Lecture 2: Red cells, haemoglobin and anaemia

Question 1

Describe the shape of the Normal Blood Cells

What is the significance of the shape?

Answer 1

Shape is discoid, _7µm diamete_r. There is no nucleus or RNA.

This shape allows:

• Flexibility (capillaries 3.5µm)
• Increased area for gas exchange

Question 2

RBC do not have _____ or ____

Answer 2

Shape is discoid, 7µm diameter. There is no nucleus or RNA.

This shape allows:

• Flexibility (capillaries 3.5µm)
• Increased area for gas exchange

Question 3

What are the functions of the RBC?

Answer 3

Function Of Red Blood Cells

• Carriage of haemoglobin (responsible for most of gas exchange)
• Allows gas exchange (oxygen from lung to tissues, CO₂ tissues to lungs)

Question 4

Describe the 3 properities of RBC

Answer 4

Properties Of Red Blood Cells

*1)Unique Shape And Deformability***

Unique shape and deformability allows gas exchange and movement through small capillaries

• This is determined by membrane (bipolar lipid layer) and c_ytoskeletal proteins_ (spectrin, actin, ankyrin)
  
  • Clinical: Inherited abnormalities of membrane proteins will cause rigid membrane, and shortened lifespan of red cell
    
    • Hereditary spherocyctosis (autosomal dominant)
      
      • Mutation in spectrin results in round cells without biconcave shape, eventually haemolysis (taken by spleen).

*2)Energy Source***

No nuclei or mitochondria but needs energy source to keeps haemoglobin in reduced state and maintain osmotic equilibrium

• Glycolytic pathways produce ATP, which maintains osmotic equilibrium
• HMP shunt produces NADPH, which keeps Hb reduced
  
  • Clinical: Inherited defects in enzyme pathways would result in haemolysis (red cell destruction), such as G6PD deficiency

Coordination Of Globin Synthesis, Haem Synthesis And Iron Reguklations

• Transferrin receptor on surface of RBC
• Iron transported into RBC to synthesis haem
• Haem is made up of protoporphyrin and iron (via ferrochelatase)

*3)Haemoglobin Carriage***

Haemoglobin is responsible for gas exchange. In adults:

• HbA is the principle Hb. HbA has 2 alpha chains, 2 beta chains and haem group
• There are small amounts of HbF (fetal, different beta chains) and HbA2 (delta chains instead of beta chains)

Defective production of globin chains (𝛼 or 𝛽) results in thalassaemia (more HbF & HbA2, microcytic hypochromic anemia)

Deficiency of iron causes reduced production of haem, resulting in low Hb

Question 5

Describe the significance of the following property of Red Blood Cells and name 1 disorder where this property is affected

Unique Shape and Deformity

Answer 5

1)**Unique Shape And Deformability

Unique shape and deformability allows gas exchange and movement through small capillaries

• This is determined by membrane (bipolar lipid layer) and cytoskeletal proteins (spectrin, actin, ankyrin)
• Hereditary spherocyctosis (autosomal dominant): Inherited abnormalities of membrane proteins will cause r_igid membrane,_ and shortened lifespan (haemolysis) of red cell
  • Mutation in spectrin results in round cells without biconcave shape, eventually haemolysis (taken by spleen).

Question 6

Describe the significance of the following property of Red Blood Cells and name 1 disorder where this property is affected

Energy Source

Answer 6

No nuclei or mitochondria but needs energy source to keeps haemoglobin in reduced state and maintain osmotic equilibrium

• Glycolytic pathways produce ATP, which maintains osmotic equilibrium
• HMP shunt produces NADPH, which keeps Hb reduced
• Clinical: Inherited defects in enzyme pathways would result in haemolysis (red cell destruction), such as G6PD deficiency

Hemoglobin forms an unstable, reversible bond with oxygen; in the o_xygenated state_ it is called oxyhemoglobin and is bright red; in the reduced state it is purplish blue.

Question 7

Describe the significance of the following property of Red Blood Cells and name 1 disorder where this property is affected

Haemoglobin Carriage

Answer 7

1)**Haemoglobin Carriage

Haemoglobin is responsible for gas exchange.

In adults:

• HbA is the principle Hb. HbA has 2 alpha chains, 2 beta chains a_nd h_aem group
• There are s_mall amounts of HbF_ (fetal, different beta chains) and _HbA2 (_delta chains instead of beta chains)
• Clinical: Defective production of globin chains (𝛼 or 𝛽) results in thalassaemia (more HbF & HbA2, microcytic hypochromic anemia)
• Clinical: Deficiency of iron causes reduced production of haem, resulting in low Hb = anemia

Question 8

Clinical: Defective production of globin chains (𝛼 or 𝛽) results in ______

Clinical: Deficiency of iron causes r_______, resulting in ________

Answer 8

Clinical: Defective production of globin chains (𝛼 or 𝛽) results in thalassaemia (more HbF & HbA2, microcytic hypochromic anemia)

Clinical: Deficiency of iron causes r_educed production of haem_, resulting in l_ow Hb_ = anemia

Question 9

What are the Morphotological stages of erythroid development? (erythroid precursor cells)

Answer 9

1) Haematopoetic stem cells

2) Common Myeloid Progenitor (also give rise to neutrophils, platelets etc.)

3) Erythrocyte

(Don’t need to know proethryoblast, basophilic erythroblast etc.)

but we need to know that…

Changes with differentiation, there is

1) Progressive increase in haemoglobin
2) c_hromatin clumbing_
3) extrude nuclues
4) loss of RNA

Reiticulocytes are produced. This can be stained. (last stage before the mature RBC is released. If you’ve been under stress, e.g. surgery, there will be an increase in production of RBC and so increase in reticulocytes in the peripheral blood. (Indirect measure of how well the bone marrow is responding to the low Haemoglobin/blood loss)

Question 10

If someone comes in with pancytopaenia and you’re wondering if this is due to a primary (aplastic anemia- BM failure), what can you do to confirm this?

Answer 10

reticulocyte count

(Last form before a mature Blood cell is released)

In aplastic anemia, you would see a low reticulocyte count.

If high, it is likely to be due to e.g. blood loss

Question 11

Red blood cells arise from myeloid multilineage progenitor in response to _______ e.g. _____ _____

Answer 11

1. Growth Factors

Red blood cells arise from myeloid multilineage progenitor in response to growth factors: IL-3 and GM-CSF

• Erythroid burst forming unit earliest (BFU-E)
  
  • Respond to IL-3, GM-CSF and high levels of EPO
• Erythroid colony forming units (CFU-E)
  
  • More EPO receptors, respond to low dose EPO

Question 12

Describe the Kinetics of Erythropoiesis

What is the significance of this?

Answer 12

4 cell divisions, 7-10 days, then 2 days later we have a mature RBC

If someone is iron deficient and they take iron supplements, no changes will be seen in the blood test in the next day.

It takes at least 10 days before we see new cells emerging

Question 13

What are the clinically relevent points around erythroid development

Answer 13

Red Blood Cell: Clinical Relevance Of Erythroid Development

• Don’t normally see nucleated red cells in the blood
• Can measure reticulocytes in the blood
  
  • Normally 1-2% of red cells
  • Will be high in blood loss, haemolysis
  • Will be low in bone marrow failuree

Question 14

Describe the regulation of erythropoiesis

Answer 14

Average life span of RBC is 120 days

Regulation: Erythropoietin

• EPO is a Glycoprotein
• Produced in kidney
• Production of EPO is in Response to low oxygen tensions
• I_ncreased erythropoietin production_ (to increase O2 delivery)

Question 15

What is required for RBC production?

Answer 15

Critical Requirements for Red Cell Production

• Iron
• Folate
• Vitamin B12

Question 16

What are the clinical implications of Erythropoietin?

Answer 16

Clinical Implications: Erythropoietin

1. Renal failure patients have l_ow haemoglobin_
2. Clinical use of r_ecombinant erythropoietin_ for anaemia of renal failure, o_ther anaemias_ (especially myepoloma [cancer], some myelodysplastic syndromes [dysfunctional RBCs])
3. Potential for abuse such as competitive cyclists use to increased oxygen supply to muscles (can lead to thrombotic events).

Question 17

Describe the effects of Erythropoietin

Answer 17

Erythropoietin acts through specific EPO receptor to increase RBC production:

1. Stimulation of BFU-E (erythroid burst-forming unit) and CFU-E (erythroid colony-forming unit)
2. Increased haemoglobin synthesis
3. Reduced RBC maturation time
4. I_ncreased reticulocyte release_
   
   • ​​Reticulocytes have RNA but no nucleus

Results in increased haemoglobin

Thus increased oxygen delivery (negative feedback to EPO receptor)

Question 18

​​Reticulocytes have _____but no _____

Answer 18

​​Reticulocytes have RNA but no nucleus

Question 19

Describe the RBC destruction

Answer 19

• Average life span of 120 days
• Cells less deformable, removed in spleen (and reticuloendothelial system RES)
• Breakdown of red cells with release of Hb

​

• Haemoglobin broken down
  
  • Globin chains
  • Haem
    
    • Iron is salvaged-
      
      • transferrin - bone marrow
    • Protoporphyrin -
      
      • metabolised to form bilirubin -
      • liver – excreted via bile (gallbladder)
  • Clinical significance:
    
    • If someone has haemolysing (breaking down more RBC than normal), they will release more haem, more protoporphyrin and more bilirubin.
    • So someone with increased haemolysis, will often be jaundiced.
      
      • Unconjugated bilirubin

Question 20

What is anaemia?

Answer 20

Anaemia is a r_eduction in haemoglobin concentration_ (not RBC) in the blood with values <135 g/l (adult males) and <115 g/l (adult females).

• HB is high in M>F

Neonates have a haemoglobin lower limit of 140 g/l however this falls dramatically during first few months of life (due to less plasma).

• Reduction in haemoglobin is usually but not always accompanied by ↓ total red cell count and ↓ packed cell volume (PCV).
• Alterations in total plasma volume also affect haemoglobin concentration. E.g. if a person is dehydrated, reduced plasma volume may mask anaemia or cause relative polycythemia.
  
  • hemoglobin or red blood cell count is perceived to be abnormally high due to an increased concentration of blood. This can happen as a result of plasma volume loss from dehydration, severe vomiting or diarrhea, or excessive sweating. Polycythemia in these situations may be called relative polycythemia, because the actual numbers of red blood cells are not abnormal.

Question 21

What is hemoglobin?

Answer 21

Hemoglobin (sometimes abbreviated as Hb) is a complex protein found in red blood cells that contains an iron molecule. The main function of hemoglobin is to carry oxygen from the lungs to the body tissues, and to exchange the oxygen for carbon dioxide, and then carry the carbon dioxide back to the lungs and where it is exchanged for oxygen. The iron molecule in hemoglobin helps maintain the normal shape of red blood cells.

Question 22

What is the body’s response to anaemia?

Answer 22

• The body responds to reduced oxygen carrying capacity of the blood by increasing cardiac output (↑SV and ↑HR).
  
  1. Increased SV
  2. Increased HR
  3. There is also a right shift in haemoglobin dissociation curve,
  4. Rise in 2,3 DPG levels.
• Anaemia can be asymptomatic, however patients will eventually develop of shortness of breath, fatigue, pallor and finally congestive cardiac failure if severe enough. The degree of symptoms experienced depends on the speed of onset of anaemia, the severity of anaemia and age of the patient.
• In addition, haemoglobin dissociaton curve shifts to the right in anaemia together with a rise in 2,3 DPG levels. This results in oxygen being more readily available in the tissues.

Question 23

What are the 2 classifications of anaemia?

Answer 23

• Physiologic:
  
  • Impaired production vs _blood loss/_reduced survival of cells (haemolysis)
    
    • High reticulocyte production index >2% means haemolytic RBCs (destroyed once out in the circulation), maybe autoimmune disease or hereditary spherocyctosis
    • _Low reticulocyte production i_ndex <2% means hypoproliferative bone marrow (reduced cells), or ineffective bone marrow (such as myelodysplastic syndromes).
• Morphology
  
  • Size of cells microcytic or macrocytic

Question 24

What are the clinical features of anaemia?

Answer 24

The body responds to reduced oxygen carrying capacity of the blood by increasing cardiac output (↑SV and ↑HR). There is also a right shift in haemoglobin dissociation curve, and rise in 2,3 DPG levels.

• Anaemia can be asymptomatic, however patients will eventually develop of shortness of breath, fatigue, pallor and finally congestive cardiac failure if severe enough. The degree of symptoms experienced depends on the speed of onset of anaemia, the severity of anaemia and age of the patient.
• In addition, haemoglobin dissociaton curve shifts to the right in anaemia together with a rise in 2,3 DPG levels. This results in oxygen being more readily available in the tissues.