الفهرس 
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Abstract
The present study showed that the prenatal buffalo spleen was enveloped with a thick capsule. Thick trabeculae extend from the capsule divided into primary and secondary trabeculae consisted of connective tissues and smooth muscles. The parenchyma was ill developed and was represented with mesenchymal tissue. The primitive white pulp was formed from an arteriole ensheathed with mesenchymal tissue or with periarterial lymphoid sheath without any lymphoid nodules. The primitive red pulp was formed mainly of mesenchymal tissue rich in diffused lymphocytes. No blood sinusoids were observed. The marginal zone was not demarcated. In the postnatal period the spleen was enclosed with a capsule of connective tissue and smooth muscles. The thickness of the splenic capsule increased with age to be the thickest in the old age groups. The structure of the splenic compartments of the buffalo in the postnatal period was composed of the white and the red puips separated by the marginal zone without prominent age related morphological difference. The white pulp of the buffalo spleen was formed from clear PALS surrounding a central artery associated with secondary lymphoid nodule. The white pulp was enclosed with marginal zone. The presence of the secondary lymphoid nodules indicates the essential role of the spleen in immune response and lymphocyte production
The red pulp of the buffalo spleen was formed from splenic cords of lymphocytes and circulating blood cells separated by small blood sinusoids, this indicates that the spleen of buffalo belong to the non sinusal spleen
This type of spleen stored only a moderate amount of blood. The hemal nodes may be a supplementary organ to assist the spleen in storage of blood.
The diameter of the white pulp was the smallest at young age group and the red pulp constitute the majority. The white pulp was largest at middle age group and this fmdings indicated that the spleen in the middle age group play the most prominent role in the immune response. In the old age group the diameter of the white pulp was slightly reduced but still larger than that of the young age. This mean that the red pulp surface area started to increased on the expense of the white pulp.
The hemal node of the Egyptian water buffalo was enclosed with a thin capsule and trabeculae of connective tissue and smooth muscles extend from the capsule. A wide subcapsular sinus connected to trabecular sinuses was observed. The hemal nodes of the buffalo possess a histological feature comparable to the splenic red pulp, as both were formed by lymphoid cords rich in various blood cells separated by blood sinuses. The blood sinuses were tightly packed with erythrocytes. The presence of concentrated blood in the blood sinuses indicated the role of hernal nodes in storage of blood.
Peripherally located lymphoid nodules with clear germinal centre formed the rest of the parenchyrna. This indicates the essential role of the hemal nodes in immunological response and in the production of lymphocytes. This morphological fmding was restricted to animals younger than 5 years.
The fetal hemal node was hardly observed, this may be due to their small size. It was formed mainly from inesenchymal connective tissue containing few diffused lymphocytes
The blood sinuses were few and contained unconcentrated blood to be clearly different from the structure feature of the hemal nodes of the post natal period.
The morphornetric studies revealed that the capsular thickness increased with age. The increased thickness of the capsule was accompanied with increased thickness of the trabeculae these were associated with reduction in the diameter of hemal nodes at age older than 5 years. All this indicates that, the stroma increased on the expense of parenchyma after 5 years as a sign of involution. All this was associated with narrowing of the subcapsular and trabecular sinuses to be partially obliterated in old age. The obliterated blood sinusoids were replaced with capillaries and arterioles. The surface area of hemal node occupied with the lymphoid nodules was smaller (about 5%) than this occupied with the non-nodular structure of lymphoid cords and blood sinusoids (about 95%). This means that the area of hernal node responsible for filtration and storage of the blood is the main bulk of the hemal node. The diameter of lymphoid nodules increased with age to reach its maximum diameter at age group 1-3 years and was completely absent after 6 years old.. The hemal nodes of buffalo developed gradually till the age of 3 years and involutes partially to be hardly seen at age older than 8 years.
There were a possible physiological relation between the hemal nodes and the spleen of the Egyptian water buffalo. The hernal nodes and the red pulp of the spleen are physiologically related and both coordinate to do a similar function. The development of the nodular region of the hemal nodes was parallel to that of the white pulp until the age of 3 years old, the surface
area of both were increased with age. The involution of the hernal nodes was associated with reduction in the surface area of the white pulp.
This is related to the age related physiological changes included all the immune system of the body.