Erythrocytes

Why are RBC red?

Because of the oxygen carrying protein, hemoglobin

How are RBC good oxygen carriers?

• Do not have nucleus or organelles

• Do not reproduce

• Do not have extensive metabolic activities

Why do RBC have large quantities of carbonic anhydrase?

It catalyses the reaction between CO2 and H2O to form bicarbonate ions

How are RBC adapted to squeeze through capillaries?

They are small, biconcave in shape and have strong and flexible plasma membranes

What are the factors that affect RBC counts and hemoglobin levels

• Age

• Sex

• Exercise

• Nutritional status

• Lactation

• Pregnancy

• Excitement

Why do RBC have limited lifespan?

Due to wear and tear on plasma membrane

Therefore how is normal quantities maintained?

New mature cells must enter circulation at an equal rate of RBC destruction

What is haemoglobin made of?

• Haeme which is a non-protein pigment associated with Fe2+

• Globin consist of 4 polypeptide chains (2a and 2B chains)

Why does foetal haemoglobin have better affinity to oxygen?

Because they have to function in low oxygen concentration environment

What are the 5 types of haemoglobins and their functions

• Oxyhemoglobins

  • Function: Functional form

• Myoglobin

  • Function: Temporary oxygen store in muscle fiber

    • Only has 1 iron and 1 haeme gorup

• Carbaminohaemoglobin

  • Function: Transient type of Hb when CO2 in bound to globin portion for transport to lungs

• Carboxyhemoglobin

  • Function: Complexed with carbon monoxide

• Methemoglobin

  • Function: Formed by oxidation of Fe2+ —> Fe3+

Describe the destruction of RBC

• Macrophage in RE system of liver, spleen and red bone marrow phagocytise worn out RBC

• Globin and heme portion split apart

  • Globin broken into amino acids and recycled

• Iron removed as Fe3+

  • Transported by transferrin

• In muscle fibers, liver cells, macrophages of spleen and liver the Fe3+ detaches from transferrin

  • Then transferred to ferritin and hemosiderin for storage

• Fe3+ taken up by RBC precursor cells through endocytosis

• Heme degraded into biliverdin (green) —> bilirubin (yellow/orange)

  • Bilirubin enters blood and transported to liver

  • Secreted into bile and large intestines

  • Becomes conjugated with glucuronic acid so it will be water soluble

  • In large intestines, bilirubin —> urobiliogen

    • Some urobilinogen absorbed back into blood and secreted in urine as urobilin (yellow pigment)

    • Most urobilinogen is elimainated in faces as stercobilin (brown pigment)