DEV2022 Study Guide - Final Guide: Thymocyte, Histocompatibility, Immunodeficiency
Document Summary
The thymus is a specialized organ of the immune system. The thymus is derived from the 3rd pharyngeal pouches. The development of the thymus is a series of epithelial/mesenchymal inductive interactions between neural crest-derived arch mesenchyme and pouch endoderm. Unlike most other lymphoid structures, the thymus grows rapidly and reaches its greatest size relative to the rest of the body during fetal life and the first years after birth. Thereafter, it continues to grow, but more slowly than the other organs. It can be said that the thymus enlarges during childhood, and atrophies at puberty. The thymus of older people is barely distinguishable from surrounding fatty tissue. As one ages, the thymus slowly shrinks, eventually degenerating into tiny islands of fatty tissue. The thymus is divided into two lobes, where the two lobes are divided into lobules by connective tissue septa that are continuous with the outer fibrous capsule.
