MEMBRANE Flashcards
Average volume RBC
90 fL (range: 80-100 fL)
Characteristic of RBC which facilitates its oxygen-carbon dioxide transport function
Biconcave disc shape
Average surface area of RBC
140 μm2
RBC plasma membrane thickness
5 µm thick
allows RBCs to adjust to small vessels in the microvasculature and still maintain a
constant surface area: volume ratio
Deformability
RBC deformability depends on:
RBC geometry
Relative cytoplasmic (hemoglobin) viscosity
Membrane elasticity (pliancy)
Changes in the surface area to
volume ratio causes
RBC fragmentation
and lysis
due to ↓ surface area
Fragmentation
due to ↑ cell volume
Lysis
Relative cytoplasmic (hemoglobin) viscosity → MCHC
32% – 36%
Normal erythrocyte Hgb concentration has a
low viscosity (fluid)
Precipitated hemoglobin →
Heinz bodies
Polymerized hemoglobin
Hb S
Crystallized hemoglobin
Hb C
3 Basic Functions of the RBC Membrane
- Regulates osmotic pressure
- Regulates cation concentration
- Regulates gas concentrations
RBC MEMBRANE COMPOSITION AND STRUCTURE
Lipids (40%)
Carbohydrate (8%)
Protein (52%)
Predominant lipids in RBCs
phospholipids and cholesterol
Arranged in a double layer called lipid bilayer leaflet | provides
membrane fluidity
Phospholipids
External surface of lipid bilayer leaflet predominant composition
phosphatidylcholine and sphingomyelin (with 5% glycolipid)
sugar-bearing lipids | support carbohydrate side chains | anchors
Glycolipid
bears blood group antigens
glycocalyx
Internal surface of lipid bilayer leaflet predominant composition
phosphatidylethanolamine and phosphatidylserine
regulates membrane fluidity and membrane permeability | maintains surface area: volume ratio
Cholesterol
Cholesterol content depends on
plasma cholesterol, bile acids, activity of LCAT (lecithincholesterol acyltransferase)
↑ cholesterol, phospholipids
Codocyte
Abnormal L/S ratio
Acanthocyte
↓ cholesterol
Ovalocyte
↑ cholesterol → ↑ membrane strength results to
↓ elasticity
layer of carbohydrates whose net negative charge prevents microbial attack and protects
the RBC from mechanical damage
Glycocalyx