Red Blood Cell Membrane

Question 1

The Red Blood Cell 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

RED BLOOD CELL MEMBRANE components and %

Answer 2

LIPIDS 40% - Phospholipids (20%), - Cholesterol (20%)
CARBOHYDRATES 10%
PROTEINS 50%

Question 3

3 Major structural elements

Answer 3

Lipid bilayer
Integral Proteins
Membrane Skeleton

Question 4

Lipid Bilayer consists of

Answer 4

Phospholipids
Cholesterol

Question 5

Integral Proteins consist of

Answer 5

Band 3
Glycophorins

Question 6

Membrane Skeleton

Answer 6

Spectrin
Ankyrin
Protein 4.1/4.2
P55
Actin
Adducin

Question 7

What are the VERTICAL INTERACTIONS that make up the rbc membrane?

Answer 7

Ankyrin
α/β spectrin
Band 3
Protein 4.2

Question 8

HORIZONTAL INTERACTION

Answer 8

α/β spectrin
Ankyrin
Protein 4.1

Question 9

Lipid bilayer functions

Answer 9

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 10

Functions of carbohydrates

Answer 10

Carbohydrates
Serve as blood group antigens

Question 11

Functions of membrane proteins

Answer 11

A. Integral
Band 3 acts as an anion exchange protein – Allows RBCs to exchange Cl- for HCO3-
Transport of CO2 from tissues to the lungs

B. Cytoskeleton
Determine RBC integrity, shape and flexibility (deformability)

Question 12

Membranopathies characteristics and examples

Answer 12

Mostly hereditary disorders
Cause haemolytic anaemias

Hereditary spherocytosis
Hereditary elliptocytosis
South-East Asian ovalocytosis
Hereditary stomatocytosis
Hereditary pyro-poikilocytosis

Question 13

HEREDITARY SPHEROCYTOSIS (HS) unique quality

Answer 13

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

Question 14

Aetio-pathogenesis of HEREDITARY SPHEROCYTOSIS (HS) - Cause

Answer 14

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 15

Clinical features of HEREDITARY SPHEROCYTOSIS (HS)

Answer 15

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

Question 16

Investigations of HEREDITARY SPHEROCYTOSIS (HS)

Answer 16

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 17

Treatment of HEREDITARY SPHEROCYTOSIS (HS)

Answer 17

Blood transfusion to correct anaemia
Splenectomy
Cholecystectomy
Haematinics

Question 18

HEREDITARY ELLIPTOCYTOSIS (HE)

Answer 18

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

Question 19

SOUTH-EAST ASIAN OVALOCYTOSIS

Answer 19

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