preview:● We have extravascular and intravascular haemolysis.
● Extravascular – maybe the RBCs have a deformity in their shape and what can happen is that macrophages within the reticular endothelial system (e.g. the spleen), as blood is passing through the spleen, realise that those red cel...
● Refamiliarize yourself with the role of antibodies, what immune cells make these antibodies
and how they can bind to different antigens – particularly important when we look at the
role of antibodies as a cause of haemolytic anaemia.
● How do we group them and how can we classify them?
● Aetiology – how do they arise, what are the different mechanisms that can drive that type of
anaemia.
● What are the sample types that we require and what are the tests we perform?
● Premature destruction of RBCs (haemolysis) gives rise to the anaemia which gives rise to the
drop in haemoglobin because the red cells that contain that haemoglobin are being
destroyed.
● Erythrocytes can be destroyed due to intrinsic defects or by external factors (attacked by a
number of factors e.g., antibodies can bind to antigens on the surface of red cells and
destroy them). External factors are referred to as acquired factors.
● We have extravascular and intravascular haemolysis.
● Extravascular – maybe the RBCs have a deformity in their shape and what can happen is that
macrophages within the reticular endothelial system (e.g. the spleen), as blood is passing
through the spleen, realise that those red cells aren’t looking quite right, so they will take
those RBCs out of the circulation and break it down into a number of constituents (globin
into amin acids, release the iron from within the haemoglobin molecule and that will bind to
transferrin, the protoporphyrin ring will be broken down into bilirubin and that will be
excreted through the kidney and the liver. Extravascular haemolysis is the destruction of
RBCs outside of the circulation within the reticular endothelial system for example.
● Intravascular – the red blood cells are being destroyed actively within the circulation within
the vasculature so they are being broken down in the circulation and the haemoglobin is
then released within the plasma, numerous things can happen to it for example it can be
excreted by the kidney.
● Here it is shown that we can classify the haemolytic anaemia based upon the site at which
those RBCs are being destroyed.
● We can also classify them due to the reason or the cause of why the RBCs are being
destroyed.
● Hereditary – the RBCs have something intrinsically wrong with them, they have hereditary
defects and that is during their premature destruction.
, 5. Haemolytic Anaemia
● That could include membrane defects so it could have a defect within its RBC membrane
structure e.g., hereditary spherocytosis, another cause is hereditary elliptocytosis (extra
reading).
● They could also have defects within their metabolic pathways or their metabolism (second
lecture).
● Haemoglobinopathies – problem within the haemoglobin molecule.
● Acquired – these are factors that aren’t inherited but factors that act externally upon those
red cells leading to their destruction – those red cells are otherwise healthy and function
correctly but factors acting upon them lead to their destruction.
● One example is antibodies so it is antibody mediated – antibodies can bind to the surface of
red cells and lead to antibody mediated destruction. As well as autoimmune you can have
alloimmune haemolytic anaemia which is again mediated by antibodies and examples of
alloimmune mediated destruction are transfusion reactions and haemolytic diseases of the
new-born.
● Drugs, bugs and infections can also lead to early red cell destruction and also mechanical
factors.
● Those shown in purple are extra reading.
● There are a number of different phospholipids that can form part of the RBC membrane, but
you do have particular components on the outer and other types of phospholipids on the
inner leaflet, whilst they can flip, generally the different types of phospholipids give rise to
this asymmetry within the red cell membrane (extra reading – understand the different
types of phospholipids and why we have this asymmetry).
● Cell membranes don’t just consist of phospholipids there are a number of other structural
components there such as cytoskeletal and transmembrane proteins, example of this
include the band 3 transmembrane protein, proteins such as ankyrin, protein 4.1 and 4.2
and the cytoskeletal proteins such as alpha spectrin and beta spectrin.
● These proteins have a number of different important roles, different proteins will interact
with each other within the phospholipid bilayer and ultimately this whole network of
transmembrane proteins and cytoskeletal proteins will help to provide strength to the RBC
membranes, shape and flexibility. Its no good if the membrane is strong but isn’t able to
deform because they have to pass through harsh and dynamic environments such as a
narrow capillary and a vein so it must be able to withstand the pressures that act upon it
otherwise, they would burst.
● The phospholipid bilayer complemented by a number of different proteins ultimately helps
to provide shape, structure, support and flexibility to the red cell membrane. Its when we
have problems with one or more proteins within the cell membrane that gives rise to
disease conditions.
● Hereditary spherocytosis is an example of that.
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