Normal Blood Cells and Haemopoiesis

Question 1

RBC basic characteristics: life span, function, shape/appearance, essential components, energy generation

Answer 1

Life span: 120 days
No nucleus
Function: carries Hb and O2 for tissue metabolism; maintain osmotic equilibrium, maintain Hb in ferrous state
Shape: biconcave to increase surface area to volume –> CENTRAL PALLOR

Generate ATP by anaerobic glycolytic pathway, generate reducing power as NADH or NADPH

Essential components:

• membrane –> e.g. defect = spherocytosis in HA (smaller, denser, loss of central pallor)
• enzyme biochemical pathway –> e.g. G6PD deficiency (oxidant stress)
• Hb structure –> e.g. thalassemia

Question 2

WBC: different types and their functions/morphology

Answer 2

Neutrophils (segmented nuclei) - bacterial infection
Eosinophils (red) - allergy and parasitic infection
Basophils (dense blue granules containing heparin and histamine) - lymphoproliferative and myeloproliferative diseases
Monocytes (larger, abundant greyish blue cytoplasm) - become macrophage in tissues
Lymphocytes (high N:C ratio) - T>B in peripheral blood and CD4>CD8 - cellular and humoral immunity
Plasma cells (BM; abundant blue cytoplasm with clockface chromatin pattern i.e. patchy) - secrete Ig

Function: protection against infection
Immunosurveillance

Question 3

Other components of blood

Answer 3

Platelets

Plasma (serum + fibrinogen) - coagulation factors, Ab, proteins, GFs

Question 4

Normal haemopoiesis: sites, stem cell properties, precursors

Answer 4

Sites:
- yolk sac (1st few wks), fetal liver (6wks-6/7 mnths) and spleen, bone marrow

Pluripotent stem cells

• CD34+, CD38-, Lin-
• common precursors for all 3 cell lineages, capable of self renewal and proliferation

Myeloid precursors

• granulocytes (neutro/baso/eosinophils)
• erythrocytes
• monocytes
• megakaryocytes (platelets)

Lymphoid precursors
- B/T/NK cells (BM as primary site of origin; spleen, LN, thymus are secondary)

Question 5

BM environment: homing, differentiation, maturation, mobilisation; M:E ratio

Answer 5

Stromal cells and microvascular network
Homing of stem cells due to cytokines (scientific basis of bone marrow transplantation)
Direction of differentiation depends on spectrum of growth factors
Maturation allow cells to mobilise (leave BM) and enter circulation (important for harvesting stem cells)

Progressive fatty replacement of BM through childhood = haematopoietic marrow confined to central skeleton and ends of long bones

M:erythroblast ratio 2:1
-M includes promyelocyte, myelocyte, metamyelocyte, band, neutrophil, eosinophil

Question 6

Haematopoietic growth factors: definition/functions, sources, EPO (source, function, stimulus), TPO (source, function), other GFs

Answer 6

= glycoprotein hormones that regulate proliferation/differentiation/maturation and prevent apoptosis of progenitor cells and function of mature blood cells

Sources: stromal cells (except for TPO, EPO)

Erythropoietin (EPO): 90% produced by kidneys

• regulate erythropoiesis, stimulated by hypoxia at kidneys
• increase in anaemia/ renal hypoperfusion
• decrease in severe renal disease or polycythaemia vera

Thrombopoietin (TPO): mainly from liver
- platelet production

Granulopoietin: GM-CSF, G-CSF, M-CSF

G-CSF + TPO: enhance effects of IL3 and GM-CSF on early haematopoietic cells
EPO, G-CSF, M-CSF, TPO, IL5 as later acting factors (increase in response to body’s needs)

Question 7

Erythropoiesis: changes in nuclear and cytoplasmic pathways, substances needed

Answer 7

Production of red cells (1-2 days in BM, then 1-2 days in spleen for maturation –> PB)

Pronormoblast

• Nucleus: big, open/fine chromatin (transcriptionally active), light colour (euchromatin)
• Cytoplasm: blue
• -> nuclear and cytoplasmic differentiation pathways
• Nucleus: smaller, heterochromatin (darker), more condensed chromatin
• Cytoplasm: more pink (HAEMOGLOBINISATION AND LOSS OF RNA)

==> EXTRUSION OF NUCLEUS – to form non-nucleated biconcave cells

Substances needed for erythropoiesis:

• metals: IRON
• vitamins: VIT B12, FOLATE, C/E/B6
• amino acids
• hormones: EPO, other GFs, androgens, thyroxine

Presence of any blastic cells in PB is abnormal! – extramedullary erythropoeisis/ marrow disease

Question 8

Reticulocytes: morphology, relation to polychromasia

Answer 8

Young RBC

• bigger than mature RBC
• bluish loose appearance due to RNA
• nucleus extruded

Circulates in PB for 1-2 days before RNA completely lost and becomes erythrocyte

POLYCHROMASIA
- RBC with various shades of blue; large purplish morphology
==> reflects presence of YOUNG RBCs = suggests RETICULOCYTOSIS (detected by staining and counting RNA abundant cells)

Question 9

Granulopoiesis: blast characteristics, maturation flow

Answer 9

Production of -phils, monocytes

Blast

• immature, only in marrow –> serious problem if in PB! (bone marrow infiltration, acute leukaemia)
• high N:C ratio
• fine chromatin

–> promyelocyte –> myelocyte –> metamyelocyte –> band –> neutrophils

Question 10

Normal BM Biopsy: expected features, cellularity

Answer 10

Tri-lineage haemopoiesis

• red cell, white cell, megakaryocyte
• polymorphic

Fat

Around 60% cellularity (excluding fat)