Haemopoiesis is the formation of blood cellular components structure and build up, usually the development of these cells in adults occurs in the haemopoietic bone marrow which is located within the vertebrae, skull, sacrum and pelvis, proximal ends of the femurs and humeri, plus the ribs. In development the multipotential hematopoietic stem cell (hemocytoblast) divide into two lines the common myeloid progenitor and common lymphoid progenitor. Myeloid stem cells are precursors of all cells apart from the lymphocytes whose precursors are the lymphoid stem cells. Myeloid stem cells form assorted lines of colony forming cells (CFU mix) the first identified CFU GEMM gives rise to the burst forming unit erythroid granulocyte-macrophaged colony forming cells. (CFU-GM) the precursor of macrophages, eosinophil colony forming unit, megakaryocytes forming unit and the basophile colony forming unit which is precursor of monocytes,eosinophils, megakaryocytes and basophiles respectively. The hematopoietic progenitors express the cell surface antigen, CD34
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The production of red blood cells is called erythropoiesis the first cell produced in the lineage of erythroid cell is organised as the burst forming unit erythoid which differentiates and become the colony forming unit erythroid which undergoes a number of differentiations to become erythrocytes. The proerythroblast are the precursor cells of erythrocytes which will extrude the nucleous and enter the circulation as a reticulocyte, the reticulocytes will finally lose their polyribosomes and become mature red blood cells. The production of white blood cells is called leucopoiesis, white blood cells are divided into lymphocytes, monocytes and granulocytes. The process of granulopoiesis is the development of the granulocytes, monocytes, neutrophils, eosinophils and basophiles. The first cell of this process is granulocyte-macrophage colony forming cells which will differentiate and give rise to (CFU-G) anf (CFU-M) which are precursors of neutrophils and monocytes respectively. Eosinophil colony forming unit are precursors of eosinophilsa, the myeloblast is the precursor of all white blood cells expect lymphocytes, this stem cell enlarges and forms promyelocyte. In this process granules start forming depending on which granulocyte will be produced ( basophilic granules form in the basophiles, eosinophilic granules form in the eosinophils and neutrophilic granules form in the neutrophils. The promyelocyte of each type of granulocytes then differentiate to form myelocytes which in turn form the metamyelorecyte. The neutrophil then enters the peripheral blood from bone marrow, 95% of granulocytes produced are neutrophils 5%, eosinophils 1% and basophiles are formed in the marrow.
Lymphopoiesis is the formation of lymphocytes in the bone marrow, thymus, spleen and lymph nodes, lymphocytes constitute of 5-10% of blood cells. The Natural killer cell and small lymphocyte all derive from the common lymphoid progenitor. The small lymphocyte goes on to produce T and B lymphocytes, in which B-cells mature in the bone marrow whilst T-cells leave the bone marrow immature to complete their development in the thymus. Thrombopoesis is the production and development of platelets and megakaryocytes.
T first cell in the lineage is high potential colony forming until megakaryocytes the next stage produces burst forming unit-MK also known as promegakaryoblast. Initially colony forming until megakaryocytes is mitotic cells, but their cellular division stops and (cytokinesis) DNA replication continues (end mitosis) to produce the polyploidy immature megakaryocytes, these immature cells differentiate into mature megakaryocytes which shed platelets into bone marrow sinusoids or growth of these haemopoietic areas are likely in certain diseases or also due to a haemorrhage. The liver and the spleen also have haemopoietic abilities if essential (extramedullary haemopoiesis) Developing cells are located outside the bone marrow sinuses and once maturing is released into circulation via the sinus spaces and the marrow microcirculation. Several hormones interleukin and colony stimulating factors support the process of cellular proliferation and cell division.
Question 2: Name the systems used to classify acute lymphoblastic leukaemia and acute
myeloid leukaemia. (Word limit: 20 words) (2 MARKS)
The French, American, British classification system (FAB) is used to classify acute myeloid leukaemia and lymphoblastic leukaemia (word count: 17) (www.cancer.org)
Question 3: Define leucocytosis and thrombocytopenia. (Word limit: 75 words)
Leucocytosis is a condition characterised by an abnormal elevation of white blood cells in the blood which often occurs during inflammation or acute infection, if only one cell line is affected it may be shown as neutrophilia, lymphocytosis etc. On the other hand thrombocytopenia is the term used to define an abnormally reduced platelet count in the blood as a result of platelet production failure or increased rate of removal from blood. (Word count: 72) (www.netdoctor.co.uk)
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Question 4: Define leukaemia and state the four main divisions of the disease.
(Word limit: 70 words)
Leukaemia is a cancer of the blood or bone marrow characterised by unusual proliferation of white blood cells (leukocytes) established in tissues and is classified by the type of leukocyte predominantly concerned. Clonal proliferation is classified by diffuse replacement of bone marrow with abnormal leucocytes which maybe immature and abnormal in function. Four main divisions (ALL) acute lymphoblastic leukaemia, (all) chronic lymphoblastic leukaemia, (AML) acute myeloid leukaemia and (CML) chronic myeloid leukaemia. (Word count: 67)
Question 5: State the typical manifestation of someone presenting with acute leukaemia
including the blood film morphology. (word limit: 200 words) (5 MARKS)
Patients with acute leukaemia usually present symptoms which include anaemia, fever increased rate of infection, easy bruising, bone pain, swollen lymph nodes, unusual swelling caused by swollen spleen or liver and fatigue. Symptoms e.g. fatigue and anaemia are vague as they are unspecific, they are also symptoms for a number of different other diseases therefore a medical diagnosis is required to verify that the symptoms displayed are caused by leukaemia. Great increase in (W.B.C.) leukoyctosis, decrease in (R.B.C.), thrombocytopenia which is a decrease in platelets is usually shown when a blood cell count and cell film examinations have been done. The blood film will also show that the majority of white blood cells will be blast cells a type of cell found only in bone marrow, in acute leukaemia bone marrow will have 25% of its cells inhabitants as leukaemia blast. These immature cells do not function normally in circulating blood. Cytopenias can be looked at in the peripheral blood when 50% of bone marrow is replaced, blasts are observed in the peripheral blood of patients with acute leukaemia. In AML blast cells are of myeloid origin, numerous nucleoli, Auer rods, greyish cytoplasm and delicate chromatin are looked at in these blasts. (Word count: 202)
Question 6: State the typical manifestation of someone with chronic leukaemia including
the blood film morphology. (Word limit: 200 words) (5 MARKS)
Chronic leukaemia symptoms are not easily noticed could go unnoticed for months or years these include tiredness due to anaemia, enlarged lymph glands, weight loss, repeated infection and many more. These symptoms are still vague and unspecific because some of them could still be associated with other diseases. Blood cell counts and blood cell film examination reveal high levels of W.B.Cs lymphocytosis exceeds 100G/l at the time of diagnosis, total W.B.Cs count is raised 10-20 fold, the blood film will show 30% myelocytic precursors and 70% mature cells. The malignant cells are able to differentiate thus bone marrow failure is not obvious until later in the course of the disease. White blood differential shows granulocytes in all stages of maturation, basophilia and thrombocytosis. In the bone marrow hypercellularity occurs, myelocyte predominant cells appear, increase in megakaryocytes and show dysplastic features also there is an increase in reticulin fibrosis. Other points of diagnosis could include looking into the reduced neutrophil alkaline phosphatase , looking into serum B12, transcobalamin, serum uric acid, lactate dehydrogenase which are increased in circulation. (Word count: 177)
Question 7: Explain the following techniques and give one example for each, of
application in the diagnosis or monitoring of leukaemia:
(word limit: 230 words) (15 MARKS)
Cytochemistry is a test involved in the exposition of cells to different chemical stain which react with some type of leukaemia cells. The stains cause a colour change which is visible under a microscope and also help identify cells present. Example Sudan Black B is a stain which help distinguish between (ALL) cells stain positive and (AML) cells stain negative, the stain causes granules of (AML) to appear as black spots under microscope but (ALL) cells do not change colour.
Immunophenotyping technique used to categorize and enumerate cells of the blood, bone marrow and lymph tissues according to their biological lineage and stage of differentiation as classified by glycoprotein and associated structures of the cell membrane. In the diagnosis of leukaemia white blood cells are labelled with antibodies directed against surface proteins on their membrane. Leukaemia cells express a cell surface antigen which can be used to identify the origin of the tumour cell, therefore choosing the appropriate antibodies the differentiation of leukaemia cells can be accurately determined. The labelled cells are identified by a process which combines fluorescently-labelled, monoclonal antibodies reagents and a flow cytometer.
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Cytogenetics a test which examines a cell chromosome under a microscope, this is useful because in (AML) changes in chromosomes e.g. deletions, insertions or additions will be identified. Cytogenesis includes routine analysis of G-Banded chromosomes and fluorescent in situ hybridization FISH used in the diagnosis of AML. ( Reily JT et al, 1996) (Word count:233)
Question 8: What is the Philadelphia chromosome? Give an example of where this is
(word limit: 120 words) (5 MARKS)
Philadelphia (Ph) chromosome is an abnormally short chromosome (ch) 22, which is a result of a reciprocal translocation between ch9 and ch22 this results in a longer ch9 than normal and a shorter ch22 than normal.DNA from ch9 contains proto-oncogene c-ABL, the break in ch22 is in the middle gene BCR. This translocation occurs on a single cell of bone marrow, which leads to the production of a mutant cell also resulting proliferation of this mutant cell cause leukaemia. Philadelphia chromosome is commonly associated with chronic myeloid leukaemia, acute lymphoblastic leukaemia (all 25-30% in adult and 2-10% in paediatric cases), raised tyrosine increase activity and also often in acute myelogenous leukaemia. (Word count: 111)
Question 9: State the difference between stem cell and bone marrow transplants.
(word limit: 100 words)
Stem cell and bone marrow transplantation are the two form of transplants used to restore/ replace stem cells which were destroyed as a result of disease, chemotherapy or radiation therapy. In stem cell transplantation the stem cells are harvested from peripheral blood by apheresis, the donor is given G-CSF to mobilise stem cells into the peripheral blood. Bone marrow transplant uses stem cells from the bone marrow either from oneself or from another individual. Bone marrow transplant require patients to be hospitalised and the use of anesthesia whereas stem cell transplant can be done on an outpatient basis. (Word count: 98)
Question 10: State the difference between autologous and allogenic transplants.
(word limit: 50 words) (4 MARKS)
Allogenic transplant involves the use of stem cells or bone marrow from a patient with human leukocyte antigen that matches the patient. E.g. sibling or matched unrelated donor.
Autologous transplantation requires bone marrow from patient themselves thus reducing the possibility of an immune response. (word count:44 ) (www.nhsdirect.nhs.uk)
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