Lec 1 Haematopoiesis - Lecture notes 1 PDF

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Lec 1 Haematopoiesis Haematopoiesis = the formation of blood cells  Tightly regulated  All blood cells made in the bone marrow  Released into periphery once they mature  55% of blood is plasma  45% of blood made up of cells of which there are 3 types o Erythrocytes (RBCs) – transport O2 from lu...

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Lec 1 Haematopoiesis Haematopoiesis = the formation of blood cells  Tightly regulated  All blood cells made in the bone marrow  Released into periphery once they mature  55% of blood is plasma  45% of blood made up of cells of which there are 3 types o Erythrocytes (RBCs) – transport O2 from lungs to tissues o Leukocytes (WBCs) – Defend body against infection o Thrombocytes (Platelets) – prevent blood loss at site of injury  The process of haematopoiesis is regulated by o Growth factors o Cytokines o Environmental factors o Apoptosis Balance  In a healthy person no of cells produced = no of cells die  Disruption of this balance = disease state Ontogeny of Haematopoiesis  Predominantly takes place in the bone marrow, this makes up 5% of healthy person weight  There are two types of marrow in a 1:1 ratio o Red marrow – Site of haematopoiesis o Yellow marrow – Fat cells  Main bone marrows for an adult are the vertebrae, ribs, sternum, skull, pelvis and proximal ends of femur  In an infant, practically all bones  In a foetus o 0-2 months – yolk sac of embryo o 2-7 months – liver and spleen o 5-9 months – bone marrow, sole sight once baby is born  in some disease states where bone marrow is unable to meet demand of body it can revert back to foetal locations

pluripotent stem cell = Haematopoietic stem cell

Bone marrow stroma  major functions of bone are to provide support and protect organs  Hollow spaces in the bone which are the sites of Haematopoiesis. Have blood vessels and heamatopetic tissues  Haematopoietic cells and non haematopoietic cells are anchored in the Extra cellular matrix  Penetrated with network of vessels to supply  

blood and provide exit route to mature cells Stromal cells e.g. endothelial cells, macrophages, fibroblasts are a source of growth factors (regulators) Adhesion molecules on the ECM retain immature cells in bone marrow o Controls both stem cells homing (retains HSC for optimum proliferation) o Mobilisation (release of HSC if injury or inflammation)

Growth factors  Development and control of blood cells  Glycoprotein hormones that regulate the proliferation and differentiation of hematopoietic progenitor cells and the function of mature blood cells  May act locally at site where the are produced by cells to cell contact of they may circulate in the plasma  Bind to extracellular niches to which stem cells and progenitor cells adhere and cause proliferation  Stimulate differentiation, maturation, prevent apoptosis and affect the function of mature cells  One single cell can secrete many different growth factors in response to various stimuli e.g. infection and each can impact on o Different cell types o Have a different effect when acting alone or in combination o Sequence of a growth factors activity

Stem cell factor = SCF

Apoptosis is require to ensure that all old blood cells are removed and to allow space for the new ones, balance is important

Erythropoiesis  RBCs – highly specialised, no nuclei or mitochondria  Flat bi-concaved disk, with a centre of pallor (no larger than 3 microns)  Produced in bone marrow with a 120 day life span  Then removed by liver or spleen Key steps involved in RBC development  Slow reduction in cell size  Loss of the nucleus to become reticulocyte Process occurs in parallel with development of haemoglobin  Tightly regulated by erythropoietin Reticulocytes  Also found in peripheral blood 0.5-1.5% on blood film, any more = disease state  Called reticulocytes due to a mash like network of ribosomal nucleic acid  New methylene blue stain reticulocytes blue Erythropoiesis is regulated by EPO  90% produced in the peritubular intestinal cells of the kidney and 10% in the liver and elsewhere  Not stored and produced In response to O2 tension (hypoxia) in the tissues of the kidney  Hypoxia induces hypoxia inducible factors (HIF-a and ß) which stimulate EPO production How EPO is stimulated-feedback mechanism  HB for some structural or metabolic reason unable to give up 02 normally (atmosphere 02 low, defective cardiac/pulmonary function, damage to renal circulation)  EPO stimulates erythropoiesis by increasing the number of progenitor cells committed to erythropoiesis  Transcription factors activated by EPO receptor, stimulate and enhance expression of erythroid specific genes, expression of apoptotic gene and transferrin receptor CD71  HB increased – increased 02 delivery Plasma EPO levels are valuable in clinical diagnosis  High levels observed if tumour secreting EPO is causing polycythaemia (abnormally increased concentration of HB in the blood)  Low in sever renal disease

Thrombopoiesis – platelet production  Platelet is smallest cell in the blood (1-4microns) they lack nuclei  Main function id the formation of platelet plug  Lifespan 7-10 days  Consist of pale basophilic cytoplasm and tiny azurophilic granules  Interact with each other during active haemorrhage to form an aggregate which is the initial haemostatic plug  Produced In the bone marrow from fragmentation of megakaryocytes  Driven by thrombopoeitin (TPO)  TPO synthesised in the liver  Megakaryocytes mature by endomitotic replication o DNA replication and expansion of cytoplasmic volume without cellular division o Because of no cellular division with each cell cycle the cell increases in size o Following replication the cytoplasm matures with ribbon like structures throughout endothelium o From these projection platelets passed into circulation

Receptor c-mpl found on Megakaryocytes and platelets o TPO binds to c-mpls on megakaryocytes – stimulates maturation o TPO binds to platelets – remove TPO from circulation Blood and bone marrow levels of thrombopoietin directly related to platelet count 

Granulopoiesis  IL-1 GM-CSF and M-CSF control proliferation and differentiation  Increased production is also a response to infection induced by stromal cells and T lymphocytes  4 types of cell o eosinophil o basophil o macrophage o neutrophil

Mature Granulocytes – bone marrow

Lymphocytes production  B and T cells – both arise from the Haematopoietic stem cells (IL-7)  Look at markers!!

Bone marrow analysis – important technique in haematology  status and capability for blood cell production  Measure of blood cells production to help diagnose o Leukaemia o Bone marrow disease o Spread of cancer o Sever anaemia  Conditions that affect the marrow can affect the number, mixture and maturity of the cells and can affect its fibrous structure  A FBC and reticulocytes count are used to help evaluate cell production in the marrow and compare it to current cell populations in the blood  Cultured for the presence of microorganisms Obtaining bone marrow

Bone marrow aspiration – smeared onto a slide and stained for examination  Romanowsky stain – assessment of population and morphology of cells  Pearls stain – specific stain o Detects iron o Abnormal in sideroblastic anaemia

M/E ratio = myeloid/erthroid ratio

Fluorescence flow cytometry  identifies blood and bone marrow cells according to the presence of CD molecules (glycoproteins) on the cells surface or in the cytoplasm  uses: o panels of markers to confirm diagnosis of malignancies (AML/CLL) o CD34 counts before bone marrow harvest o Minimal residual disease detection...