This course is intended for further in-depth study of the gastrointestinal physiology and immunology. The lymphoid tissues in the gastrointestinal tract contain the largest number of immune cells in the body, termed gut-associated lymphoid tissue (GALT). The gastrointestinal tract serves as a first line defense system against potential pathogens and antigens in ingested foods. At the same time, the gastrointestinal tract has to provide oral tolerance to food proteins without developing an adverse immune reaction against exogenous particles. The balance between tolerance and immunity in the gut plays a crucial role in the pathogenesis of various gastrointestinal diseases.