complete blood count is among the most common blood tests done to evaluate the number and morphology of various blood cell types. A manual or automated cell counter provides a detailed hemogram report. Peripheral blood smears allow visual examination of blood cells under a microscope and detection of abnormal morphologies. Additional specialized hematological tests include coagulation studies, blood typing,stem cell enumeration and cytokine/immune marker levels. Bone marrow aspiration and biopsy help diagnose bone marrow disorders and obtain samples for cytogenetic/molecular testing in leukemia/lymphoma. Hematology has wide clinical applications like managing anemia, bleeding/clotting disorders, transfusion support, bone marrow failure states and hematological cancers. Point-of-care testing allows rapid evaluation of blood counts in emergency settings. Use of blood components and targeted therapies is revolutionizing the care of hematological patients.
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