Red blood cell (RBC) production (erythropoiesis) takes place in the bone marrow under the control of the hormone erythropoietin (EPO). Juxtaglomerular cells in the kidney produce erythropoietin in response to decreased oxygen delivery (as in anemia or hypoxia) or increased levels of androgens. In addition to erythropoietin, red blood cell production requires adequate supplies of substrates, mainly iron, vitamin B12, folate, and heme.
Anemia, a decrease in the number of red blood cells (RBCs), hemoglobin (Hb) content, or hematocrit (Hct), can result from decreased RBC production (erythropoiesis), increased RBC destruction, blood loss, or a combination of these factors. (See also Approach to the Patient with Anemia.)
At the end of their normal life span (about 120 days), red blood cells (RBCs) are removed from the circulation. Hemolysis is defined as premature destruction and hence a shortened RBC life span (< 120 days). Anemia results when bone marrow production can no longer compensate for the shortened RBC survival; this condition is termed uncompensated hemolytic anemia. If the marrow can compensate, the condition is termed compensated hemolytic anemia.
Eosinophils are granulocytes (white blood cells that contain granules in their cytoplasm) derived from the same progenitor cells as monocytes-macrophages, neutrophils, and basophils. They are a component of the innate immune system. Eosinophils have a variety of functions, including
Typical adults lose about 1 mg iron (Fe) per day in shed epidermal and gastrointestinal cells; menstruating females lose on average an additional 0.5 to 1 mg/day from menses. This iron loss is balanced by absorption of a portion of the 10 to 20 mg of iron in a typical US diet. Iron absorption is regulated based on the body's iron stores and is usually in balance with the body's needs. However, because there is no physiologic mechanism to remove iron from the body, iron absorbed in excess of bodily needs (or acquired through repeated transfusion) is deposited in tissues.
Leukemia is a malignant condition involving the excess production of immature or abnormal leukocytes, which eventually suppresses the production of normal blood cells and results in symptoms related to cytopenias.
Leukopenia is a reduction in the circulating white blood cell (WBC) count to < 4000/mcL (9/L). It is usually the consequence of a reduced number of circulating neutrophils, although a reduced number of lymphocytes, monocytes, eosinophils, or basophils may also contribute. Thus, immune function can be generally decreased.
Myeloproliferative neoplasms are clonal proliferations of bone marrow stem cells, which can manifest as an increased number of platelets, red blood cells (RBCs), or white blood cells (WBCs), alone or in combination, in the circulation and sometimes with fibrosis in the bone marrow and extramedullary hematopoiesis (cell production outside the marrow). Based on these abnormalities, they are classified as
Platelets are circulating cell fragments that function in the clotting system. Thrombopoietin helps control the number of circulating platelets by stimulating the bone marrow to produce megakaryocytes, which in turn shed platelets from their cytoplasm. Thrombopoietin is produced in the liver at a constant rate and its circulating level is determined by how much is bound to circulating platelets and possibly to bone marrow megakaryocytes and the extent to which circulating platelets are cleared. Platelets circulate for 7 to 10 days. About one third are always transiently sequestered in the spleen.
In healthy people, homeostatic balance exists between procoagulant (clotting) forces and anticoagulant and fibrinolytic forces. Numerous genetic, acquired, and environmental factors can tip the balance in favor of coagulation, leading to the pathologic formation of thrombi in veins (eg, deep venous thrombosis [DVT]), arteries (eg, myocardial infarction, ischemic stroke), or cardiac chambers. Thrombi can obstruct blood flow at the site of formation or detach and embolize to block a distant blood vessel (eg, pulmonary embolism, embolic stroke).
There has been a gradual decrease in overall transfusion due to patient blood management programs. The latest information shows the total components transfused in 2019 was about 15 million ( 1), down from about 16 million units of blood components transfused in 2017 in the US ( 2). Although transfusion is probably safer than ever, risk (and the public’s perception of risk) mandates informed consent whenever practical.
Many tumor cells produce antigens, which may be released in the bloodstream or remain on the cell surface. Any molecule capable of being recognized by the immune system is considered an antigen. Antigens have been identified in most of the human cancers, including Burkitt lymphoma, neuroblastoma, melanoma, osteosarcoma, renal cell cancer, breast cancer, prostate cancer, lung cancer, and colon cancer. A key role of the immune system is detection of these antigens to permit subsequent targeting for eradication. However, despite their foreign structure, the immune response to tumor antigens varies and is often insufficient to prevent tumor growth (see also Host Response to Tumors).