5. Haemopoiesis Flashcards
What is haemopoiesis?
Production of mature blood cells and platelets
Where does production of blood cells occur?
Production of blood cells occurs in the bone marrow
Where is bone marrow found in children and adults?
- Bone marrow extensive throughout the skeleton in infant
- More limited distribution in adulthood - It can be found in the axial skeleton; pelvis, sternum, skull, ribs and vertebrae.
What is the process by which bone marrow can be extracted?
Bone marrow can be exctracted using a trephine biopsy to allow examination
What is the differentiation of haemopoietic stem cells in bone marrow Determined by?
- Hormones
- Transcription factors
- Interactions with non-haemopoietic cell types (e.g.endothelial cells)
What is erythropoietin?
Erythropoietin is a hormone secreted by kidney and stimulates red blood cell production
What is thrombopoietin?
Thrombopoietin is a hormone produced by liver and kidney and regulates production of platelets.
What is the function of Haemopoietic stem cells (HPSCs)?
- Capable of self-renewal (more than any other adult tissue)
* Given appropriate stimuli can differentiate into variety of specialised cells
Are Haemopoietic stem cells found in the plasma ?
HSPCs are never normally found in the blood - their presence indicates pathology
In which condition would HSPCs be found in the plasma?
In pathological conditions e.g. myelofibrosis or thalassaemia HSPCs can mobilize into circulating blood to colonise other tissues (extramedullary hematopoiesis)
What are the Sources of HSPC?
- Bone marrow aspiration (rarely done)
- GCSF mobilised peripheral blood stem cells (collected by leucopharesis)
- Umbilical cord stem cells
What is the Reticuloendothelial system (RES)?
Part of immune system and made up of monocytes in blood and a network of tissues which contain phagocytic cells
What is the function of Reticuloendothelial system (RES).
Role to remove dead or damaged cells and identify and destroy foreign antigens in blood and tissues.
What are the main organs of the Reticuloendothelial system (RES)?
Main organs are spleen and liver
Give the function of RES cells in the spleen
RES cells in spleen dispose of blood cells, in particular damaged or old red cells
What are the 2 types of pulp in the spleen?
Red pulp: sinuses lined by endothelial macrophages and cords
White pulp: similar structure to lymphoid follicles
What are the functions of the spleen?
• Sequestration and phagocytosis - old/abnormal red cells removed by macrophages
• Blood pooling - platelets and red cells can be rapidly mobilised during bleeding
• Extramedullary haemopoiesis - pluripotential stem cells
proliferate during haematological stress or if marrow fails (e.g. in myelofibrosis)
• Immunological function - 25% of T cells and 15% of B cells are present in spleen
How does blood enter the spleen?
Blood enters via the splenic artery
Where does white blood cells and red blood cells pass through in the spleen?
- White cells and plasma preferentially pass through the white pulp - where foreign material is taken to stimulate immune system
- Red cells preferentially pass through the red pulp
Why would the spleen grow(splenomegaly)?
• Back pressure as fibrosis of liver makes it hard for blood to flow through which increases pressure in splenic artery - portal hypertension in liver disease
• Over work (red or white pulp)
• Reverting to what it used to do- extramedullary haemopoiesis
• Expanding as infiltrated by cells
> Cancer cells of blood origin e.g. leukaemia
>Other cancer metastases
• Expanding as infiltrated by other material
> Sarcoidosis (granulomas)
How is examination of the spleen done?
- It is never normal for the spleen to be palpable below the costal margin
- Start to palpate in Right Iliac Fossa (RIF) or may miss massive splenomegaly
- Feel for spleen edge moving towards your hand on inspiration
- Feel for the splenic notch
- Measure in cm from costal margin in mid- clavicular line
What can multipotential hematopoietic stem cells differentiate into?
Common myeloid progenitor and common lymphoid progenitor
What can common myeloid progenitors differentiate into?
Megakaryocytes
Erythrocytes
Myeloblasts
What can common lymphoid progenitors differentiate into?
Small lymphocytes
In which tissues are the following macrophages found? Kupffer cell Tissue histiocyte Microglia Peritoneal macrophage Red Pulp Macrophage Langerhans cell
Kupffer cel l= Liver Tissue histiocyte = Connective tissue Microglia = Central nervous system Peritoneal macrophage= Peritoneal cavity Red Pulp Macrophage = Spleen Langerhans cell = Skin and Mucosa
Give causes of massive, moderate and mild splenomegaly
Massive
• Chronic myeloid leukaemia• Myelofibrosis • Malaria
• Schistosomiasis
Moderate – as above, plus
• Lymphoma • Leukaemias • Myeloproliferative disorders
• Liver cirrhosis with portal hypertension
• Infections such as Glandular Fever
Mild – as above, plus • Infectious hepatitis • Endocarditis
• Infiltrative disorders such as sarcoidosis
• Autoimmune diseases such as AIHA, ITP, SLE
Hypersplenism definition
Hypersplenism refers to overactivity of the spleen causing the spleen to remove blood components at an excessive rate.
An enlarged spleen means more blood can pool in the spleen which cause blood levels to be low as more of the blood is pooling in the spleen and less is in circulation. - results in low blood count
What is the Effect of splenomegaly on daily life of the patient
Risk of rupture if spleen enlarged and no longer protected by rib cage - Need to Avoid contact sports and vigorous activity
Hyposplenism definition
Lack of functioning splenic tissue
What are the causes of Hyposplenism?
• Splenectomy May be required due to splenic rupture from trauma or because of cancer • Sickle cell disease In older children and adults due to multiple infarcts & fibrosis • Gastrointestinal diseases > Coeliac disease > Crohn’s disease > Ulcerative colitis • Autoimmune disorders > Systemic lupus > Rheumatoid arthritis > Hashimoto’s disease
What are Patients with hyposplenism at risk of? How can the risk be reduced?
Patients with hyposplenism are at risk of sepsis
from encapsulated bacteria e.g.
• Streptococcus pneumonia
• Haemophilus influenzae
• Meningococcus
Patients must be immunised and given life long antibiotic prophylaxis
What is visible in blood in hyposplenism?
Howell Jolly bodies (DNA remnants) - Red cells containing these inclusion bodies would normally be removed by a fully functioning spleen. Thus their presence indicates that the spleen is not functioning properly
What are vital statistic of erythrocytes?
• RBC (Red Blood Cell Count) How Many?
4.4 - 5.9 x 1012/l
• Hb (Haemoglobin) How effective?
13.5 - 16.7 g/dl
• MCV (Mean Corpuscular Volume) How large?
80 - 100fl
• Biconcave flexible disc ~8mm diameter Shape?
What are the functions of Erythrocytes?
• Deliver oxygen to tissues • Carry haemoglobin • Maintain haemoglobin in its reduced (ferrous) state • Maintain osmotic equilibrium • Generate energy
Structure of haemoglobin
Haemoglobin is a tetramer of 2 pairs of globin chains
each with its own haem group which contains iron.
What is the Position of globin genes in chromosomes
Globin gene clusters on Ch 11 & 16.
At what age during the life span is there the switch from fetal to adult Hb?
The switch from fetal to adult Hb occurs at ~3-6 months of age
What are the 2 configuration of Hb?
The relaxed R state
The tight T state
How can RBC change shape?
RBCs change shape by changing the components of the cell membrane.
Why is it important for the RBC to be able to change shape?
This is because as a part of their role RBCs are constantly having to squeeze into small areas, this means that they’re have to be flexible to bend and fit into small areas or else they’ll break down forcing themselves into these tight areas.
What effect can changes in the plasma membrane have on RBCs?
- Changes to the plasma membrane cause cells to become less deformable & more fragile.
- Spleen recognises cells as ‘abnormal’ and removes them from circulation
- Haemolytic anaemia can result
What is haemolytic anaemia?
Hemolytic anemia is a form of anemia due to hemolysis, the abnormal breakdown of red blood cells (RBCs), either in the blood vessels (intravascular hemolysis) or elsewhere in the human body (extravascular, but usually in the spleen).
Give the proteins involved in hereditary spherocytosis
• Spectrin: actin crosslinking and molecular scaffold protein that links the plasma membrane to the actin cytoskeleton.
• Ankyrin: links integral membrane proteins to the
underlying spectrin-actin cytoskeleton.
• Band 3: facilitates chloride and bicarbonate exchange
across membrane and also involved in physical linkage of membrane to cytoskeleton (binds with ankyrin and protein 4.2).
• Protein 4.2: ATP-binding protein which may regulate the association of band 3 with ankyrin
What is hereditary spherocytosis?
Hereditary spherocytosis is an abnormality of red blood cells, or erythrocytes. The disorder is caused by mutations in genes relating to membrane proteins that allow for the erythrocytes to change shape.These proteins facilitate vertical interactions with the cytoskeleton of the cell which are essential for maintaining the red cell’s biconcave shape and deformability. The abnormal erythrocytes are sphere-shaped (spherocytosis) rather than the normal biconcave disk shaped.
Explain the degradation of haem
• Senescent rbc are engulfed by macrophages in the reticuloendothelial system
• The haem is removed and the Fe2+ is recycled
• Haem without Fe2+ becomes bilirubin - Unconjugated
bilirubin transported in blood bound to albumin. Excess unconjugated bilirubin in blood (e.g.from haemolytic anaemia) can cause jaundice
• Bilirubin is conjugated by the liver with glucuronic acid forming Bilirubin diglucoronide
• Bilirubin diglucoronide is Secreted in Bile into duodenum
• In the duodenum,Glucuronic acid removed by bacteria. Bilirubin converted to Urobilinogen which is subsequently oxidised to Stercobilin - Brown colour in faeces comes from stercobilin
• Some urobilinogen absorbed into blood and transported to kidney. Oxidised to Urobilin and excreted in urine - Yellow colour in urine comes from urobilin
In terms of haemopoiesis terminology define cytopenia, …cytosis and …philia
- Cytopenia is a reduction in the number of blood cells.
* …cytosis or …philia is an increase in the number of blood cells
What are the Stages of maturation and development of a neutrophil?
It starts off as a myeoblast and over stages develops into a neutrophil granulocyte.
Which immune system step are neutrophils involved in?
Its involved in the innate immune system and acts as a first responder phagocyte when innate barriers are breached.
Give the process of action for neutrophils
Neutrophils circulate in the blood and when pathogens invade they’ll invade bodily tissues. Here the neutrophils will phagocytose invading microbes and destroy them by releasing reactive oxygen species
Where are neutrophils found in the body?
Circulating in the blood.
Lifespan of neutrophils?
1-4 days
Give the hormone that controls the maturation of neutrophils
G-CSF
Describe the action of G-CSF
It works by:
• Increases production of neutrophils
• Speeds up release of mature cells from BM
• Enhances chemotaxis
• Enhances phagocytosis and killing of pathogens
When are recombinant G-CSF be used?
Recombinant G-CSF is routinely administered in cases when more neutrophils are needed e.g. a patient with severe neutropenia and sepsis after chemotherapy
What is neutrophilia?
This is an increase in the absolute number of circulating neutrophils.
List the causes of neutrophilia
- Infection - main
- Tissue damage
- Smoking
- Drugs (e.g. steroids)
- Myeloproliferative diseases - main
- Acute inflammation
- Cancer
- Cytokines (G-CSF)
- Metabolic disorders
- Endocrine disorders
- Acute Haemorrhage
How can you test for neutrophilia?
By taking a blood test to identify neutrophil count
Compare the marginated and circulating pool of neutrophils
The circulating pool refers to the neutrophils moving freely in the blood whilst the marginated pool refers to the neutrophils stuck to the endothelial walls.
Only those cells in circulating pool are actually measured in a blood count
What effect can haemorrhage have on the neutrophil levels?
Haemorrhage brings more cells out from marginated pool causing the level of neutrophils to appear to be raised.
What is neutropenia?
Neutrophil count <1.5 x 109/L (severe if < 0.5 x 109/L)
What are the Consequences of neutropenia?
- Severe life threatening bacterial infection
- Severe life threatening fungal infection
- Mucosal ulceration e.g. painful mouth ulcers
medical emergency - intravenous antibiotics must be given immediately
What are the two causes of neutropenia?
1) reduced production
2) increased removal or use
What are the 7 causes of reduced production of netrophils?
- B12/folate deficiency - insufficient DNA synthesis
- aplastic anaemia - empty marrows, no precursors
- viral infection -
- congenital
- drugs - chemotherapy, antibiotics… - poison marrow and inhibit blood cell production
- radiation - mature cells killed, precursors stunned
- infiltration - malignancy and fibrosis - no room for blood cell production
What are the 3 causes of increased removal or use of neutrophils?
1) immune destruction - autoantibodies kill neutrophils
2) sepsis - rapid migration of neutrophils into tissues. Marrow unable to synthesise neutrophils fast enough to keep up circulatory numbers
3) splenic pooling - sequestration of neutrophils in the spleen means that less are available for general circulation - also occurs during splenomegaly
What is the lifespan of monocytes?
They circulate for ~1-3 days before migrating into tissues where they differentiate into macrophages or dendritic cells.
What is the function of monocytes?
- Phagocytose microorganism and breakdown/remove cellular debris
- Antigen presenting role to lymphocytes
- Important in defence against chronic bacterial infections (e.g. tuberculosis and chronic fungal infections)
Definition of monocytosis
An increase in the amount of monocytes
Causes of monocytosis
• Bacterial infection e.g. tuberculosis
• Inflammatory conditions e.g. rheumatoid arthritis, Chron’s
Ulcerative colitis
• Carcinoma
• Myeloproliferative disorders and Leukaemias
Which are the largest cells in the blood?
monocytes
What is the time of circulation for eosinophils?
In circulation for ~3-8 hours before migrating into tissues
What is the lifespan of eosinophils?
8-12 days
What is the function of eosinophils?
• Responsible for immune response against multicellular
parasites e.g. Helminths
• Mediator of allergic responses
• Phagocytosis of antigen - antibody complexes
What do eosinophil granules contain?
Granules contain array of cytotoxic proteins (e.g. eosinophil cationic protein & elastase)
What is the effect of inappropriate activation of eosinophils?
Inappropriate activation responsible for tissue damage and inflammation e.g. in asthma
What are the common causes of eosinophilia?
- Allergic diseases - asthma, eczema, hay fever
- parasitic infection - round worms, tape worms
- drug hypersensitivity -
- churg-strauss - very rare autoimmune condition resulting in inflammation of small blood vessels
- skin diseases - e.g bullous pemphigoid
What are the rare causes of eosinophilia?
- Hodgkin lymphoma
- acute lymphoblastic leukaemia
- acute myeloid leukaemia
- myeloproliferative conditions
- eosinophilic leukaemia
- idiopathic hypereosinophilic syndrome
Functions of basophilia
Active in allergic reactions and inflammatory conditions
What are the contents of basophil granules
Large dense granules containing histamine, heparin, hyaluronic acid, serotonin
What is the Colour basophils when stained
Granules stain deep blue to purple and often so numerus they mask nucleu
What are the causes of basophilia?
Reactive
• Immediate hypersensitivity reactions
• Ulcerative Collitis
• Rheumatoid Arthritis
Myeloproliferative
• Chronic Myeloid Leukaemia
• MPN: ET/PRV/MF
• Systemic mastocytosis
Where do lymphocytes originate from?
Originate in bone marrow
Role of B cells, T cells and Natural killer cells
• B cells - (humoral immunity) Antibody (immunoglobulin) forming cells • T cells (cellular immunity) - bind to and kill pathogens CD4+ helper cells, CD8+ cells • Natural killer cells (cell mediated cytotoxicity)
Definition of lymphocytosis
Lymphocytosis is a higher-than-normal amount of lymphocytes
Definition of Lymphoproliferative
Lymphoproliferative disorders are a set of disorders characterized by the abnormal proliferation of lymphocytes into a monoclonal lymphocytosis.
List and give causes of the 2 types lymphocytosis
Reactive • Viral infections • Bacterial infections-especially whooping cough • Stress related: MI/cardiac arrest • Post splenectomy • Smoking
Lymphoproliferative i.e. malignant
• Chronic Lymphocytic Leukaemia (B cells)
• T- or NK- cell leukaemia
• Lymphoma (cells ‘spill’ out of infiltrated bone marr
Describe thrombopoiesis
Thrombopoiesis results in the ultimate formation of platelets (also called thrombocytes) involved in clot formation. Platelets have no nuclei and are essentially membrane bound fragments of cytoplasm that bud off from megakaryocytes. Megakaryocyte formation is driven by thrombopoietin (TPO). They are very large mononucleate cells with several copies of each pair of chromosomes
Describe Granulopoiesis
The granulocytes (basophils, neutrophils and eosinophils) arise from myeloblast cells which in turn arise from common myeloid progenitor cells.
What is the function of macrophages?
Macrophages protect tissues from foreign substances by phagocytosis, antigen presentation and cytokine production
How do monocytes recognise what to phagocytose?
Monocytes in the blood can perform phagocytosis after recognising antibodies or complement that coats pathogens or by binding directly via pattern recognition receptors that recognize pathogens.
Describe the development of b lymphocytes
The development of B lymphocytes commences in the fetal liver and bone marrow and during their development immunoglobulin genes rearrange to allow production of antibodies with a wide array of specificities. Final maturation of B-cells requires exposure to antigen in the lymph nodes and results in mature B- lymphocytes with the capacity to recognize non-self antigens and produce large quantities of specific antibodies
Describe the devlopment of t lymphocytes
T lymphocytes progenitors arise from fetal liver and migrate to the thymus early in gestation. Immature T cells undergo rearrangement of the T cell receptor genes resulting in the ability to produce a vast array of different T cell receptors which can recognise a wide range of antigens presented to them by antigen presenting cells.
Describe Erythropoiesis
Erythropoiesis is the process by which red blood cells (erythrocytes) are produced in the bone marrow. This needs to be a continual process since red blood cells have a lifespan of around 120 days in the bloodstream and lack the ability to divide.. Erythropoietin production by the kidneys increases in response to a decrease in the oxygen level in the bloodstream (hypoxia) thereby stimulating more red blood cell
What commits progenitor cells in the marrow to the erythroid lineage?
Expression of the transcription factors GATA1, FOG1 and PU.1 commits progenitor cells in the marrow to the erythroid lineage and, once committed, further expansion of the erythroid precursors is largely driven by the hormone erythropoietin released from the kidneys
Describe the function of erythropoietin
Erythropoietin production by the kidneys increases in response to a decrease in the oxygen level in the bloodstream (hypoxia) thereby stimulating more red blood cell
Erythropoietin is a hormone and its main function is to inhibit apoptosis (programmed cell death) of CFU-E (colony-forming units of the erythroid cell line) progenitor cells.
What is formed in Erythropoiesis after erythropoietin is activated?
Activation of the erythropoietin receptor on cells allows them to develop, proliferate and differentiate. During this process nucleated erythroblasts extrude their nucleus and most of their organelles ultimately forming reticulocytes (immature red blood cells) which are then released into the circulation. Once in the bloodstream
reticulocytes extrude their remnants of organelles such as mitochondria and ribosomes and take ~1 to 2 days to mature into red blood cells. The reticulocyte count from a blood sample therefore provides a good diagnostic estimate of the amount erythropoiesis occurring in a patient’s bone marrow
What is the advantage of the shape of red blood cells?
They are anucleate biconcave discs ~ 8 µm in diameter with a flattened depressed centre which gives them a dumbbell-shaped cross section. This distinctive shape
optimises the laminar flow properties of blood in large vessels as well as allowing the cells to deform to squeeze through the smallest capillaries
Why is the oxygen dissociation curve for hameoglobin sigmoidal?
.When shifting between the oxygen unbound and
oxygen bound states haemoglobin undergoes a conformational change which enhances the binding affinity of subsequent oxygen molecules. This enables haemoglobin to load oxygen in in the lungs where there is a high oxygen tension and release it in the tissues where there is a low oxygen tension and is what gives the oxygen binding curve a sigmoidal shape.
can people survive without a spleen
Patients can usually survive without a spleen, as sometimes happens in the case of surgical removal after accidental rupture due to trauma or to treat diseases such as hereditary spherocytosis. In such cases there
is an increased risk of sepsis and patients are usually given various vaccinations to compensate for inadequate opsonisation of bacteria.
What mode of inheritance does hereditary spherocytosis display?
autosommal dominant
Clinical consequences of splenomegaly?
Hypersplenism - low blood counts can occur due to pooling of blood in enlarged spleen
Risk of rupture - spleen no longer protected by rib cage so avoid contact/ vigorous sports/ activity
What is a carcinoma?
a cancer arising in the epithelial tissue of the skin or of the lining of the internal organs.
