Red blood cells

[WG21:p534-539]

Basic characteristics of RBC

• Life span = 120 days
• Dimension
  * 7.5 micrometer in diameter
  * 2 micrometer in thickness
• Contains 4 major proteins in the inner side of cell membrane
  * Spectrin
  * Actin
  * Ankyrin
  * Band 4.1
  * [PK1:p237]

Normal values

Red blood cell count
= 5.4 million/microliter in male
= 4.8 million/microliter in female

Total red blood cell in average men
= 3 x 10^13 RBC in circulation
= 900g of Hb

NB:

• [KB2:p211] Total body Hb = 750g

Different measurements of RBC/Hb quantity

• Hematocrit (Hct)
  = % of volume occupied by cells
• RBC count   (10^6/microliter)
• Haemoglobin (Hb)   (g/dL)
• Mean corpuscular volume (MCV)
  = Hctx10/RBC   (fL)
  * i.e. Average volume of one RBC
• Mean corpuscular haemoglobin (MCH)
  = Hb/RBC   (pg)
  * i.e. Average Hb content of one RBC
• Mean corpuscular haemoglobin concentration
  = Hb/Hct   (%)
  * i.e. Average Hb concentration in RBCs

RBC fragility

At normal fragility,

• RBC begins to hemolyse when suspended in 0.5% saline
• 50% lysis occurs in 0.4-0.42% saline
• Complete lysis in 0.35% saline

Fragility is increased in

• Hereditary spherocytosis
• Deficiency of glucose-6-phosphate dehydrogenase
  * Which catalyzes the first step in pentose phosphate pathway
  * Which allows generation of NADPH+H
  * Deficiency of NADPH+H impairs removal of H2O2
  --> Accumulation of H2O2 decrease life span of RBC
  * [HH26:p166]

Formation of RBC

[PK1:p236]

Proerythroblast
--> Basophilic erythroblast
--> Polychromatic erythroblast
--> Pyknotic erythroblast
--> Reticulocytes enters circulation

Reticulocyte still has some RNA and is capable of synthesizing Hb

• Final stage of RBC maturation
• Matures into RBC after 1-2 days in circulation
• Loses RNA on maturation
• Normally accounts for 1% of circulating RBC
  --> % increases when erythropoiesis is increased

Metabolism in RBC

• ATP is generated by anaerobic glycolysis (Embden-Meyerhof pathway)
  * ATP is needed for Na-K ATPase pump
• Embden-Meyerhof pathway also generates NADH
  --> Used by methaemoglobin reductase to reduce MetHb to Hb
• Some 2,3-DPG is generated in Rapoport-Luebering shunt
• 5% of glycolysis occurs by hexose monophosphate shunt (aka pentose phosphate pathway)
  --> NADPH is generated
  --> Used to prevent accumulation of H2O2