TBL14 - Bone Marrow Flashcards
Endothelial cells and blood cells are derivatives of what type of cell? What do these cells initially form in the embryo? What does this develop into and when?
1) Endothelial cells and blood cells are derivatives of hemangioblasts
2) Hemangioblast-derived hematopoietic stem cells initially form blood islands in mesoderm surrounding the yolk sac
3) The stem cells subsequently colonize the liver, which is the major hematopoietic organ from the 2nd to 7th month of gestation
What occurs in the 7th month of the embryo/fetus?
In the 7th month, stem cells from the liver colonize the bone marrow that becomes the definitive blood-forming tissue after birth
Compare the two microscopic methods for studying bone marrow. Define common sites for aspirations and needle biopsies of the bone marrow and compare their clinical applications.
1) Smears and trephine needle biopsy (for preparation of bone marrow sections) are used to sample and examine bone marrow
2) The optimal site for both aspiration and trephine biopsies is the posterior iliac crest, other sites being the sternum and tibia
3) Smears are the best preparations for evaluating cell details, studying maturation of hematopoietic cells, making differential counts, and assessing the ratio of myeloid (leukocyte) to erythroid (erythrocyte) cells. An advantage is preservation of individual cells so that subtle morphologic changes and infiltration by malignant cells in disease can be detected. Smears can also detect anemias, leukemias, and myeloma
4) The trephine biopsy entails cutting out a solid core of bone marrow, including some trabecular bone, with a large-bore cutting needle. Sections are less valuable than smears for elucidating cell details but provide a panoramic view of bone marrow and its normal architecture. They are also useful for estimating bone marrow cellularity, which is an index of the proportion of hematopoietic cells to adipocytes. Bone marrow cellularity is high in young persons, is reduced in the elderly, and may be altered in disease
How do autologous and allogeneic bone marrow transplants differ?
1) Autologous transplantation is used in certain forms of lymphoma in which malignant cells contaminate marrow. It involves harvesting bone marrow stem cells from a patient, followed by highdose chemotherapy and then intravenous injection of reconstituted marrow
2) A stem cell transplant from another person is an allogeneic transplant. Its success requires donor matching for the major histocompatibility complex (MHC) on chromosome 6
Are blood cells long- or short-lived? What is a result of this?
Most blood cells are short-lived; thus, continuous blood cell replacement is provided by hemangioblast-derived pluripotential hematopoietic stem cells that reside in the bone marrow and have the capacity for self-renewal, replication, and differentiation
What is the difference between a progenitor cell and a colony-forming unit (CFU)?
1) Progenitor cells are direct descendants of the pluripotential stem cells
2) When injected experimentally into the spleen, progenitor cells proliferate into colony-forming units (CFUs); thus progenitor cells and CFUs are interchangeable terms
Name the CFUs. What do CFUs differentiate into?
1) CFUs committed to erythroid lineage production contain progenitor cells known as colony-forming unit-erythrocytes (CFU-E)
2) Granulocyte and monocyte cell lines develop from one progenitor cell known as the colony-forming unit-granulocyte-monocyte (CFU-GM). As cells mature, progeny become committed to either granulocytes or monocytes
3) Cells of the lymphocyte lineage are generated from colony-forming unit-lymphocytes (CFU-L)
4) Progenitor cells for megakaryocytes produce colonies that contain colony-forming unit-megakaryocytes (CFU-Me)
5) CFUs differentiate into precursor cells that can be recognized microscopically as members of specific blood cell lineages i.e., like the CFUs, there are erythrocytic, granulocytic, monocytic, lymphocytic, and thrombocytic precursor cells
What are RBCs derived from? What are PMNs, eosinophils, basophils, and monocytes derived from? What are lymphocytes derived from? What are platelets derived from?
1) RBCs are derived from CFU-E via erythropoiesis
2) PMNs, eosinophils, basophils, and monocytes are derived from CFU-GM via granulopoiesis and monocytopoiesis
3) Lymphocytes are derived from CFU-L via lymphocytopoiesis
4) Platelets are derived from megakaryocytes
What are the first precursor cells derived from CFU-E? What characterizes the lineage of erythroblasts? Distinguish the basophilic, polychromatophilic, and orthochromatophilic erythroblasts.
1) During erythropoiesis, proerythroblasts are the first precursor cells derived from CFU-E
2) During the differentiation of erythrocytes, progressive cytoplasmic color changes characterize the lineage of erythroblasts
3) BE have a large dark purple central mass; PE has a smaller dark purple central mass with a slightly lighter shade of purple surrounding it; No has a very dark purple mass with an extremely light pink shade surrounding it
What occurs to the nucleus during erythropoiesis? What is different between reticulocytes and erythrocytes?
1) The progressive nuclear condensation during erythropoiesis
2) Nuclear extrusion occurs in the later stages
3) Reticulocytes are anucleate but unlike erythrocytes, lack central pallor
What does erythropoietin do? Define the normal duration of erythropoiesis.
1) Erythropoietin, which is produced in the kidneys, stimulates and sustains erythropoiesis
2) Erythropoiesis, from the proerythroblast to the mature erythrocyte, takes 7-8 days
Why is hypoxia the principal stimulus for erythropoietin secretion?
1) Erythropoiesis is regulated by the glycoprotein hormone erythropoietin, which is secreted by interstitial peritubular cells of the kidneys, mostly in response to hypoxia
2) This is due to the fact that bodily tissues are not receiving enough oxygen and require more erythrocytes to bind and transport oxygen to the body
Why does cytoplasmic color change from blue to reddish pink during erythropoiesis?
1) The CFU-erythrocyte first differentiates into the earliest recognizable cell of this series: a large, round proerythroblast, with a diameter of 15-30 mm. Its deep blue cytoplasm is due to abundant ribosomal RNA, which has affinity for basic dyes
2) Central pallor causes pink color (lack of nucleus/rRNA)
What are the first precursor cells derived from CFU-GM? What is noticeable about them microscopically?
1) During granulopoiesis, the first precursor cells derived from CFU-GM are myeloblasts that appear similar to the proerythroblasts microscopically
2) Thus, you are not expected to distinguish myeloblasts and proerythroblasts in the bone marrow smears
What do myeloblasts differentiate into? What occurs during the transformation of promyelocytes into myelocytes?
1) Myeloblasts differentiate into promyelocytes with large, round nuclei and reddish blue cytoplasmic granules (lysosomes)
2) During transformation of promyelocytes into myelocytes, the nuclei become eccentrically positioned and flattened on one side
