Haemoglobin Structure and Function

Haemoglobin Lecture Notes

• Haemoglobin has a structure allowing it to load and unload oxygen
• Different types of haemoglobin exist, including:
  • Haemoglobin A (HbA): 95-98% in adults, with two alpha and two beta chains (α₂β₂)
  • Haemoglobin A2 (HbA₂): 1.5-3% in adults, with two alpha and two delta chains (α₂δ₂)
  • Fetal haemoglobin (HbF): present at birth, at 0-0.5% in adults, with two alpha and two gamma chains (α₂γ₂). Has greater affinity for oxygen than HbA, which facilitates oxygen transfer from mother to foetus.
• Haemoglobin abnormalities can cause anaemia and reduced oxygen-carrying capacity in the blood due to insufficient or malformed haemoglobin. Examples include thalassemias (reduced or absent alpha or beta chains) and haemoglobinopathies (abnormal polypeptide chains like haemoglobin C, E, I, J, S).
• Haemoglobin S (sickle cell haemoglobin) results from a single amino acid substitution (valine for glutamic acid) in beta globin chains. Low oxygen causes the haemoglobin to change shape, causing cells to become stiff and deformed, clogging blood vessels, leading to pain and anaemia.

Haemoglobin Breakdown

• Old or damaged red blood cells (RBCs) are broken down by macrophages within the spleen.
• Haemoglobin is broken into haemoglobin and globin components.
• Globin is reused or broken down to amino acids.
• Haem molecules are broken down first into biliverdin then bilirubin.
• Iron is reused in haemoglobin synthesis
• Bilirubin is carried by albumin from the spleen to the liver and metabolised there, in the production of bile.
• Bilirubin buildup results in jaundice (yellowing skin and eyes).

Haemoglobin Levels and Anaemia

• The World Health Organization defines anaemia by haemoglobin levels below:
  • 7.7 mmol/L (13 g/dL) in men
  • 7.4 mmol/L (12 g/dL) in women.
• Abnormally low red blood cell count or haemoglobin concentration can also indicate anaemia.

Laboratory Test Results:

• Specific lab results were reported -RBC count -HGB / haemoglobin level -HCT / haematocrit -MCV / mean corpuscular volume -MCH / mean corpuscular haemoglobin -MCHC / mean corpuscular haemoglobin concentration -WBC count -Differential white blood cell count components (e.g., neutrophils, lymphocytes, monocytes, eosinophils, basophils)
  • Platelets (PLT) -Serum iron -Total iron binding capacity (TIBC) -Serum Ferritin -Transferrin saturation
• Specific examples of results from a patient case were included.

Recommended Textbooks for Immunology

• Basic Immunology: Functions and Disorders of the Immune System by Abbas, Abul K., Andrew H. Lichtman, Shiv Pillai, and David L. Baker (7th ed., 2024, Elsevier)
• Immunology for Medical Students by Helbert, Matthew, and Roderick Nairn (3rd ed., 2017, Elsevier)

Other Important Points

• Co-operative binding: Binding of one oxygen molecule to haemoglobin causes a conformational change in the neighbouring polypeptide chains, increasing the affinity of the haemoglobin for further oxygen molecules.  
• Oxygen uptake and release.
• Normal developmental profile of haemoglobins. This displays the relative percentage of different types of haemoglobin (Hb) throughout development from fetus to newborn.

This quiz covers the structure and types of haemoglobin, including Haemoglobin A, A2, and fetal haemoglobin. It also discusses haemoglobin abnormalities and their impact on health, such as anaemia and sickle cell disease. Test your knowledge on this essential component of blood function!