Skip to 0 minutes and 15 secondsBlood consists of a mixture of cells and fluid. If you spin blood in a centrifuge, it will separate into three layers, an upper liquid layer of plasma, a lower layer consisting of red blood cells, called erythrocytes, and a small middle layer of white blood cells called leukocytes. The different blood cells can be divided into three categories, erythrocytes, leukocytes, and platelets. The average life span of these cells varies from a few days for platelets and neutrophils to a few months for erythrocytes, and even up to a few years for monocytes and lymphocytes. This means that new blood cells must be constantly produced to replace cells as they die and this is achieved via a process known as haemopoiesis.

Skip to 1 minute and 3 secondsHaemopoiesis is a process that occurs throughout adult life. This process is continuous with specialist stem cells called haemopoietic stem cells responsible for making all the different types of mature blood cells. These are found in the bone marrow. The haemopoietic stem cells have the ability to divide and form new stem cells, a process called self renewal as well as the capacity to differentiate rapidly into all the different types of cells in the blood. Leukemias are thought to arise from a single cell in the bone marrow, thymus, or peripheral lymphoid system. In other words, they are clonal diseases.

Skip to 1 minute and 44 secondsThe cell of origin will have undergone a genetic change, a somatic mutation, leading to a malignant transformation, ie, it has acquired properties of a cancer cell. Transformed cells then proliferate excessively and are resistant to apoptosis, leading to the accumulation of an abnormal high white blood cell count. Leukemias are caused by a number of factors which are usually a combination of genetic predisposition and environmental factors. They can be characterised by the predominant white blood cell type which accumulates. Lymphocytic leukemias involve T or B lymphocytes. Myeloid leukemias involve monocyctes, eosinophils, or granulocytes. They can also be characterised as chronic or acute with acute being the more aggressive form of the disease.

Skip to 2 minutes and 40 secondsAs with other cancers the genetic changes which occur either result in the cell activating a proto-oncogene or losing the function of a tumor suppressor gene. There are several types of genetic changes which may be involved. First, mutation can occur at a single site. This occur in an oncogene like Ras, which is involved in growth factor signalling, making the oncogene more active. Or in a tumour suppressor gene, such as P53, PTEN or notch, causing loss of function. Alternatively, larger scale genomic changes may occur. Tumour suppressor genes may be deleted completely and the number of copies in the genome of oncogenes can be increased leading to oncogenic activity.

Skip to 3 minutes and 27 secondsFinally, translocations or chromosomal rearrangements may occur so that a normally suppressed gene ends up next to a regulatory region of the genome resulting in an oncogene being transcribed into the active oncoprotein. These changes result in the transformed cells gaining a strong proliferative advantage and over a period of weeks to months for acute leukemias to years for chronic leukemias, signs and symptoms of leukaemia develop.

Introduction to blood cells and leukaemia

Dr Helen Wheadon outlines the background to leukaemia, before we go on to explore how it is treated.

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This video is from the free online course:

Cancer in the 21st Century: the Genomic Revolution

University of Glasgow