THE RED CELL MEMBRANEBLOOD BANKING

Prepared by:JOSEPHINE C. MILAN, RMT, MSMT

DEPARTMENT OF MEDICAL LABORATORY TECHNOLOGY

UNIVERSITY OF TABUK

OBJECTIVE and FOCUSTo correlate the structure of the red cell membrane with the occurrence of blood group antigens and how it is influenced by storage conditions.

RATIONALEQ: WHY DO WE STUDY THIS TOPIC ?The main purpose of blood transfusion is to supply

red cells which should remain viable and functional in the transfused patient/ recipient.

We have to understand the nature of RC membranes.

Mainly, blood groups antigens are located in /on the red cell membranes. The structure of the red cell membranes has certain roles for its functionality. There are important things to remember about the characteristics of red cell membranes.

TOPIC OUTLINE (based on syllabus)1. Red cell membrane structure2. Blood group antigens on the red cell

membrane3. Other properties of the red cell membrane

Main reference: Modern Blood Banking and Transfusion Practices by Denise M. Harmening. F.A. Davis Company. Philadelphia 5th ed

RED CELL FUNCTIONMain function of red cells:

To transport oxygen to tissues, and bind carbon dioxide from tissues to be brought to the lungs for excretion.

 

Important for RBC survival and function:

1. normal chemical composition and structure of the RBC membrane

2. hemoglobin structure and function

3. RBC metabolism

  

RED CELL MEMBRANE STRUCTURE

RBC Membrane:

1. RBC membrane is a semipermeable lipid bilayer supported by a protein meshlike cytoskeleton structure.

2 layer of lipidsproteins

RED CELL MEMBRANE STRUCTURE

RED CELL MEMBRANE STRUCTURE

2. Behaves as semisolid, with elastic and

viscous properties

important and critical for survival in the

circulation for 120 days going through numerous

cycles and passages through narrow veins and

sinusoids in the spleen.

in RBC deformability and permeability (crucial /

critical characteristics)

Biochemical structure

3. The cell membrane consists of :

protein,

lipids, and

carbohydrates

Ratio of- 52 (P) : 40 (L) :

8 (C)

PROTEINS IN THE MEMBRANEProteins : form a meshwork that traverse the lipid bilayer,

called membrane skeleton

2 types of proteins:

a. “integral” membrane proteins-which are in contact with both sides of the membrane; provides anion channels through the RBC membrane

b. “peripheral” proteins – located and limited to the cytoplasmic/inner surface of the membrane forming the RBC cytoskeleton; gives the cell its biconcave structure

Types of membrane PROTEINS

Integral Proteins Peripheral Proteins

Glycophorin A

Glycophorin B

Glycophorin C

Anion- exchange channel

protein

(band 3)

Spectrin

Actin (band5)

Ankyrin (band 2.1)

Band 4.1 and 4.2

Band 6

Adducin

jcm 11/2008

LIPIDS on the membrane phospholipids = 50 %;

cholesterol = 40 %;

glycolipids = 10 %

PHOSPHOLIPIDS form a bilayer

hydrophobic (nonpolar) tails towards inside of cell

hydrophilic (polar) head groups towards outside (extracellular) or the inside (cytoplasmic ) surface

the outer leaflet (external layer) contains electrically neutral glycolipids and choline phospholipids; while

the inner leaflet (internal cytoplasmic layer) predominantly contains phosphatidyl serine which is negatively charged.

CARBOHYDRATES on the membrane

Carbohydrates : forms the glycocalyx, serving as a negatively charged barrier , around the outside of the RBC membrane.

important in preventing cells from

adhering (attachment) to one another, or adhering to the endothelium (vein wall)

BLOOD GROUP ANTIGENS on the RC membrane

Majority carried on transmembrane proteins

Few antigens carried on glycosylphosphatidyl -inositol (GPI)- linked proteins or on glycolipids

Some transmembrane proteins interact with other transmembrane proteins

Ex: (band 3 and GPA) like Kell and Kx, Rh and RhAG

Some antigens are adsorbed from plasma : Lewis, Chido

Red cell membrane antigens

Red cell membrane antigens

PROPERTIES of RC membraneRBCs are biconcave disks, mean diameter of

7-8 µmHave more surface area than volume, which

creates a soft, pliable cell.Mature cells have no nucleus or

mitochondria, but it is packed with enough metabolism to exist for 120 days.

PROPERTIES of RC membraneDEFORMABILITY

red cell must be easily deformed/change shape advantageous when these pass through small openings or

channels, as in the spleen

Causes of loss of deformability / rigidity of cell :

Loss of ATP decreased phosphorylation of spectrin

Increase deposition of calcium onto cells

examples : spherocytes, “bite cells”

cell become easily lyzed

PERMEABILITY

important to prevent colloidal hemolysis and control the volume of RBC:

favorable to active cation transport

permeable to water and anions, like chlorides and bicarbonate

relatively impermeable to cations like Na and K

Intracellular : extracellular ratio of Na -1:12;

K -25:1

cationic pump for active transport (requiring ATP) of Na and K .

Ca is transported outward from cell, depends on Ca- ATPase pump

Calmodulin ( calcium-binding protein)- control the ATPase pump; prevent excessive intracellular buildup which leads to rigidity.

When ATP is depleted, Na and Ca accumulate intracellularly, K and water get out of the cell

dehydration and rigidity of cell easily sequestered

(trapped) in the spleen , thus decrease in RBC survival.

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