1. BONE MARROW

The normal bone marrow architecture consists of wedges of hemopoietic cells supported by a meshwork of connective tissue and blood vessels. There are numerous wide sinuses lined by endothelium. The hemopoietic tissue consists of immature blood cells. It is remarkable the presence of numerous megakaryocytes. Numerous adipocytes can also be observed.

2. MAMMALIAN BLOOD SMEAR

Blood smear, dog
Mature erythrocytes of domestic mammals are non-nucleated cells, with a central pale area because their biconcave morphology. Among the leukocyte group, neutrophils are the most numerous in this species; the mature neutrophil has a lobed nucleus. Eosinophils can also be observed; they have lobed nuclei surrounded by acidophilic granules. Basophils are usually rare in the blood of carnivorous because only account for 0.5% of the leukocytes. Lymphocytes have sparse light blue cytoplasm surrounding a fairly dense nucleus. Monocytes have bigger size than lymphocytes.

Neutrophil





Eosinophil

Lymphocyte

Monocyte

3. AVIAN BLOOD SMEAR

Blood smear, chicken
Erythrocytes are nucleated oval cells with an eosinophilic cytoplasma. Heterophils are numerous and have a bilobed nucleus with amphophilic granules in the cytoplasm. Eosinophils are less frequently seen. Agranular leukocytes are identical to the lymphocytes and monocytes of the mammals. Thrombocytes are functionally analogous to the mammalian platelet, oval shaped and with a basophilic nucleus. Usually thrombocytes form aggregates.

Heterophil



Thrombocytes



Lymphocytes and thrombocytes

4. ELASTIC ARTERIES

Aorta
The internal tunic or tunica intima includes the epithelial inner lining the endothelium, and the underlying subendothelial connective tissue.

The tunica media is the thickest of the three layers and consists of concentrically arranged, fenestrated elastic laminae. Smooth muscle cells can also be observed.

The tunica externa or adventitia has bundles of collagen fibers intermixed with a few elastic fibers and fibroblasts. Small blood vessels (the vasa vasorum) supply the tunica externa and outer half of the tunica media. The remainder of the media receives nutrients through diffusion.

5. MUSCULAR ARTERIES

Muscular arteries are characterized by a thick tunica media, composed mainly of smooth muscle cells. Elastic fibers and collagen fibers can also be observed.
The tunica externa consists of many elastic and collagen fibers and fibroblasts.

6. VEIN

Vena cava
The layers are much thinner than those in the corresponding arteries, particularly the tunica media. The tunica externa is prominent and composed of bundles of smooth muscle cells, with collagen and elastic fibers.

7. ARTERIOLES, CAPILLARIES, AND VENULES

Heart
Arterioles, capillaries and venules can be identified in the loose connective tissue surrounding the cardiac muscle cells of the myocardium. Arterioles have a tunica media of 1-2 layers of smooth muscle cells. Capillaries have not tunica media. Venules are similar in structure to capillaries but are larger. As the venules increases in size, they first become incompletely surrounded by muscle cells.

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Vasa vasorum (Aorta)
Arterioles, capillaries and venules can be observed in the tunica externa or adventitia of the aorta.

8. HEART

Endocardium: is the inner layer of the heart and is continuous with the tunica intima of the large blood vessels leaving and entering the heart. The endocardium consists of a continuous endothelium on a thin basal lamina, followed by the subendothelium (composed of dense irregular connective tissue), and a layer composed of loose connective tissue. Adipose cells may be present.

Myocardium: is the middle and thickest layer of the heart, composed of groups of bundles of cardiac muscle cells. They are embedded in loose connective tissue that contain a dense capillary network.

Purkinje fibers are specialised conducting cardiac muscle fibers with abundant glycogen granules and mitochondria; they have a pale staining central area with most of the red-staining myofibrils around the periphery of the cell.

Epicardium: it consists of the mesothelial cells of the visceral pericardium and an underlying subepicardial connective tissue layer with collagen and elastic fibers. A subepicardial layer of loose connective tissue and adipose tissue is particularly abundant around the coronary blood vessels.