the red cell membrane
DESCRIPTION
THE RED CELL MEMBRANE. BLOOD BANKING Prepared by: JOSEPHINE C. MILAN, RMT, MSMT DEPARTMENT OF MEDICAL LABORATORY TECHNOLOGY UNIVERSITY OF TABUK. OBJECTIVE and FOCUS. - PowerPoint PPT PresentationTRANSCRIPT
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THE RED CELL MEMBRANEBLOOD BANKING
Prepared by:JOSEPHINE C. MILAN, RMT, MSMT
DEPARTMENT OF MEDICAL LABORATORY TECHNOLOGY
UNIVERSITY OF TABUK
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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.
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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.
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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
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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
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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
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RED CELL MEMBRANE STRUCTURE
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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)
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Biochemical structure
3. The cell membrane consists of :
protein,
lipids, and
carbohydrates
Ratio of- 52 (P) : 40 (L) :
8 (C)
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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
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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
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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.
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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)
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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
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Red cell membrane antigens
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Red cell membrane antigens
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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.
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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
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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 .
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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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