Anatomy and Physiology II Practice Test

The thymus is the organ that undergoes involution, which is the process where an organ decreases in size and is replaced by connective tissue and fat over time. This process is particularly significant after puberty.

In infants and children, the thymus is relatively large and plays a crucial role in the development and maturation of T-lymphocytes, which are vital for the adaptive immune system. As a person ages, especially post-puberty, the thymus gradually shrinks and begins to be replaced with adipose tissue. This involution reflects the decreased requirement for thymic activity as the immune system matures after childhood.

In contrast, other organs listed, such as the spleen, thyroid, and tonsils, do not undergo the same type of involution or significant replacement with connective tissue and fat in the same way that the thymus does. The spleen remains reasonably stable in size throughout life and does not significantly undergo histological changes like the thymus. The thyroid may change in functionality but generally maintains its tissue architecture without extensive involution, and the tonsils can also undergo changes due to immune activity but do not follow the same involution pattern.