Veterinary Histology of Blood

Compiler : Sina Taefehshokr

DVM student atAzad University of Tabriz, Veterinary Medicine Faculty

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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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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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PlateletsPlatelets 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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Platelet of Sheep

Platelet of Cat

Platelet of Pig

Thrombocyte of Chicken

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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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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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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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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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Granulocytes of Human 1. Neutrophils 2. Eosinophils 3. Basophils

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NeutrophilsThe 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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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.

ChickenRabbits, 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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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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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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BasophilsOnly 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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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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Agranulocytes of Human 1. Lymphocytes 2. Monocytes

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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 ) Cat5. Lymphocyte (small ) Dog

Lymphocytes

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2. Lymphocyte (large) Cow3. Lymphocyte (binucleate) Sheep5. Lymphocyte Chicken6. Lymphocyte (Small) Sheep

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MonocytesMonocytes 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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Monocyte of Cow

Monocyte of Dog

Monocyte of Sheep

Monocyte of Chicken

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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/Basophilic5) Https://ahdc.vet.cornell.edu/clinpath/modules/rbcmorph/

images/eqplt.jpg6) Https://ahdc.vet.cornell.edu/clinpath/modules/rbcmorph/

images/dogrbcpl.jpg7) Https://www.visualhistology.com/products/atlas/

VHA_Chpt3_Connective_Tissue.html8) Https://www.slideshare.net/adjutant_reflex/lecture-1-

animal-cell-types-and-tissues

( بافت شناسی و اطلس 1390رضاییان، م ( (9رنگی دامپزشکی، چاپ سوم، انتشارات دانشگاه

85-82، 62-57 تهران، صفحات

References

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