RBC EXAM(Graded A+ actual test)

What is the first type of cell produced by the developing embryo? A. Erythrocyte B. Granulocyte C. Lymphocyte D. Thrombocyte - A. Erythrocyte The need for oxygen delivery to developing tissues results in the production of erythrocytes before other blood cells. Erythropoiesis commences in the yolk sac as early as the fourteenth day of embryonic development. These primitive red cells produce embryonic hemoglobins that temporarily serve oxygen needs of the fetus. Myelopoietic and lymphopoietic activities beginw ehn the liver and spleen become sites of production at 6-9 weeks of gestation; however, erythropoiesis still predominates. At this time, the red cells produce hemoglobin F, which is the chief oxygen carrier during fetal life. What percentage of tissue located in the bone marrow cavities of adults is fat? A. 10% B. 25% C. 50% D. 75% - C. 50% In the infant, there is an increased demand for blood formation because of the rate of growth. At birth, all bone marrow cavities are filled with hematopoietic tissue (active red marrow). As the growth rate slows, there is less need for active marrow. Fatty infiltration of the marrow becomes noticeable at about 4 years of age as cell production diminishes within the shafts of the long bones and is filled with yellow inactive tissue. Fat comprises 50% of the total marrow space in the adult. Except for lymphopoiesis, hematopoiesis is confined to the flat bones and pelvic area by the age of 25 years. Which of the following is not characteristic of pluripotent hematopoietic stem cells? A. Possess self-renewal ability B. Produce progenitor cells committed to a single cell lineage C. Express the stem cell marker CD13 D. Are morphologically unrecognizable - C. Express the stem cell marker CD13Hematopoietic stem cells can make copies of themselves to maintain the stem cell pool and possess the ability to generate cells of all lineages (pluripotential). These stem cells give rise to multipotential myeloid and lymphoid progenitor cells, which ultimately produce progenitor cells that are restricted to a specific cell lineage. With appropriate cytokine stimulus, the committed progenitor cells undergo proliferation to recognizable precursors that produce an amplified number of mature end-stage cells. Stem cells and progenitor cells cannot be morphologically distinguished (look similar to small lymphocytes) but can be identified phenotypically by markers such as the stem cell marker CD34. CD34 expression is lost as antigens for a specific cell lineage are expressed. CD13 is a marker expressed by myeloid precursors. As an adult, what are the two best areas for obtaining active bone marrow by aspiration? A. Vertebra, tibia B. Sternum, vertebra C. Anteroir iliac crest, tibia D. Posterior iliac crest, sternum - D. Posterior iliac crest, sternum Unlike the infant, in which all BM is capable of forming blood cells, the active marrow in an adult is confined to the flat bones of the skeleton such as the sternum and posterior iliac crest. Although the spinous processes of the vertebrae contain active marrow, these sites are rarely used for aspiration in adults because of the danger of damage to the spinal cord. Sternal puncture also presents a possibility of serious damage to underlying structures but may be used because of easy accessibility or if the aspirate is a dry tap in the iliac crest. To obtain both a BM aspirate and core biopsy, most marrow specimens are taken from the posterior iliac crest. The anterior iliac crest may occasionally be used in adults and sometimes the tibia in children less than 2 years of age. What is the normal ratio of myeloid to erythroid precursors in bone marrow (M:E ratio)? A. 1:1 B. 1:3 C. 4:1 D. 8:1 - C. 4:1 The ratio between all granulocytes and their precursors and all nucleated red cell precursors represent the myeloid-to-erythroid ratio. Myeloid precursors outnumber erythroid precursors by about 3 or 4 to 1 in the normal BM. Although there are many more RBCs in the peripheral blood than granulocytes, RBCs have a much longer life span in circulation (120 days) as compared to granulocytes (about 8 hours).Granulocytes, therefore, require a more continual production than erythrocytes and are the most numerous marrow precursors. Alteration in the M:E ratio such as 1:1 or 8:1 may indicate erythroid hyperplasia or granulocytic hyperplasia, respectively. Which of the following does not accurately describe hematopoietic growth factors? A. Bind to target cell receptors to express activity B. Action of majority is lineage restricted C. May promote or suppress cell death D. Can stimulate or inhibit cell proliferation - B. Action of majority is lineage restricted A diverse group of growth factors (cytokines) regulate and maintain hematopoiesis in a steady state. Most are not lineage restricted but can act on more than on cell type and have multiple functions. IL-3 and colony stimulating factors (GM-CSF) affect multiple cell lines; whereas erythropoietin action is limited to erythroid cells. Cytokines are glycoproteins that usually express activity by binding to specific receptors on target cells. The action of growth factors on hematopoietic progenitor and precursor cells can stimulate or inhibit cell proliferation and differentiation as well as promote or suppress cell death. Growth factors may act alone or together to exert a positive or negative influence on hematopoiesis as well as on the function of mature cells. A determining factor for controlling the rate of cell production is cytokine stimulation in response to physiological need. In the third month of gestation, what is the primary site of hematopoiesis? A. Liver B. Marrow of long bones C. Spleen D. Yolk sac - A. Liver