The tongue is an amazing organ capable of performing several important functions such as speaking, chewing, and even tasting. It is also the first organ of our digestive system.
To control food, the tongue is covered with two types of taste buds: filiform and taste buds. The filiform papillae (indicated in blue in the image) are small bulges oriented toward the back of the tongue that direct food toward the throat. They are more or less coated with keratin (like nails and hair), which gives them hardness and resistance to heat, and can sense the texture of food through a nerve leading to their end.
On the other hand, the taste buds (the spirals in the image) are less numerous. They are fairly evenly distributed over the surface of the tongue, but there are a few more of them in the middle and also towards the front of the tongue. These are structures made up of different so-called taste cells that cluster into little balls just below the surface of the tongue and allow us to distinguish between different tastes (sweet, salty, sour, bitter, or umami). Contrary to the dogma that there are areas of the tongue for each of these tastes, all taste buds are capable of distinguishing these five tastes. Indeed, in most mammals (including humans), each of our taste buds is made up of all types of taste cells and is therefore capable of detecting salty as well as sweet, bitter, sour, and umami. These cells then connect to nerves that relay signals to the brain, which then processes the information and the associated taste. This is when we know the tastes of our food!
Macrophages: multifunctional tools
Due to its location, the tongue is the first contact with air and food. When we eat, food and our teeth damage the surface of our tongue. We also occasionally bite ourselves, which can lead to mouth ulcers, which are small, localized inflammations. To counter these infections, the human body then launches an immune response during which various white blood cells come in to destroy the pathogens. Among them, you can find macrophages located under the surface (epithelium) of the tongue, as well as in its muscular area. Macrophages are white blood cells whose main function is to phagocytose (eat) dead cells and microbes to prevent inflammation caused by an excessive immune response.
Finally, the tongue is an organ that, unlike the skin, is able to heal without leaving scars. Macrophages may also play a role in promoting perfect healing of the tongue, as well as some other mucous membranes, which also heal without leaving marks.
In other organs, macrophages are known to play specific roles, such as helping to maintain electrical signals in the heart or participating in contractions during digestion in the intestines. On the tongue, they may be necessary to maintain the various cells that make up the taste buds, as well as the proper functioning of the nerves that carry information to the brain. They may also play a role in surface and muscle repair, as well as immune defense against tongue injuries.
Confocal fluorescence microscopy (used to capture the image above) is one of the many methods used to unravel these mysteries, and we hope to be able to provide more information very soon through our experiments.