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swedishstreakMécanique

22 févr. 2014 (il y a 3 années et 3 mois)

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Hemtology


Lecture 10

Definition


the study of

blood, the blood
-
forming
organs, and blood diseases.


Hematology includes


Etiology


Diagnosis


Treatment


Prognosis


Prevention of blood diseases that affect
the production of blood


Mechanism of

coagulation.


Haematological

tests are mainly used
:




To investigate
anaemia
,




To investigate infections and pyrexia (fever) of


unknown origin (PUO),




To investigate clinically important
haemoglobinopathies
,




To monitor patients receiving antiretroviral


therapy (ART).

TESTS


Measurement of
haemoglobin

and basic
investigation of
anaemia


(
Hb
)



Measurement of packed cell
volume and
calculation of
red
cell indices (PCV)


White blood cell (WBC)
count (TLC)



Platelet count



Differential WBC count
(DLC)



Reporting blood films: red cells,
white cells
,
platelets



Erythrocyte sedimentation rate



Reticulocyte

count





Investigation of sickle cell disease



Blood film appearances in
thalassaemia

syndromes



Haemoglobin

electrophoresis



Tests to screen for a bleeding disorder

Standard operating procedures


SOPs are written, up to date instructions and information


An SOP
needs to
include
:


Value
of test, i.e. reasons for performing it
.


Principle of test, i.e. type of technology used
.


Specimen details, including volume required,



container to use


Equipment required: its use,
performance checks
,
cleaning, maintenance and source
of replacement
parts.


Reagents or stains used



Control
material


Method of test including details of procedure
, calculations
,
quality
control


Sources of
error


Reporting test
result


Verification of test result and action to take
when a
result is
seriously abnormal or
unexpected


Interpretation of test result and when indicated,
a
reference
range
.


Information on the cost of a test, e.g. high
, medium
, low.

Composition of blood


Pale yellow fluid part plasma (55%)


95% water


Solute part (
proteins, mineral ions, organic molecules,



hormones
, enzymes, products of digestion, and



waste
products for
excretion)



Cellular part (45%)


Red blood cell


White blood cell


Platelets

Main functions of the blood


Transportation and
distribution


Functions of blood


Transportation and distribution (oxygen,
carbondioxide
, nutrients, hormones)


Regulatory (buffer system with pH 7.35
-

7.45,
plasma osmotic pressure, temperature
regulation)


Protective (coagulation, leukocytes)


Blood cell formation


All blood
cells originate
from a common population
of
pluripotent

stem
cells
in the bone marrow. The
pluripotent

stem cells
proliferate and differentiate
into two distinct
cell lines
:
myeloid and lymphoid
.


Myeloid
stem
cells:


blood cell
committed progenitor
cells


monocytes



basophils


neutrophils



red
cells


Eosinophils


platelets

Lymphoid stem
cells


lymphoid progenitor
cells


B & T
lymphocytes



Early
development of B lymphocytes



takes
place in the bone marrow and



lymphoid
tissues, and development of T

lymphocytes in
the thymus.


Regulation of
hematopoiesis


Haematopoiesis

is regulated by a range of
cytokines
(
growth factors) which include interleukins, stem
cell
factors
, colony stimulating factors, erythropoietin
and


thrombopoietin
.


They interact with specific
receptors on
the surface of
haematopoietic

cells, regulating the


proliferation
and differentiation of progenitor cells
, and
the maturation and functioning of mature cells.

Disorders of red blood cells


Anaemia



Haemoglobinopathies

(
thalassaemias
, abnormal


haemoglobins
)



Disorders due to red cell enzyme defects, e.g.


G6PD
deficiency



Disorders due to red cell membrane defects, e.g.


hereditary
spherocytosis



Polycythaemia


Morphologically
anaemia

can be classified by:



Red cell size
with the terms:




Normocytic

referring to normal size red cells


(approximately 8
μ
m in diameter),




Microcytic

referring to smaller than normal


red cells,




Macrocytic

referring to larger than normal


red cells.


Haemoglobinization

of red cells with the terms:




Normochromic
, describing normal staining
of red
cells as
seen when
haemoglobinization

is adequate
. The cells contain
a small area
of central
pallor (no more than one third of
the
cell’s
diameter) due to the biconcavity of
red cells
.




Hypochromic
, describing pale staining of
red cells
, as seen
when
haemoglobinization

is inadequate
.
Hypochromic

cells
show
an increased
area of central pallor.

Structure of hemoglobin


Adult type hemoglobin contains 4 polypeptide chains.



two alpha (
α
) chains containing 141 amino acids



two beta (
β
) chains containing 146 amino acids



Each polypeptide chain is combined with an iron
containing
porphyrin

pigment called
haem

which is


the oxygen carrying part of the
haemoglobin

molecule.

THALASSAEMIA SYNDROMES


Thalassaemia

syndromes are inherited
disorders caused
by a reduction in the rate of synthesis
of alpha (
α
)
or
beta
(
β
)
haemoglobin

chains
.


Alpha
thalassaemias

are caused by defective


synthesis
of
alpha (
α
) chains
.



Beta
thalassaemias

are caused by defective


synthesis
of
beta (
β
) chains
.


Significant imbalance in the synthesis of
alpha and beta


chains
leads to:




Inadequate
haemoglobin

production and
the red cells
appear
microcytic

and
hypochromic
.




Accumulation of free uncombined
globin

chains in
normoblasts

and red cells, causing the destruction


of
red cell precursors in the bone
marrow (
ineffective
erythropoiesis
) and red cell
destruction by
the spleen.

ABNORMAL HAEMOGLOBINS


HbS

which has a wide distribution in tropical Africa, parts
of India, the Caribbean, Mediterranean region and
elsewhere in people of African descent.


valine

replaces
glutamic

acid in the beta
globin

chain



HbC

which is found only in West Africa and elsewhere
in people of West African descent.


glutamic

acid is replaced by lysine in the beta
globin

chain

Hemoglobin D


In
HbSDPunjab

disease there is moderate to severe
haemolytic

anaemia

and the blood film is similar to that
seen in sickle cell
anaemia
.



HbE


The blood film shows
microcytosis

and
hypochromia

with
target cells