Structure and function of Normal Red Cells Flashcards
(23 cards)
Properties of RBC
Haemoglobin to carry oxygen
Enucleated - deformable, more room for oxygen
No mitochondria - can be a problem
High SA to volume ratio - efficient gas exchange
Flexible to squeeze through capillaries
Drawbacks of RBC properties
Full of Hb means high oncotic pressure and risk of swelling
No nucleus - no replication power, limited lifespan
No mitochondria- limited glycolysis and energy pressure
Flexibility means specialised membrane required
Role of red cell membrane proteins
Since they are proteins there is scope for genetic mutation in these membrane proteins which leads to disease
Why do red cells need energy?
To maintain specific ion concentration gradients and keep water out - pumps in the membrane that do this require energy
What is the structure of hemoglobin?
Tetramer - 4 globular protein elements
One Heme group with iron (Fe2+) in the centre
What is the molecular composition of adult Hb?
2 alpha and 2 beta chains
Where does RBC production occur?
Bone marrow
What is the role of the kidney in RBC production?
kidney has built in o2 sensory system
JGA in the nephron respond to hypoxia and sense RELATIVE LACK of O2
This generates erythropoietin which enters bloodstream and enters bone marrow, stimulating the proliferation of erythroid progenitor cells
How are red cells destroyed? Where does this occur
Site: Spleen (and liver)
Globin part changed to amino acids
Heme part changed to iron and bilirubin which is taken to liver and conjugated and further excreted in bile
Name the pathway used by RBC to generate ATP
Embden Meyerhof pathway (Glycolysis)
Which ion is used to protect Fe2+ from oxidation to Fe3+? Where does it come from?
NADH from Embden Meyerhof pathway
What are reactive oxidative species? Name some
Reactive oxidative species are free radicals with unpaired free electrons
Superoxide, Hydrogen peroxide
What is the effect of oxidative reactive species?
Interact with proteins of the RBC and damage their structure
How does a RBC protect itself from hydrogen peroxide?
Glutathione (GSH) is sacrificed by reacting with water to form an oxidised glutathione product (GSSG)
How are glutathione reserves replenished?
NADPH produced by hexose monophosphate shunt pathway gives H molecule to replenish GSH.
Whats the significance of G6PD?
It is the rate limiting step of the hexose monophosphate shunt which is responsible for NADPH production.
(No G6PD, No NADPH, No glutathione, increased oxidation and damage)
How does a RBC protect itself from superoxide?
Superoxide dismutase converts superoxide to hydrogen peroxide
How does Hb act as a buffer for CO2?
In high CO2 environments (tissues):
Equilibrium shifts to right
H+ ions buffered by deoxygenated Hb
HCO3 - ions pumped out and Cl- pumped in –> Cell swells
At lungs:
Equilibrium shifts to left
More CO2 produced which is blown off by lungs
HCO3- imported and Cl - excreted–> Cell shrinks
Describe the shape of the oxygen binding curve for adult Hb. Why?
Sigmoid curve
As one oxygen molecule binds to one subunit the shape of Hb molecule changes making it easier for the binding of the subsequent O2 molecules
This is called ALLOSTERIC EFFECT
Explain the oxygen dissociation curve
Curve shows that Hb has the capacity to tightly bind to O2 in areas of high PO2, and is able to dissociate with O2 to deliver it to areas of low PO2
What is the composition of foetal Hb? How is it different from adult Hb?
Composition - a2g2
At each PO2, foetal haemoglobin has a higher O2 saturation than adult Hb
This allows foetal blood to absorb more oxygen from maternal circulation
Name the small molecules that disrupt the Hb dissociation curve
1-3 BPG and 2-3 BPG
Which factors cause more O2 to be delivered to tissues (curve shifts right)?
H+
CO2
DPG (2-3BP)
Increased temperature
