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thumbnail thymus h&e 4x thumbnail thymus h&e 10x
thumbnail thymus h&e 20x thumbnail thymus h&e 40x

Lymphatic tissues in the mice include thymus, lymph nodes, spleen, and gut-associated lymphatic tissue (GALT). GALT includes Peyer’s patches in the gut and the diffuse lymphatic tissue in the gastrointestinal tract and respiratory system; mice have no tonsils. Thymus morphology changes dramatically with age. The thymus reaches full development at sexual maturity and then starts a gradual involution, which is incomplete in the mouse. The histological structure of the murine thymus is similar to that of the thymus in other mammals: a well-defined cortex and medulla surrounded by a thin capsule of connective tissue. The capsule forms septa dividing the body of the thymus into characteristic lobules. The cortex is composed of lymphocytes, especially differentiating T-cells. The medulla contains epithelial cells, but Hassall’s corpuscles are small and sparse. Ectopic thymic tissue may be found in the thyroid gland.

The micrographs show the thymus of a 3-week-old mouse. The 4X micrograph shows part of a septum formed by the connective tissue capsule. The 10X and 20X micrographs present the cortex and medulla of the thymus. The 40X micrograph shows the different cell types present in the thymus.

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