Rbc Membrane

Question 1

Rbc characteristics

Answer 1

7-8μm in diameter
•Flexible biconcave
•Disc shaped
•Anuclear
•Central area of pallor
•Enclosed in a thin membrane called the RED BLOOD CELL MEMBRANE

Question 2

Structure of rbc membrane

Answer 2

LIPIDS 40% -
Phospholipids (20%), - Cholesterol (20%)

•CARBOHYDRATES 10%

•PROTEINS 50%

Question 3

Major structural elements

Answer 3

• lipid bilayer ( phospholipids and cholesterol)
• integral proteins (band 3 and glycoproteins)
• membrane skeleton (Spectrin, ankyrin,adducin, protein 4.1 and protein 4.2, p55, actin.

Question 4

Vertical interaction proteins

Answer 4

These are structural elements that are vertically arranged and are responsible for vertical interactions
They include:
•Ankyrin
•α/β spectrin
•Band 3
•Protein 4.2

Question 5

Horizontal interaction proteins

Answer 5

These are structural elements that are horizontally arranged and are responsible for horizontal interactions
They include:
•α/β spectrin
•Ankyrin
•Protein 4.1

Question 6

Rbc membrane fxns ( lipid bilayer)

Answer 6

•Forms a matrix in which membrane proteins reside
•Aids selective permeability of substances into and out of the cell
•Plays a role in red cell adhesion to endothelium

Question 7

Rbc membrane fxns ( carbohydrate)

Answer 7

Serve as blood group antigens

Question 8

Rbc membrane fxns ( proteins)

Answer 8

A. Integral
•Band 3 acts as an anion exchange protein – Allows RBCs to exchange Cl- for HCO3-
•Transport of C02 from tissues to the lungs
B. Cytoskeleton
•Determine RBC integrity, shape and flexibility (deformability)

Question 9

Membranopathies

Answer 9

These are defects in the rbc membrane
They are mostly hereditary disorders
They cause hemolytic anemias
They include:
Hereditary spherocytosis
Hereditary elliptocytosis
South-East Asian ovalocytosis
Hereditary stomatocytosis
Hereditary pyro-poikilocytosis

Question 10

Hereditary spherocytosis

Answer 10

Most common among the membranopathies
•Most common cause of haemolytic anaemia among Northern Europeans

Question 11

Aetiopathogenesis of hereditary spherocytosis

Answer 11

Caused by defects in the proteins responsible for the VERTICAL INTERACTION
•Autosomal Dominant (rarely may be autosomal recessive)
•RBCs progressively loose membrane (loss of surface area relative to volume)
•The red cells consequently appear spherical instead of biconcave disc shaped

Spherocytes are not flexible, thus cannot pass through the micro-circulation
•Consequently, they are destroyed by the spleen

Question 12

Clinical features of hereditary spherocytosis

Answer 12

➢Symptoms and signs of anaemia (can present at any age)
➢Jaundice
➢Epigastric pain (due to pigment gallstones)
➢Splenomegaly

Question 13

Investigations of hereditary spherocytosis

Answer 13

•Full blood count and differentials - ↓PCV
•Reticulocyte count - ↑
•Blood film – microspherocytes
•Eosin-5-maleimide rapid stain analysis
•Membrane protein electrophoresis
•Osmotic fragility test
•Direct Coombs test – To exclude autoimmune haemolytic anaemia

Question 14

Treatment of hereditary spherocytosis

Answer 14

•Blood transfusion to correct anaemia
•Splenectomy
•Cholecystectomy
•Haematinics

Question 15

Hereditary elliptocytosis

Answer 15

Another cause of hereditary haemolytic anaemia

Question 16

Aetiopathogenesis of HE

Answer 16

Due to defects in the HORIZONTAL INTERACTION
•RBCs appear as elliptocytes
•There may be no evidence of haemolysis
•Occasionally, patients MAY require splenectomy.

Question 17

South- east Asia ovalocytosis

Answer 17

Common in the Philippines, Malaysia and Indonesia
•Caused by a defect in the Band 3 protein
•Most cases are asymptomatic
•RBCs appear as oval shaped called ovalocytes
•Ovalocytes are rigid and resistant to malaria
•Heterozygote states thus confer protection from P.falciparum and P.vivax malaria

Question 18

Hereditary stomatocytosis

Answer 18

Cell membrane “leaks” sodium and potassium ions
•Increased tendency of RBCs to swell and burst
•Due to various mutations in Band 3 protein affecting ion exchange
•RBCs take the shape of a cup with a mouth- shaped area of central pallor (stoma)