Red blood cell structure and function Flashcards
(27 cards)
describe the structure of RBCs
→Mammalian RBCs are biconcave disc-shaped.
→ have flexible membranes with a high surface-to-volume ratio.
→They are 8 microns in diameter but are able to deform and pass through capillaries or RES without fragmentation.
→The RBC is unique amongst eukaryotic cells as it lacks a nucleus, mitochondria and ER, and its cytoplasm is essentially rich in haemoglobin.
what is the function of red blood cells and what are the requirements for this ?
→ transport of respiratory gases to and from the tissues.
→ RBC should be capable of transversing the microvascular system without mechanical damage, and retain its shape
→the red cell membrane should be extremely tough, yet highly flexible
describe the structure of the red blood cell membrane and what it consists of
→semipermeable lipid bilayer with proteins scattered throughout.
It consists of
→an outer hydrophilic portion composed of glycolipids, glycoproteins and proteins
→ a central hydrophobic layer containing proteins, cholesterol and phospholipids
→an inner hydrophobic layer of mesh-like cytoskeletal proteins to support the lipid bilayer
how much by % do RBC membrane lipids make up?
and describe the distribution of RBC membrane lipids
→RBC membrane lipids make up about 40% of the membrane.
→There is an asymmetrical phospholipid distribution throughout the RBC membrane.
→ unesterified free cholesterol between the phospholipids
what are the types of phospholipids in the RBC membrane and where are they found?
UNCHARGED PHOSPHOLIPIDS IN THE OUTER LAYER →phosphatidylcholine (PC)
→sphingomyelin (SM)
CHARGED PHOSPHOLIPIDS IN THE INNER LAYER →phosphatidyl ethanolamine (PE)
→ phosphatidyl serine (PS)
how does membrane cholesterol exist within a RBC?
→Membrane cholesterol exists in free equilibrium with plasma cholesterol.
what does an increase in free plasma cholesterol mean?
→An increase in free plasma cholesterol results in an accumulation of cholesterol in the RBC membrane.
what % of the membrane do RBC membrane proteins make up?
50%
what are the two categories of RBC membrane proteins?
→integral membrane proteins and peripheral membrane proteins
describe integral membrane proteins and give examples
→extend from the outer surface and traverse the entire membrane to the inner surface.
→Two major integral membrane proteins are Glycophorins (types we’ve identified are A, B and C) and Band 3 (an anion transporter).
→other integral membrane proteins:
→ Na+/K+ ATPase
→Aquaporin 1
→surface receptors (eg. TfR)
describe peripheral membrane proteins and give examples
→limited to the cytoplasmic surface of the membrane and form the RBC cytoskeleton.
Major peripheral proteins include: → spectrin →ankyrin →protein 4.1 →actin
what are the functions and properties of spectrin?
→Spectrin is the most abundant peripheral protein.
→composed of α and β chains
→ important in RBC membrane integrity as it binds with other peripheral proteins to form the cytoskeletal network of microfilaments.
→It controls the biconcave shape and deformability of the cell.
what is the function of ankyrin?
→anchors the lipid bilayer to the membrane skeleton via interaction between spectrin and Band 3.
what is the function of protein 4.1?
→links the cytoskeleton to the membrane by means of its associations with glycophorin.
→It also stabilizes the interaction of spectrin with actin.
what is the function of actin?
→responsible for the contraction and relaxation of the membrane.
what are the functions of the RBC membrane?
→shape : provides the optimum surface area to volume ratio for respiratory exchange
→provides deformability and elasticity : allows for passage through microvessels (capillaries)
→regulates intracellular cation concentration
what are red cell metabolic pathways for?
Metabolism provides energy required for:
→maintenance of cation pumps
→maintenance of Hb in its reduced state
→maintenance of reduced sulfhydryl groups in Hb and other proteins
→maintenance of RBC integrity and deformability
what are the key metabolic pathways in RBCs?
→Glycolytic or Embden-Meyerhof Pathway
→ Pentose Phosphate Pathway
→Methaemoglobin Reductase Pathway
→ Luebering-Rapoport Shunt
what does the glycolytic or Embden-Meyerhof pathway do?
→It generates 90-95% of the energy needed by RBCs.
→In it, glucose is metabolised and generates two molecules of ATP.
→It functions in the maintenance of the RBC shape, flexibility and cation pumps.
what does the pentose phosphate pathway do?
→RBCs need GSH to protect them from oxidative damage.
→The pentose phosphate Pathway provides the reducing power, NADPH.
→NADPH maintains glutathione in its reduced form (GSH).
what is the methaemoglobin reductase pathway for?
→It maintains ion in its ferrous state (Fe2+).
→In the absence of this enzyme, methaemoglobin accumulates and cannot carry oxygen.
what does the Luebering-Rapoport shunt do?
→permits for the accumulation of 2,3-DPG, which is essential for maintaining normal oxygen tension, regulating haemoglobin affinity.
what are the methods RBCs use to avoid structural deterioration?
→geometry of cell & surface area to volume ratio facilitates deformation whilst maintaining constant surface area
→membrane deformability
spectrin molecules undergo reversible changes in conformation, some are uncoiled and extended, whilst others are compressed and folded
→cytoplasmic viscosity determined by MCHC :
as MCHC rises, viscosity rises exponentially
what determines the strength and flexibility of RBCs?
→ interactions between the membrane & cytoskeletal proteins
