The red blood cell structure and function Flashcards
Shape of RBC
Biconcave disc-shaped
Membrane of RBC
Flexible membrane but tough
RBC(surface area to volume ratio)
High surface area to volume ratio
Diameter of RBC
8 microns
What does RBC lack?
Lacks:
Nucleus
Mitochondria
ER
What is the cytoplasm of a RBC rich in?
Rich in haemoglobin
Primary function of RBC
• Primary function is transport of respiratory gases to and from tissue
RBC should be capable of traversing microvascular system without mechanical damage
In a red blood cell, what determines strength and flexibility?
Interactions between membrane and cytoskeletal proteins determines strength and flexibility
What is the outer hydrophilic region portion of an RBC composed of?
Outer hydrophilic portion composed of glycolipids, glycoproteins and proteins
What is the central hydrophobic layer of an RBC composed of?
Central hydrophobic layer containing proteins, cholesterol and phospholipids
What is the inner hydrophilic layer of an RBC composed of?
Inner hydrophilic layer of mesh like cytoskeletal proteins to support lipid bilayer
Distribution of membrane lipids
Asymmetric phospholipid distribution
What is between membrane lipids?
Unesterified free cholesterol between them
What lipids are on the outer layer of the membrane?
○ Uncharged phospholipids on outer layer:
§ Phosphatidyl choline
Sphingomyelin
What lipids are on the inner layer of the membrane?
○ Charged phospholipids on inner layer:
§ Phosphatidyl ethanolamine
Phosphatidyl serine
What does increased cholesterol cause in RBC?
RBC with increased cholesterol appear distorted resulting In acanthocytosis
What is a cause of target cells(RBC)?
Increase in cholesterol and phospholipid is a cause of target cells
Integral membrane proteins in RBC
Extend from outer surface and traverse entire membrane to inner surface
2 major integral membrane proteins
Glycophorins
Band 3:anion transporter
Other integral proteins
Na+/K+ ATPase, surface receptors
Peripheral proteins in RBC
Limited to cytoplasmic surface
What do peripheral proteins in RBC form?
Forms the RBC cytoskeleton
Peripheral protein (Spectrin)
§ Most abundant
§ Composed of alpha and beta chains
§ V.important in integrity of RBC membrane
□ Binds with other peripheral proteins to form cytoskeletal network of microfilaments
Controls biconcave shape and deformability of cell
Peripheral protein (Ankyrin)
Anchors lipid bilayer to membrane skeleton by interactions with spectrin and band 3
Peripheral protein (Protein 4.1)
§ Link with cytoskeleton to the membrane by means of its associations with glycophorin
Stabilises interaction of spectrin with actin
Peripheral protein (Actin)
Responsible for contraction and relaxation of membrane
What maintains surface area in RBC?
Strong cohesion between bilayer and membrane skeleton maintains surface area
Function of RBC(SHAPE)
Provides optimum surface area to volume ratio for respiratory exchange and essential to deformability
Function of RBC(Elasticity)
○ Provides elasticity:
Allows for passage through micro vessels
What do RBC regulate?
Regulate intracellular cation concentration
What do RBC act as?
Act as interface between the cell and its environment via membrane surface receptors
Membrane abnormalities with RBC
○ Hereditary elliptocytosis
§ Shape becomes eliptical
○ Hereditary spherocytosis:
Shape becomes spherical
Haemoglobin structure
• 4 polypeptides
2 alpha and 2 beta chains
RBC metabolism provide energy for:
○ Maintenance of cation pumps
○ Maintenance of Hb in reduced state
○ Maintenance of reduced sulfhydryl group in Hb and other proteins
Maintenance of RBC integrity and deformability
RBC metabolism in glycolytic pathway
○ Generates 90-95% of energy needed by RBC’s
○ Glucose is metabolized and generates 2 molecules of ATP
Functions in the maintenance of RBC shape, flexibility and the cation pumps
RBC metabolism in pentose phosphate pathway
○ RBC needs GSH to protect from oxidative damage
○ Pentose phosphate shunt provides the reducing power, NADPH
NADPH maintains glutathione in reduced form
RBC metabolism in methaemoglobin reductase pathway
○ Maintains Fe2+ state
In absence of this enzyme, methaemoglobin accumulates and cannot carry oxygen
RBC metabolism in Luebering Rapoport shunt
Permits the accumulation of 2,3-DPG which is essential for maintaining normal oxygen tension, regulating haemoglobin affinity
What is cytoplasmic viscosity of a RBC determined by?
Cytoplasmic viscosity determined by MCHC
• As MCHC rises, viscosity rises exponentially
