Haemopoiesis and Haematology Principles

Vocabulary practice flashcards covering haemopoiesis, stem cell differentiation, erythropoiesis, RBC membrane structure and metabolism, hemoglobin variants, oxygen dissociation dynamics, and laboratory blood measurement principles.

Haemopoiesis

Blood cell production and development.
Consists of erythropoiesis (red blood cells), leucopoiesis (white blood cells), and thrombopoiesis (platelets).

All blood units in adults normally originates in the bone marrow (medullary haemopoiesis) where most complete their maturation/development.

Medullary Haemopoiesis

Normal state

• Myeloid:Erythroid precursors ratio = 3:1

Abnormal state

• Disease infiltration in BM or an increased demand for red cells e.g. thalassemia major

• leads to massive marrow expansion in axial skeleton and may activate extramedullary haemopoiesis e.g. spleen and liver

Extramedullary Haemopoiesis

Blood cell production or maturation occurring outside the bone marrow

Some blood cells (e.g. T cells) matures in the thymus

Yolk Sac (Haemopoiesis)

Extramedullary Haemopoietic site

embryo: 1-2 months

Fetal Liver (Haemopoiesis)

Extramedullary Haemopoietic site

Embryo & Fetus: 2-9 months

Fetal Spleen (Haemopoiesis)

Extramedullary Haemopoietic site

fetus: 3-6 months

Myeloid:Erythroid Precursor Ratio

Normal state of Erythropoiesis
3:1

Totipotential Stem Cells

Undifferentiated stem cells

Can differentiate into all types of cells

Pluripotential Haemopoietic Stem Cells

Able to generate all types of blood cells

Multipotential Stem Cells

Stem cells committed to either the myeloid (CFU-GEMM) or the lymphoid (CFU-L) lineage.

Unipotential Stem Cells

Stem cells committed to a single cell lineage

Erythropoiesis

Production of RBC
Regulated by erythropoietin (EPO), with feedback mechanism by the kidneys in response to low tissue oxygen tension and decreased RBC production
Effects of EPO: shortens cell cycle, increased rate of RBC maturation, release of RBC from BM to peripheral blood
GM-CSF + EPO acts on CFU-GEMM to produce BFU-E
BFU-E increases CFU-E to increase RBC proliferation by mitosis

Burst Forming Unit-Erythroid (BFU-E)

Increases CFU-E to increase RBC proliferation by mitosis

Pronormoblast

The earliest morphologically identifiable red blood cell precursor in the erythroid maturation series.

Reticulocyte

An immature, anucleate red blood cell containing residual ribosomal RNA networks that matures over $1\text{--}2\text{ days}$ in the bone marrow and peripheral blood before becoming a mature erythrocyte.

Myelopoiesis

Production of granulocyte and monocyte

Leucopoiesis

Production of WBC
Regulated by Interleukins (IL-3 & IL-4) and level of lymphocytes in circulation; drug induced (corticosteroid)
A mononuclear leukocyte comprising bone marrow-derived B cells (from BM) —> differentiate into plasma cells)
T cells (from Thymus) —> ($\text{CD4}^+$ helper and $\text{CD8}^+$ cytotoxic cells).

Thrombopoiesis

Thrombopoiesis = Production of platelets

• Regulated by Thrombopoietin (TPO), feedback mechanisms by platelet levels and level of TPO in circulation

• Arises from megakaryocytes

Megakaryocyte

A large, polyploid bone marrow cell derived from CFU-Meg that produces thrombocytes (platelets) via cytoplasmic fragmentation.

Platelet (Thrombocyte)

A small, anucleate cytoplasmic fragment shed from mature megakaryocytes into the circulation to perform primary hemostasis and clotting.

RBC Membrane Composition

Semipermeable lipid bilayer supported by cytoskeletons (intergral proteins + peripheral proteins)

• intergral proteins: glycoproteins: A, B, C, D, anion exchange proteins

• peripheral proteins: spectin, ankryin, protein 4.1, actin

lipids: glycolipids, free cholesterol, phospholipids
carbohydrates: glycoprotein, glycolipids
50% glycoprotein, 40% lipids, 10% carbohydrates

RBC Integral Membrane Proteins

glycoprotein: A, B, C, D, anion-exchange protein

RBC Peripheral Membrane Proteins

spectrin, ankyrin, protein 4.1, actin

Embden-Meyerhof (EM) Pathway

1. Generates 2x Adenosine-triphosphate (ATP) for each molecule of glucose, provides energy for Na+K+ pumps within the RBC.

2. Generates NADH - helps to reduce non-functional methaemoglobin containing ferric iron (Fe 3+), to functional haemoglobin (Hb) containing ferrous (Fe 2+) [Methaemoglobin reductase pathway].

Hexose Monophosphate (HMP) Pathway

generates NADPH also help to reduce non-functional Hb to

functional Hb.

Glutathione Cycle

• NADPH (from HMP) helps glutathione reductase to reduce oxidised glutathione (GSSG) to reduced glutathion (GSH)

• GSH is an important antioxidant in RBC as it protects RBC from oxidatative stress (e.g. hydrogen peroxide)

• Failure of glutathion cycle (e.g. in G6DP deficiency) leads to the appearance of Heinz bodies (denatured Hb) in RBC —> RBC hemolysis

Heinz Body

denatured Hb, resulting from oxidative stress when the glutathione cycle is compromised (e.g., in G6PD deficiency), triggering RBC hemolysis.

Luebering-Rapoport Shunt

• generates 2,3-disphosphoglycerate (2,3-DPG)

• important for regulation of Hb oxygen affinity

Hemoglobin A (HbA)

The predominant adult hemoglobin tetramer consisting of two alpha and two beta globin chains ($\alpha_2\beta_2$), making up $>95\%$ of normal adult hemoglobin.

Hemoglobin A2 (HbA2)

A minor adult hemoglobin variant composed of two alpha and two delta globin chains ($\alpha_2\delta_2$), typically accounting for $2.2\text{--}3.5\%$ of adult hemoglobin.

Hemoglobin F (HbF)

Two alpha and two gamma globin chains ($\alpha_2\gamma_2$), <1%

Has greater affinity to oxygen than normal adult Hb; important for oxygen distribution during fetal life

as oxygen is readily transferred from maternal circulation to fetal circulation in the placenta

Tense (T) State

The deoxygenated, low-affinity quaternary conformation of hemoglobin (Deoxy-Hb) characterized by separated $\beta$ chains that form a cleft accommodating 2,3-DPG, closer $\alpha$ chains, and closed haem pockets.

Relaxed (R) State

The oxygenated, high-affinity quaternary conformation of hemoglobin (Oxy-Hb) where 2,3-DPG is expelled, $\beta$ chains move closer together, $\alpha$ chains move apart, and haem pockets open.

P50 Oxygen Tension (P50O2)

The partial pressure of oxygen at which hemoglobin is $50\%$ saturated, having a normal physiological baseline of $27\,\text{mm\,Hg}$.

Bohr Effect

The physiological decrease in hemoglobin's oxygen affinity caused by an increase in carbon dioxide tension ($\uparrow\text{CO}_2$) and hydrogen ion concentration ($\uparrow\text{H}^+$, acidosis/decreased pH), promoting oxygen unloading in peripheral tissues.

Right Shift (Oxygen Dissociation Curve)

A displacement of the hemoglobin-oxygen dissociation curve reflecting decreased oxygen affinity and enhanced oxygen unloading, provoked by high 2,3-DPG, high $\text{H}^+$ (acidosis), high $\text{CO}_2$, or elevated temperature.

Left Shift (Oxygen Dissociation Curve)

A displacement of the hemoglobin-oxygen dissociation curve reflecting increased oxygen affinity and hindered oxygen release, provoked by low 2,3-DPG, low $\text{H}^+$ (alkalosis), low $\text{CO}_2$, or the presence of fetal hemoglobin (HbF).

Hemocytometer

A specialized ruled glass chamber used for manual blood cell enumeration, providing direct cell counts without generating red cell indices such as MCV or Hb.

Aperture Impedance (Coulter Principle)

An automated counting methodology that measures cell count and volume based on transient increases in electrical resistance (voltage pulses) as blood cells suspended in a conductive diluent pass through an aperture between two platinum electrodes.

Cyanmethemoglobin Method

A reference spectrophotometric method where potassium ferricyanide oxidizes hemoglobin ($\text{Fe}^{2+}$) to methemoglobin ($\text{Fe}^{3+}$), which then combines with potassium cyanide to produce cyanmethemoglobin, measured spectrophotometrically at $540\,\text{nm}$.

Sodium Lauryl Sulfate (SLS) Method

A non-toxic, cyanide-free automated reagent method that lyses erythrocytes and converts released hemoglobin into colored chromogen compounds for spectrophotometric reading at $540\,\text{nm}$.