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Abstract
This study was carried out on thymus obtained from clinically healthy male
camels (Camelus dromedarius). Their ages ranged between 6 months to 20 years old. The specimens were used for the following studies:
- Processing for light microscopy
The specimens were routinely processed for paraffin sections: using H&E, Crossmon’s trichorome, Gomori’s reticulin, Weigert’s resorcin fuchsin and Periodic acid Schiff.
2- Ultrastructure examination using the transmission electron microscope.
Histological structure of the camel thymus
The thymus of one humped camel was composed of stroma and parenchyma. The stroma was composed of capsule and septa. The parenchyma was composed of lobules each one had a cortex and medulla.
1-Stroma
Capsule and septa
At the age of 6 months to 5 years old camels, thymus was surrounded by a delicate capsule of thin fibrous connective tissue of reticular and collagen fibers. At the ages of 5-10 years old camels, the capsule showed marked increase in its thickness. White adipose tissue started to appear within the interlobular septa. At the ages of the 15-20 years old, the capsule increased in thickness and became more dense and its inner part was invaded by very thick layers of white adipose tissue that were replacing the outer thymic tissue.
Septal blood vessels
The thymus were supplied by a- Muscular arteries which accompanied by medium sized veins. b- Large and small arterioles that were accompanied bS’ large vennules.
Lymphatic vessels
The thymus had typical lymphatic vessels. Lymphatic vessels were wide and lined with a single layer of endothelial cells.
Cells of the stroma
Fibroblasts and fibrocytes were found within the capsule and septa. Eosinophils were observed within the stroma. They were found either singly within the capsule or by little group within the interlobular septa. Small and large sized lymphocytes were found within the interlobular septa. Epithelial cells, two kinds of the epithelial cells were observed within the interlobular septa. One of them was numerous and. randomly distributed. The second type was forming tubular structures lined by layer of cuboidal cells but two layers were also seen in some parts of them. Mast cells were also observed within the capsule.
2-Parenchyma
At the ages of 6 months to 5 years old camels, the thymic parenchyma was divided by septa into complete and incomplete lobules. At the ages of 5 to 10 years old, the very thick septa divided the thymus into complete and incomplete lobules and small isolated of cortical tissue. At the ages of 10 to 15 years old, the lobules were in general elongated in shape of cortical and medullary tissue. At the ages of 20 years old, the cortex and medulla were separated by extended reticular connective tissue septa.
A- Cortex
It contained different cell types include lymphocyte, epithelial reticular cells, macrophages and Eosinophils.
Lymphocytes were classified according the nuclear size into small, medium, and large lymphocytes. Small lymphocytes were characterized by small spherical nuclei and a little cytoplasm. Medium and large lymphocytes contained large nuclei and much cytoplasm.
Epithelial reticular cells were classified according their position into type-I was located under the capsule, around the cortical capillaries and septa. Ultrastructurally, were characterized by tigeriod nuclei and empty vacuoles within the cytoplasm. Type-Il was located in the mid and outer cortex. Ultrastructurally, were characterized by euchromatic nuclei and electron dense granules within the cytoplasm. Type-Ill was located in the inner cortex. And by, TEM were characterized by irregular shaped nucleus, tonofilments and electron dense granules.
Blood thymus barrier was formed of endothelial cells with their basal lamina, perivascular space with macrophages and epithelial reticular cells and their basal lamina.
Macrophages were found within the mid and irnier cortex but of little number within the medulla and of high number within the degenerated Hassall’s corpuscles. They were characterized by irregular outlines, lightly stained and eccentrically situated nucleus with prominent nucleoli.
Eosinophils were sporadically distributed within the cortex and medulla and numerous at the cortico-medullary junctions. Ultrastructurally were characterized by bibbed nuclei and membrane specific granules with crystalloid core in their cytoplasm.
B. Medulla.
It contained lymphocytes, numerous epithelial reticular cells, macrophages, eosinophils, multinucleated giant cells, plasma cells and Hassall’s corpuscles as well as blood capillaries.
Epithelial reticular cells were more easily defined and had different forms and distributions within the medulla. Type-IV was cortico-medullary junctions, sometimes within the deep and mid cortex and might be associated with the Hassall’s corpuscles. By TEM, These cells had a heterochromatic electron dense irregularly shaped nucleus with one nucleolus. The dark cytoplasm contained spherical vsicles contained amorphous material of moderate to high electron density. Type-V was located in the medulla. By TEM, were characterized by euchromatic nuclei and little electron dense granules.