Which of the following glands disappears in old age?

The gland that disappears in old age is [D] Thymus. The thymus gland, a crucial part of the immune system, gradually diminishes in size and function as individuals age. Situated in the upper chest behind the sternum, the thymus is most active during childhood and adolescence, where it plays a pivotal role in the development and maturation of T lymphocytes, a type of white blood cell involved in immune responses.

However, as individuals reach adulthood, the thymus undergoes involution, a process in which it progressively decreases in size and becomes replaced by adipose (fat) tissue. By old age, the thymus is typically reduced to a small, fibrous remnant. This decline in thymus function contributes to age-related changes in immune response and susceptibility to certain infections and diseases. Therefore, the disappearance of the thymus gland is a characteristic feature of aging.