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Organ system histology
Lymphoid tissue and organs contain a lot of lymphocytes and other white blood cells.
The primary lymphoid organs include the thymus and bone marrow.
This organ is most active during childhood, reaching its largest size around puberty, with a weight of approximately 30 to 40 grams.
This process, along with regulatory T cells help prevent autoimmunity.
This is a low power image of a neonatal thymus.
At this magnification, the thin collagenous capsule is a little hard to see, but if we zoom in a little further, we can see the capsule more clearly, as well as the connective tissue that extends inward from the capsule into the thymus, forming incomplete lobules.
The thymus is a flat encapsulated lymphoid organ located behind the sternum. It's most active during childhood and slowly involutes in adulthood, with fatty infiltrates and decreased thymic tissue. The thymus gland has two lobes, each of which has an outer cortex that's very basophilic and stains dark purple, whereas the inner medulla stains a lighter purple and pink color. The cortex consists of many basophilic T lymphoblasts that are supported by a meshwork of thymic epithelial cells (TECs), which have a pale cytoplasm with cytoplasmic processes. The inner medulla also has an abundance of TECs, but will also contain Hassall's corpuscles, which are the structures formed by closely packed and concentrically arranged TECs.
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