Thymus is an important lymphoid organ especially in the neonatal and pre-adolescent periods.  Its function is to mature the T-lymphocytes that are part of the adaptive immune response.  Thymus aplasia can lead to profound immunodeficiency and is one of the symptoms of a congenital disorder known as DiGeorge syndrome in which patients have a deletion within chromosome 22.

Histologically, each thymus lobule has a cortex (the outside, darker colored portion) and a medulla.  In particular, the thymus is distinguished by a structure known as Hassall’s Corpuscle that has an unknown function.

Fetal Thymus.jpg
Fetal thymus (TM: ~2.5x, picture taken with a Nikon Coolscan V slide scanner)
Human Thymus (TM: 100x, picture taken with a Olympus DPlan 10/0.25 on Sony A7ii)
Hassall’s corpuscles of Human Thymus (TM: 400x, picture taken with a Zeiss F40/0.8 on Sony A7ii)
Hassall’s Corpuscle of Human Thymus (TM: 1000x, picture taken with a Zeiss Neofluar 100/1.3 on Sony A7ii)

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