01 / Location & anatomical relationships
Behind the breastbone, especially prominent in childhood.
02 / Structure & organization
The thymus contains lobules with cortical and medullary regions. Developing T cells undergo selection that supports useful immune recognition while limiting harmful self-reactivity. Its proportion of active tissue changes substantially with age.
03 / Function
It helps certain immune cells, called T cells, mature during childhood.
04 / Mechanism
Developing T cells enter the thymus and go through selection steps. This helps build cells that can recognize useful defense targets while limiting harmful reactions to the body itself. The organ becomes smaller after childhood.
Working together: lymphatic & immune systems
Lymph vessels collect extra fluid from tissues. Lymph nodes filter that fluid, and immune cells help recognize and respond to germs.
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Connect structure with function
The thymus is a primary lymphoid organ involved in immune-cell development. It differs from secondary lymphoid structures where mature cells encounter many foreign antigens.
Check your understanding
Locate the thymus in relation to its neighbors. Explain how the structural features described above support its function, then distinguish it from a nearby structure with a different role.
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Continue with OpenStax Anatomy and Physiology for system-level study. This atlas is educational and has not undergone independent medical peer review.