F8vi: Describe the physiology and consequences of foetal haemoglobin

Types of Normal HB

Type

%

Chains

HbA

97%

2α + 2β

HbA2

>2%

2α + 2δ

HbF

<1%

2α + 2γ

Adult Hb = HbA

  • Normal adult Hb
  • Globin chains α : β produced 1 : 1
  • Δ chain is synthesised before birth & HbA2 remains at low levels

Foetal Hb

  • 2α + 2γ chains
  • Very smart to ditch the β chain
  • DPG binds b/w the two β chains
  • DPG ↓Hb affinity for O2
  • ∴by rendering their Hb without β chains it means DPG binds less avidly
  • ∴foetal Hb has high affinity for O2, moving ODC LEFT
  • Enables HbF to extract O2 avidly from maternal blood
  • Adult Hb quickly replaces HbF at birth & normal levels <2.5%
Foetal Hb