A tonsil is any collection of lymphoid tissue but the term tonsils are almost used to describe the palatine tonsils, a pair of structures at the back of the throat. They are part of the immune system and form the first line of defence for the digestive tract against ingested pathogens. However, their role is not fully understood. The tonsils reach their largest size at puberty, and generally start to atrophy as an adolescent nears adulthood. Like many other organs, persons who have their tonsils removed generally live normal lifespans.