Scheme of the thymus during ageing (human)

Physiological changes in the course of human ageing lead to almost complete degeneration of the thymus (age involution). Both cortex and medulla become depleted of lymphocytes, and the distinction between both layers gradually becomes less. The remaining reticular meshwork of connective tissue is gradually replaced by adipose tissue, and finally only scarce remnants of the original tissue are left. Thymus: A. neonate+ B. adult+ C. senium 1. capsule; 2. connective tissue septa partially delimiting thymic lobules; 3. cortex or remnants of cortical areas in A-B; 4. medulla or remnants of medulla in A-B; 5. Hassall bodies (corpuscles); 6. blood vessel; 7. fat tissue (adipocytes)