Blood constituents

Master answer

RBC

Role

• Oxygen transport
• Carbon dioxide transport
  • Bound to N-terminal of globin → carbamino-Hb
• Buffering function
  • Imidazole group on Hb Histadine residues
• Iron storage
  • 65-70% of total iron stores

Normal Values

• 40-50% of the blood volume
• Usual value 4-5 x 10¹²/L

RBC Production

• 3-4w embryionic → Mesenchymal stem cells in yolk sac
• 6w-7mo
  • → Liver (and spleen to lesser extent)
  • continues until birth
• 7mo onwards:
  • Bone marrow
  • Proximal ends of femur/humerus
    • fat replacement of long bone marrow occurs by age 18-20 y.o.
  • Central skeleton (vertebrae, pelvis, ribs, sternum and skull)

Takes 7 days

• Proerythroblast propagates
• From proerythroblast to reticulocyte
  • Concentration of haemoglobin increases
  • Nucleus disappears
  • Endoplasmic reticulum disappears
• Reticulocyte
  • Ribosomes
  • Mitochondria
• Reticulocyte released into circulation
• Matures to RBC in 1-2 days

EPO increases rate of differentiation
Produced in the kidney (in response to low PO₂)

RBC Destruction

Globin chains → aa’s 

Haem → Biliverdin + Fe + CO

• Biliverdin
  • Haeme + Haem oxygenase → biliverdin
  • Biliverdin + biliverdin reductase → bilirubin
  • Free bilirubin + albumin → transported to hepatocytes
  • Conjugated with glucuronide to ↑ water solubility
  • Excreted to bile canniliculus
  • Secreted to gut at D2 (duodenum)
  • Intestinal flora hydrolyse and reduce → urobilinogen
  • 3 fates:
    • 1) Gut bacteria form the dark pigment stercobilin, which is egested in the faeces
    • 2) Urobilinogen reabsorbed unchanged by the portal system and recycled by the liver
    • 3) Remainder is reabsorbed by the portal system and then excreted in the urine
• Fe²⁺ → oxidised to Fe³⁺ → recycled
• CO (only endogenous source of CO)

Gladwin 2016

Answer by Gladwin