The diffuse chemosensory system (DCS) is an anatomical structure composed of solitary chemosensory cells

Solitary chemosensory cells

Solitary chemosensory cells are isolated elements located in epithelia of the apparatuses of endodermic origin . In the aquatic vertebrates, SCCs are also present in the skin. In oral cavity, SCCs precedes the development of taste buds...

 and chemosensory clusters

Chemosensory clusters

Chemosensory clusters are aggregates formed by a small number of chemosensory cells with characteristics similar to those found in the taste cells of the oro-pharyngeal cavity. The chemosensory clusters are similar to the taste buds but are smaller, resembling the developing taste buds...

. The concept of DCS has been advanced in 2005, after the discovery that cells similar to gustatory elements are present in several organs of the respiratory and digestive

Digestion

Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones....

 apparatuses.

The elements forming the DCS share common morphological

Morphology (biology)

In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....

 and biochemical characteristics with the taste cells located in taste buds of the oropharyngeal cavity

Oropharynx

The Oropharynx reaches from the Uvula to the level of the hyoid bone.It opens anteriorly, through the isthmus faucium, into the mouth, while in its lateral wall, between the two palatine arches, is the palatine tonsil....

. In particular, they may express molecules of the chemoreceptorial cascade (e.g. trans-membrane taste

Taste

Taste is one of the traditional five senses. It refers to the ability to detect the flavor of substances such as food, certain minerals, and poisons, etc....

 receptors, the G-protein gustducin

Gustducin

Gustducin is a G protein associated with basic taste and the gustatory system. Due to its relatively recent discovery and isolation, not all is known about its nature and its associated pathways. It is known that it plays a large role in the transduction of bitter, sweet and umami stimuli and...

, PLCbeta2, IP3R3, TRPM5).

Morphologically, the elements of the DCS are polymorphic

Polymorphism (biology)

Polymorphism in biology occurs when two or more clearly different phenotypes exist in the same population of a species — in other words, the occurrence of more than one form or morph...

. Some of them have an apical tuft of rigid microvilli (brush cells).
Other elements have secretory exocrine granules and others may have endocrine differentiation. Often these elements are innervated.

To date, the functional role for the DCS is unknown also if several hypotheses have been advanced.

Questions remain about the role of the diffuse chemosensory system in control of complex functions (e.g. airway

Airway

The pulmonary airway comprises those parts of the respiratory system through which air flows, conceptually beginning at the nose and mouth, and terminating in the alveoli...

 surface liquid secretion) and about the involvement of chemoreceptors in respiratory disease

Respiratory disease

Respiratory disease is a medical term that encompasses pathological conditions affecting the organs and tissues that make gas exchange possible in higher organisms, and includes conditions of the upper respiratory tract, trachea, bronchi, bronchioles, alveoli, pleura and pleural cavity, and the...

s. The chemoreceptive capacity of the DCS seems to protect against exogenous

Exogenous

Exogenous refers to an action or object coming from outside a system. It is the opposite of endogenous, something generated from within the system....

substances.