الفهرس 
Introduction and aim of the workOnly 14 pages are availabe for public view
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Abstract
Introduction: The thymus gland plays a critical role in cellmediated immunity through production of T lymphocytes. The gland reaches its maximum size at the age of puberty. Physiologically, the thymus is diminishing in size after puberty, but still producing some new lymphocytes
Aim of the work: The aim of this work is to examine the effect of advancement of age on the thymus of albino rats histologically, and immunohistologically by detection of apoptotic cells by light microscope. Methods: Experimental animals were classified into six age groups, one day, one week, two weeks, one month, four months and one year old. The thymus gland was dissected out. Paraffin sections were prepared and stained with H&E, Mallory trichrome stain and TUNEL immunohistochemical technique. Fresh frozen sections were prepared and stained with Sudan black stain. Quantitative morphometric studies were done to determine the thickness of the cortex, medulla, capsule, interlobular septa, the diameter of Hassalls corpuscles and counting the number of apoptotic cells for each age group.
Results: The neonatal thymus appeared surrounded by a thin connective tissue capsule with thin septa. The thickness of the capsule and the interlobular septa increased steadily with age. At the age of 2 weeks, some fat cells was detected in the capsule and the amount of fat cells was increased with age. Each lobule was formed of an outer cortex and a central medulla. The thickness of the cortex and the medulla increased steadily with age advancement till the age of one month after which the thickness is decreased again. Lymphocytes and epithelial reticular cells are the two main types of cells present in the gland. The normal architecture of the gland was preserved at all age groups. Hassalls corpuscles were present in the medulla of all age groups. The number and the size of the corpuscles were increased in older groups. The maximum number of apoptotic cells, detected by TUNEL technique, was at the one yearold rats. Conclusions The rat thymus undergoes age related changes in the form of thickening of connective tissue capsule and interlobular septa with invasion by fat cells. The thickness of the cortex and the medulla decrease after the age of one month. The diameter of Hassalls corpuscles is increasing with age. The basic thymic architecture and thymopoiesis are preserved in the adult and aged rat. The density of apoptotic cells in the thymus is increasing with age.