Taste is closely related to intake of food. Taste perception is also influenced by type of food ingested, and nutrition and health status. Bitter taste plays an important role in the survival of human and animals to avoid probable toxic and harmful substances. Vertebrate animals recognize bitter taste through type 2 taste receptors (T2Rs). Several T2Rs have been expressed extra-oral such as the gastrointestinal tract, respiratory tract, urogenital tract, brain and immune cells, and parts of their functions are being revealed. This review will discuss physiological roles of T2Rs in relation to innate immunity, secretion and smooth muscle contraction expressed in extra-oral cells and tissues, and we summarize relationships between polymorphisms in T2Rs and general or oral diseases. It is not a coincidence that animals pay much genetic costs for taste and smell during evolution.

Basic taste and bitter taste
 T2Rs signaling pathway
 Bitter taste receptors functions at the cellularlevel
 Physiological roles of extra-oral T2Rs
  Immunity
  Secretion
  Contraction of smooth/cardiac muscles.
  Male reproduction and micturition
 Polymorphisms of T2Rs
 T2Rs and diseases.
 Perspectives
 References

• Su-Young Ki(Department of Physiology and Neuroscience, College of Dentistry, Gangneung-Wonju National University)
• Kyung-Nyun Kim(Department of Physiology and Neuroscience, College of Dentistry, Gangneung-Wonju National University, 2Research Institute of Oral Sciences, Gangneung-Wonju National University) Correspondence to