Red blood cells - structure and function Flashcards
What is the primary function of a RBC
To transport respiratory gases to and from the tissues
How does a RBC travel through the microvascular system without mechanical damage
The RBC membrane is extremely tough yet flexible
Interactions between the membrane and cytoskeletal proteins determines strength and flexibility
What does the outer part of the RBC membrane consist of
A hydrophilic portion containing glycolipids, glycoproteins and proteins
What does the central part of the RBC membrane consist of
A hydrophobic layer containing proteins, cholesterol and phospholipids
What does the inner part of the RBC membrane consist of
A hydrophilic layer of mesh-like cytoskeletal proteins to support the lipid bilayer
Where is phosphatidyl situated in the RBC and why
On the inside of the cell membrane since macrophages can detect it
Which phospholipids are on the outer layer
Uncharged phospholipids, phosphatidyl choline and sphingomyelin
Which phospholipids are on the inner layer
Charged phospholipids, phosphatidyl ethanolamine and phosphatidyl serine
What does an increase in free plasma cholesterol mean for RBC’s and why
It will result in an accumulation of cholesterol in the RBC membrane since membrane cholesterol exists in free equilibrium with plasma cholesterol
What happens if a RBC has too much cholesterol
Acanthocytosis (spur cells) - Cells appear to have spikes on the cell membrane
What happens if a RBC has too much cholesterol and phospholipid
Target cells - Cells look like a bullseye because of a disproportional increase in the ratio of surface membrane area to volume
Where are integral membrane proteins found
Extend from the outer surface and transverse the entire membrane to the inner surface
What are the 2 major integral membrane proteins
- Glycophorins (A,B and C)
- band 3 (anion transporters)
What are some other integral membrane proteins
- Na+/ATPase
- Aquaporin 1
- Surface receptors e.g. TfR
Where are peripheral proteins found
Limited to cytoplasmic surface of membrane and forms the RBC cytoskeleton
What are the major peripheral proteins include
- Spectrin
- Ankyrin
- Protein 4.1
- Actin
What are spectrin proteins and what are they made of
The most abundant peripheral protein
Composed of alpha and beta chains
What do ankyrin proteins do
Primarily anchors lipid bilayer to membrane skeleton via interaction with spectrum and band 3
What does protein 4.1 do
Links the skeleton to the membrane by means of its associations with glycophorin
Stabilises interaction of spectrin with actin
What do actin proteins do
Responsible for contracting and relaxation of membrane
Strong cohesion between bilayer and membrane skeleton maintains surface area
What is the function of spectrin proteins
Very important in RBC membrane integrity since it binds with other peripheral proteins to form the cytoskeleton network of microfilaments
Controls biconcave shape and deformability of cell
How does the shape of the RBC relate to its function
- Provides the optimum surface area to volume ratio for respiratory exchange
- Provides elasticity allowing the passage through micro vessels
What is hereditary elliptocytosis and how does it happen
RBC is permanently elliptical since there is a problem with ankyrin or spectrin
What is hereditary spherocytosis and how does it happen
RBC cannot retain its shape since there is a problem with band 3 and actin and ankyrin/spectrin
What requires energy to be maintained in the RBC
- Cation pumps
- Hb in reduced state
- Reduced sulfhydryl groups in Hb and other proteins
- RBC integrity and deformability
What are the different RBC metabolic pathway
- Glycolytic pathway or Embden-Meyerhof pathway
- Pentose-phosphate pathway
- Methaemoglobin reductase pathway
- Luebering-rapoport shunt
What does the glycolytic pathway do and how do it work
- Generates 90-95% of energy needed by RBCs
- Glucose is metabolised and generates two molecules of ATP
- Functions in the maintenance of RBC shape, flexibility and cation pumps
Why is the pentose phosphate pathway needed and how does it work
RBC needs reduced glutathione (GSH) to protect from oxidative damage
This pathway provides the reducing power, NADPH
NADPH maintains GSH and protects Hb and membrane proteins
What does the methaemoglobin reductase pathway do
Maintains iron in the ferrous (Fe2+) state
In the absence of this enzyme, methaemoglobin accumulates and it cannot carry oxygen
What does the Luebering-rapoport shunt
It permits the accumulation of 2,3-diposphoglycerate
This is essential for maintaining normal oxygen tension, regulating haemoglobin affinity
What features of the RBC help it to withstand life without structural deterioration
- The geometry of the cell; SA to V ratio - facilitates deformation whilst maintaining a constant surface area
- Membrane deformability - spectrin molecules undergo reversible change in conformation, some uncoiled and extended, others compressed and folded
- Cytoplasmic viscosity determined by MCHC - as MCHC rises, viscosity rises exponentially
