Medical Terminology: The Hematologic System

1. What is The Hematologic System?
The hematologic system refers to the blood and blood-forming organs. The formation of red blood cells (RBCs), white blood cells (WBCs), and platelets begins in the bone marrow. Stem cells are produced in the bone marrow. Initially, these cells are not differentiated and may become RBCs, WBCs, or platelets. In the next stage of development, the stem cell becomes committed to a particular precursor cell, to become either a myeloid or lymphoid type of cell, and differentiates into a particular cell type when in the presence of a specific growth factor.
The spleen is found in the left upper quadrant of the abdomen. The spleen filters whole blood. It removes old and imperfect WBCs, lymphocytes and macrophages, and RBCs. The spleen also breaks down hemoglobin and stores of RBCs and platelets.
The liver is found in the right upper quadrant of the abdomen and is the main production site for many of the clotting factors, including prothrombin. Normal liver function is important for vitamin K production in the intestinal tract. Vitamin K is necessary for clotting factors VII, IX, X, and prothrombin.

2. Anemia
A low hemoglobin or RBC count results in decreased oxygen-carrying capability of the blood. This may be because of blood loss, damage to the RBCs due to altered hemoglobin or destruction (hemolysis), nutritional deficiency (iron, vitamin B12, folic acid), lack of RBC production, or bone marrow failure. Some patients have a family history of anemia caused by genetic transmission, such as thalassemia or sickle cell.

3. Aplastic Anemia (Pancytopenia)
The bone marrow stops producing a sufficient amount of RBCs, WBCs, and platelets, thereby increasing the risk of infection and hemorrhage. The red cells remaining in circulation are normal in size and color. This may be because of chemical exposure, high-dose radiation exposure, or exposure to toxins. Cancer treatments such as radiation therapy and chemotherapeutic agents may suppress bone marrow function, which results in anemia (low RBC), thrombocytopenia (low platelets), and leukopenia (low WBC). The cause may also be unknown or idiopathic.

4. Iron Deficiency Anemia
A lower-than-normal amount of iron in blood serum results in decreased formation of hemoglobin and a decreased ability for the blood to carry oxygen. Iron stores are typically depleted first, followed by serum iron levels. Iron deficiency may be a result of blood loss, dietary deficiency, or increased demand because of pregnancy or lactation. As RBCs age, the body breaks them down and the iron is released. This iron is reused for the production of new blood cells. A small amount of iron is lost daily through the gastrointestinal tract, necessitating dietary replacement. When RBCs are produced without a sufficient amount of iron, the cells are smaller and paler than usual.

5. Pernicious Anemia
The body is unable to absorb vitamin B12, which is needed to make RBCs, resulting in a decreased RBC count. More common in people of northern European descent, the anemia typically develops in adulthood. The intrinsic factor is normally secreted by the parietal cells of the gastric mucosa and is necessary to allow intestinal absorption of vitamin B12. Destruction of the gastric mucosa because of an autoimmune response results in loss of parietal cells within the stomach. The ability of vitamin B12. to bind with intrinsic factor is lost, decreasing the amount that is absorbed. Typical onset is between the ages of 40. and 60.

6. Disseminated Intravascular Coagulation (DIC)
Blood coagulates through the entire body within the vascular compartment. This depletes platelets and the body’s ability to coagulate, resulting in an increased risk of hemorrhage. It occurs as a complication of some other condition. The coagulation sequence is activated, causing many microthrombi to develop throughout the body. The clots that form are the result of coagulation proteins and platelets, resulting in the risk of bleeding or severe hemorrhage. It is often caused by obstetric complications, post trauma, sepsis, cancer, or shock.

7. Hemophilia
The patient is missing a coagulation factor that is essential for normal blood clotting and as a result, the blood does not clot when the patient bleeds. It is an X-linked recessive inherited disorder, passed on so that it presents symptoms in males, and rarely in females. Hemophilia A is the result of missing clotting factor VIII. Hemophilia B is the result of missing clotting factor IX and is also known as Christmas disease.

8. Leukemia
Replacement of bone marrow by abnormal cells results in unregulated proliferation of immature WBCs entering the circulatory system. These leukemic cells may also enter the liver, spleen, or lymph nodes, causing these areas to enlarge.
Leukemia is classified according to the type of cell from which it is derived, lymphocytic or myelocytic, and as either acute or chronic. Lymphocytic leukemias involve immature lymphocytes originating in the bone marrow and typically infiltrate the spleen, lymph nodes, or central nervous system. Myelogenous or myelocytic leukemia involves the myeloid stem cells in the bone marrow and interferes with the maturation of all blood cell types (granulocytes, erythrocytes, thrombocytes).
The exact cause of leukemia is unknown. There is a higher incidence in people who have been exposed to high levels of radiation, have had exposure to benzene, or have a history of aggressive chemotherapy for a different type of cancer. There may be a genetic predisposition to develop acute leukemia. Patients with Down’s syndrome, Fanconi’s anemia, or a family history of leukemia also have a higher-than-average incidence of this disease.

9. Multiple Myeloma
A malignancy of the plasma cells causes an excessive amount of plasma cells in the bone marrow. Masses within the bone marrow cause destructive lesions in the bone. Normal bone marrow function is reduced as the abnormal plasma cells continue to grow. Immune function is diminished and the patient develops anemia. The disease typically affects older adults.

10. Polycythemia Vera
Polycythemia vera is a myeloproliferative disorder that results in an overproduction of blood cells and a thickening of blood. The hallmarks of polycythemia vera include excessive production of RBCs, WBCs, and platelets. The excess of cells present in the blood causes problems with the flow of blood through vessels, especially the smaller ones. There is an increase in peripheral vascular resistance causing increased pressure, and vascular stasis in the smaller vessels, potentially causing thrombosis or tissue hypoxia. Organ damage may result because of these changes.

11. Sickle Cell Anemia
This is an autosomal recessive disorder in which an abnormal gene causes damage to the RBC membrane. The abnormal hemoglobin within the RBC is called hemoglobin S. Dehydration or drying of the RBC makes it more vulnerable to sickling (forming a crescent-like shape), as do hypoxemia and acidosis. Hemolytic anemia results as RBCs are destroyed because of the damage to the outer membrane. The sickled cells can also clump together, causing difficulty getting through the smaller vessels.

12. Deep Vein Thrombosis (DVT)
Thrombophlebitis, or the formation of a clot within the vein, commonly occurs within the deep veins in the legs, and may also occur in the arms. Initially platelets and white cells clump together, sticking to the inside of the vessel wall. As blood flows over the area, other cells may deposit on the area, making the thrombus larger. Compression of blood flow that increases the venous pressure or sluggishness of the blood flow can increase the risk of clot formation. Immobility, obesity, or hormonal changes such as pregnancy can all contribute to increased risk.

13. Idiopathic Thrombocytopenic Purpura (ITP)
Idiopathic thrombocytopenic purpura (ITP) is an autoimmune disorder in which antibodies are developed in the patient’s own platelets. Antibodies attach to the platelets and macrophages within the spleen. The body destroys the platelets within the spleen. ITP is typically more common in women and becomes chronic in adults who are in early to mid-adulthood.

14. Bone Marrow Biopsy
Bone marrow biopsy is the removal of bone marrow by needle or aspiration to determine blood cell formation.

Basic Questions
Hematologic System

1. What are stem cells?
Stem cells are produced in the bone marrow. Initially, these cells are not differentiated and may become RBCs, WBCs, or platelets. In the next stage of development, the stem cell becomes committed to a particular precursor cell, to become either a myeloid or lymphoid type of cell and will differentiate into a particular cell type when in the presence of a specific growth factor.

2. What is the function of the spleen?
The spleen filters whole blood. It removes old and imperfect WBCs, lymphocytes and macrophages, and RBCs. The spleen also breaks down hemoglobin and stores of RBCs and platelets.

3. What is anemia?
A low hemoglobin or RBC count results in decreased oxygen carrying capability of the blood.

4. What causes anemia?
This may be caused by blood loss, damage to RBCs resulting from altered hemoglobin or destruction (hemolysis), nutritional deficiency (iron, vitamin B12, folic acid), lack of RBC production, or bone marrow failure. Some patients have a family history of anemia caused by genetic transmission.

5. What is aplastic anemia?
The bone marrow stops producing a sufficient amount of RBCs, WBCs, and platelets, thereby increasing the risk of infection and hemorrhage.

6. What is a common cause of aplastic anemia?
Cancer treatments are a common cause of aplastic anemia.

7. What is iron deficiency anemia?
A lower-than-normal amount of iron in blood serum results in decreased formation of hemoglobin and a decreased ability for the blood to carry oxygen. Iron stores are typically depleted first, followed by serum iron levels.

8. What causes iron deficiency?
Iron deficiency may be caused by blood loss, dietary deficiency, or increased demand because of pregnancy or lactation.

9. Where does the body get a large amount of iron?
As RBCs age, the body breaks them down and the iron is released. This iron is reused for the production of new blood cells. A small amount of iron is lost daily through the gastrointestinal tract, necessitating dietary replacement.

10. What is a pernicious anemia?
The body is unable to absorb vitamin B12, which is needed to make RBCs, resulting in a decreased RBC count.

11. What enables the body to absorb vitamin B12?
The intrinsic factor is normally secreted by the parietal cells of the gastric mucosa and is necessary to allow intestinal absorption of vitamin B12.

12. What is a common cause of pernicious anemia?
Destruction of the gastric mucosa because of an autoimmune response results in loss of parietal cells within the stomach.

13. What is disseminated intravascular coagulation (DIC)?
Blood coagulates through the entire body within the vascular compartment. This depletes platelets and the body’s ability to coagulate, resulting in an increased risk of hemorrhage.

14. What is the cause of disseminated intravascular coagulation?
DIC is often caused by obstetric complications, post trauma, sepsis, cancer, or shock.

15. What is hemophilia?
The patient is missing a coagulation factor that is essential for normal blood clotting and as a result, the blood does not clot when the patient bleeds.

16. What is leukemia?
Replacement of bone marrow by abnormal cells results in unregulated proliferation of immature WBCs entering the circulatory system. These leukemic cells may also enter the liver, spleen, or lymph nodes, causing these areas to enlarge.

17. What is myelocytic leukemia?
Myelogenous or myelocytic leukemia involves the myeloid stem cells in the bone marrow and interferes with the maturation of all blood cell types.

18. What are lymphocytic leukemias?
Lymphocytic leukemias involve immature lymphocytes originating in the bone marrow and typically infiltrate the spleen, lymph nodes, or central nervous system.

19. How is leukemia classified?
Leukemia is classified according to the type of cell it is derived from, lymphocytic or myelocytic, and as either acute or chronic.

20. What is the exact cause of leukemia?
The exact cause of leukemia is unknown.

21. What is multiple myeloma?
A malignancy of the plasma cells causes an excessive amount of plasma cells in the bone marrow. Masses within the bone marrow cause destructive lesions in the bone. Normal bone marrow function is reduced as the abnormal plasma cells continue to grow. Immune function is diminished and the patient develops anemia.

22. What is polycythemia vera?
Polycythemia vera is a myeloproliferative disorder that results in an overproduction of blood cells and a thickening of blood. The hallmarks of polycythemia vera include excessive production of RBCs, WBCs, and platelets. The excess of cells present in the blood causes problems with the flow of blood through vessels, especially the smaller ones.

23. What is sickle cell anemia?
Sickle cell anemia is an autosomal recessive disorder in which an abnormal gene causes damage to the RBC membrane. The abnormal hemoglobin within the RBC is called hemoglobin S. Dehydration or drying of the RBC makes it more vulnerable to sickling (forming a crescent-like shape), as do hypoxemia and acidosis. Hemolytic anemia results as RBCs are destroyed because of the damage to
the outer membrane. The sickled cells can also clump together, causing difficulty getting through the smaller vessels.

24. What is deep vein thrombosis (DVT)?
Thrombophlebitis, or the formation of a clot within the vein, commonly occurs within the deep veins in the legs, and may also occur in the arms. Initially platelets and white cells clump together, sticking to the inside of the vessel wall. As blood flows over the area, other cells may deposit onto the area, making the thrombus larger. Compression of blood flow that increases the venous pressure or sluggishness of the blood flow can increase the risk of clot formation.

25. What is idiopathic thrombocytopenic purpura (ITP)?
ITP is an autoimmune disorder in which antibodies are developed to the patient’s own platelets. Antibodies attach to the platelets and macrophages within the spleen. The body destroys the platelets within the spleen.