This document provides an overview of the components of blood in veterinary histology. It discusses the main formed elements - erythrocytes, leukocytes, and platelets - as well as plasma. For each component, it describes the typical appearance under microscopy for various species, including differences in size, shape, and granule characteristics. It provides examples of cell morphologies for erythrocytes, granulocytes like neutrophils and eosinophils, agranulocytes like lymphocytes and monocytes, and platelets for several common veterinary species.

1. Veterinary Histology of
Blood
Compiler : Sina Taefehshokr
DVM student at
Azad University of Tabriz, Veterinary Medicine Faculty
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2. 3. Erythrocytes
(RBC)
4. Leukocytes
(WBC)
8. Plasma
Blood is a specialized type of CONNECTIVE TISSUE , composed of formed elements in
fluid matrix . Blood circulates throughout the body and is well adapted for its various
functions in transporting nutrients, oxygen, waste products, carbon dioxide, hormones,
cells, and other substances. Plasma (55%) is the fluid portion, called serum when
depleted of Fibrin & Fibrinogen. The formed elements of blood (45%) include
Erythrocytes (Red Blood Cells), Leukocytes (White Blood Cells) and Platelets
(Thrombocytes).
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3. Plasma
Blood plasma is the pale-yellow
liquid component of blood that
normally holds the blood cells in
whole blood in suspension. It makes
up about 55% of the body's total
blood volume. It is mostly water (up
to 95% by volume), and contains
dissolved proteins (6-8%) (i.e.
albumins, globulins, and fibrinogen),
glucose, clotting factors, electrolytes
(Na+, Ca2+, Mg2+, HCO3
-, etc.),
hormones and carbon dioxide
(plasma being the main medium for
excretory product transportation).
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4. Platelets
Platelets play an important role in
hemostasis. Although also referred to as
thrombocytes, they are not cells. They are
membrane-bound fragments of cytoplasm
from large cells called megakaryocytes,
found in the bone marrow and sometimes
the lymph nodes and spleen. Platelets are
small and pale blue, and they have purple
central granules in stained smears. They
occur singly or in clusters in smears of
peripheral blood. Platelets are called
thrombocytes in avian. Thrombocytes are
nucleated cells, related in function to the
platelets of mammals. They are smaller
and less elongated than erythrocytes and
have a larger, more round nucleus. The
pale, dull blue cytoplasm is characterized
by one or more small magenta granules
and vacuoles.
Platelet of Goat
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5. Platelet of Sheep
Platelet of Cat
Platelet of Pig
Thrombocyte of Chicken
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6. Erythrocytes
Mature erythrocytes are small, anucleate cells uniquely adapted to transport oxygen and
carbon dioxide to and from tissues. The average diameter of erythrocytes varies with the species.
The erythrocytes of the dog are the largest (7.0 µm), while those of the goat are the smallest (4.1
µm). In most species the cells are disc-shaped, although in young goats they may also be
angulated. Central pallor, resulting from its biconcave shape, is best defined in the erythrocyte
of the dog, but may be seen in other domestic mammals. Red blood cells sometimes adhere to
each other, forming an arrangement resembling a stack of coins, called a Rouleaux .
Human Erythrocytes
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7. Canine : Cells are large (7 μm),uniform in size
and have central pallor (biconcave disc).
Equine : Erythrocyte have rouleaux formation,
Average diameter 5.7 μm ,uniform in size no central
pallor .
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8. Camelid : Erythrocytes normal elliptical in shape
and no central pallor.
Avian, Amphibian, Fish : Mature erythrocytes
of the chicken are very different from those of
domestic mammals. They are large, elongated,
flat cells with an oval nucleus.
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9. Leukocytes
Leukocytes are basic cellular
components of the immune
system. They are nucleated cells
that are larger and less
numerous than erythrocytes.
They are classified, depending
on the presence or absence of
specific cytoplasmic granules,
as either Granulocytes
(neutrophils, eosinophils, and
basophils) or Agranulocytes
(lymphocytes and monocytes)
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10. Granulocytes of Human
1. Neutrophils
2. Eosinophils
3. Basophils
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11. Neutrophils
The neutrophil, or the Heterophil in
birds, reptiles and some mammals, is the
predominant granulocyte. In many species
it is the predominant leukocyte in health.
The mature neutrophils of many animal
species do not have a distinct lobe and
filament arrangement (they do have
constricted nucleus or irregular/knobbly
nuclear outlines), nevertheless, they also
are called segmented neutrophils.
Canine neutrophils have white
cytoplasm that contains small
pink specific or secondary
granules.
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12. Feline neutrophils have cytoplasm that is white
and lacks visible granules.
Ruminant neutrophils have white cytoplasm
with small pink granules; these impart an
overall pink tint compared to the other species.
Equine neutrophils have white or slightly pink
cytoplasm with no visible granules. The nuclei
of equine neutrophils typically are long, thin
and "knobby" with clumps of condensed
chromatin projecting from the sides.
Chicken
Rabbits, birds, amphibians and reptiles have
heterophils. In contrast to the inconspicuous
granules of neutrophils, granules in heterophils
are large and stained deep orange to red.
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13. Eosinophils
Eosinophil granules in most animals are
orange but there are always exceptions.
The granules in eosinophils of iguanas
and some birds are actually pale blue. In
general, nuclei of mature eosinophils
are shorter and less segmented than
neutrophil nuclei and the cytoplasm, if
visible, is pale blue. Marked species
variation exists regarding the number,
size, and shape of eosinophil granules.
A specific and predictable morphologic
variant of the eosinophil is seen in
greyhounds and other sighthounds (eg,
whippets, deerhounds). Eosinophils in
these breeds lack visible granules and
appear as cells with slightly segmented
nuclei, gray cytoplasm, and vacuoles.
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14. Eosinophils of the cat have small rod-
shaped orange granules that fill the
cytoplasm.
Eosinophils of the horse have very large
globular orange granules.
Ruminant eosinophils have many small
very round orange granules.
The most intraspecies variation is
found in dog eosinophils.
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15. Basophils
Only a small percentage (0.5 to 3%) of the
leukocytes of domestic mammals are
basophils. Hence, they are not often
found in blood smears. The basophil
nucleus may be irregular, bilobed, or
highly segmented. The granules of
basophils vary in size, number, and
staining intensity. They are often fairly
large, round to oval, and stain reddish
purple to dark purple. The granules are a
dumbbell or coccoid shape in the pig. The
basophil of the cat is much different from
that of the other domestic mammals. The
granules are small and not deeply stained.
They are dull gray to lavender in a
lavender cytoplasm.
The basophils of the chicken are much
more numerous than in mammals. Their
specific granules are deeply basophilic,
and the nucleus is usually unlobed and
pale.
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16. Canine basophils are difficult to recognize since
many do not have readily apparent granules. Canine
basophils have a long and folded nucleus, described
as ribbon-like, and the unusual gray to lavender hue
of the cytoplasm.
Basophils of horses and ruminants are similar to each other and to human basophils.
These cells contain many small deep purple granules that obscure the nucleus in many
cells. Arrows point to nuclear lobes in the picture of a cow basophil.
Feline basophils are packed with small, slightly oval granules that
are pale lavender rather than deep purple. The nucleus in many
appears to have vacuoles, which are actually granules lying on top
of the chromatin. Basophils are rare in blood of healthy cats.
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17. Agranulocytes of Human
1. Lymphocytes
2. Monocytes
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18. Lymphocytes are the predominant
leukocytes in ruminants, avian and
rodents. The cells range in size from 6 to 15
µm and are sometimes classified as small,
medium, and large. Most of the
lymphocytes in carnivores, horses and pigs
are small. Larger cells occur more often in
ruminants. Some of the lymphocytes of
ruminants are binucleate. Only a thin rim
of cytoplasm may be visible in the small
lymphocyte. The cytoplasm is basophilic
and may show a lighter region (perinuclear
halo) adjacent to the nucleus.
3. Lymphocyte ( Medium ) Cat
5. Lymphocyte (small ) Dog
Lymphocytes
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19. 2. Lymphocyte (large) Cow
3. Lymphocyte (binucleate) Sheep
5. Lymphocyte Chicken
6. Lymphocyte (Small) Sheep
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20. Monocytes
Monocytes are the largest of the leukocytes (15 to
20 μm in diameter). The nuclear chromatin tends
to be diffuse, appearing lacy or sometimes patchy.
The shape of the nucleus is highly variable and
may be oval, irregular, kidney-shaped, or
horseshoe-shaped. In the horse the nucleus is
frequently kidney-shaped. In ruminants the
nucleus may appear amoeboid and sometimes
has a three-pronged configuration or is shaped
like a cloverleaf. The cytoplasm is generally pale
gray-blue and may contain dustlike, azurophilic
granules. It often contains vacuoles that give it a
foamy appearance. In ruminants the cytoplasm
can be more basophilic and either granular or
mottled in appearance. Monocytes are usually
larger than lymphocytes in avian. The nuclear
chromatin tends to be more diffuse. Vacuoles are
often seen in the cytoplasm.
Monocytes of Horse
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21. Monocyte of Cow
Monocyte of Dog
Monocyte of Sheep
Monocyte of Chicken
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22. 1) William J. Bacha, Jr. Linda M. Bacha Color Atlas of Veterinary
Histology Second Edition. 27-36
2) Leslie P. Gartner, Games L. Hiatt Color Atlas and Text of Histology
Sixth Edition. 108-126
3) Https://www.slideshare.net/leukocyteswhitebloodcells/
4) Https://en.wikipedia.org/wiki/Basophilic
5) Https://ahdc.vet.cornell.edu/clinpath/modules/rbcmorph/images/eqp
lt.jpg
6) Https://ahdc.vet.cornell.edu/clinpath/modules/rbcmorph/images/dog
rbcpl.jpg
7) Https://www.visualhistology.com/products/atlas/VHA_Chpt3_Conne
ctive_Tissue.html
8) Https://www.slideshare.net/adjutant_reflex/lecture-1-animal-cell-
types-and-tissues
9)
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References
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