Red Blood Cell Structure And Function Flashcards
What three major cell organelles are not present in erythrocytes?
Nucleus, mitochondria or ER
How big is a RBC?
8 microns
What is the primary function of a RBC?
Transport of respiratory gases to and from tissues
What determines the strength and flexibility of a RBC?
Cytoskeletal proteins interacting with the membrane lipid bilayer
What does a RBC membrane consist of (%wise)
50% proteins
40% lipids
10% carbohydrates
What is the outer hydrophilic portion of a RBC membrane composed of?
Glycolipids, glycoproteins and proteins
What is the central hydrophobic portion of a RBC membrane composed of?
Proteins, cholesterol and phospholipids
What is the inner hydrophilic portion of a RBC membrane composed of?
Mesh-like cytoskeletal proteins to support lipid bilayer
What proteins do the membrane include?
Sphingomyelin
Phosphatidyl ethanolamine
Phosphatidyl serine
Phosphatidyl choline
Where is phosphatidyl normally expressed?
Inside layer of membrane
Where is phosphatidyl serine expressed when its undergoing apoptosis?
It is expressed to the outer layer
What happens when phosphatidyl serine is expressed on the outer layer?
Macrophages recognise and engulf it to move it from the tissue
What is the breakdown of lipids in the RBC membrane?
60% phospholipids
30% cholesterol
10% sphingolipids
Where is there unesterified free cholesterol in RBCs?
Between the uncharged phospholipids of outer layer (phosphatidylcholine and sphingomyelin)
Between the charged phospholipids of inner layer
What are the two major integral membrane proteins in RBCs?
Glycophorins
Band 3 anion transporters
What are the three types of glycophorins?
A, B and C
Give some other integral proteins (that aren’t glycophorins or band 3)
Na/K ATPase, aquaporin surface receptors
What are peripheral proteins?
Limited to the cytoplasmic surface of membrane and forms the RBC cytoskeleton
What does the cytoskeleton do in the RBC?
Acts as a tough framework to support the bilayer
What are the 4 major peripheral proteins in RBCs?
Spectrin
Ankyrin
Protein 4.1
Actin
What is spectrin composed of?
Alpha and beta chains
What is the most abundant peripheral protein?
Spectrin
What does spectrin do in the RBC membrane?
Binds with other peripheral proteins to form the cytoskeletal network of microfilaments
What does spectrin control?
Biconcave shape and deformability of a cell
What does ankyrin primarily do in the RBC?
Anchors lipid bilayer to membrane skeleton
How does ankyrin anchor the lipid bilayer to the membrane skeleton?
By interacting with spectrin and band 3
What does protein 4.1 do in the RBC membrane (2)?
Link the cytoskeleton to the membrane by means of it’s associations with glycophorin
Stabilises interaction of spectrin with actin
What does actin do in the RBC membrane?
Contraction and relaxation of the membrane
What maintains the surface area in the RBC membrane
Strong cohesion between bilayer and membrane skeleton
Where are carbohydrates found in the RBC?
External surface
How are carbohydrate groups attached to proteins and lipids in RBC?
Glycosylation
How many monosaccharide units may carbohydrates contain?
2-60
Name the monosaccharides found on the erythrocyte membrane (8)
Galactose Mannose Fructose N-acetyl galactosamine Glucuronic acid Glucose Sialic acid N-acetyl glucosamine
Where are blood group antigens found?
On the RBC membranes and determines the blood group
Name the examples of RBC membrane protein antigens (3)
Rhesus, Duffy and Kidd
Name the examples of RBC membrane carbohydrate antigens (2)
ABO, Lewis
What are the 4 functions of RBC membranes?
Provides shape
Provides deformability and elasticity
Regulates intracellular cation concentration
Acts as the interface between the cell and its environment
How does the RBC membrane act as an interface between the cell and its environment
Membrane surface receptors
Why does RBC membrane provide deformability and elasticity?
Allows for passage through micro vessels (capillaries)
What does the RBC membrane shape provide?
The optimum surface area to volume ratio for respiratory exchange
What does an increase in free plasma cholesterol in the RBC membrane result in?
An accumulation of cholesterol in the RBC membrane
What is an acanthocyte?
RBC with increased cholesterol
What do acanthocytes look like?
Distorted- kinda spiky
What causes target cells?
Increase in cholesterol and phospholipids
What is a microcyte?
Where most RBCs are smaller than normal
What causes microcytes?
Less haemoglobin
What is hypochromia?
Less haemoglobin
What is a macrocyte?
Most RBCs are bigger than usual
What causes macrocytes?
More haemoglobin
What is anisocytosis?
Different red cell sizes
What is poiliocytosis?
Different red cell shapes
What is hereditary spherocytosis?
Defects in ankyrin, A or B spectrin, band 3 and protein 4.2
Where are the mutations in hereditary elliptocytosis?
A or B spectrin mutation
What does hereditary spherocytosis look like?
RBCs look like doughnuts (Hb gathers round the outside and none in the middle)
What does hereditary elliptocytosis look like?
Long thin cells
What does the SA:vol ratio facilitate in RBC membrane?
Deformation whilst maintaining constant surface area
What is cytoplasmic viscosity determined by in RBC membrane?
MCHC
How does MCHC determine cytoplasmic viscosity in RBC membrane?
As MCHC revises, viscosity rises exponentially
What does metabolism provide the energy for in RBC (4)?
Maintenance of canon pumps
Maintenance of RBC integrity and deformability
Maintenance of Hb in a reduced state
Maintenance of reduced sulfhydryl groups in Hb and other proteins
What are the 4 key metabolic pathways in erythrocytes?
Glycolytic
Hexose monophosphate shunt
Methemoglobin reductase pathway
Lumbering rapaport shunt
How much energy (%) does the glycolytic pathway generate for RBC?
90-95%
Where does the glycolytic pathway function in RBCs?
The maintenance of RBC shape, flexibility and the cation pumps
What provides the reducing power for NADPH in the RBC?
Pentose phosphate pathway
What does the RBC use GSH for?
To protect it from oxidative damage
What does the methemoglobin pathway do?
Maintains iron in the ferrous (Fe2+) state
What happens in the absence of methemoglobin reductase?
Methemoglobin accumulates and cannot carry oxygen
What does the lumbering rapoport shunt do?
Permits the accumulation of 2,3-DPG which is essential for maintaining normal oxygen tension, regulating haemoglobin affinity
