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Clinical pathology …………………………………………………………………………………………….. Haematology
Haematology
Haematology : is the study of the cellular elements of the blood , which can
be divided into three categories :
1. The erythrocytes or red blood cells: are responsible for oxygen
transport from the lung to all tissues of body .
2. The leukocyte or white blood cells: are responsible in various ways
for repelling foreign invaders
3. The thrombocyte or platelets : are responsible for routine maintenance
and repair of blood vessels.
Occasionally other cells which are not normally present in circulation can
also be detected in ablood sample , such as mast cells or plasma cells –
usually because the cells are neoplastic .
The erythron : is the name given to the organ of the body technically
classified as connective tissue, which comprises all the red cells plus red
cells producing tissue – essentially the relevant fractions of the blood ,
spleen and bone marrow. The single function of the erythron is oxygen /
carbon dioxide transport between the tissue and the lungs, with haemoglubin
as O2/CO2.
Characteristics of Blood
1.
bright red (oxygenated)
2.
dark red/purplish (unoxygenated)
3.
much more dense than pure water
4.
pH range from 7.35 to 7.45 (slightly alkaline)
Dr. Hella J. Al- Fatalwy
Clinical pathology …………………………………………………………………………………………….. Haematology
5.
slightly warmer than body temperature.
Major Functions of Blood
1. Distribution & Transport
a.
oxygen from lungs to body cells
b.
carbon dioxide from body cells to lungs
c.
nutrients from GI tract to body cells
d.
nitrogenous wastes from body cells to kidneys
e.
hormones from glands to body cells
2.
Regulation (maintenance of homeostasis)
a. maintenance of normal body pH
i.
blood proteins (albumin) & bicarbonate
b. maintenance of circulatory/interstitial fluid
electrolytes aid blood proteins (albumin)
c. maintenance of temperature (blushed skin)
3.
Protection
a.
platelets and proteins "seal" vessel damage
protection from foreign material & infections
i. leukocytes, antibodies, complement proteins
Dr. Hella J. Al- Fatalwy
Clinical pathology …………………………………………………………………………………………….. Haematology
Red cell production : this take place in the red (haemapoeitic ) bone
marrow ( not in the white fatty marrow). this haemapoeitic bone marrow is
much more extensive in young animals than in mature one where it retreat to
the centers of the bone.
When the erythrocytes mature and when they are flexible enough they can
slide into the circulation through openings in the sinusoidal walls. The total
maturation time varies between species from about 4-5 days in cattle to
about 1 week in dog.
start of all blood cells
series
large nucleus , nucleoli
no nucleoli
early contain viable nucleus
,late nucleus become non
viable
adult red cells anuclear in
mammals biconcave disc
Dr. Hella J. Al- Fatalwy
Clinical pathology …………………………………………………………………………………………….. Haematology
Erythrocyte life spin
This varies between species ,about 120 days in human ,2 months in bigs and
over 5 months in cattle , sheep are unique in having to populations of red
cells , one short lived (70) days , and the other long lived 150 days . In
certain diseases particularly some nutritional diseases , the survival time of
erythrocyte is shortened like ( iron, vitamin B12, folic acid ).
Erythrocyte breakdown
This occurs in three ways :
1. The cell may be fragmented into pieces enough for the
reticuloendothelial system to take up
2. When the enzymes present in the cell membrane are used up the much
more fragile cell breaks up and is phagocytosed .
3. The whole cell may be phagocytosed directly .
The hemoglobin from the defunct red cells is also break down . the protein
(globin) fraction is lysed into its components (amino acids ) which join the
general body amino acids pool, either being restructured into new protein as
needed or being deaminated with the amino acids residue axcreted as urea.
The hemoglobin fraction loses its iron atom which is not excreted but is
recycled into a new hemoglobin molecule.
Control of erythropoiesis
Normally , production and destruction of red cells are kept in balance , so
that , total erythrocyte numbers are constant (e.g.) .
Dr. Hella J. Al- Fatalwy
Clinical pathology …………………………………………………………………………………………….. Haematology
The hormone responsible for the regulation of the rate of erythropoiesis is a
glycoprotein with a molecular weight of about 60000- 70000 Daltons called
erythropoietin (EP) it is not species specific . fetal and maternal EP are quite
separate because the hormone does not cross the placenta . the principal site
of EP production is the kidney . the fundamental stimulus to EP production
is tissue hypoxia.
Erythropoietin affects the red cells production in four ways
1. More stem cells differentiate to red cells precursor .
2. Stages of red cells development are speeded up .
3. Transit time out of bone marrow is reduced .
4. Immature red cells are released.
The certain endocrine organs involved in the modification EP production are
the pituitary , adrenal ,thyroid and gonads. The hormones actually affect cell
membrane and hence tissue oxygen requirements and so have a feed back on
EP synthesis.
1. Hormones which increase EP production : androgens , cortisol ,
thyroxin , adrenaline , nor adrenaline, prolactin , growth hormone ,
TSH and ACTH .
2. Hormones which decrease EP production : estrogen .
Dr. Hella J. Al- Fatalwy
Clinical pathology …………………………………………………………………………………………….. Haematology
Basic interpretation of red cell parameters
There are main red cell parameters which used in veterinary haematology.
1. The packed cell volume (PCV) or haematocrit
 The primary red cells measurements which gives a basic
assessment of the size of the circulating erythron
 This is simply measurement of the fraction of the blood
volume which is occupied by erythrocyte .
 It is expressed as either a percentage or as a decimal fraction.
 Normal values vary slightly with species , about 0.30 -0.40 in
large animal , wide ranging 0.35- 0.65 in dogs.
2. Mean corpuscular volume (MCV)
 Its calculated parameters in veterinary haematology
 It’s a measure of the size of the red cells and is obtaind by a
simple arithmetic from the PCV and the total red cells count of
the sample .
MCV(fl) ={ PCV (%) / RBC (× 1012 /L) } × 10
 Normal values vary widely with species and are independent of
the size of the individual animals as in table below
Dr. Hella J. Al- Fatalwy
Clinical pathology …………………………………………………………………………………………….. Haematology
Species
Mean red cell volume
Man
90
Dog
70
Pig
60
Cow
50
Cat
45
Horse
45
Sheep
30
Goat
15
 Younger animal tend to have rather smaller red cells than adult.
 The size of the red cells can also be assessed by looking at a well
made blood film , this is done partly by comparing the red cells with
the white cells which vary very little in size .
3. Mean corpuscular haemoglobin concentration (g/100 ml) (MCHC)
 It is a measure of the haemoglobin concentration in the red cells and is
obtained from the PCV and the total haemoglobin concentration of the
sample .
MCHC (g /100ml) = whole blood haemoglobin concentration / PCV
 The normal value is about 35g/100ml irrespective of species or size of
the red cells .
Dr. Hella J. Al- Fatalwy
Clinical pathology …………………………………………………………………………………………….. Haematology
 MCHC can also be assessed by eye on a well made blood film with
the hypochromic cells (low haemoglobin concentration having
noticeable pale centers.
 Abnormally , high MCHC is not possible as such , there is no such
thing as hyperchromic red cells , this abnormal MCHC value of over
40g/100ml may be due to three possible reasons:
1. Haemolysed blood sample ( either due to bad collection technique or
more rarely intravascular haemolysis .
2. Other interfering substances in the plasma (e.g lipaemic plasma) may
cause high haemoglobin reading
3. Excessive osmotic shrinkage of the red cell , rarely in vivo
phenomenon , but is common when a EDTA tube is underfilled
leading to an excessive concentration of EDTA in the sample.
4. Simple laboratory errors in either haemoglobin or PCV measurement.
4.MCH ( mean cell haemoglobin ) (pg)
 This obviously varies with cell size and so with species
 It can be useful in assessing whether hypochromic macrocytic cells
actually have the normal absolute amounts
5. Erythrocyte sedimentation rate (ESR)
 involves measuring how fast red cells will settle out on standing , a
measurement which depend on some extent on plasma viscosity which
alter when inflammatory proteins present.
Dr. Hella J. Al- Fatalwy